Big news: first "solid" exoplanet found!

By Phil Plait | January 10, 2011 12:34 pm

[UPDATE (January 15, 2011): Mea culpa. It's getting hard to keep up with all the exoplanets being found now, and a few folks have let me know that the planet CoRoT 7b, while bigger than Kepler-10b, is also likely solid and not a gas giant. In fact, they're pretty similar in size and distance from their respective stars! So this planet is not the first one of its kind to be found, though still very cool and exciting. My apologies for this, and next time I write about planets I'll make sure to go through the database first!]

Astronomers have just announced the discovery of the first planet orbiting another star that is unequivocally not a gas giant: it must be a very dense, rocky-metallic object not much bigger than the Earth!

The planet, discovered by the orbiting Kepler telescope, is called Kepler-10b. The star (Kepler 10) is roughly the same mass and temperature as the Sun, and is located over 500 light years away.

The planet was detected because it passes directly between us and the star as it orbits. When it does that, it makes a mini-eclipse, blocking a bit of light from the star. By knowing how big the star is and how much light is blocked, the size of the planet can be measured (the bigger the planet, the more light is blocked). In this case, Kepler-10b is only about 1.4 times the diameter of the Earth, making it the smallest exoplanet ever found!

However, there’s more. The planet’s gravity tugs on the star as it orbits, so as the planet makes a big circle around the star, the star makes a little circle in response (I like to use the analogy of a father dancing with his small daughter; as he swings her around she makes a big circle around him and he makes a little circle, because he’s much more massive than she is). As the star moves slightly toward and away from us we can measure the change in velocity using the Doppler shift, and that in turn tells us the mass of the planet. It turns out Kepler-10b is a lot more massive than the Earth, tipping the scales at 4.6 times the Earth’s mass.

So it’s not terribly earth-like; if you stood on its surface you’d weigh almost 2.5 times what you do now!


Even worse, it orbits extremely close in to its star, circling over the star’s surface at a distance of roughly 3 million kilometers (1.8 million miles) — amazingly, it takes less than an Earth day to make one circuit. But being that close to a star comes at a price: the surface temperature of the planet must be several thousand degrees! So yeah, you’d weigh more there, but not for long. You’d burn through those extra calories pretty rapidly. Literally.

And even worse, it’s almost certain the planet is tidally locked to its star, meaning it always shows one face to the star (like the Moon does to the Earth). So the side facing the star is scorching hot and probably glowing brightly with heat, as shown in the artist’s depiction above. This is truly a scary, hellish world.

I’ve seen a lot of reports already calling the planet "solid", but I think it’s clear that it must actually be molten. I I think the reports are trying to distinguish it from the usual hot super-Jupiters found around other stars, planets that are bloated gas giants. Kepler-10b is certainly much smaller and therefore not a gas giant.

So this planet is not even close to being earth-like and habitable, but it’s still the lowest-mass and smallest planet ever found orbiting a sun-like star. This is a huge milestone, because it shows without doubt that Kepler has the potential to fulfill its mission of finding a truly earth-like planet orbiting a distant star. How long will it be before we see one of those? If they exist and Kepler can spot one it’ll still be a couple of years, sadly, but the good news is we should be able to see it. And that’s exciting enough for me for now.

Image credit: NASA


Related posts:

- Gallery of exoplanets: real images of alien worlds
- Kepler works!
- Sunburned planets turns hot face away from star


CATEGORIZED UNDER: Astronomy, Cool stuff

Comments (86)

  1. BLA

    Is it merely a product of our discovery methods that we only find planets so close to their parent star (with a few exceptions)?

  2. Oli

    Could there not be at least islands of solid rock on the other side?

  3. That’s an interesting point. I wonder what the temperature gradient would be, given that half of it is always in shadow.

  4. The STAR is called “Kepler 10″?

    Does that mean that the Kepler telescope observations were the first to see and identify this star?

  5. Keith Bowden

    Hefty little speed demon. I’m always astounded at reports of planets orbiting stars at speeds of less than 24 hours. Say these speeds happened further out in the habitable zone. What would Earth be like if we whizzed around the sun in a several days/a few weeks instead of our current year? (Or if we moved more slowly so that our year is two or three times as long?)

    Go Kepler!

  6. Hmmm … at 1.4 Earth diameters but 4.6 Earth masses, Kepler 10b would have an average density of 9-and-a-quarter grams per cubic centimeter.

    It sounds like it’s made almost entirely out of metals*, with very little rock.

    *) And when I say “metals”, I mean what chemists and geologists mean by metals, not what stellar spectral anaslysts mean by “metals”.

  7. Kevin

    Isn’t that Mustafar, where Obi-wan and Anakin fought?

  8. Keith Bowden asks:

    “Say these speeds happened further out in the habitable zone. What would Earth be like if we whizzed around the sun in a several days/a few weeks instead of our current year? (Or if we moved more slowly so that our year is two or three times as long?)”

    If the Earth tried to go around OUR SUN every few weeks, at its current distance, it would go so fast it would be flung out of the solar system very rapidly. If the Earth tried to go around our sun once every two years at its current distance, it would fall into a higly elliptical orbit that would take it so close to the sun it would incinerate the atmosphere. If you want a circular orbit at distance A (expressed in Astronomical Units) around a star that weighed M solar masses, you *MUST* orbit at a speed P = SQRT(A^3 / M) revolutions per year. It’s Kepler’s Third Law.

    Now, if you REPLACED the sun with, say, a very dim (and somewhat less massive) red dwarf star, so that you’d have to orbit CLOSER to the star to get the same amount of light that we currently do with our sun, then that’s another matter.

  9. Chris

    Maybe a better name would be Vulcan.

  10. SL

    Hmmm… How come some bodies are tidally locked to other bodies? Seems to me it occures when the bodies are close together, but I guess other factors such as mass or mass ratio might be important as well…

  11. Aaron

    @3. tracer:
    It probably just means that this is the 10th star in Kepler’s catalogue. It could easily have other designations in other catalogues (i.e. the Andromeda Galaxy is the 31st object in the Messier catalogue -and- the 224th object in the New General Catalogue).

    Phil, this is -hot- news!

  12. andy

    Er, anyone remember CoRoT-7b? I know 2009 was a while ago…

  13. Kullat Nunu

    Kepler 10 b is not the first rocky extrasolar planet, the first one is CoRoT-7b which was found already in 2009. While this is the first rocky planet found by Kepler, and certainly a very interesting find, it is a bit dishonest for NASA PR people not to mention it.

  14. Adrock

    I thought there were solid exoplanets orbiting Gliese 581.

  15. Grizzly

    Later this year we should begin to see the first “habitable zone” findings from Kepler. It is looking for planets with orbits in that zone which will equate to +/- one year depending on the size of the star, but if we take our Sun as an example then it will pretty much fit.

    Assuming the correct orientation of the extra-solar system to our own, it will take more than one year to observe a complete cycle of two occultations to confirm the finding. What we will get until then are these small rocky zippers and super Jupiters.

  16. Rick Morris

    I wonder what the percentage of stars is that have plants orbiting on a plane which allows the planet to eclipse the star as seen from our vantage point? Gotta be a pretty small percentage, but it still could end up being a large number. I’ve seen stats on the number of earth like planets that there might be in the whole MW galaxy, but I have never seen a stat on how many of those planets that we could discover with our current technology.

  17. Regner Trampedach

    tracer @ 6: That planet, at 8.8+/-2 g/cm^3, is only 1.6 times denser than the average Earth. Earth’s core is about 10-12 g/cm^3 and its mantle about 4 g/cm^3 – maybe Kepler 10b is the Ni-Fe core (a la Jupiter’s) of a formerly massive gas giant that had most of its gas blown/evaporated off by its host star…?…
    tracer @ 4: Stars can figure in several star-catalogs at the same time, and Kepler 10 is a fairly bright star. With an absolute magnitude (in V) of 4.746 it is naked eye visible (6 being the faintest normally visible with dark, clear skyes) – so hardly “discovered” by Kepler.
    Take a look at kepler dot nasa dot gov for more details.
    Cheers, Regner

  18. DrFlimmer

    So the side facing the star is scorching hot and probably glowing brightly with heat,[...]

    This somehow reminds me of the Krell door in “Forbidden planet”, when the monster of the ID tries to burn its way through the door.

  19. andy

    @Regner Trampedach: the planet is more massive than Earth so there is greater gravitational compression of the interior. The mass and radius values are compatible with a composition intermediate between Mercury and Earth: according to the paper “Mass-radius relationships of solid exoplanets” by Seager et al. (2007) a planet with Earthlike composition with 4.6 Earth masses would have a radius roughly 1.5 times that of Earth, while a “super-Mercury” would be at about 1.3 Earth radii.

    Also that V magnitude is the absolute magnitude not the apparent magnitude – this star is roughly 10th magnitude and therefore not naked-eye visible.

  20. Arthur Maruyam

    @ BLA (1): Kepler can only detect the mini-eclipses when the planet passes in front of its star. The scientists will only confirm that there really is a planet and not some temporary phenomena like a starspot after several such mini-eclipses. So far there has only been time to make confirmation of close orbiting planets. Confimation of those that are more Earth-like in terms of their orbits about their stars will require a several years of observation–likewise those that are more Jupiter-like in terms of their orbits will require decades of observations.

  21. timur

    This is amazing!

    At several thousand degrees, can metals still stay liquid?

  22. MarshallDog

    @10. SL – If I understand tidal locking correctly, it occurs because the gravity of the two objects distorts their shapes, causing “bulges” in the surface. Since the bodies are rotating, the bulge in one is trying to be pulled away from the gravity of the other, which creates drag and causes the rotation to slow. Since the star is many magnitudes more massive, and the distance so small, the gravity pulling on the planet is enormous. The planet’s rotation would have no chance overcoming this force for very long.

    Anyway, that was a terrible explanation, so you can read more here: http://en.wikipedia.org/wiki/Tidal_locking

  23. QuietDesperation

    How stable is this orbit? How sure are they of their figures?

    Maybe it’s the Planet Jacker star from Invader Zim where they keep their star alive by dropping planets into it.

  24. Arenvalde

    @BLA: larger objects and objects closer to their sun will block out more light when they pass between it and us, making them far easier to detect.

    @SL: generally, proximal objects with a greater discrepancy in mass will be more likely to become tidally locked. Well, more likely for the smaller object to become tidally locked with the larger one. It’s a matter of the force of gravity being acted upon the object with reference to its initial spin and mass: the smaller the object, the more quickly tidal locking occurs. Pluto and Charon are a case where both objects have become tidally locked to each other.

  25. Dallas Krentzel

    “In this case, Kepler-10b is only about 1.4 times the diameter of the Earth, making it the smallest exoplanet ever found!”

    You know better than to say that: http://blogs.discovermagazine.com/badastronomy/2008/04/10/no-its-not-the-smallest-exoplanet-found/

    To your credit, you do qualify such a statement later by saying “but it’s still the lowest-mass and smallest planet ever found orbiting a sun-like star,” which is probably true. Ever since you posted what I just linked to though, I’ve always been very vigilant of such statements about exoplanets; it seems like every one of them we find is construed to be the first something. I guess that’s good if it gets them press though, because they deserve it. Very very interesting discovery.

  26. Luke

    1. BLA:

    “Is it merely a product of our discovery methods that we only find planets so close to their parent star (with a few exceptions)?”

    I’d also like to know this. Is it that much harder to observe planets in larger orbits? Is it because the further away from a star a planet gets, the less likely it is to pass in front of its star while we’re watching or something?

  27. Chet Twarog

    @ 9 Chris and friends, see NASA short video about Kepler 10b at:
    http://www.nasa.gov/topics/universe/features/rocky_planet.html
    Dr Batalha calls it: Vulcan.

  28. I’ve seen a lot of reports already calling the planet “solid”, but I think it’s clear that it must actually be molten.

    I suspect this confusion arises from planetary scientists’ deplorable use of the word ‘rocky’ to mean ‘of silicate and iron chemical composition’. For example, one often sees debate about Jupiter’s ‘rocky’ core, giving the impression to the average punter that Jupiter may have a solid core when what is under discussion is a fluid core of heavy elements.

    So, Kepler 10b is probably a lava (or magma) planet (with, no doubt, an iron core).

    See also ‘ice’ as in “Uranus is an ice giant” – i.e. it’s predominantly made up of superheated steam.

    Agreed about CoRoT-7b, though there’s a certain schadenfreude seeing CoRoT getting a taste of its own medicine, as they’ve been guilty of presentational sharp practice themselves in the past.

  29. Theta1

    This is an interesting discovery, but not the Holy Grail, which would be an Earth-sized planet orbiting a Sun-Like star in the Habitable Zone. I think that the Kepler team will eventually find some of those. Even then, Kepler is monitoring stars that are 2,000 Light-Years away, much too far for any follow-up spectroscopic or imaging studies.
    There is a mission, SIM, the Space Interferometry Mission, which can detect Earth-sized planets orbiting Nearby F,G,K stars in the HZ. These planets will be only 10 – 40 Light-Years away! However, NASA canceled it at the end of last year, 2010. This occurred after 10 years of work on the design, and prototype-testing, of hardware. This mission is ready to enter Phase C/D, which is detailed design and construction.
    The SIM planets will be close enough, and BRIGHT enough, for follow-on space observatories to obtain good spectra, and to even produce crude maps.
    NASA’s Exoplanet Roadmap is being thrown out the window, because according to committee recommendations, a mission such as SIM is needed to provide the targets for those follow-up missions.
    If you wish to express your opposition to the cancellation of SIM, then please visit the “Save SIM!” petition web site, and add your signature and comment. It can be found here -

    http://www.thepetitionsite.com/1/save-SIM-Earth-Finder/

  30. andy

    @Luke, BLA: the median orbital period for radial velocity-detected exoplanets listed at the Extrasolar Planets Encyclopaedia is about 180 days. The long-period planets are not rare exceptions, despite the fact that there are indeed biases against their discovery (at least for radial velocity and transit searches).

  31. Luke

    @23. andy:

    Ahh, interesting, so I just need to pay more attention. Thanks!

  32. @1 BLA and 21 Luke:

    Luke, you’ve got the right concept. It’s just a matter of likelihood: Kepler detects a planet when the planet passes between the star and the Earth. For a planet like Kepler-10b, that happens more than once a day. But for a planet at an orbital radius of 1 AU around a solar-mass star, that happens once once per year. Ideally, we would want Kepler to detect a planet several times to get solid confirmation of the planet’s existence, so we’d only find those 1 AU-orbit planets after several years of Kepler observation. Planet detection via tracking Doppler shifts in the radial velocity of a star is similarly biased towards planets that are close to their stars, because we get more orbital periods to average over.

    @10 SL

    Orbiting bodies tend to evolve towards a tide-locked state over time, e.g. after a couple more eons the Earth is going to end up tide-locked to the Moon. This is because even the most rigid bodies in space, like the rocky Moon, flex a little under the influence of tides and this flexing causes energy loss. The energy comes out of the body’s orbital or rotational motion. Eventually the bodies reach a low energy state, usually some resonance between the orbital and rotational periods, and get stuck there. For a pair like the Earth and the Moon, the eventual lowest-energy state is for both bodies to be tidally locked in a 1-to-1 spin-orbit resonance.

    However, for more complex systems, there are other resonances. For instance, Jupiter’s moons Io, Europa, and Ganymede are in a 4:2:1 resonance (Io orbits 4 times for every 2 Europa orbits and 1 Ganymede orbit). The combination of this orbital resonance with tide-locking of the moons to Jupiter itself is responsible for, among other things, squishing Io so much that it’s covered with volcanoes and squishing Europa enough to keep its sub-ice ocean liquid.

  33. Aha! Re CoRoT-7b, Emily points to Frank Marchis’ post (http://www.cosmicdiary.org/blogs/nasa/franck_marchis/?p=953 ) showing Daniel Fischer’s snap of Natalie Batalha’s AAS presentation slide. Apparently the uncertainties in CoRoT-7b’s mass mean a non-rocky composition can’t be ruled out.

    Man, you gotta keep your eyes peeled (assuming you want to meet the xkcd 386 standard of never being wrong on the internet).

  34. Chief

    It seems that the majority of the finding are large bodies either far out or very close. Does this mean that the finding of mid range bodies are harder to observe in the movement of the star. I wonder what our own sun gives in terms of the mathematics in the wobble in relation of 10+ bodies with non orbiting less than 88 days.

  35. KC

    I’m seeing this touted in the media as the First “Rocky Planet” discovered by Kepler. From the description however it doesn’t seem to be very rocky. With a density close to iron, it seems to me to be more of a denuded core of a gas giant.

  36. Worlebird

    @BLA (#1) Since the primary method for discovering these smaller planets is by observing the dip in light that occurs when the planet transits the star, it is more likely that we will find planets that orbit close to their stars. There are two big reasons that planets further from their stars are less likely to be picked up. #1 the further out they are, the less likely it will be that the angle of the orbit lines up exactly with us so we can see a transit (like how the moon does not eclipse the sun every single month, but rather passes above or below it most months). #2 the further out the planet is from its star, the longer the orbital period, so the less likely that we will be able to pick up a repeatable transit. If a transit doesn’t repeat, we can’t be sure it was actually a planet, and also have no way to calculate the mass.

    @SL (#10) If I understand the physics correctly, all orbiting bodies will eventually become tidally locked, given sufficient time. A number of things can affect how quickly this will happen, including the distance between the two, relative masses, orbital speed, rotational speed, and fluidity of the bodies involved.

    EDIT: @Joseph (#25) Nice job, beat me to it. You probably explained it better than I did too. *chuckle*

  37. andy

    @KC: density is affected by gravitational compression, it turns out it is compatible with being a rocky planet with an iron core (see my post @18).

    To take a somewhat more extreme example of what compression can do, consider a red dwarf star like Proxima Centauri. Proxima is mainly composed of hydrogen and helium, but with a radius of 0.145 times that of the Sun and a mass of 0.123 solar masses it has a mean density of 57 g/cm³, over twice the density of osmium at room temperature and pressure.

    Then again Kepler-10b is rocky in much the same way that the Amazon rainforest is icy…

  38. Keith Bowden

    Thanks, Tracer!

    (I really should have had that worked out at least rudimentally, and realized just how close and large those planets are. D’oh!)

  39. Jamie

    I think it’s awesome that we can spot something so small, so close to it’s parent star, yet the search for the Vulcans in our own system is still on going. Good job Kepler team, I look forward to a year full of exoplanet excitement!

  40. amphiox

    I thought there were solid exoplanets orbiting Gliese 581.

    The Gliese 581 planets aren’t definitely solid. They weren’t discovered by the transit method, so we don’t know their diameters, only their masses, so we don’t know their densities. They could be rocky (Super Earths) or gaseous (mini-Neptunes), or something intermediate like a mostly water world.

  41. Just so we’re clear: The yellow/orange/brownish pic associated with the article is the actual expoplanet? Not the star it circles? Is the whole round thing the planet, or are we meant to see a tiny dot against the backdrop of Kepler 10 that’s the actual planet?

    Is it an artist’s rendition or a (color corrected?) photo?

    Followup: Apparently, it is an artist’s rendition, and I skipped over that part in the article:

    http://www.cosmicdiary.org/blogs/nasa/franck_marchis/?p=953

  42. r0blar

    @Joost Schuur: If you want to see how does exoplanets look like in our data go to:

    http://www.planethunters.org/

    and you’ll also have an opportunity to find some by yourself ;)

  43. Nice! I wonder…given its density I wonder if the planet is actually the dense core of a former Jovian planet whose atmosphere has been blow off by the star.

    I also wonder, if it is mostly metals: could it have an atmosphere made of metals in gas form? Or maybe a rock vapor atmosphere?

  44. Dr. Plait,
    When you say:

    “So yeah, you’d weigh more there, but not for long. You’d burn through those extra calories pretty rapidly. Literally.”

    it sounds a little like you are entangling the extra weight due to this planet’s gravity with the extra weight caused by consuming additional calories. Of course, I fit a certain middle-aged North American body type that does, in fact, have extra calories to burn, on any planet!

  45. Jamie

    @33 Dude, of course it’s an artists rendition. We can barely get a picture of mars that looks that good! It’ll be a little while longer before we are directly imaging small rocky planets of other stars.

  46. Aleksandar Kuktin

    Dibs on a mining operation!

    Or, should I say, “slurp up molten metal from the “surface” with a hose” operation. XD XD

  47. Monkey

    Any particulars on where in the sky this is located? Distance is cool, but point in the sphere would be cool too! I love looking up and thinking “somewhere around there is ______”. Puts an extra dimension to the night sky to think that you *know* where a hidden object lurks…

  48. viggen

    but the good news is we should be able to see it

    Kepler should see it… iff the ecliptic plane of the system in question is edge on toward us.

  49. CB

    “Kepler should see it… iff the ecliptic plane of the system in question is edge on toward us.”

    Which was implicit in the first half of the sentence you quoted the second half of. ;)

  50. Grimbold

    This really gets you thinking. The near side of the planet must be molten, but the far side would be in permanent shadow so it could in fact be quite cold. Perhaps there is a hemispherical shell of solid rock floating on a planet that is otherwise entirely lava. Or perhaps there are internal currents of molten rock in the planet strong enough to circulate heat everywhere. Wouldn’t that be something.

    (edit): is this really the first rock exoplanet discovered? I thought there was a pulsar with a couple of small asteroidal planets too small to be made of gas.

  51. Kappy

    Phil: When you say we can tell the mass of the planet by the influence it has on the Star, what if the system has other planets that are also influencing the Star. Won’t that put the Doppler effect out of whack and cause us to incorrectly identify the mass of the planet we viewed in transit?

  52. Chris Winter

    Tracer, you’re way ahead of me. With a density like that, the planet must be a treasure trove. And (probably) no indigenous life forms to get in the way. (I guess I can’t rule out the Horta or something like it.) ;-)

  53. yet the search for the Vulcans in our own system is still on going

    For a moment I thought you meant…

    Live long and prosper.

  54. Menyambal

    Tidal locking tends to occur when a body is in close to its primary, where the gravity gradients are steeper. Locking occurs when the body departs from it spherical shape and assumes a more ellipsoidal shape–this planet, being half melted, had no rigidity to resist the tide-induced distortion.

    We tend to detect planets in close to their stars for two reasons. As was said above, a close-in planet eclipses more often. I add that a close-in planet is more likely to be in an orbital plane that eclipses from our point of view. Consider that a planet that brushes the surface of its sun would have to be in a plane exactly perpendicular to us to *avoid* eclipsing. Consider that a planet like Jupiter, big though it is, so far from its sun, would have to be in a plane exactly horizontal to us to *ever* eclipse. Chance favors close-in planets, time favors close-in planets, so close-in planets are what we detect.

  55. KC

    @andy Thanks I haven’t seen the details yet – the NASA press release states:

    “In the case of Kepler-10b, the picture that emerges is of a rocky planet with a mass 4.6 times that of Earth and with an average density of 8.8 grams per cubic centimeter — similar to that of an iron dumbbell.”

    I think the dumbbell analogy is misleading.

  56. Sam H

    More discoveries from the amazing Kepler. It just keeps getting better and better! Soon we’ll have that rocky HZ planet, at long last :)

    Now, Kepler is looking in one direction only (between Cygnus and Lyra), and most of these stars are likely thousands of LY out in the Orion and Perseus arms. How close would the closest stars in that direction be, and what kind of stars? (Probably red dwarf, my guess). If the Earthlike candidate systems are close enough, could Spitzer possibly carry out a spectral analysis of their atmospheres? With coolant having run out, could it even do this? How far out could it perform the analysis?

    Or, if Spitzer is not suitable, will the JWST be able to perform spectral analysis for the signs of life when it comes online sometime in 2015 (or later, depending on launch date?) With aperture like that plus the predicted results for Kepler, atmosphere chemistry should certainly be a viable mission goal.
    Let’s hope peak oil hits after 2015 :) !

  57. Ciaran

    @Kappy We know the orbital period of the planet so we can isolate doppler effects at that frequency.

  58. Now we just need to find some aliens.

  59. Messier Tidy Upper

    Yikes! I go off line for a day or two because Real Life intervenes and I come back & find this news! :-o :-)

    Wow.

    Superluminous. (Beyond just brilliant.) I love it! 8)

  60. Messier Tidy Upper

    @7. Kevin :

    Isn’t that Mustafar, where Obi-wan and Anakin fought?

    Sure looks like it could be! ;-)

    Compare & contrast for yourselves here :

    http://www.youtube.com/watch?v=pSwy412nttI

    via Youtube & also for a more textural and less visual approach see :

    http://en.wikipedia.org/wiki/Mustafar

    here on Wikipedia. :-)

    Although of course SW was supposed to be in a galaxy far away and a long time ago! So maybe in the Milky Way’s larger (than life too?) twin galaxy UGC 12158 with a really unlikely case of convergent evolution producing near human aliens along with their miticlorian symbiotes then :

    http://blogs.discovermagazine.com/badastronomy/2011/01/07/the-milky-ways-almost-identical-twin/

    Perhaps? ;-)

  61. I read the name of the planet as “Kepler Bob” for some reason.

  62. Paul

    Objects become tidally locked due to distortion. This object is molten — more easily distorted.

    Anyone care to speculate how distorted this body has become? Bonus points for working out the flow patterns.

  63. Nigel Depledge

    Joost Schuur (43) said:

    Is it an artist’s rendition or a (color corrected?) photo?

    Followup: Apparently, it is an artist’s rendition, and I skipped over that part in the article

    I think you might also have missed the bit that said it’s over 500 light-years away!

    We’ve only just developed our technology to be able to see that level of detail on Jupiter or Saturn without having to send a space probe to take close-ups. And they are only 1 or 2 light-hours away (well, at opposition they are).

  64. Nigel Depledge

    KC (57) said:

    @andy Thanks I haven’t seen the details yet – the NASA press release states:

    “In the case of Kepler-10b, the picture that emerges is of a rocky planet with a mass 4.6 times that of Earth and with an average density of 8.8 grams per cubic centimeter — similar to that of an iron dumbbell.”

    I think the dumbbell analogy is misleading.

    I agree. There’s no way it’ll be dumbbell-shaped! ;-)

    Seriously, though, I think the “iron” analogy is misleading, as several comments in this thread appear to indicate.

    A large object like a planet will have a density that depends on both its composition and its mass. Planets in the solar system tend to have densities that are mostly determined by composition, but consider Jupiter and Saturn. Both have a similar composition, but Jupiter is quite a bit more dense (Saturn’s average density is about 0.7 gcm-3 and Jupiter’s is about 1.2 gcm-3). This is because of the difference in mass.

    More mass = more gravity squeezing the centre of the planet = higher density irrespective of composition.

    Of course, to have that density at that relatively small mass, this must be a rocky / metal-rich planet, but – as another commenter has already pointed out – its composition is most likely something between Earth and Mercury.

    So, no, it won’t be covered in huge lakes of molten nickel or iron, but it may well have magnesium-silicate-rich magma on its surface.

  65. Messier Tidy Upper

    @42. amphiox :

    “I thought there were solid exoplanets orbiting Gliese 581.”

    The Gliese 581 planets aren’t definitely solid. They weren’t discovered by the transit method, so we don’t know their diameters, only their masses, so we don’t know their densities. They could be rocky (Super Earths) or gaseous (mini-Neptunes), or something intermediate like a mostly water world.

    Yes, indeed. The Gliese 581 c & d worlds are all around five Earth masses which is in a mass range that’s not occuring in our solar system (where we have a big gap between the 14 earth-mass Ouranos & the 1 Earth mass er ..Earth!) and thus outside our observational knowledge.

    It seems quite likely that these worlds could well be “hot ice” or “ocean type” exopanets or “gas dwarfs” rather than anything remotely resembling Earth.

    See :

    http://en.wikipedia.org/wiki/Gliese_581

    &

    http://en.wikipedia.org/wiki/GJ_1214_b

    for more info.

    Additionally, as this link :

    http://blogs.discovermagazine.com/80beats/2010/10/12/um-that-goldilocks-exoplanet-may-not-exist/

    explains; it is, sadly, not yet even really certain that Gliese 581 g the smallest and potentially most habitable – “Goldilock’s planet” – there even exists at all.

    ***

    BTW. Semi-interesting interference based on the Obi-Wan Vs Anakin duel – Mustafar must have an ecosystem of oxygen producing extremophile bacteria or something very similar in order to produce a breathable atmosphere. Wonder if they can eat arsenic? ;-)

    Either that or the Jedi / Sith can happily breathe gases other than O2 for at least a fair while. ;-)

  66. Gary Ansorge

    Only three million kms from its sun? I wonder how long it will be before it is absorbed?

    Now we need to observe its siblings.

    Gary 7

  67. CB

    “Either that or the Jedi / Sith can happily breathe gases other than O2 for at least a fair while. ;-)

    Yes, in the same way they (and their clothes) can resist the intense heat of lava while standing only a few feet from it… until their concentration is broken by, say, having their limbs lopped off and then they burst into flames as expected. :P

  68. BA:

    (I like to use the analogy of a father dancing with his small daughter; as he swings her around she makes a big circle around him and he makes a little circle, because he’s much more massive than she is.)

    Sounds like you speak from experience here. :-)

  69. And even worse, it’s almost certain the planet is tidally locked to its star, meaning it always shows one face to the star (like the Moon does to the Earth). So the side facing the star is scorching hot and probably glowing brightly with heat, as shown in the artist’s depiction above. This is truly a scary, hellish world.

    So, if a tidally-locked planet can be hot enough on the sun-facing side to be molten, and “cool” enough on the opposite side to remain solid, what, exactly, would it look like? It’s hard to picture such an object.

    And, being so close to its sun, would the solar wind be enough to flatten the sun-facing side? Would the planet be raindrop-shaped? (A “real” raindrop shape, not the “artistic” version we usually think of.)

  70. Messier Tidy Upper

    BTW. I meant to ask before :

    Big news: first “solid” exoplanet found!

    Is that finding solid then? ;-)

    Sorry couldn’t resist the pun.

    Incidentally, there can never such a thing as a “solid lead” -
    in glaciological terms anyhow because by definition – “leads are stretches of open water within fields of sea ice.”

    Source : Wikipedia – Lead (sea ice)

    @70. CB : Yes, indeed. Amazing thing the Force is. :-)

    @64. Jeremy : I read the name of the planet as “Kepler Bob” for some reason.

    Hmm .. I like it & prefer it over the numerical designations but that name would tend to suggest a water world more than a lava one wouldn’t it? Maybe we’d be better to reserve that one for Kepler 80-b? ;-)

  71. qbsmd

    “Kepler-10b is certainly much smaller and therefore not a gas giant. ”

    I understand that the density indicates it isn’t gas, but I am curious about what the minimum possible size for a gas giant is and why. Could an earth-mass of hydrogen be classified as a planet, for example?

  72. Nigel Depledge

    qbsmd (76) said:

    Could an earth-mass of hydrogen be classified as a planet, for example?

    This so depends on local conditions.

    Anywhere near a star, an Earth-mass of H2 gas will simply be blown away by solar winds.

    (This is why free H2 gas is so very rare on Earth – it rises to the top of the atmosphere and gets blasted into space by the solar wind.)

    Farther away from a star, I suspect that the conditions required to accrete one Earth-mass of H2 into a planet-shaped thing would never arise. IIUC, both of our hydrogen gas-giants (Jupiter and Saturn) have cores of “metals” (i.e. stuff heavier than helium) and it was these cores accumulating gasses (far enough from the nascent sun that the solar winds didn’t blow it all off into space) that led to the formation of the planets we know and love.

    Away from the immediate influence of a solar wind, I suspect an Earth-mass of hydrogen gas would be a very large cloud indeed.

  73. Nigel Depledge

    MTU (75) said:

    Incidentally, there can never such a thing as a “solid lead” -
    in glaciological terms anyhow because by definition – “leads are stretches of open water within fields of sea ice.”

    On first glance, I read that as solid lead (the heavy metal, Pb, pronounced “led”), not lead (pronounced “leed” that is the open water in sea ice or the verb).

    I was about to get all shirty about it, too. After all, I’ve fired solid lead out of a Stirling SMG at a solid lead target.

    Stupid homonyms.

  74. “…so as the planet makes a big circle around the star,…”

    I think you mean “So as the planet makes a big ellipse around the star…”
    ;) This will be the first, and only time I ever get to correct you. I will now slink away.

  75. @79. Some Canadian Skeptic : Well spotted! :-)

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