Study: Strange Planet Has Atmosphere of Gaseous Rock—and It Rains Pebbles

By Eliza Strickland | October 1, 2009 2:43 pm

Corot-7bThe exoplanet Corot-7b has earned a reputation as one of the most interesting planets yet spotted outside our solar system, mostly because of its similarities to Earth: Astronomers have determined that it’s rocky, like Earth, and it’s only about five times more massive than our home planet. But the dissimilarities are just as fascinating. In the latest twist, a new study has suggested that storm fronts on Corot-7b may bring a rain of pebbles.

The alien planet is extraordinarily close to its parent star, and researchers think that it’s tidally locked so that one hemisphere always faces the star’s blasting heat. On that side, temperatures are thought to reach about 4,220 degrees Fahrenheit—hot enough to vaporize rock. So unlike the much cooler Earth, COROT-7b has no volatile gases (carbon dioxide, water vapor, nitrogen) in its atmosphere. Instead it’s atmosphere consists of what might be called vaporized rock. “The only atmosphere this object has is produced from vapor arising from hot molten silicates in a lava lake or lava ocean” [], says study coauthor Bruce Fegley Jr.

Using computer models, the researchers set out to determine how this strange atmosphere would behave. The results, which will be published in The Astrophysical Journal, suggest that during storms, pebbles may condense out of the atmosphere. “As you go higher the atmosphere gets cooler and eventually you get saturated with different types of ‘rock’ the way you get saturated with water in the atmosphere of Earth,” Fegley explained. “But instead of a water cloud forming and then raining water droplets, you get a ‘rock cloud’ forming and it starts raining out little pebbles of different types of rock” [].

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Image: European Southern Observatory. An artist’s impression of Corot 7b.

MORE ABOUT: exoplanets
  • Bill

    I can’t see how anyone can believe this BS

  • Buzz Aldrin

    Simulations can be [cough] doctored. I give an A+ for really fascinating imaginations, though.

  • Ryan

    What does something that hot and rocky actually look like then? The article sounds pretty reasonable to me.

  • AJ

    no no no this sounds so improbable. ill be waiting for hard evidence this sounds ridiculous

  • Alastair McKinstry

    Whats the point in doctoring simulations ? They may be wrong (probably are, I think), but accusing people of wrong-doing is flat out unjustified.

    Popular reports like this frequently miss the point of doing such simulations. Yes, it paints a pretty picture for what they could be like. But more importantly, the simulation tell us “to the best of our scientific understanding, _this_ is what is _should_ look like. From the simulation you get predictions of the spectra of the atmosphere, which you then try to measure to compare reality and theory.

    CoRoT-7b is a transiting planet. With finer resolution observations, it should be possible to determine the atmospheric spectra on transit, and compare it with the simulation, ie. theory.

  • BJM

    That’s as ridiculous as thinking that chunks of solid water the size of potatoes could form in Earth’s atmosphere and fall to the ground.

  • MutantJedi

    Why would it be hard to imagine vaporized rock condensing as pebbles? As McKinstry pointed out, with finer resolution observations, the theory can be put to the test. But at least someone has the imagination to provide something to test.

  • amphiox

    I should point out that the process of vaporized rock condensing as pebbles and falling to the ground is something that we can conceivably test, right here on earth, in an oven capable of generating the appropriate temperature and pressure ranges.

  • Anna

    @ BJM: Um, chunks of solid water the size of potatoes DO form in Earth’s atmosphere and fall down. We call them “hail stones.”

  • greenappleman7

    What’s so unbelievable about this. Personally, I think, those who are criticizing this idea are just being narrow-minded.
    Though, why wouldn’t lava be the equivalent of rain? Would the pebbles be the equivalent snow?

  • amphiox

    #6 and #9

    I’m guessing here, but one or both of you are being ironic, right?

  • Darknesss

    I don’t see what is so hard to believe about this report… the critical facts that are being overlooked are the temperature ranges for solid rock compared to ice, as well as the fact that they believe the planet is tidally locked with the sun.

    That means that one side of the planet is always facing the sun,it isn’t hard to believe that the other side is much cooler, as is the outer atmosphere of that side, which could potentially cause rock to change from vapor to liquid to solid and rain back down.

    If the earth were slightly cooler, we could have more hail?

  • ooGIBONoo

    seriously everyone on here who doubts that it is improbable for rock to form as a vapor condensate above a planet with an atmosphere that is not even close to ours, is an idiot and needs to go back to school. Gravity and pressure can have some serious varying effects. The proven physics of space thus far can suggest that anything is possible. Stop thinking in the past people, open those blocks of ignorance, if you do, and others follow, the collective consciousness will progress faster, and these negative theories of ‘no’ will be quite surprising. I will say however until they actually get close enough to measure it, they really cant be sure. Unless theres something were NOT being told.

  • Marshap

    This is a very interesting story. It seems like fascinating science to me. However I have no understanding of the mindset behind comments 1, 2 and 4 – and several others. I am also a scientist, albeit a neurophysiologist and I love my job and love reading about and doing science. I would suggest that if people want to comment, on any subject, that they are able to construct a coherent critical argument, rather than “this is BS”, or “I am waiting for hard evidence”. What kind of moronic comments are these?! I’d like to see you guys doing some computer modelling.

    For example which programming environment would you use, and what variables and constants would you put in – just to get us started? I presume you are seasoned astrophysicists and are able to compute the orbits of planets, accounting for gravity and momentum, whilst also being able to compute the physical properties of light, heat, gas, and matter, whilst accounting for pressure and gravity? Then we might be able to have a more sensible and intellectually rigorous discussion.

    On the other hand, this is the internet..

  • Thomas Hazard

    Buzz Aldrin is correct in his observation. I have however no problem w/trying to combine imagination with scientific reasoning to help understand the possibles. ‘ Nor did Viktor Weisskopf, Phillip Morrison or Hans Lucas Teuber.
    MIT 73

  • FAIL

    #9 … Looks like someones sarcasm meter is broken 😉

  • amphiox


    I think your skepticism here is a little extreme. Gravity and pressure aren’t magical forces forever beyond the ken of man, you know. We have a fairly good grasp of how they work, and pretty good reason to presume that they will work elsewhere the same they work here. And there is nothing occult about the transformation of matter in gaseous, liquid, and solid states – we have a fairly decent handle on how this works too.

    The likelihood of variable conditions across an entire planet’s surface actually increases the likelihood that the simulation will be broadly correct – that is to say, that somewhere on the planet rock vapor will condense into solid form and fall to the ground. Let’s not forget that there are many different substances in rocks with many different freezing/boiling points, so its not as if the temperature and pressure ranges are required to be all that stringent.

    The probability that the simulations will be exactly right in all the particulars might be exceedingly low, but the probability that the simulations will be broadly correct on something as general as a phases changes of matter will be almost certainly considerably higher than “improbable”.

    It will be a long, long time before we can actually get close enough to make direct measurements. Does not mean we should simply give up thinking? Can’t know for sure, no point guessing? Just accept our ignorance and forget about it? No, we make what inferences we can with the data we have, and move on.

  • Eric

    We do see the atmospheres of low-mass stars and failed stars (“brown dwarfs”) that have atmospheres with clouds of “rock” — actually tiny grains of “dust” dominated by silicates. These are the so-called L-type dwarfs (cooler than the M-type “red” dwarf stars that are a dime-a-dozen in the Sun’s Galactic neighborhood — things like Proxima Centauri). When you have a thick atmosphere with temperatures of ~1300-2000K, you can have clouds of some substances that you are used to thinking of as a solid on Earth. On the other end of the coin — on the coldest bodies in the solar system, things like nitrogen and methane become solid. Welcome to your universe.

  • Eric

    These are of course theoretical calculations, but the conclusions are quite reasonable given what we know about rocky planets.

  • TheCritic

    It was good to see so much actual discussion after those initial comments. I was concerned that suddenly the community had become fully devoid of intelligence.

  • Susanna

    Re: #s 6, 9 & 11.
    In California I’ve personally been in a brief hailstorm producing hailstones the size of one-inch gumballs. Fortunately I was indoors looking out a window, not being personally bombarded. Some potatoes are the size of gumballs. I saw a car with a number of significant dents in its roof and hood. The driver told me he’d driven through a hail storm in Texas with hailstones the size of baseballs. Many potatoes are that size. That’s almost evidence. Isn’t there posted somewhere on the internet a collection of photographs of record- sized hailstones, to satisfy those of us who like seeing the evidence? It seems to me I’ve heard of someone being knocked out by a hailstone.

    In any case planet CoRoT-7b doesn’t sound like a safe neighborhood to move to, even if rents are free and real estate values depressed below trackability.


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