Another Kepler milestone: Astronomers find two Earth-sized planets orbiting the same star!

By Phil Plait | December 20, 2011 11:18 am

Astronomers have achieved a big milestone in the search for another Earth: the two smallest confirmed planets ever found orbiting another star… and they’re both about the size of Earth!

Artist’s illustration of the Kepler-20 planets with Earth and Venus for size comparison.

The planets are called Kepler-20e and Kepler-20f, and as you can see by the illustration above they are very close to the same size as our home world: 20e is about 11,100 km (6900 miles) in diameter, and 20f about 13,200 km (8200 miles) across. For comparison, Earth has a diameter of 12,760 km (7930 miles). This makes them the smallest confirmed exoplanets seen orbiting another star! The previous record holder was Kepler-10b, which has a diameter about 40% bigger than Earth’s.

To be clear: while these planets are the size of Earth, they are nowhere near Earth-like. The star, Kepler-20, is very much like the Sun, though a bit smaller and cooler (and 950 light years away). However, both planets orbit the star much closer than Earth does; 7.6 million km (4.7 million miles) and 16.6 million km (10.3 million miles), respectively. This is so much closer that both planets must have surface temperatures far hotter than ours, 760°C and 430°C (1400°F and 800°F). Even on the "cooler" planet Kepler-20f, it’s hot enough to melt tin and zinc.

So don’t start packing your bags to visit, even if you could spare a few million years to get there via rocket (950 light years is a bit of a hike). I’ll note that we don’t know the masses of these planets either. I’ll explain that in a moment, but given their sizes it’s expected they’ll have masses similar to Earth’s.

So this is very exciting! For one thing, it shows that Kepler can indeed find planets the size of Earth orbiting distant stars. That right away is fantastic; that’s the main goal of Kepler in the first place.

For another, it shows that our solar system is not entirely unique. We do know of several other stars hosting solar systems of their own, but those planets tend to be very massive; they’re easier for us to find. Since Kepler-20e and f are so close to Earth-sized, this is a big achievement.

And we’re still not done: there are three other planets in the Kepler-20 system! The others are much larger than the Earth: named Kepler-20b, c, and d, they have diameters of 24,000, 40,000, and 35,000 km (15,000, 24,600, and 22,000 miles); smaller than Uranus and Neptune, but still pretty hefty. We do have the masses for them: 8.7, 16.1, and about 20 times the mass of the Earth. Call them "super-Earths" if you like.

All these planets huddle pretty closely to their star; the orbit of Kepler-20f, the farthest from the star, would still fit comfortably inside the orbit of Mercury! Oddly, the configuration is very different than our own solar system. While ours has the lower-mass planets close in and the bigger ones farther out, in the Kepler-20 system they alternate, going big-little-big-little-big.

So how do we know all this? The Kepler observatory is in space, staring at one patch of sky all the time. There are 100,000 stars in its field of view, including Kepler-20. If there are planets orbiting a star, and we see the orbit of that planet edge-on, then once per orbit the planet directly passes between us and the star, blocking its light a little bit. This is called a transit, and the bigger the planet, the more light it blocks. That’s how the sizes of the five planets were found.

As these planets orbit their star their gravity tugs on it, and that can be measured by carefully observing the star’s light. As a planet pulls it one way and then another, there is a very small Doppler shift in the starlight, and the amount of that shift tells us how hard the planet is tugging on the star, and that in turn depends on the mass of the planet. Only the three bigger planets in the Kepler-20 system pull hard enough for us to measure, which is why we don’t have the masses of 20e and 20f; they’re too small to measure.

Also, to be clear, we don’t have direct images of these planets (those pictures above are drawings). They were found indirectly by how they affected their star. But these methods are now tried-and-true, and the existence of these five planets has been confirmed. They’re real.

This is a fantastic discovery for so many reasons: the smallest planets found orbiting another star, the first Earth-sized planets seen by Kepler, both in the same solar system, and in such an oddly-configured and compact system at that. This means we need to think more about how such planets can form, of course, since it’s so weird… but no matter what, it means we’re that much closer to finding the ultimate goal: an Earth-sized planet orbiting a Sun-like star in that star’s habitable zone, where liquid water can exist.

Every time I hear news like this, I wonder how much longer we’ll be waiting to hear that news… and I strongly suspect it won’t be too much longer.

Image credit: NASA/Ames/JPL-Caltech


Related posts:

- Kepler confirms first planet found in the habitable zone of a Sun-like star!
- A boiling superEarth joins the exoplanet roster
- Big news: first “solid” exoplanet found!
- Two exoplanets discovered by "citizen scientists"

CATEGORIZED UNDER: Astronomy, Cool stuff, Top Post

Comments (58)

  1. jason

    This is great news, I am waiting for us to start confirming planets that are within a few percentage points of earth and in the “goldilocks” zone. Then the next step is to get images or at least spectrographs of these worlds. It would be fantastic to find one with free oxygen.

  2. Smedley

    How do the scientists figure out how hot or cold a planet is?

  3. Ken

    So the clouds and the hint of ocean and continent on the artist’s illustration of Kepler 20-f are a bit optimistic?

    Seriously, how are these illustration decisions made? As I understand it, the available data is just one number, the diameter, so “featureless sphere” would be my personal preference.

  4. Chris

    Five planets all closer than Mercury. How stable is that solar system? I would think that would cause some serious perturbations in the orbits. I’m finishing grading, maybe someone can figure that out.

  5. Brian Too

    Bizarre alternating sequence for the large and small planets. The people who study planetary formation must be like kids in a candy store. A surfeit of data, solar systems that contradict all expectations, and all theoretical models up for grabs.

  6. Jeffery Keown

    There goes Bode’s Law out the window… if it weren’t already disproven. I love this stuff!

  7. Question: from what we have seen, are most planetary systems aligned similarily in both orientation and spin direction around their stars or is it a random distribution? I would assume the former because the formation of the galaxy they are in (ours) followed a process, has greater mass coreward than it does rimward. The question is, what determines the spin of the Galaxy? Random distribution of material in the formation of it or something else?

  8. Kepler doesn’t have the ability to detect systems where the planets don’t pass between us and the star, so what we see is going to be heavily biased towards systems where the plane planets orbit in is aligned with the galactic plane, irrespective of what the actual distribution of orbital planes is.

  9. Rod

    Layman’s question, here. How would we be sure of the existence of liquid water on planets as far away as those when, it seems, we’re having a hard time confirming it in our own neighboring planets/moons?

    Thanks

  10. Georgia

    The main factors that determine the temperature of a planet is how far away it is from its sun and how hot the sun is. Of course our atmosphere does a lot to change the temperature of our surface (look at how different say Venus and Mars are and would be even if they had the same orbit as Earth). The main determining factor though is the sun.

  11. Dave

    @silence (8) The Galactic tidal potential is very weak on scales of the size of the Solar System. There’s no reason to think that there’s any generic trend in the distribution of orbital planes. The default expectation should be that the orbital planes of single-planet systems should be isotropically distributed (i.e., the vectors perpendicular to the orbital planes should point in all directions with equal probability). It is true, though, that Kepler is much likelier to find multiplanet systems with coplanar orbits than ones with mutually inclined orbits.

  12. Dave

    @Georgia (9), You’re absolutely right that the incident flux on a planet is a very important factor, even the most important. However, even given a flux level, there is a huge amount of uncertainty in what the surface temperature will be (in addition to your Mars/Earth/Venus examples, consider the fact that Venus has a hotter surface than Mercury, despite Mercury’s receiving 3.5x as much insolation). There is, therefore, a great deal of uncertainty regarding the surface temperatures of these newly announced Kepler planets.

  13. Jess Tauber

    Re 10. I wonder, though- I remember some report awhile back that claimed that galaxies in clusters tended statistically toward the same rotational orientation. It would be really interesting if there was some nonrandom spread of planetary systems’ orientations. But it might be due to something having to do with the central bar of our galaxy, the arms, or some such. That said, one of the things I’ve often noticed when out with my telescopes and binoculars is that stars themselves in open clusters appear more often than not (and this seems little discussed) arranged along large spiral patterns, often with the brightest members towards the astrographical center of the system. The spirals aren’t necessarily extended linearly, but themselves can have further folding (reminding me of DNA). I’m guessing a lot of this has to do with the magnetic fields and huge solar winds of the largest, earliest members of the clusters, doing something to the larger molecular clouds that later form other solar systems. All it takes is a little geometrical bias to crystallize things. If this is true, then while all the resulting systems may not be in-plane, they may still be nonrandomly/nonarbitrarily arranged around the central stellar cores.

  14. > it means we’re that much closer to finding the
    > ultimate goal: an Earth-sized planet orbiting a
    > Sun-like star in that star’s habitable zone, where
    > liquid water can exist.

    Didn’t we already find one: Kepler 22b?

  15. Special One

    Jeffery, Kepler 11 already blew Bode’s Law out of the water. Oddly enough, it’s system also has the small-big-small-big-small-big pattern but without as much difference in size. Plus 5 of its 6 planets would also fit within Mercury’s orbit.

    Be champions!

  16. MaDeR

    “two smallest confirmed planets ever found orbiting another star…”
    I would expect better from astronomer than that. Why everyone forgets about pulsar planets?

    “This makes them the smallest confirmed exoplanets seen orbiting another star! ”
    No, they do not.

  17. Diego Barizo

    I am curious about the star’s name. Does it have another name besides Kepler-20(Lyra-x)?

  18. Yep, another couple years and the announcement will surely be made.
    We’re going to need more Kepler missions to map the whole sky!

  19. Whitney

    If kepler 22b has liquid like water, it means the allians are also there meaning that a human being can also survive. Right? Or I’m a wrong? @Confused student.

  20. GrogInOhio

    Wonderful! IMHO, it’s just a matter of time before Kepler, or something else, finds multiple earth like planets.

  21. Dave

    @Jess_Tauber (12): True, but galaxies are much closer to each other than stars are, relative to their sizes. The cluster tidal potential is nonnegligible on galaxy scales, but the Galactic tidal potential IS negligible on solar system scales. If a cluster is the size of a Chicago city block (8 to the mile) , then a galaxy in the cluster would be roughly the size of a Smart car. In contrast, if our galaxy were the size of the same city block, then the diameter of Pluto’s orbit would be the size of a single large bacterium (about 2 microns). The point is, galaxies are a reasonable size of a cluster’s diameter, but solar systems are a tiny fraction of a galaxy’s diameter, so there’s no reason to think that solar systems care about the orientation of the Galaxy. Doesn’t mean it’s impossible that they do care for some as-yet unrealized reason, but as of now there’s no reason to think that the distribution of orbits has anything to do with the shape of the Galaxy.

    @Dotan_Cohen (13): Kepler 22b has 2.4 times Earth’s radius, 62% of Neptune’s radius. It’s much larger than Earth and, while we do not know whether it might have any sort of life on it or not, it’s certainly not a close Earth analog.

  22. @Smedley (2): You asked:
    >
    >How do the scientists figure out how hot or cold a planet is?
    >

    They know how bright the star is.
    They know how far away from the star the planet is.
    Thus, they can tell how much energy that planet is receiving from its star, relative to (say) the Earth.

    The actual temperature a planet ends up at is a balancing act between (A) how much energy it’s receiving from its sun, and (B) how much heat it’s radiating out into space. That second term, the heat loss to radiation, depends severely on the planet’s temperature — the more its sun warms it, the more heat it sheds, until it reaches a point (called “thermal equilibrium”) where its radiation loss is exactly equal to the energy it’s receiving.

    However, this is a gross estimate. The one factor we CANNOT determine about these extra-solar planets (yet) is their albedo — that is, how reflective they are. Earth’s moon only has a 7% albedo, which means that 93% of the incident solar energy is absorbed and goes into heating its surface. Earth, by contrast, has about a 40% albedo, so only 60% of the incident solar energy is absorbed. The whiter and shinier the surface, the higher the albedo. Since Kepler’s observations tell us nothing about how reflective these planets are, we have to assume an “average” value for their albedos and calculate their surface temperatures based on that guess.

  23. If a planet orbits its star at a distance permitting liquid water on its surface, how likely is water to be there? Going by the presence of frozen water in our system, the odds are pretty high.

  24. Grand Lunar

    So, two Earth-sized planets, but their conditions are Venus-like then, huh?

    Cool (or should I say ‘hot’?) stuff!

    Neat that when we started out, we were finding Jupiters and super-Jupiters.
    Then we got down to Neptunes, and now here we are at Earths!

    If we give these places proper names, lets use the ones from various sci-fi works!

  25. Dragonchild

    There’s some serious confirmation bias at work here. . . but rather than get frustrated, I think this really seems to say people are free to imagine a lot about planetary systems (at least, there seems to be a vanishing correlation between size and orbit). Bear in mind many of our methods wouldn’t work for an extrasolar analogue of Neptune; for example, if you try radial velocity or transit you’ll be waiting a LONG time. On the extreme end, based on Hill sphere calculations, the Sun can easily have a planet orbiting out as far as one light-year!

    There are a LOT of ways planets can orbit a star, and while we can expect scientists to stick to facts, the possibilities seem to be endless.

  26. Brett

    The smaller “big” planet (8.7 Earth masses) could be a Super-Earth, but it’s more likely a Gas Dwarf. The ~20 Earth masses one is probably a “hot Neptune”, considering its radius and mass (Neptune is “merely” 17 Earth masses in comparison).

  27. Justin

    Everyone is waiting for a planet in the habitable zone, but isn’t it expected that we probably won’t see anything just yet? If the habitable zone corresponds to a orbital period of about a year then we should just now start to see these objects since Kepler has to see 3 transits to call it a detection, so that is about 3 years. Since Kepler was launched in 2009 we are coming up on the three year mark and maybe we will see some earth-like habitable zone planets soon!

  28. ND

    So what sort of instruments (current or theoretical that can be implemented in the near future) would be needed to be able to create a 100×100 pixel image one of these planets? Or another planet closer than this system. I chose this images size as a conservative, and I’m guessing achievable, goal that could give us an image of a planet that shows surface variation. The existing images of planets are I believe only several pixels wide. Even a low-res image such as this would be exciting.

    I’m tired of seeing computer generated planets on sci-fi shows. I want something real :)

  29. Chris

    @29 ND
    From the Rayleigh criterion, the resolution limit is given by
    alpha = 1.22*lambda/D
    where alpha is the angular resolution, lambda is the wavelength and D is the aperture

    Now to make very conservative estimates lets assume we are looking in blue light (lambda=400 nm) and at a Jupter sized planet (70,000 km radius) circling Alpha Centauri (4.3 light years=4*10^13 km) That would have an angular size of 3.5*10^-9 radians

    Plugging that in, we’d need a telescope 139 m across. (Largest telescope is the Extremely Large Telescope with an aperture of 39 m) Now you want 100×100 pixels, so now we need 13.9 km wide telescope. Now if you went further out it’s going to scale as the distance (double the distance, double the size, half the planet size, double the telescope size). It will get very big very fast. Now this could theoretically be achieved using interferometry (that’s those giant radio telescope arrays), but not on the earth, even with adaptive optics, over this large of a distance I don’t think it’d work. You’d need something space or moon based and I haven’t heard of anything on the drawing board.

    You may want to check my math, long day and in case a factor of two fell out, but order of magnitude sounds about right. Long story short, we’ll be relying on the artists imagination for a long time.

  30. Messier Tidy Upper

    Whoah! Superluminously brilliant news this! :-D

    Congratulations Kepler team and thanks for this prompt write-up BA. :-)

    I’m blown away by this. :-)

    So many thoughts and questions on it. So little time before i have to head out for the evening. This would have to be announced on the day I don’t get to the computer before now of course. Oh well.

  31. Messier Tidy Upper

    What the .. Duplicate comment deleted.

  32. Messier Tidy Upper

    Er .. don’t know why but the one comment I clicked submit too has come out thrice. Then of course my computer had to crash. Aaaarrgh! Computers! :-(

  33. Messier Tidy Upper

    We do have the masses for them: 8.7, 16.1, and about 20 times the mass of the Earth. Call them “super-Earths” if you like.

    But I don’t like, I really don’t. I think that term is misleading in a number of ways. :-(

    First the term “gas dwarf” (coined by exoplanet hunter Sara Seager) or mini-neptune is probably a lot more accurate given the masses if exoplanets are anythinglike tehones inour solar system. For comparison Neptune has 17 earth masses and Ouranos 14 so these are closer in mass to those ice giants in our solar system.

    Also given their locations brushing up against their suns ferocious surfaces calling them Mustafar class worlds or SuperVenuses or SuperMercuries is certainly more likely to match their nature and character.

    Still this is a marvellous even if strange and densely packed planetary system and so astounding that we can dtect and discover it in such detail from so far away. Mind bogglingly wonderful accomplishment. :-)

    Only the three bigger planets in the Kepler-20 system pull hard enough for us to measure, which is why we don’t have the masses of 20e and 20f; they’re too small to measure.

    Directly perhaps but how about the perturbations they may produce in the other exoplanets of the system? Could we deduce their masses from those eventually?

    Also again, does anyone have the primary stars spectral class please?

    I’d so love to see a map of this planetary system and its worlds – and I wonder if it boatss other exoplanets more distant and as yet undetected and how many planets it may have in total. If only we had FTL drive .. Sigh.

    Even on the “cooler” planet Kepler-20f, it’s hot enough to melt tin and zinc.

    Its hot enough to do so on Mercury too as this quote :

    “A tin can placed on the sunlit side of Mercury or on the surface of Venus would melt.*”
    - Page 12, ‘Amazing Facts about Australia’s Southern Skies’,Steve Parish, Steve Parish Publishing Pty, no year listed.

    * On Venus the can would also be instantly crushed by the immense atmospheric pressure – SCR.

    observes. Well for tin anyhow, not sure zinc~wise! ;-)

  34. @7 Pete Mancini: Question: from what we have seen, are most planetary systems aligned similarily in both orientation and spin direction around their stars or is it a random distribution? I would assume the former because the formation of the galaxy they are in (ours) followed a process, has greater mass coreward than it does rimward.
    As far as I’ve read, the orientation of star systems appears pretty much random. Our own solar system isn’t even close to being aligned with the galactic plane.
    On the other hand, there is such a thing as the galactic tide. I don’t know what the scientific consensus is on how/if it affects star system formation.

    The question is, what determines the spin of the Galaxy? Random distribution of material in the formation of it or something else?
    That takes some pretty complex math to model, but as for what little I understand, the process is similar for galaxies and for solar systems – that is, any cloud of gas and particles. I’m not the best person to try and describe it, but apparently the ultimate angular momentum of the galaxy/solar system is a product of the average direction and velocity of all the chaotically collapsing/coalescing stuff.

  35. Anyway, this is too awesome for me to properly gush over in my tired state. I’ll get back to ya tomorrow :)
    WOOooooooooo

  36. In the UK, this was reported last night on the BBC TV news – with yet another fine exemple of how even the “reputable” media get science spectacularly wrong.
    The headline was announced as “Astronomers have found a planet the size of Earth, orbiting another star, which might once have supported life.”
    An astronomer, who was interviewed, said something along the lines of: “The planet is closer to its star than Earth, so it’s too hot to support life. But if, at some time in the distant past, it was further from the star, then it might have been suitable to support life.”
    The newsreader somehow translated this to: “The planet was further from its star in the distant past, so it used to be cooler, and it could have supported life.”
    I despair.

  37. Pete Jackson

    The fact that Kepler is finding so many multiple planet systems seems to suggest that most multiple planet systems are closer to being coplanar than is our solar system. An imaginary Kepler out there observing our own solar system would not see more than one of the solar system planets transiting, I suspect. Has anybody done this analysis on how our own solar system would look to some distant Kepler orbiting around another star?

  38. SLC

    It is highly possible that Kepler 20 has other planets further out then these. These will be harder and take longer to find as their “years” will be commensurately longer. An observer on one of Kepler 20′s planets with the same technology as ours would not be able to detect the presence of planets around the Sun.

  39. alfaniner

    I hope they end up being named Romulus and Remus.

  40. Mejilan

    This is so exciting. So exciting!
    Some new technology is launched.
    Some cautious and encouraging findings begin to trickle in.
    And before we all know it, we find ourselves opening our arms wide to a flood of new science and information!

    Hubble got off to a rocky start but after a couple of refurbishing missions, led to some of the greatest imagery of celestial entities imaginable. Heck, some beyond imaging.

    Now in a much shorter time frame, Keppler has started to knock our socks off. It would be borderline criminal to NOT extend its mission, at this point.

    And with a hopefully successful James Web mission hitting before the end of the decade… I am all a-quiver with anticipation!

  41. Messier Tidy Upper

    @ ^ Mejilan : Agreed on all of that. Well said & me too! :-)

    @38. Pete Jackson : December 21st, 2011 at 6:33 am

    An imaginary Kepler out there observing our own solar system would not see more than one of the solar system planets transiting, I suspect.

    Well, we see transits of both Venus and Mercury so if any alien Kepler equivalent is out there – at exactly our right angle or maybe just the slightest fraction off it they should be able to see those – and Earth – transiting our Sun and maybe Mars and others too as well.

    Provided they look long enough. Right?

    (Remember that to confirm Earth’s existence would take at least 1,095 (Earth) days & probably more assuming they too need at least three transits as proof of existence. Also assuming no leap year is involved! ;-) )

    @37. Neil Haggath : Yeah, the mainstream media reporting on this can be .. (searches for a polite way of putting it) .. utterly infuriating.

    Mind you, I still wish exoplanetary and astronomical discoveries generally got more mainstream media coverage and in more prominence and depth too. ;-)

  42. amphiox

    An astronomer, who was interviewed, said something along the lines of: “The planet is closer to its star than Earth, so it’s too hot to support life. But if, at some time in the distant past, it was further from the star, then it might have been suitable to support life.”
    The newsreader somehow translated this to: “The planet was further from its star in the distant past, so it used to be cooler, and it could have supported life.”

    It’s almost as if scientists need to keep a mental dossier on “phrases which, if uttered in the remotest presence of a news reporter, WILL, with certainty of p < 0.000000001, be misquoted and misconstrued", and that "support life" is one of these….

  43. casper114

    Why does it matter if the planet is the same size as earth?

  44. Beau

    @ 18 Richard

    “Yep, another couple years and the announcement will surely be made.
    We’re going to need more Kepler missions to map the whole sky!”

    The Kepler mission is a statistics mission, not a mapping mission. They want to know the percentage of earth-like planets orbiting a sun-like star there are in the habitable zone. Out of the 100,000 stars that Kepler is watching, there’s a good chunk of them that have planets that we can’t see because the planets don’t transverse their star from our vantage point. Trying to map the entire exo-planet sky with a Kepler like mission would be impossible.

    That’s why we need warp drive and Starfleet ;)

  45. Jess Tauber

    Except that warp drive damages space, and Starfleet isn’t always the friendliest organization. Besides, all this takes time, money, organization, and resources that could be used for other things, like junk mail and unwanted holiday gifts. No, what we need is a way to simply de- and re-cohere ourselves elsewhere, instantaneously. No machinery, no Spice. Just grab ‘n go. You’d think an Intelligent Designer would have included this in the package, for those enlightened enough to figure out how.

  46. John

    One thing that I’ve been wondering is: Do these mass/radius measures incorporate the possibility/probability that these extrasolar worlds have moons? How much would that change the viability of a second earth if we were to discover that a world were x% less massive than we thought?

  47. amphiox

    You’d think an Intelligent Designer would have included this in the package, for those enlightened enough to figure out how.

    Ah, but maybe it did, and the enlightened figured it out back on Sigma 957 2 billion years or so ago.

    Earth being just a neglected side-effect of the big plan.

  48. amphiox

    Why does it matter if the planet is the same size as earth?

    It demonstrates unequivocably that Kepler really can (is sensitive enough) to detect planets that small, as we had hoped, but until now had not known for certain.

  49. amphiox

    It is highly possible that Kepler 20 has other planets further out then these. These will be harder and take longer to find as their “years” will be commensurately longer.

    I wonder if this might end up being the solution to the apparent paradox of the planets’ size/distance from star distribution. Given that what we’ve got here are two earth-sized, one super-earth/mini-Neptune, and two Neptune/Uranus sized worlds here. The mystery of the big-small-big-small-big distribution might end up simply actually being a mirage, with the system actually being small-small-small-small-small, with bigger Jupiter class worlds further out yet to be discovered.

    After all, I believe we know of several other multiplanet systems where there is at least one gas giant closer in than smaller, super-earth class planets.

  50. amphiox

    Also given their locations brushing up against their suns ferocious surfaces calling them Mustafar class worlds or SuperVenuses or SuperMercuries is certainly more likely to match their nature and character.

    Personally, I think trying to pigeon-hole planets discovered by Kepler as “Earth-like” versus “Venus-like” is an exercise in nit-picking.

    Considering that Kepler isn’t actually able to distinguish the difference between planets like Earth and planets like Venus, and if there was an alien Kepler mission looking at Sol, if it could detect Earth and Venus at all, those alien astronomers would not be able to predict with any great certainty which one of the two is like Earth and which one is like Venus, and would most assuredly classify both planets into the same category, I think that for the purpose of considering Kepler planets, Venus-like worlds ARE Earth-like worlds.

    We often call Venus Earth’s “evil twin”, and these days people tend to focus on the evil part, but we seem to forget the second word there all too often.

  51. ND

    Chris,

    Thanks for your response. I don’t doubt your numbers as I’m familiar enough with the relationship between telescope size to know even the Keck telescopes would be unable to meet the 100×100 challenge. A 100×100 image would be quite detailed. I think a 25×25 would be a great starter.

    After searching for space based interferometry I came across this http://en.wikipedia.org/wiki/Astronomical_interferometer#Labeyrie.27s_hypertelescope

    I should have done more reading before posting my question. Here are some possible missions to image other planets.

    http://en.wikipedia.org/wiki/Darwin_%28ESA%29
    http://en.wikipedia.org/wiki/Terrestrial_Planet_Finder

  52. Deepak

    Kepler efforts are great but the planets are too far away to even think of getting there. And why such a slow progress on settling down on Mars? The Earth is getting filled up and has no more space to live for the incoming generation. When we reached moon the in 1960′s it was thought that by 2000 we would be settling on Mars. We seem to be lost on science and astronomy not knowing where to go.

  53. John Dodds

    Re 9, 12, 22 & others.
    Question: are you all assuming that the only source of planet radiated energy comes from absorbed E/M sun radiated energy?
    ie Earth radiates, but much of the Earth temperature comes from the decay heat being radiated, not from the reflected or absorbed and reradiated solar insolation?
    Then Jupiter apperently radiates more heat that it absorbs because the incoming E/M sun radiation is so small.
    So my question is is this method (#22) of determining temp etc valid?

    Same point but different presentation: The Earth temp varies. It is higher by up to 10-15C in daytime than at night. Hence solar insolation probably accounts for a max of 15C or 5% out of the total 289K. Decay heat apparently is 52% of Earths heat (Nature Geoscience July 2011) and if Solar E/M radiation is a max of 5%, where does the rest come from? Could it be that the force of eccentric gravity from Jupiter sized (& all other)planets actually adds and subtracts energy (force of gravity causes angular momentum, or spin and if the planet has layers (solid core, liquid core, and atmospheres) this spin causes friction which tranports gravity into temperature Heat So if these are three different sources of energy on a planet does the item 22 mechanism for caluculating the temperature still work?
    How about comparing Venus & Earth? Venus has a surface pressure 90+ that of earth, Does this impact the temp? PV=nRT says yes. So Does the #22 mechanism still work?.
    Regardless of these trivial little validity questions, Congrats to Kepler team & ALSO to #9 & 22 for thinking of the questions & answers. Keep thinking!

  54. @54 John Dodds: The Earth temp varies. It is higher by up to 10-15C in daytime than at night. Hence solar insolation probably accounts for a max of 15C or 5% out of the total 289K.

    I don’t think that follows. If the earth had no liquid oceans or atmosphere ,and a day lasted for a couple of years, then I could see taking the temperature of the night side, comparing it to the day side, and calling that the sun’s contribution to average surface temperatures. But night time isn’t all that long. If it were, I’m sure you’d see much, much greater temperature changes between night and day. I’m sure decay heat is a measurable component, but I can’t imagine it’s that much.
    Look at Jupiter’s moon Io. It experiences a whole lot of tidal heating, driving its famously prolific volcanism, and its mean surface temperature is about 110k.

  55. Messier Tidy Upper

    @51. amphiox : December 21st, 2011 at 9:05 pm

    Personally, I think trying to pigeon-hole planets discovered by Kepler as “Earth-like” versus “Venus-like” is an exercise in nit-picking.

    I disagree because it makes the, I think, rather important different between a habitable (well for Humans) planet and an uninhabitable one. For me the word “earth like” conjures up a planet that is, well, like our Earth. In more ways than just mass and radius.

    Venus has an almost identical size and mass as Earth but few would call conditions there “earthlike” at all. Venus is, in fact, perhaps the most hellishly hostile and unearthly planet in our solar system – certainly out of the four rock dwarf “terrestrial” planets.

    Considering that Kepler isn’t actually able to distinguish the difference between planets like Earth and planets like Venus, and if there was an alien Kepler mission looking at Sol, if it could detect Earth and Venus at all, those alien astronomers would not be able to predict with any great certainty which one of the two is like Earth and which one is like Venus, and would most assuredly classify both planets into the same category,

    Or would they? Interesting point there but I’m not so sure its really accurate. Such aliens may not be able to tell with complete certainty – assuming a technology level the same as ours – but they and we can certainly calculate and make educated guesses based on the planets size, distance, sun type, the likely effects of probable atmospheres , etc..

    I’m guessing if we found a system like our own with two earth-mass exoplanets equivalent to where Venus and Earth are from a star the same spectral type, luminosity and age as our sun we could correctly deduce that the inner one was Venus-like and the outer one was earth-like. If we could do that it makes sense to me that equally intelligent aliens could do so as well.

    I think that for the purpose of considering Kepler planets, Venus-like worlds ARE Earth-like worlds.

    That’s rather a subjective assessment. I think calling a world that is like Venus otr Mercury or Mustafar “earth-like” creates the wrong impressions in the general public and is very misleading and I wish we would describe things just that bit more accurately so that a world that is described as “earthlike” is a very probably habitable planet where we could live comfortably without spacesuits in earth-like temperatres and pressures. Conversely, a world that is more like Venus or a supersized version of Mercury or Mustafar in surface conditions is , I think, better described as Venus-like / Mercury-like / Mustafar -like.

    We often call Venus Earth’s “evil twin”, and these days people tend to focus on the evil part, but we seem to forget the second word there all too often.

    Perhaps so, yeah. The planet named for the goddess of love seems to get precious little from us sometimes! But that doesn’t change what I’ve said above. I see what your getting at I think but I don’t really agree.

  56. reidh

    There is no data to show that planets have wandered in orbit distances in this solar system, so why think they do so in other realms? Just because your lousy ( really pathetic ) theory of evolution of the solar system ( and thereby all others ) doesn’t fit with any other exo system found our of hundreds? thats called infantile reasoning, or that is to say NONE.

NEW ON DISCOVER
OPEN
CITIZEN SCIENCE
ADVERTISEMENT

Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!

ADVERTISEMENT

See More

ADVERTISEMENT
Collapse bottom bar
+

Login to your Account

X
E-mail address:
Password:
Remember me
Forgot your password?
No problem. Click here to have it e-mailed to you.

Not Registered Yet?

Register now for FREE. Registration only takes a few minutes to complete. Register now »