Thursday, October 1, 2009

An Earth-Like Exoplanet With a Very Alien Atmosphere

Some time ago, I missed posting about the discovery of a (large) Earth-like planet discovery. COROT-7b was discovered earlier this year. It's about 1.7 times the diameter of Earth, and has about the same density. That is, it's made of rock. Most exoplanets we've seen are made of gas, so this was a cool discovery. I dropped the ball on posting about it. I apologize.

Now, however, some people whose modeling (PDF) work is exemplary decided to have a little fun with this planet. See, it orbits its star with a year that is about 20 hours long. That's very, very, very close to the star. Mercury's orbital period (its year) is about 88 of our days. The closer you are to the sun, the faster your orbit.

So, this rocky planet is very close to its sun. That means that it is so close that its daytime temperatures reach 1800 to 2600 Kelvins (there is no "degrees kelvin", it's just Kelvins). That's hot enough to vaporize rock. Therefore, rock will likely be vaporized from the surface of this planet.

Now, whether this planet has a day-night cycle or is tidally locked so one face always sees the sun is unclear. And not particularly relevant to this discussion. See, if the planet has a diurnal cycle, then the nighttime comes for the area that had rock vaporized. If it doesn't, then the hot atmosphere moves to the cold side due to density (and other) differences. Either way, this hot atmosphere of minerals will condense out as it moves to the cold side of the planet. That is, you would see molten rock falling from the sky. Then (possibly very short-lived) rivers of molten rock flowing on the surface. In some instances, you might even get pebbles raining out (think hail) if the winds are strong enough and the temperatures low enough.

Not only that, but because of the atmospheric temperature differences, you'd have different layers of mineral vapors at different heights. Quite a view, I would imagine.