Exoplanet Explorer: COROT 7b

September 26, 2017

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.