HUGE NEWS: first possibly Earthlike extrasolar planet found!

By Phil Plait | April 24, 2007 3:24 pm


Artist’s impression of the planetary system around Gliese 581. Courtesy ESO.

The European Southern Observatory is reporting that they have found the most Earthlike planet yet orbiting another star. It has about 1.5 times the Earth’s diameter, and five times its mass. This makes it the smallest extrasolar planet yet found (two other planets have already been found orbiting that star, with 15 and 8 times Earth’s mass).

This is amazing enough! But it gets far, far better. The parent star, Gliese 581, is a red dwarf, meaning it’s smaller and cooler than the Sun. The as-yet unnamed planet orbits this star much closer than the Earth does the Sun; it stays about 11 million kilometers (6.7 million miles) from its star, while the Earth is 150 million km (93 million miles) from the Sun.

But remember, Gliese 581 is cooler than the Sun, so at this distance the planet would actually be very temperate: models show it would be between 0 and 40 Celsius! If that doesn’t grab you, then consider this:

That is warm enough for water to be a liquid.

So what we may have here is a terrestrial planet with liquid water on its surface.

Let me be clear: this is not a guarantee! We have not actually gotten an image of the planet; its presence is indicated by the gravitational effect it has on its star as it orbits (once every 13 days, incidentally). So we don’t know if the planet is dry, or covered in oceans, or even if it’s rocky like the Earth — though models indicate it will either be rocky or possibly even covered by oceans.

And this planet is Earthlike, but not Earth! The surface gravity is more than twice that of Earth’s (22 m/s/s versus 9.8 m/s/s on Earth) and who knows what the atmosphere is like. But the basic characteristics are certainly provocative! Almost all the planets detected using this method are more massive than Jupiter, and extremely hot, way too hot to be hospitable to our kind of life.

Why is this planet important? Well, one of the major goals of science right now is to find out if life has arisen and evolved elsewhere in the Universe. Up until 1995 we weren’t even sure if any other stars had planets! Now we know of hundreds, and as the technology gets better, we can find smaller and smaller ones. We’re right on the verge of being able to find ones just like Earth. And while of course we cannot know if this newly found planet has life or not, it’s our best bet yet!

There is much more to learn about this planet. Getting an image of it is currently not possible: at a distance of 20 or so light years, Gliese 581 one of the closest stars in the sky, but still far too distant to separate the planet from the star. So I’m left wondering about this planet. Does it rotate once every orbit due to the gravitational interaction with its star? This is what has happened to every moon in the solar system; they spin at the same rate they go around their parent bodies, so they always show one face to their parent (which is why the Moon always has the same face toward us here on Earth). If so, how does this affect the atmosphere? Models indicate that the air should carry the warmth of the star around the planet, so the temperatures should actually be fairly moderate on both the day and night sides of such a world. But if it’s covered by an ocean, how does having one side of the planet eternally locked into daylight affect it?

Criminy, what would life be like on a tidally-locked ocean world?

Wow. One of my favorite aspects of science is taking an idea and running with it. I don’t encourage too much speculation beyond what’s known — and in this case we don’t know all that much — but it sure can be fun. Especially when what we’re starting with is so exciting.

So hat’s off to the team of scientists who made this momentous discovery. May they make many more… and may their results get ever smaller, and ever cooler.

CATEGORIZED UNDER: Astronomy, Cool stuff, Science

Comments (179)

Links to this Post

  1. kreuz und quer » Blog Archiv » Erdähnlicher Planet gefunden! | April 24, 2007
  2. Science After Sunclipse | April 24, 2007
  3. Truth and the Devil » First potentially Earth-like planet found | April 24, 2007
  4. Alias Tex » Wow | April 24, 2007
  5. My View » Gliese 581 | April 24, 2007
  6. Trikinhuelas » Blog Archive » Encuentran indirectamente un planeta similar a la tierra | April 24, 2007
  7. Mike’s Blog » Planet Earth - But not us! | April 25, 2007
  8. Moonage SpaceDream | April 25, 2007
  9. butchbailey.com » Blog Archive » Potentially “Earth-like” Planet Found Outside Our System | April 25, 2007
  10. Participate Media » Blog Archive » Today, April 25, on BuzzTracker | April 25, 2007
  11. Brit bookmakers lower odds of "aliens" to 100 to 1... « Homeless on the High Desert | April 25, 2007
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  13. News of the Day » Blog Archive » Judge cancels news conference to speak on misconduct charge (The Clarion-Ledger) | April 25, 2007
  14. Flying hamsters and other strange tales… » Earthlike exoplanet discovered in the Libra constellation | April 25, 2007
  15. Slacker Astronomy » A star wiggles thrice | April 25, 2007
  16. Earth like planet found in Habitable Zone capable of having liquid water | April 25, 2007
  17. The Web Pen Blog » Blog Archive » Roundup - Week Of Apr 21 | April 28, 2007
  18. Astrolink [Global Edition] » Welcome from the DarkSyde | Latest astronomy news in 11 languages | April 28, 2007
  19. Sexy Secularist! » Blog Archive » Kal-El Takes on Mineralogy, Astronomy, and SETI | April 28, 2007
  20. Phil’s NewsPhlash » HUGE NEWS:first possibly Earthlike extrasolar planet found | May 3, 2007
  21. HUGE NEWS: first possibly Earthlike extrasolar planet found! « darwinian remix | May 4, 2007
  22. And dreamed about things that I cannot say « Pseudo-Intellectual Ramblings | June 15, 2007
  23. A Planet Nowhere Near Mars ~ Chris Pirillo | August 31, 2007
  1. drbuzz0

    I’m not saying there would be life on such a planet, or even that it has a high likelihood of being earth-like in it’s characteristics, (IE: liquid water, dense atmosphere, similar chemistry).

    But just the same… What do you say we give it a once-over with a radio telescope and take an extra close look at what it picks up?

  2. George

    Yeeh Ha!!! Huge day for astronomy. Nice going!

    Does the planet transit so that you can get atmospheric data?

    So….can I buy land there yet?

  3. George

    Oh, btw, the first link doesn’t work for me.

  4. Xenu

    Wow, Twitter is fast :)
    Lets hope some exploration will be going on again soon, mebbe next administration will spend less on stupid wars and more on science and exploration….
    Observing is cool, but actually going there, well…

  5. Michelle Rochon

    Very cool. It was bound to be discovered sooner or later, but hey, it’s now! Here it is, smack in our face.

  6. Henry

    Looks like we can at least put some kind of upper bound on the ne term in the Drake equation.

  7. Meh. Just crunched a quick number…if the planet is really 1.5 Earth radii, then even the Darwin IR interferometry array won’t be able to observe it directly (required resolution about 2 * 10^-5 arcsecond, Darwin peak resolution around 10^-3 arcsecond). Dernit, I want my microarcsecond interferometry NOW!

  8. Yeah, the ESO hasn’t made the link live yet. I was VERY VERY careful not to break embargo, so they are just slow here. Sigh. I know there are images to be seen too (probably an artist’s drawing and some images of the star) but I can’t link to ‘em until i see ‘em!

  9. bswift

    Bah, I’d like to see paper rather than the press release anyway. Still can’t wait to read it!

  10. Chip

    This is exciting news. How much more can be learned with the available tools? Too bad the Terrestrial Planet Finder was cancelled.

  11. Dave Kary

    I have a question about the estimated temperature. What are the assumptions that go into it? What albedo are they asssuming? How about greenhouse effects? The temperature range seems pretty narrow compared to the experience of our own solar system, where greenhouse effects can make a 500 degree difference in surface temperature on a planet.

    DK

  12. Jason

    Awesome. Cant wait to get some hard data on this.

  13. bswift

    Phil mentioned briefly that this star also has two other known planets orbiting this star with masses ~15 and ~8 earth masses. What’s interesting is that this newly announced planet is in between the two. They were all found using the radial velocity technique that measures the wobble of the parent star, so since the inclination of the system is not known, this mass is only a MINIMUM mass.

    What I would like to know is how the diameter is modeled. A naive calculation suggests that the radius should be 5^(1/3)=1.7 times the radius of the earth, not 1.5. (But their models are probably better than mine.)

  14. Jason

    Hey sorry someone mentioned wanting an artists rendering…
    http://www.cbc.ca/technology/story/2007/04/24/science-planet.html

    Not sure if this is of any help, if not sorry.

  15. Christian Burnham

    20 light years. That’s close enough to send a signal to E.T. (if she’s there). I wonder how many Earth-like planets are yet to be discovered in this radius.

  16. Chris

    bswift: Maybe they’re assuming a different density? (But on what grounds?)

    Correct me if I’m wrong, but it seems to me that the chance of water in *some* phase is very high. The system must contain elements heavier than helium (any planet too small and warm to hold molecular hydrogen must be built out of something less volatile or it wouldn’t be there); oxygen is a common product of the processes that produce heavy elements; hydrogen is common everywhere; and they combine readily to form water. Molecular oxygen is a rare and highly reactive substance that we ought to be astonished to find. Water is not.

    So the main uncertainty would be whether or not they have the temperature range right and the water might be liquid? If their estimate is just a little high then there might only be ice.

  17. Oooops, the trackback was my fault. Just wanted to link your article and clicked the wrong link (and the wrong mouse button :)) Well it’s kind of late here in vienna so I guess such things can happen at this time.
    Just delete it if it’s not supposed to be here or bothersome(my blog-entry is short and in german, listed your blog as source for the information)

    Well as for the news: That’s really something I’d call HUGE NEWS. I’m looking forward to further information :)
    Regarding this discovery, would it be legitimate to assume that there must be (is a great chance for) more earth like planets? I mean how are the odds of looking at an arbitrary nearby star and finding a planet like this?
    If they are extremly small, we must consider ourselfs lucky. But if they are that small, wouldn’t it be more likely that they are’nt so small after all?

  18. Christian Burnham

    Chris:

    Liquid water isn’t all that common. It needs the right temperature and pressure to remain liquid. The planet also needs to have enough mass to hold the liquid.

    I should say- I’m not an expert in these things, so someone correct me if I’m wrong.

  19. Lemme ask a stupid question…how long would it take to get there?

  20. Christian Burnham

    Rasputin:

    A long long time. 20 light years away means that it would take 20 years traveling at the speed of light.

    It would be impossible to make the trip in one human lifetime at current technology. Maybe a few thousand generations would do it. The BA would know!

    Of course, once we wreck this planet (in a century or so), we might start thinking a little more seriously about interstellar travel.

  21. seperlinky

    20 Light Years = 117515527950310.55 Miles

  22. TheBlackCat

    Darwin IV, here we come!

    Except it’s smaller than Earth, isn’t it.

  23. “how long would it take to get there?”

    Well, even if speed was no issue, we are still limited to the amount of acceleration the human body can stand. Half the trip there would be accelerating, the other half decelerating.

    150 metres per second per second has been tolerated by astronauts in training for short periods before blackout. 30m/s/s is a better number tolarated for long periods of time. Going with that number, we could accelerate to light speed in just 115 days if we could transfer all energy to velocity… again a lot of IFs…

    I would guess a few hundred years.

  24. Just one quick comment: you say “This makes it the smallest extrasolar planet yet found.” That is not true. The original millisecond pulsar planets are all a few Earth masses or smaller: http://en.wikipedia.org/wiki/PSR_B1257+12

    This is a very cool discovery nonetheless…

  25. drbuzz has a good idea.

    Surely, SETI must have scanned that section of the sky at some point. Are they thinking of going back through that data to see if they can learn anything interesting?

    Even if they don’t find a message from ET, it couldn’t hurt to look.

  26. If you accelerate such that the “g-force” squeezing you against the floor is the same as you feel on Earth (1 g), you can reach Gliese 851 in about three and a half years, ship time (20.5 years or thereabouts, as the clocks tick on Earth). I work out the figures here.

  27. # Martin Lawrence Says:
    April 24th, 2007 at 6:12 pm

    “how long would it take to get there?”

    Well, even if speed was no issue, we are still limited to the amount of acceleration the human body can stand. Half the trip there would be accelerating, the other half decelerating.

    I would guess a few hundred years.

    Let’s see.. dug out my old copy of Arthur C. Clarke’s THE PROMISE OF SPACE, which has a table showing distances at a constant 1G.

    Duration (out and back)
    Ship Time Earth Time Distance (LY)
    1 1 0.06
    2 2.1 0.25
    5 6.5 1.7
    10 24 10
    15 80 37
    20 270 137
    (etc.)

    So, 20LY would require less than 15 Ship Years, 80 Earth Years.

    J/P=?

  28. Considering that red dwarfs last a long time, and should not be confused with a white dwarfs. this could keep going for a long time. It might be a good place to move to if we ever get to that point.

  29. ‘(which is why the Moon always has the same face toward us here on Earth)’

    Wow, that is more than a little WRONG there. The Moon always has the same face to the sun not the earth. The bright portion of the moon that we see is always lit because the sun gives off light, the earth does not. We would see the dark side when the moon isn’t full if we just had some enormous lights to shine on it. Funny how that bit above was overlooked…

    Phil Hanner
    Founder – CCP

  30. Ross Smith

    Re the diameter and density: the interior of planets is compressed by their gravity. The Earth’s bulk density is quite a bit higher than it would be if you broke it up into smaller pieces, because the core is substantially compressed. The same thing would happen for this planet, but even more so because of its higher mass. If its mass is 5 times Earth’s and its composition is similar, its diameter would be somewhat less than 5^(1/3) times Earth’s.

  31. Davidlpf

    I wish I could go there next week on my vacation, but is a little far. :-)

  32. Jason

    22 m/s^2 is the gravity…
    I’m no expert on exactly how much this would be if someone could enlighten me…
    Would it be akin to the gravitron (or whatever centrifugal force ride one comes across at a carnival), or am I grossly under/over-estimating the force?

  33. Criminy, what would life be like on a tidally-locked ocean world?

    I’m more interested in how a planet without seasons would be different. Even if it does have significant axial tilt, 13 days is way too short for the slight difference to cause a yearly variation (seasons on Earth lag behind the effects of axial tilt by around a month).

    I’ve heard many people say that intelligent life couldn’t evolve on a planet without seasons, as it wouldn’t allow for yearly cycles to encourage plant growth. Frankly, I have my doubts about this. The life we see is the product of our environment; in a different environment, we’d see a different type of life (if any). Of course, this does imply that if life evolves on that planet, it will likely have major differences from life on Earth. That doesn’t mean it can’t be intelligent, however.

  34. jokermage

    Phil Hanner wrote “Wow, that is more than a little WRONG there. The Moon always has the same face to the sun not the earth.”

    This is like a cast iron skillet calling some blue willow china “black”.

    There is no dark side of the moon. There is the near side which we always see and the far side, which we only know from probes and Apollo astronauts. If you want, you can do the math. Tidal force is over distance cubed, as I recall, which seriously limits the sun’s tidal force on the moon compared to earth’s.

  35. Ati

    >>(which is why the Moon always has the same face toward us here on Earth)’

    Wow, that is more than a little WRONG there. The Moon always has the same face to the sun not the earth.

  36. Ati

    (:note to admin: less-than and greater-than signs are not parsed properly:)

    “(which is why the Moon always has the same face toward us here on Earth)’

    Wow, that is more than a little WRONG there. The Moon always has the same face to the sun not the earth.”

    WRONG correction, the original is right. The Moon, just like several other moons in the Solar system, is tidally intelocked with Earth, showing roughly the same face to *us* (not the Sun) at all times. Think about it: if the Sun had more gravitational pull here than the one between the Earth and the Moon, then tides in the ocean would follow the Sun (making high tide *always* around noon), instead of following the Moon.

    ~

    At 1G, theoretically it would take about a year to accelerate up to light speed. But the limiting factor is maximum speed, which is *much* less than the speed of light.

    Some here calculated a (few) hundred years to get to the star 20 light years away, while current propulsion allows for up to the 30-40 km/s speed range (and that only for unmanned space probes), which is about 4 *magnitudes*, a very far cry from light speed. That is unlikely to improve even .5 magnitudes in the next century.

    And that’s just speed, we haven’t mentioned that humans are genetically suitable for *this* environment — think air, food, water, light, radiation, gravity etc. The *worst* spot on Earth is much friendlier than any place on Mars, in space (in the long run), or, probably, this newly discovered planet.

    Realistically, it is in our absolute best interest to learn to take better care of our planet, and each other, while we can.

  37. Kid Cool

    what is the SAO designation for this star?

  38. Buzz Parsec

    Damn thing ate my post. Nice explanation about how to see for your self that Phil Hanner is wrong wrong wrong. Just watch the moon through a telescope for a month and you can see with your own eyes that it isn’t rotating with respect to the earth, and all the while it *is* rotating with respect to the Sun, because you can watch the shadows shorten as the sun rises and lengthen as it sets.

    Also, the Earth does give off tons of light – reflected sunlight. The earth is much brighter at “full Earth” than the Moon is at Full Moon. You can easily see landmarks on the Moon by earthlight a few days before and after new moon (“the old Moon in the new Moon’s arms”), and you can check for yourself that the Moon hasn’t rotated with respect to the Earth.

    This is what science is all about. Anyone can repeat the experiment and verify the results for themselves. It is not necessary to believe anything just because someone says so.

  39. NElls

    Phil Hanner, I think that what the BA wrote means that the same terrain on the moon is always facing us, not that the illuminated portion of the moon is always facing us.

  40. Ryu

    It really is just amazing how these discoveries keep piling up. It does give me more hope that we will find real evidence in my lifetime. And the idea that there is another planet that resembles our own in the slightest gives me goosebumps.

    One question. I understand the planet may have the same rate of rotation and revolution, but what would it mean to be “tidally-locked”?

  41. Scott

    “Criminy, what would life be like on a tidally-locked ocean world?”

    Ask the colony living on Nemesis, they should have a good idea of what that’s like.

  42. bswift

    Phil Hanner: no, the moon always has the features side facing toward the earth. If you don’t believe it, go check it out yourself.

    Chris & Ross Smith, re diameter & density: I agree that the models probably are taking into account the equation of state (relation between pressure and density)

    Ryu: yes, that means it would be tidally locked.

  43. The Bad Astronomer:

    May they make many more… and may their results get ever smaller, and ever cooler.

    Not much cooler, I hope — the estimated temperature for Gliese 581 C is zero to 40 Celsius. Hoth, anyone?

    Ryu:

    One question. I understand the planet may have the same rate of rotation and revolution, but what would it mean to be “tidally-locked”?

    Tides, over time, can slow the planet’s rotation down by friction, until the planet’s rate of rotation equals its rate of revolution. The tides of the Sun and Moon have already slowed the Earth down somewhat, but well short of the “tide-locking” point. I don’t have the formulas at hand, but it turns out that if you pick star-planet combinations such that the planet is in the habitable zone, dimmer stars produce larger tides on the planet than brighter ones. By the time you get down to red dwarfs (a few percent the solar luminosity) the tides are much stronger and tidal locking is a real possibility.

  44. I’m not sure if Phil Hanner was joking or not. Either way, what I said was right, and what he said was wrong. :-)

    And I cannot believe I said this was the lowest mass extrasolar planet– of course the pulsar planets are smaller. I am usually the one to point stuff like that out! I of course meant lowest mass exoplanet orbiting a main sequence star.

    One image in the press release says the planet’s gravity is 1.6 times ours, but I get it being more than twice, using the radius and mass they supply. Maybe the numbers they give (mass x 5 and radius x 1.5) aren’t quite accurate.

  45. Tim G

    SETI’s Seth Shostak is on “Coast to Coast AM” talking about this announcement now.

    There are some issues with red dwarfs (dwarves?) and habitability. One is that flares are proportionally much greater than the sun’s. Another is the possible much weaker accumulation of volatiles (read water) in temperate zones.

    ”
    Centauri-Dreams article #2
    Centauri-Dreams article #3

    Blake Stacy should also give the specific power and specific energy requirements of such a craft using the highest specific impulse theoretically possible.

    Update: Richard Hoagland is also speaking on the radio about the announcement.

    Why?

  46. llewelly

    I’ve heard many people say that intelligent life couldn’t evolve on a planet without seasons, as it wouldn’t allow for yearly cycles to encourage plant growth. Frankly, I have my doubts about this.

    For most of the Cretaceous, most of the Paleocene, Eocene, and Oligocene, most of Earth had little or no annual variation in surface air temperature. (Those earlier ages had much higher levels of CO2, and therefor water vapor, resulting in a much better insulated world. More importantly, ice caps were small or nonexistant. Ice caps greatly enhance the effect of axial tilt.)

    The idea that plant growth can’t be encouraged without yearly cycles is clearly bogus, at least here on Earth.

  47. Shane

    Way cool. I just don’t know how they can “know” so much about it while we can barely get photos or details of pluto.

  48. Isn’t there going to be some serious tidal force scrunching on this guy, what with a planet 5 times bigger on a 5-day orbit inside its 13-day orbit?

  49. bswift

    BA Phil: the paper states (without stating how it was calculated…grrr…) that the radius is “close to 1.5 R_earth”, so the gravity would be (5/1.5^2)g = 2.2g, like you get.

    If the assumption is made that R~M^1/3, then you get 1.7g.

    Still, it should be important for everyone to note that this a minimum mass, so the actual mass is likely to be greater (though not by much). Still, it’s the smallest minimum mass planet detected with radial velocities!!

  50. dale

    Breaking Update: The European Southern Observatory is now reporting that they have found which appears to be a single Starbucks coffee shop on the planet. Although not maned, the coffee shop is proof of the coffee chain’s secretive deep space expansion efforts.

  51. Delysid

    What would the light cast by this planet’s red dwarf be like?

    Obviously it would be “reddish”. But how different from our own sun’s light would that be?

    Would it be like the deep pure redness of the red light used in photographic dark rooms, where a human eye can barely perceive any other colour and everything looks like a black & white photo except red instead of white?

    Or would it be more like the reddish golden hues of certain sunsets, where the light still includes most of the spectrum of human-visible colour but with a heavy skew to the red end of the spectrum?

    And perhaps most important for a future tourist industry on the planet after the invention of faster-than-light travel: could one get a decent tan in the planet’s red dwarf sunlight?

  52. Tim G

    My original comment didn’t go because I goofed the links:

    There are some issues with red dwarfs (dwarves?) and habitability. One is that flares are proportionally much greater than the sun’s. Another is the possible much weaker accumulation of volatiles (read water) in temperate zones.

    Centauri-Dreams article #1
    Centauri-Dreams article #2
    Centauri-Dreams article #3

    Blake Stacy should also give the specific power and specific energy requirements of such a craft using the
    highest specific impulse theoretically possible.

  53. BC

    Phil Hanner:
    There are pictures of the “backside” of the moon – this is the side that we never see (but if you send a satellite up there, you can get pictures). If one side of the moon always faced the sun, then no pictures would exist of the ‘other’ side of the moon because it would be permanently hidden in shadows.

  54. K

    @ColoRambler: 0C – 40C is a very comfortable temperature. Remember that water freezes at 0C (on Earth at least, don’t know about that planet).

  55. Al

    I’m no expert but I doubt you would notice much difference in the light than here on Earth for two reasons. One is that even though the star is faint compared to Sol there is still a lot of light hitting the surface. It would be hard to discern that much color with light as bright as this (do you really notice much yellow in the sun’s light?). Of course it would still not be as bright as our sun from what I read so color might be a little easier to detect.
    More importantly the human brain tries “normalize” the light reaching our eyes so this would greatly effect how we would perceive the lighting on this planet. For example look at a fluorescent light then take a photo of it. To our eyes there is little cast to it because the brain adjusts for it but in the photo (if the lab or camera itself hasn’t tried to suppress it) you will notice how the green cast really jumps out.
    So while the planet wouldn’t look too unusual to the eye it would show up more in photos.

  56. Criminy, what would life be like on a tidally-locked ocean world?

    There was a show on History/Discovery/National Geographic? titled “Extraterrestrial” (which I recorded and burned to DVD) that looked at two ‘discovered’ worlds, and went into the science of a tidally-locked world, extrapolating the life forms. This computer doesn’t have a DVD player or I’d give more information from what it had.
    (Michael Dorn, WORF of ST:TNG/DS9 did the narration)

    J/P=?

  57. bswift

    BC: IF (big if) the same side of the moon always faced the sun, we could still get pictures of the backside by using earth-shine to illuminate the shadowed side.

    Al: The light emitted by an M dwarf is much redder than by the sun and is perceptible to the human eyes. Imagine spending all your time under a bright darkroom bulb. Your eyes would sort of get used to it, but reflected light from objects in the “sunlight” wouldn’t look quite the same.

  58. If the mass and radius figures given are correct to two significant figures, then the planet has a density of around 8200 kg/m^3. This makes it a fairly dense body, either stony or metallic. There would definitely have to be elements heavier than Helium present, and Oxygen is a good bet. And given the temperature range, so is water.

    However, before we get all excited about this newly-discovered planet, I want to point out that a planetary surface is probably not the best place for a spacefaring society. ;) We’d be better off dismantling Ceres and making enough Stanford Tori to house a trillion people, than we would be if travelling to this distant planet and attempting to live in ~2 g.

  59. SCR

    Thanks for posting this superluminous news BA.

    I’ve emailed some others incl. my local Astronomical Society (of which I’m a member) & my writer’s group quoting you and referring to your site. Cheers! Huge Breaking News indeed – and I heard it from you first! ;-)

    Now to imagine how the star looks and its other planets from whatstrange new world is unfolding befroe our eyes ..

  60. Gravity about twice that of Earth? Orbits a red sun? Temperature range permits liquid water? Massive tidal forces from being so close to its parent star?

    They’ve discovered pre-explosion Krypton.

  61. Random thought:
    I wonder if SETI responds to news like this.

  62. Michael

    Wow! just wow.
    How do they work out the radius? Wouldnt an ice(well,water in this case) planet have a different radius to a rocky planet.
    In any case, looks like we have our first target for the terrestrial planet finder and its various ilk.

  63. rpdelgado

    “But remember, Gliese 581 is cooler than the Sun, so at this distance the planet would actually be very temperate: models show it would be between 0 and 40 Celsius! If that doesn’t grab you, then consider this:

    That is warm enough for water to be a liquid.

    So what we may have here is a terrestrial planet with liquid water on its surface.”

    Yep. that did grab my attention.. Big discovery…How many possibilities…..This is great !!!!!

  64. MartinDalsgaard

    It’s the most exciting time we live in! There is so much happening, you can barely believe it!

    If this world shows out to hold water and perhaps oxygen (Wich would be rather lucky), the only problem is the distance. 20 light years is a long way for our tiny race – so we won’t see it up close in our lifetime. But damn, this is so exciting. Say it meets the demands of humans in terms of atmosphere and other raw materials, wonder what the human race would look like after inhabiting that sort of planet for a 100 generations?

    Our starchildren would probably be dwarfs, with massive legs, and bigfoot syndrome. I can’t believe that some people would’nt find these sort of news interesting.

    I can’t wait to see more!

  65. Of course, the important question is…

    Are there cephalopods there?

  66. PK

    Ati, you can keep accelerating at 1g until you run out of fuel, but otherwise there is no limit. Special relativity ensures that you never go faster than light (but you get arbitrarily close to it as you keep on accelerating). I wonder whether Arthur C Clarke got his numbers that way.

  67. Darth Robo

    “I wonder if SETI responds to news like this.”

    Apparently it already has. Twice.

    http://www.richarddawkins.net/forum/viewtopic.php?t=13317

  68. To MartinDalsgaard: The human race would only change if we let natural selection have a go.
    So if we want humans to adapt, we should just let people loose without any support until nature have done its work.
    Or alternatively, do selective breeding…

  69. Kevin

    Phil said “And I cannot believe I said this was the lowest mass extrasolar planet– of course the pulsar planets are smaller. I am usually the one to point stuff like that out!”

    You’re forgiven. This is the sort of news item that makes us all get giddy like schoolgirls. :D

  70. Arne

    The star is of magnitude 10, and is also called HO Librae. But the variations is minimal, just about 0.02 magnitudes. It belongs to variables of type BY Draconis. Here are some names for the red dwarf star: HO Librae = Gliese 581 = BD-07d4003 = Hip 74995 = SAO 31048 = HD 234677.

  71. So if we want humans to adapt, we should just let people loose without any support until nature have done its work.

    I find this a curious expression: to “let people loose”. Who is currently holding the leash? Are you under the impression that natural selection has zero impact on Homo sapiens? If that is true, then please demonstrate that heritable factors such as risk for heart disease, diabetes, CF, cancer… etc have zero impact on evolutionary fitness (i.e. count children).

    Natural selection, to reduce it to a single word, is about death. If we “let people loose”, are you suggesting we deny these colonists access to any medical technology post-1900, and that we richly supply their stores with rats, fleas, and a range of bacterial, fungal, and viral pathogens? Perhaps the ship should have random severe weather events, and the occasional famine?

    Put lots of people in a ship and aim it at this newly-discovered world. If it takes generations (ship-time) to get there, then the genetic makeup of the settlers when they arrive will be determined by who reproduced on board. For a smallish population, like 1000 or 10000, over a few generations (less than 100), selection is going to have very little effect. The evolution of this spacefaring population is going to be dominated by genetic drift, a stochastic sampling procedure that is the inescapable result of a population size smaller than infinity. Strong selection gradients would either purge deleterious alleles from the population very rapidly, or simply wipe out the population entirely.

    I’m not going to speculate about any cultural changes that may occur on the journey.

    My question: what kind of spectrum do red dwarf stars put out? Earth-type DNA is fairly resistant to wavelengths in the ‘visible’ range, but is chemically altered by UV and higher-energy photons. Could complex (i.e. multicellular) life arise in a very-low-mutation-rate environment?

    Also, very cool news.

  72. K:

    Yes, I know 0 C to 40 C is perfectly comfortable. I was making a joke about discoveries that were “ever cooler” than the current one.

  73. Robert Horning

    I can’t believe the sheer ignorance of those who claim the Moon is tidally locked with the Sun. It really is locked with the Earth, which is why you always see the “Man in the Moon” view of the lunar maria. The tidal lock also produces some interesting physical structures on the Moon, where the lunar core (relative to its physical center) is actually skewed toward the Earth, and the lunar crust is thinner on the “near side” as opposed to the “far side” where it is much thicker. This is another reason for the lunar maria, where magma came up and filled in the craters. The far side only has the “Sea of Moscow”, which is one of the smaller maria. The far side of the moon is dominated by cratering.

    Due to these maria and the off-center nature of the lunar core and “mascons” or mass-concentrations (with the maria) that make the local “gravity” vary by quite a bit, orbital characteristics for going around the moon are mostly unstable. This is one of the reasons why you can’t have satellites which orbit the moon for any substantial length of time (the Apollo missions were only for a few days, and they had active pilots in the command module to make corrections as needed). In fact, there are only three orbital inclinations that are stable for even a medium-length orbital period (aka more than a few months) in spite of the fact you don’t have an atmosphere which causes drag on the spacecraft. Atmospheric drag is a much bigger concern for low-earth orbits like the International Space Station which has to be boosted up to a higher orbit in a routine basis… and why Mir and Skylab both crashed and burned due to orbital decay.

    While solar tides also exist on both the Earth and the Moon, the gravitational influence of the Earth is at least an order of magnitude larger than that of the Sun with respect to the Moon. It is for this reason that the Earth dominates the equation.

    Most of the other moons in the solar system also have tidal locks with their “parent” planets. The Galliean moons (Io, Europa, Ganymede, Callisto) have this characteristic, as well as the two moons of Mars: Phobos and Deimos.

    Of all of the strange things in the solar system that havn’t been completely explained, however, is the seeming tidal lock of Venus with respect to the Earth. The retrograde motion of Venus as well as its rotation rate is sufficient that from something “standing on the surface”, the Earth is seen in nearly the same spot in the sky for the entire day as the Earth and Venus reach conjunction.

  74. I’m no astronomer, but I’m keen to do a calculation about how long it would take to get to this new planet. Setting aside the Starship Enterprise in favor of current technology, using, say a probe we could put together for a couple hundred million dollars in short order, I offer the following simple model (I ignore acceleration time).

    20 light year from Earth: 20 * 9,460,730,472,580 km (the distance of one light year) = 189,214,609,451,600 km

    The fastest probe to date is the Helios 2, so lets build another one of those:
    (Helios 2) 241,350 km/h * 8,760 hrs/yr = 2,114,226,000 km/yr

    189,214,609,451,600 km / 2,114,226,000 km/yr = 89,496 years for a Helios 2-type craft to travel 20 light years.

    You can see a few years of acceleration and gravity assists won’t add much to the overal travel time.

  75. For those that wanted it, there is a pre-print of the paper online (not yet accepted for publication). Also, the model that they use to estimate the radius is from a paper by Valencia et al (2006).

    Ed Minchau, I wouldn’t take the quoted numbers to be accurate to two significant figures. The final numbers depend on several models so are open to systematic errors due to various assumptions.

  76. andy

    If we take Earth’s equilibrium temperature using the same model as was used for Gliese 581 c, it is around -10 degrees C, so this planet is probably quite a bit warmer than Earth (the lower temperatures of around 0 degrees C comes from assuming a Venus-like reflective cloud cover, but greenhouse effect of an atmosphere which could support such cloud cover is neglected – in such a model, Venus in our solar system has an equilibrium temperature of MINUS 40 degrees C), and it seems Earth orbits quite close to the inner boundary of the habitable zone.

    If this planet is an ocean world, there would likely be major greenhouse heating going on there, since water vapour is a very good greenhouse gas. Boiling oceans anyone? Might even end up with supercritical oceans…

    Alternatively, if the planet is volatile-poor, you wouldn’t get so much greenhouse heating, so liquid water would be able to survive for a time. However the planet is likely tidally locked, which could mean all the volatiles (including atmosphere) get frozen out on the darkside, since a good supply of greenhouse gas is required to keep the darkside warm enough to prevent freezeout. You’d end up with a dead rockball with an icecap on the darkside.

  77. andy

    Hmmm… may have plugged the wrong albedo value for Venus in there, it’s more like minus 10-20 than minus 40. But still.

  78. Jim Baerg

    Re: apparent color of the sunlight on this planet.
    There’s an interesting article on what planets of red dwarfs would be like in the November 2005 Analog magazine. In it the author points out that the temperature of the filament of an incandescent light bulb is less the temperature of even the coolest red dwarf. So although the light might be perceptibly different from sunlight, the difference would be less than going from sunlight on earth into a room lit only by incandescent electric lights.

  79. KingNor

    this is a major boon for astrology, since this is the planet that governs gullability.

    Turns out it affects all the signs equally and significantly.

  80. Just a thought about getting there — our prospective crew is going to have to adapt to 2.2g anyway when it gets there, right? So why accelerate at a constant 1g? Why not accelerate differentially and do the acclimatization over the period of the trip? Probably easier on the asrtonauts/colonists, plus it should shave some time off the trip.

  81. Phil

    It’s a shame it’s so far away.

  82. To TheBrummell: I was merely trying to explain how evolution works.
    If you use artificial means to help people survive in high a gravity environment, like medical technology that strengthens your bones, helps your blood circulation and whatever it takes (exoskeleton?, if we are gonna go cool sci-fi), you will not see any adaptation.
    We could give them rats and fleas if you really want to, it might even be necessary with certain things we don’t like to keep an eco-system going (think Brussels sprouts and broccoli).

  83. Pal

    If you have discovered the planet, why can’t you photograph it?

  84. A few idle thoughts: Gliese 581 is apparently a variable star, although the preprint linked to above says the star isn’t all that variable. At one point the paper also suggests the planet’s orbit might have an eccentricity of about 0.28, slightly more than Pluto. If so, and the planet’s tidally locked, the libration would be pretty substantial, wouldn’t it? I couldn’t guess how any of these factors would affect habitability. Perhaps someone’s already crunched the numbers.

    I don’t suppose there’s any reliable way to tell how old the star is, is there? Since the star’s a red dwarf, it could be vastly older than the sun. Supposing life ever evolved there, we really don’t know how long life persists once it evolves, or how long the host planet remains habitable. It’s comforting to think the answer to both is “forever”, but we don’t actually know that.

    And most importantly: If the planet’s inhabited, there’s bound to be oil there, which tells us that the inhabitants hate freedom and are hiding WMDs. On the bright side, once our space marines arrive there, we can be absolutely certain they’ll be greeted as liberators. Hey, it’s always worked before.

  85. AndreasB

    Re: What would the light cast by this planet’s red dwarf be like?

    Given that the light given off by a star as well as those given off by incandescent light bulbs is pretty much blackbody radiation, we should be able to compare those two. For Gliese 581 I find a surface temperature between 2000 K and 3350 K, whereas light bulbs usually operate between 2000 K and 3300 K depending on type and voltage.

    So it should look pretty much like indoor lighting with light bulbs.

  86. “Christian Burnham Says:
    April 24th, 2007 at 5:57 pm

    Rasputin:

    A long long time. 20 light years away means that it would take 20 years traveling at the speed of light. ”

    In Earth’s frame of reference. If we suppose some method by which a rocket can be accelerated at 9.8 m/s/s indefinitely [1], then the people on the ship would only measure about about six years (3.7ish if you just accelerate all the way and slow down with a lithobraking episode).

    [1]: Note how I avoid speculating how this might be done. The traditional ways of doing this (Bussard ramjets or rockets that emit tachyons) have serious problems (Bussard ramjets seem to be about a billion times better at radiating energy than they could be a generating it, making them not so much a propulsion method as an excellent brake. Tachyons don’t seem to exist, tachyon rockets look a lot like perpetual motion machines and there’s some theoretical reason to think that universe that do have tachyons are not stable. Nobody wants to live in a blowy-uppy universe).

  87. andy

    Where is the habitable zone around Gliese 581? As a star of spectral type M3, it has a surface temperature of around 3500 K (rough value), as compared to the Sun at 5800 K, and a radius of about 0.38 times the solar radius (from Extrasolar Planets Encyclopaedia). Assuming both the Sun and Gliese 581 are blackbodies, this means that Gliese 581 has 0.19% of the luminosity of the sun. Taking the square root of this quantity gives the factor by which we scale the habitable zone – 0.14.

    This suggests that to get the same amount of radiation as Earth, a planet must be located at a distance of 0.14 AU from Gliese 581. This 5-earth masses planet is at 0.073 AU, which would make it uncomfortably warm. In fact, if we take the habitable zone of our Sun to be 0.95-1.65 AU (I’ve got a reference for these values somewhere, but can’t find it right now), scaling it to Gliese 581 gives a habitable zone of 0.13-0.23 AU. This puts the third planet at the outer edge of the habitable zone. In fact, because it is in an eccentric orbit, the third planet moves in and out of the habitable zone as it circles its star – so a thick greenhouse-gas laden atmosphere (as would be expected on an ocean planet) would aid this planet’s habitability rather than hinder it.

    Perhaps more hospitable conditions (at least in terms of temperature, the gravity situation on an 8.2 Earth-mass planet wouldn’t be pleasant!) would be found on Gliese 581 d, rather than the boiling oceans of Gliese 581 c.

  88. Skepted56

    How old is the star? If we’re trying to determine the probability of this planet having any kind of biosphere or even a civilization, its age is very important to know.

    Also, it’s probably better that the planet is larger than Earth instead of smaller. It’ll take much longer to cool off and geological processes will occur for a longer period of time. A liquid core is necessary for a magnetic field to protect the planet’s atmosphere.

  89. Skepted56

    andy, the luminosity is related to the surface temperature of the star to the fourth power. So a small difference in temperature will create a very large difference in luminosity. Rough numbers won’t cut it, unfortunately.

    From this news article:

    However, the research team believes the average temperature to be somewhere between 32 and 104 degrees and that set off celebrations among astronomers.

    I believe they are measuring temperature in the Fahrenheit scale.

  90. Stu

    Classic quote from Natasha Kaplinsky, news presenter, on BBC News just now, humourously wrapping up the “new planet” story…

    “So, liitle green men might be coming, but not for 20 light years…”

    sigh…

  91. I guess this means that our instruments are good enough to detect Mesklin, right?

  92. Skepted56:

    andy, the luminosity is related to the surface temperature of the star to the fourth power. So a small difference in temperature will create a very large difference in luminosity. Rough numbers won’t cut it, unfortunately.

    Turns out he’s pretty close. The absolute magnitude is +11.58, easily calculated from the apparent magnitude and the distance, which then works out to a luminosity of 0.20% solar. The uncertainty on this value is at most a few percent, mostly in the distance measurement. However, he’s off on the habitable distance: it’s 0.0447 AU, not 0.14. 0.14 is the square root of 2%, not 0.2%.

  93. Stuart: thanks a million for the links to the papers.

  94. Note: just a warning to anyone going after the full source of the Valencia paper: it’s on arXiv, they have to run scripts to make the PDF for you on the fly (probably from LaTeX), so they get a bit mad if you keep hitting it. Save it locally, if you want to go over it, and tend to jitter around your back/forward browser buttons.

  95. If this has already been mentioned forgive me and let me know.

    but wouldn’t we be able to get a pic of this planet with this?

    http://www.space.com/businesstechnology/070418_tech_wednesday.html

  96. Jim Rix

    What the age of this solar system?

  97. Nolwe

    Could you supply a link to the original article, please? Is it somewhere on arxiv?

  98. andy

    Turns out he’s pretty close. The absolute magnitude is +11.58, easily calculated from the apparent magnitude and the distance, which then works out to a luminosity of 0.20% solar. The uncertainty on this value is at most a few percent, mostly in the distance measurement. However, he’s off on the habitable distance: it’s 0.0447 AU, not 0.14. 0.14 is the square root of 2%, not 0.2%.

    True, the absolute VISUAL magnitude is +11.58. However, red dwarfs like Gliese 581 radiate primarily in the infrared, rather than the visual range. This means that taking the absolute V magnitude significantly underestimates the star’s luminosity. So your analysis provides the “visible light habitable zone”, in which the planet receives the same amount of visible light as Earth does.

    I don’t have the apparent bolometric magnitude (the magnitude taken across the entire spectrum) of the star, so I’ve basically put in 3500 K as an approximate value. The fourth power dependency on the value is definitely worth considering: supposing it could be 100 kelvin out, this gives a scale factor ranging between 0.131 and 0.146), so my estimate of 0.14 is not far out! My analysis attempts to take into account the total amount of radiation received by the planet, rather than just in the spectral range that our biology happens to allow us to see.

    In fact, it turns out that for stars significantly hotter or cooler than our Sun, the visible light habitable zone lies closer to the star than the bolometric habitable zone. So planets around such stars receiving the same total amount of radiation would receive less radiation in the visible region of the spectrum: cooler stars radiate more in the infrared, hotter stars radiate more in the ultraviolet.

  99. peenworm

    I’ve done some quick space math science and concluded that if life did develop on that planet, were it ever to come to earth it would be able to leap tall buildings in a single bound.

  100. Tim G

    Here are links to video:

    Video #1
    Video #2

  101. Mick

    I wonder if maybe the planet isn’t 50% larger, but it turns out it seems larger then it is because it has a large moon.

  102. Rick

    andy-
    You figured a luminosity for Gl 581 of .019 that of the sun, for a scaling factor of .14. The preprint gives the luminosity as .013, which gives a scaling factor of .11, and thus a h.z. (for your 0.95-1.65 AU) of .10 – .18 AU. Planet 2, at .07 AU, is still too close, but closer.

  103. For people asking about the radius estimate:
    They assume a composition identical to the best estimate for the bulk Earth composition, and then scale it, taking phase transitions and potential melting into account. The high density is due to the gravitational self-compression of the planet. In vacuum, iron has a density of about 8 g/cc. In the Earth’s core, it is compressed to about 13 g/cc. In a super Earth, it can get up past 20.

    My take on this whole business here:
    http://lablemminglounge.blogspot.com/2007/04/possible-terrestrial-planet-around.html

  104. Irishman

    TheBlackCat said:
    >Darwin IV, here we come!
    >Except it’s smaller than Earth, isn’t it.

    Darwin IV? No, this planet is bigger than Earth.

    Blake Stacey said:
    > If you accelerate such that the “g-force” squeezing you against the floor is the same as you feel on Earth (1 g), you can reach Gliese 851 in about three and a half years, ship time (20.5 years or thereabouts, as the clocks tick on Earth).

    That’s a mighty big “if”. ;-)

    Pal said:
    > If you have discovered the planet, why can’t you photograph it?

    It has to do with size of the object versus distance. It’s like seeing a flea on the back of a dog 50 ft away. You can see the dog, but the flea is too small to see. This planet has not been seen. No light from the planet (reflected off or emitted) has been seen. Rather, what was detected was a variation in the behavior of the star it orbits. The variation can best be acounted for by the presence of a planet of this size at this orbital distance. Play around with those numbers, and you would have a different effect to the star.

  105. Irishman says,

    That’s a mighty big “if”.

    Naturally. That’s why, in the best professorial tradition, I left the details as an exercise for the interested reader. (-:

  106. My analysis attempts to take into account the total amount of radiation received by the planet, rather than just in the spectral range that our biology happens to allow us to see.

    Oh, drat. I know about this difference, but didn’t really pay attention to it in any detail here. I was working strictly with the V magnitude, as you point out.

  107. Yes, yes, very exciting. Barely containable. !!! That’s why I’m pushing past the “how do we get there” bit to “I’m there, now how do my plants grow”. Because maybe I’m hungry and I need to think about how I’m going to eat for the next, um, however long I’m going to be there, because clearly commuting’s an issue.

    Photosynthesis: will it work differently with a less-bright sun? With a sun that’s a different color? Will it be a faster process, or slower? And will the sun still provide vitamin D, or different nutrition? Ultraviolet radiation, too — will that be as destructive there as it is here on Earth, or will we have other sun-borne worries? I know part of the UV problem we have here is our degrading atmosphere, and we have yet to learn about this planet’s atmosphere. But what do we know about the effects a red sun will have on us and our food sources? (Are these answerable questions for grade school science fair projects??? asks the art teacher who is also a naturalist for local park district and natural history museum…)

    The big number parts of this discovery make this such a pure and beautiful astronomy discovery. And well it should be!!! But I for one CAN’T WAIT to find out what waits for us on the planet’s surface — the geology, the botany, the meteorology (ok, hovering over the surface, but contributing to erosion patterns), microbiology, omigod if there are large animals on this planet??!?!?!!!

    As I said: barely containable. But it will have to be contained, because how long will it take to get more information? It will seem like light years. Sigh.

  108. Aaaargh. NBC News just reported this story using a graphic that said “In a galaxy far, far away…”. They then pointed out that it would take twenty and a half years to get there if you could travel at the speed of light, 186,000 miles per HOUR.

    Aaaaaaaargh.

    In brighter news, NPR reported this today without using their “this is just technogeek stuff, folks, no need to take it seriously” packaging which is standard for all science and technology stories.

  109. andy

    You figured a luminosity for Gl 581 of .019 that of the sun, for a scaling factor of .14. The preprint gives the luminosity as .013, which gives a scaling factor of .11, and thus a h.z. (for your 0.95-1.65 AU) of .10 – .18 AU. Planet 2, at .07 AU, is still too close, but closer.

    Taking the empirical formulae for the relation between B-V colour index, bolometric correction and temperature at this website and plugging in the B and V values from SIMBAD into the formulae, it gives a scaling factor of 0.14, although the star is somewhat cooler and larger than what I assumed. However, the scaling factor agrees with the scaling factor obtained from my assumed 3500 K star (from stellar class) and 0.38 solar radii (from Extrasolar Planets Encyclopaedia).

    Since you refer to the Bonfils et al. paper, I’ve downloaded it, I agree that they say 0.013 M_sol (Bonfils et al. 2005, not sure how they get that, don’t have time to research it right now. I’m assuming a perfect blackbody law, so I am probably out by some way, since cool stars are able to form molecules in their atmosphere which result in quite strong deviations from the ideal blackbody law), which gives a scaling factor of 0.11 – this still puts the habitable zone outside the orbit of this planet. In fact, if you take the luminosity scales as mass^3.5 law as presented in a past Bad Astronomy post, you get a scaling factor of 0.12 for a 0.31 solar mass star like Gliese 581.

    Plus, if you take Kuchner, 2003 (Astrophysics J 596 L105-108 “Volatile-Rich Earth-Mass Planets in the Habitable Zone”), the region in which ice planets give a liquid ocean rather than a supercritical one actually lies outside the orbit of the Earth, once again suggesting that if Gliese 581 c is an ocean world, it is more like a layer of supercritical water overlaying an ice mantle (presumably with a smooth transition from atmosphere to supercritical ocean).

    Another factor to consider is that a red dwarf during its pre-main sequence phase is around 10 times as luminous as during its main sequence phase (see Lissauer, ApJ 660 L149 “Planets Formed in Habitable Zones of M Dwarf Stars Probably are Deficient in Volatiles”), so this could kick the outer planet into an oceanic+greenhouse atmosphere state rather than a solidifed iceball.

    I’d say an optimistic but more realistic scenario for Gliese 581’s planets is three ocean worlds: the innermost “b” being supercritical, the middle planet “c” being either boiling (but still with a distinct atmosphere/ocean transition) or supercritical (smooth transition between atmosphere and ocean), and the outermost “d” having more temperate conditions, i.e. that Gliese 581 does host a habitable planet, but it isn’t the one the media are shouting about.

  110. Casey

    ColoRambler said:

    “Not much cooler, I hope — the estimated temperature for Gliese 581 C is zero to 40 Celsius. Hoth, anyone?”

    Were you trying to suggest that a planet cooler than Gliese 581 would be Hoth-like, or that Gliese 581 itself was already Hoth-like (if it has water)?

    Just in case you meant the latter, don’t forget that 0 Celsius is freezing, and that 20-22 Celsius is room temperature (~70 Farenheit) and that 37 degrees Celsius is average human body temperature. So, if the 0-40 Celsius range estimate for Gliese 581 is even close to correct, it is a quite temperate place indeed. I imagine Hoth being the sort of place that might reach a top warm temp of -10 Celsius on the warmest day at the equator.

  111. Casey

    ColoRambler, I rescind my comment above, I hadn’t read down to K, and your reply to K yet.

  112. Andy:

    I don’t have the apparent bolometric magnitude (the magnitude taken across the entire spectrum) of the star, so I’ve basically put in 3500 K as an approximate value. The fourth power dependency on the value is definitely worth considering: supposing it could be 100 kelvin out, this gives a scale factor ranging between 0.131 and 0.146)…

    My penance here, for not thinking this problem through clearly, is going to the original literature.

    Table 3 in This paper reports a relationship, applicable to main sequence and regular giant stars, between the bolometric magnitude, which is hard to calculate, and the color index (B – V), which is very easy to determine.

    Since I’m not a professional astronomer, I’m not in a position to determine the validity or quality of the results, so I take this with a little caution. In particular, I note that their data set for main-sequence stars (which Gliese 581 is) has only a few cool stars (which Gliese 581 also is). Still, given that Gliese 581 has a B-V color index of 1.61, this paper suggests a bolometric magnitude correction of -1.595, and a temperature of 3774 K (log T = 3.5768). This would make its bolometric absolute magnitude +9.98 instead of +11.58, and give it a total luminosity just under 1% solar, rather than the 0.2% I figured from just the V magnitude.

    Since this is an empirical (fit to data) relationship, it’s unlikely this figure is perfectly accurate for a given star, like Gliese 581, but it seems like an interesting starting point. At B-V > 1.5, the relationship is very sensitive to small changes, even as small as a few hundredths of a magnitude, so it wouldn’t surprise me if the bolometric correction for Gliese 581 differs by several tenths of a magnitude from this estimate.

    If any bona fide professionals want to elaborate on this, please do.

  113. between the bolometric magnitude, which is hard to calculate, and the color index (B – V), which is very easy to determine.

    bolometric correction, that is.

  114. The artist’s impression could stand some improvement. The planet itself is half full, when means the sun should be about 90 degrees away from it in the sky — but we see what presumably is meant to be a red dwarf *above* and to the right. With the planet and the sun in those positions, the planet should be in a narrow crescent phase, with the thickest part of the crescent pointing directly at the sun.

    The other body (a moon? another planet?) is a crescent, but again, the orientation is wrong. And the other planets in the system still probably aren’t close enough to show a visible disk to the naked eye.

    And just because the sun is a red dwarf, that doesn’t mean it isn’t *bright*. If the sun is in your field of view like that, you’re not going to be able to see anything nearby. I can accept that as artistic license, but not the incorrect orientations.

    Accurate astronomical art is *prettier* than inaccurate astronomical art.

  115. MJB

    My understanding is that the paper was submitted to Astronomy & Astrophysics — but was rejected. The link to their preprint is here: http://obswww.unige.ch/~udry/udry_preprint.pdf

    Looking at the paper, I have several questions as to their results.

  116. Jesse Cohen

    Wow, after finding so many gas giants, it’s great to finally see an earth like plant. You can’t help but feel optimistic about the chance for alien life when there’s an earth like planet so close to us. hmm, maybe there are life forms on that planet looking at us right now.

  117. Laguna2

    Sometimes I feel the desire to throw my radio out of the window.
    My radio station just had an expert from ESA to talk about this topic.
    And what were their questions?
    When can we see pictures?
    When will we be able to colonize that planet?
    And so on.

    I guess that poor ESA guy was banging its head against his office wall afterwards…

  118. Melusine

    Woo hoo, it’s nice to see 135 posts on an astronomy issue! :-)

    Hey, does the guy/gal who broke the press embargo on this story get in trouble or anything?

  119. MichaelS

    Harold, the speed of light is actually 186,000 miles per SECOND, not per HOUR. (According to Google Calculator, it’s 186,282.397 mi/sec, and according to Wikipedia, it’s exactly 299,792.458 km/sec.)

    You are correct that it would take around 20 years for a light-speed space ship to reach a star 20 light years away, but that’s measured in Earth-time. If you could instantly accelerate to the speed of light, then instantly decelerate once you got there, the trip would take literally no time at all for the people on the ship, because of relativity. Since acceleration is not instant and we can’t actually get to light speed, the travelers would experience more time than 0 going by, but less time than the people back on Earth (or the people already at the planet).

  120. Rick

    A follow up on Andy’s calculation of the habitable zone above.

    The preprint gives a luminance of 0.013 that of the sun, and a distance of planet c from the star of 0.073. Using a simple inverse square calculation this would seem to give an solar constant (with that of Earth = 1) of the planet of 0.013/0.073^2 = 2.44. Venus is about .7 AU, so the solar constant for Venus is about 2.0. So planet c would seem to receive a 23% higher intensity of radiation as does Venus, which is not known for having liquid water (except in old science fiction stories). So it seem that the liquid water claim may be questionable.

    Or is this approach all wet? (pun intended).

  121. andy

    In fact, we can have a bit of fun if we apply the calculations used to get the “habitable” temperatures to the planets in our solar system. If we assume (as the paper does) that the planet’s albedo varies between that of the Earth (0.35) and Venus (0.64), we get the following:

    Earth: -58 to -23 degrees C
    Venus: -20 to +21 degrees C
    Mercury: +73 to +130 degrees C

    So it looks like, according to the media hype about Gliese 581 c, Earth is a frozen iceball, but both Mercury and Venus have a chance of being habitable, and would presumably be shouted about in all the press releases (“two habitable planets discovered around distant star” anyone?), while the presumably dead third planet would barely get a mention.

    Also note that the effective temperature of Venus (-20 degrees C) and Earth (-23 degrees C) are very similar. Effective temperature is a poor discriminator of habitability!

  122. MichaelS, yes, I know that the speed of light is 186,000 miles per second. Anyone who paid attention in their grade school science classes knows that. However, millions of people who were watching NBC News last night now “know” that the speed of light is 186,000 miles per hour. It was on TV, so it must be true, right? Hence the “Aaaaaargh.”

  123. Actually, I expressed my frustration a little bit more explicitly on my own blog:

    http://anothermonkey.blogspot.com/2007/04/bad-astronomy-nbc-style.html

    WARNING: This links to a post that links to this post. If you go there, be careful not to get stuck in a loop.

  124. bigal11

    great… another 10 million illegal aliens … all on welfare

  125. Rick

    Playing with numbers:

    A planet radiates energy per unit area T^4 to maintain a constant average temperature; thus the energy it radiates away is equal to the solar constant (S) at the planetary orbital distance. Thus we have the equation S = k*T^4, with k being a constant depending on the geometry, albedo, etc.

    With estimated values of k and the local solar constant, we can estimate the average temperature of other planets by T = (S/k)^(1/4).

    Let the solar constant = 1 for earth at a distance of 1 AU, and thus S = 1/d^2 for other planets in our solar system, where d is the distance from the Sun in AU.

    The preprint gives for Gliese 581 a luminosity of .013, and planet c has an orbital distance of .073 AU, for an estimated solar (steller?) constant for planet c of 2.44,

    Using various rocky planets in our solar system to obtain estimates for k, we can get estimated average temperatures for planet c:

    Mercury (d = 0.39 AU, T = 440 K) : planet c temperature = 343 K (106 C)
    Venus (d = 0.72 AU, T = 737 K) : planet c temperature = 782 K (544 C)
    Earth (d = 1.00 AU, T = 288 K) : planet c temperature = 360 K (123 C)
    Mars (d = 1.52 AU, T = 218 K) : planet c temperature = 336 K ( 99 C)
    Pluto (d =39.48 AU, T = 43 K) : planet c temperature = 338 K (101 C)

    Not looking good for liquid water on planet c.

  126. andy

    Rick: I’d say the Venus model there is going to be the most realistic for an ocean world, since such a planet would form a thick atmosphere of water vapour (very good greenhouse gas), which would function in much the same way as the carbon dioxide atmosphere on Venus.

    Also to note, your temperature estimate for the Venus-like model is above the critical point of water (647 K), so it looks like any ocean on Gliese 581 c is supercritical (thus would exhibit very different solubility properties to liquid water) and merges smoothly into the atmosphere.

  127. Rick

    Andy-

    I would agree that probably the Venus-type model is more likely if there is a significant atmosphere. If there isn’t much of an atmosphere then there can’t be liquid water because of the low pressure, but I would think a planet with that mass would have a significant atmosphere, and with that amount of energy being supplied by it’s primary, it would look more like Venus than Earth.

  128. GaterNate

    There’s a cool animation of all three planets around this star on solstation.com as well as lots of other info about the star. Looks like there are a lot of other red and a couple orange dwarfs all within 9 light years of 581. One system is a triple. Could 581 be part of a loose cluster?

    Also I was wondering if anyone knows, since this system is 20 light years away, does this mean we’re done looking at closer stars? I know there’s a planet at Epsilon Eridani, and I can’t help but wonder why we haven’t yet found a planet at Alpha Centauri or 61 Cygni or Epsilon Indi for examples. Is the jury still out on whether or not closer stars have planets?

  129. Rick

    Oops. I had an error in, of all things, my temperature conversion from K to C. Assuming I got it right this time, the values for C (the others are the same) are:

    Mercury (d = 0.39 AU, T = 440 K) : planet c temperature = 343 K (70 C)
    Venus (d = 0.72 AU, T = 737 K) : planet c temperature = 782 K (508 C)
    Earth (d = 1.00 AU, T = 288 K) : planet c temperature = 360 K (87 C)
    Mars (d = 1.52 AU, T = 218 K) : planet c temperature = 336 K (63 C)
    Pluto (d =39.48 AU, T = 43 K) : planet c temperature = 338 K (65 C)

  130. MichaelS

    Harold, sorry, I missed that. It looked a little odd the way you wrote it, but I wasn’t sure what you meant. Guess I know now. :)

  131. YosemiteGail

    If it is a Red Dwarf Star, wasn’t it hotter before?? So how could there be any habitable planet?? Wouldn’t these planets have been sterilized by the heat of the star before it became a Red Dwarf Star?? If they have been sterilized by the previous heat, how could they then become habitable once the star became a Red Dwarf?? Or contain water??

  132. Hallo, but topic starter, you are sure?
    prof.Preobrajensky.
    Good luck!

  133. Dave

    Andy and Rick:
    There is an additional factor in the Kasting, Whitmire & Reynolds (1993; Icarus, 101, 108) paper. The planetary albedo is expected to drop in the infrared, so a larger fraction of the stellar radiation is absorbed for an M-dwarf planetary host star. For an M0 star this is supposed to be a 30% effect, so it would move the habitable zone outward by about 15%. With minimum masses of 5 and 8 Earth masses, Gl 581 c & d are likely to have denser atmospheres than Kasting et al assume. So, the greenhouse effect could well be stronger than on Earth. So, if there is a habitable planet in this system, it is more likely to be Gl 581 d.

    If you download the preprint available from the ESO press release web site, you’ll find that it has changed in the last few days. The orginal version had the title: “The HARPS search for southern extra-solar planets XI. An habitable super-Earth (5M_earth) in a 3-planet system”, and the new title is “The HARPS search for southern extra-solar planets XI. Super-Earths (5 & 8M_earth) in a 3-planet system.”

    Also, 5 Earth-masses is the minimum mass – not the actual mass, so it is not clear if this planet is the lowest mass planet found around a main sequence star or not. The median prediction for the mass of Gl 581 c is 5.5 Earth masses, which is the same as the median prediction for OGLE-2005-BLG-390Lb, the lowest mass planet found by microlensing.

  134. Rick

    Dave-

    The have also added into the body of the paper the following:

    “It is however obvious that the actual surface temperature of the planet very much depends on the highly uncertain composition and thickness of its atmosphere, which govern both the planetary albedo and the strength of the greenhouse effect. It is probable that the planet is located towards the “warm” edge of the habitable zone around the star. A detailed study will also need to consider the possible tidal locking of the planetary rotation to the orbital period.”

  135. Darvo

    WOW..this is exciting!! I can’t wait to learn more about this planet!

  136. the planetary scientists at the systemic blog http://oklo.org suggest that this planet formed further out & has about one earth-mass of hydrosphere. a rough calculation of mine leads to the estimate of a worldwide ocean 622 miles deep.

    its eccentricity means a variation range of the graybody temperature around 23 degrees celsius either way.

    i can’t see it not having a substantial greenhouse effect but my most optimistic “dry planet” calculations come to an average temperature of around 70 celsius.

    the redness of the star is not so important as the less energy for plant life, also over much of the planet the sun s low in the sky & the land would be in shadow.

    m.

  137. andy

    Dave: cheers for the info there, feeds quite well into my case that Gliese 581 c is going to be a really unpleasant place. Definitely I am aware that this is a minimum mass, however I think the small scale of the system suggests the masses cannot be too much greater, or planets b and c would very likely be unstable. I’m also (obviously) working under the assumption that the planets of Gliese 581 are ocean planets (in the sense that they are composed of a rocky core surrounded by a significant ice shell amounting to a large fraction of the total planetary mass, not that they have liquid water).

    Actually, the more I am finding out about Gliese 581 c, the more it seems likely to be a kind of hot mini-Neptune, but probably lacking the hydrogen envelope of our solar system’s ice giants (the low mass and proximity to the star probably would cause the planet to lose what hydrogen it may have accreted). This would give the planet deep, water-rich (rather than hydrogen/helium) atmosphere, which would transition smoothly from atmosphere to supercritical fluid rather than having a liquid/gas surface. Perhaps Gliese 581 b and c are examples of worlds close to the ocean planet/gas giant transition.

    If the planets are terrestrials then they might be able to have carbon dioxide atmospheres, perhaps similar to Venus, but are likely to be dry (particularly if they formed in situ – collision velocities so close to the star would be high and tend to drive volatiles off forming planets, rather than causing accretion).

    graywyvern: I doubt you can have an ocean that deep, since at some point the pressure reaches the point where you can form high-pressure ice (I’d guess in the case of a hot planet like Gliese 581 c, you’d get ice VII and/or ice X below the probably supercritical ocean, cold worlds like Ganymede probably have ices V and/or VI below the liquid water ocean).

  138. StevoR

    Epsilon Indi has two brown dwarfs – actually a binary brown system orbiting thousands of AU from the main orange dwarf star.

    Esilon Eridani has at least one exoplanet in a slightly eccentric Jovian type orbit with indications of another exoplanet further out.

    For more detail on these see the planet project section of James Kaler’s ‘stars’ website :

    http://www.astro.uiuc.edu/~Kaler/

    Hope the link works.

    Some interesting calculations here, folks – thanks. I wonder if the authors of that paper (Udry, Bonfils, Mayor et al) took them into account already or not. If only they were able to veiw some of the comments here.
    Hmmn .. someone should send them a message and invite them to respond! Well, here are worse ideas … ;-)

  139. StevoR

    Okay that first link doesn’t seem to be working try this one :

    http://www.astro.uiuc.edu/~kaler/sow/pp.html

    Hope he adds Gliese 581 to it soon too! ;-)

  140. SCR

    “graywyvern: I doubt you can have an ocean that deep, since at some point the pressure reaches the point where you can form high-pressure ice (I’d guess in the case of a hot planet like Gliese 581 c, you’d get ice VII and/or ice X below the probably supercritical ocean, cold worlds like Ganymede probably have ices V and/or VI below the liquid water ocean).”

    Sorry to have to ask but please could someone explain what exactly is meant by “supercritical” & the different ices?

    I’m guessing supercritical = some sort of superheated but superpressurised state of liquid water but to be honest I’m really not sure …

    Also while I very vaguely recall reading or hearing somewhere that there are more than one type of ice I’m not sure what all the varieties are and what differences they make ..

    Finally, whats the (n) etiquette on quoting / using elsewhere these comments posts that other people have raised? Would Andy (post of May 1st 2007 here) & Rick (ditto, but April 26th) & Graywyvern (ditto but April 29th) be very upset if I quoted them in a not-for profit letter / article for an Astronomical society newsletter thingummy I’m working on? I’ll certainly attribute as best I can – I would contact but unsure of e-mails of course and even surnames for that matter. If they read this pleaseletme know -Iwon’t use their material without permission either don’t worry.

    Interesting calculations and conclusions that I’d like to discuss tho’ .. Please let me know via this post or a BA forum – I give the BA permission to pass myemailaddress ontothem if they request it & will if known addres stosend to send them a copyvia e-mail of whatever I produce.

    Not sure of (n)etiquette here but hope this is okay ..

  141. StevoR / SCR

    GaterNate Says: [April 26th, 2007 at 6:24 pm ]

    “here’s a cool animation of all three planets around this star on solstation.com as well as lots of other info about the star. Looks like there are a lot of other red and a couple orange dwarfs all within 9 light years of 581. One system is a triple. Could 581 be part of a loose cluster?”

    Can’t see why not altho’ I gather its an old ~ish star and thus likely to have
    moved a fair way from its original birthplace & companions .. Could they
    have stuck together this long – not sure but its an interesting thought &
    thanks for bringing it to our notice …

    “Also I was wondering if anyone knows, since this system is 20 light years away, does this mean we’re done looking at closer stars? I know there’s a planet at Epsilon Eridani, and I can’t help but wonder why we haven’t yet found a planet at Alpha Centauri or 61 Cygni or Epsilon Indi for examples. Is the jury still out on whether or not closer stars have planets?”

    I suspect the jury _is_ still very much out. What our lack of finding exoplanets round them -if we’ve already searched throughly~ish so far ’bout ‘em is that anyplanets theydo ahve are eitherlow-mass or further out from their star -perhaps both. HotJupiters stand out becauseof tehradial velocity technique -their closeness and highmass gives them a bigger push-pull signal FXT on their star.

    Alpha Centauri at least too is I’ve read somewhere, less likely tohave Jupiters because of the binary factor – Alpha B woudl perturb the protoplanetary disk creating Joves but is far enough away that planets to
    about Mars equivalent orbits could still form around both stars. I think.

    Aha! ‘Infinite Worlds’ by Lynette Cook – a non-fict’n book by a space artist – had a mention of that and of the implication that such planets
    would thus be dry – lacking water because of the gravity of the twin
    stars.

    61 Cygni is also a binary of orange dwarf stars whereas Epsilon Indi as mentioned already hastwobrown dwarfs orbiting it -but at a very bigf spearationso for all intents & purposes it mayaswellbe single – and low-mass stars we seem to be finding have more low mass planets esp. when metal-poor as I think Eps Indi is..

    Yup, I would’nt give up on finding planets nearer to home and nicly low
    mass yet. Epsilon Indi, 61 Cygni & the Alpha Centauri twins I’d still think
    were in the running.

    Indeed the Okri (?) site linked toabove seemd tosugegst aworld around Alpha Cen B was hinted at in the data so far collected but I’m not althogethrsure if that’s only simulation or real world ..???

  142. spud

    It’s an exciting discovery. One wonders if the atmosphere can be better analyzed by observing the spectral changes as the planet transits the star.

  143. Hi My Name Is ivanes.

  144. andy

    Now we have a better analysis of the habitability of these planets: The habitability of super-Earths in Gliese 581

    Just as I predicted, the planet Gliese 581 c is too close to its star to be habitable, while Gliese 581 d might be able to support liquid water.

  145. Boubou

    What is the name of this planet they found?

  146. gelese 687 c. i think thats is the name i am not shure thou… “first earth like planet” pshhh…-.- i don’t beleive that 0.0 but i do beleive they have found gelese 687 c. nasa never will lie.. but the government will lie i think are 51 is hideing something that may be related to gelese 687 c. a some sort a’ crash happened in 2000 the government has put up signs saying”if you travel beyond this point we will kill you” or something like that >_>. btw 20 light years is a whole humans life time if it got back we would be dead at the time it got back lol about 1,000 years waiting for the probe to get back ^^ just saying

  147. This blog somethin related to the planet. It indecate that the planet is Earthlike, but not Earth! The surface gravity is more than twice that of Earth’s (22 m/s/s versus 9.8 m/s/s on Earth) and who knows what the atmosphere is like. But the basic characteristics are certainly provocative! Almost all the planets detected using this method are more massive than Jupiter, and extremely hot, way too hot to be hospitable to our kind of life.

  148. Batman

    Ok, just a few observations here.

    First, It shouldn’t take too long to get there, all we need is warp drive, a navigational-deflector force-field to keep from having grain-of-sand sized particles from destroying the ship, and inertial dampeners to keep from becoming a thin paste on wall when accelerating to warp 5 or 7.

    Second, how cool would it be to have your kids there, then bring them back here so that they can fly, have x-ray and heat vision, freeze breath, run real fast, and be super strong?

    Sign me up! I’m ready to go!!!!

  149. jackie

    could this be the 10th planet that the ancient Meyans predicted that I have been hearing about as in Nibiru? If so thats not such a good thing. I am praying that the Nibiru planet is just a myth. For those of you who don’t know what I am talking about research that planet (Nibiru or some call it the planet x) and come up with your own conclusions. Let me know what you think. I’m not saying I believe it or not I just want to do my research and find out the truth thats all.

  150. wow!! cool, thats great!! hope 2 see some aliens on that new planet.i’ll surely see some other info. if possible.hope u all get amazing results 4 ur such a wonderful research.BEST OF LUCK!!!!

  151. Scott Wegener

    I happen to be producing a feature sci if film about a colonizing effort on Gliese 851d. Can someone answer a few speculative questions for me?
    1. Assuming 851d is in a zone that should be tidally locked to the star, could two (heretofore) undiscovered moons potentially overpower that lock?
    2. If that could happen, would the resultant forces make the planet tectonically unstable? (I hope not!)
    3. Does anyone know where, relative to the earth and the galactic core Gliese is? Further out? Closer in?
    4. I feel stupid for this one: If gravity is twice earth, does that translate to mean a 180# man would weigh 360#? Or 540#?
    Thanks! Scott Wegener, Exec. Producer “The Last Race” [davidgpro@gmail.com]

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