In 2009, the French-built COROT space telescope made an astonishing discovery: a planet. A planet that was, at least at the time, the most Earth-like exoplanet ever discovered. Except as we’ve discussed previously, “Earth-like” exoplanets are not necessarily much like Earth. In this case, the term chthonian planet may be a better fit.
Exoplanets are often named after the telescope used to discover them; therefore, this planet has been officially designated COROT 7b (the T, by the way, is silent… it’s a French thing). A press release announcing COROT 7b’s discovery said it has a surface you can walk on. That’s true enough, but I don’t recommend going for a stroll there. The weather forecast sounds terrible.
It’s believed that COROT 7b started out as a gas giant, like Jupiter or Saturn, but it was drawn into an orbit way too close to its parent star. Due to the star’s intense heat and radiation, COROT 7b’s entire atmosphere would have boiled away, leaving only the shrunken, shriveled core of the planet behind.
That shrunken core, which is still orbiting way too close to its parent star, is predicted to be tidally locked, meaning one side of the planet is always facing the sun and the other side is always turned away. That creates an enormous temperature discrepancy similar to, but more extreme than, the temperature discrepancy on Mercury.
And according to this paper from the Royal Astronomy Society, the temperature on the daylight side is high enough to vaporize rock. Allow me to emphasize that point. It’s not just hot enough to melt rock; oh no, that would be too normal. It’s hot enough to vaporize rock. So while COROT 7b seems to have lost its original atmosphere, it may have developed a new atmosphere composed of gaseous sodium and silicon and iron, along with other things we’re not accustomed to thinking of as atmospheric gases.
Then on the night side, where the temperature is much colder, all that vaporized rock would condense to form “mineral clouds,” and pebbles would fall like rain. Or perhaps hail is a more apt analogy. Anyway, if you’re going to go for a walk on COROT 7b, you’ll need more than an umbrella to deal with the weather.
Planet Pailly 
How I wish for a star ship to travel, to see these exoplanets for myself! This is what it must have been like in the 19th century to look at the objects in the Solar System, knowing they wouldn’t be explored in-person in your lifetime.
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That’s a really good analogy!
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Yeah, I wonder what it must have been like to be Galileo and seeing Jupiter’s moons and Saturn’s rings for the first time…. ever. Seeing and discovering all of these exotic exoplanets seems like it could be a really similar experience.
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This is a really interesting train of thought to me. I feel like I appreciate a little better how Galileo and his contemporaries must have felt. It also makes me wonder, because Galileo made a few mistakes and faulty assumptions about what he was seeing all those centuries ago. My favorite was that Galileo thought Saturn had “ears” sticking off either side of it.
I know there’s a fair bit of guesswork involved in any description of an exoplanet, but I wonder how close we are to the mark, or how many Saturn-ear-style mistakes we’re making.
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Yes! Exactly! Really well said! It’s those mistakes that I kind of find most inspiring. I remember reading the “ears” story a gazillion years ago (give or take), and thinking “what? really?” It seemed like such a ridiculous mistake. But then, as I’ve written about a bunch, we learned. Then we found Uranus, and learned we were wrong about there being six planets. Then seven, Then eight…. on it goes. Are these mistakes, really, or just things we haven’t learned enough to get right yet?
It’s the same thing with our search for life. What haven’t we learned yet about how life evolves? Maybe carbon and water aren’t needed at all. Maybe the combination of extreme heat and titanum air at WASP-19b is the exact right soup for some other type of life. All of this makes my mind race. I feel like a kid again.
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This leads back to one of my all time favorite essays on how science works: Asimov’s “The Relativity of Wrong.” http://chem.tufts.edu/answersinscience/relativityofwrong.htm
It’s such a lovely little piece of writing. Asimov’s basic premise is that we’re always going to be wrong, but with each new discovery we’re a little less wrong than we were before.
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I always learn something here! I had no idea planets could be tidally locked. Fascinating.
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There are a surprising number of tidally locked planets out there. Just about every major moon in our Solar System is tidally locked as well. I used to think our Moon was sort of a rare case, but tidal locking seems to be a fairly common phenomenon.
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For a real long time astronomers thought Mercury was tidally locked to the Sun. They eventually figured out it wasn’t, but, instead, the relationship between its orbit, its day (it has a 3-days to 2-orbits resonance), and our view on it made it seem like it was.
I think of of the coolest examples of tidal locking in our solar system is the Pluto-Charon one. Here, the Moon is tidally locked to Earth, so we always see one side of the Moon, while the Earth rotates away in most or less the same spot in the Moon’s sky. Charon and Pluto are tidally locked to each other, so both of them always see the other in the same place, with the same face showing.
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Mercury’s situation still boggles my mind. Because of that resonance, the sun travels one direction through Mercury’s sky, then it appears to turn around and travel backwards for a while, then turn back the way it was originally going. I’ve never quite been able to wrap my head around that one, no matter how many times I read about it.
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