Exoplanet Has Showers of Pebbles

mmmscience writes "The newly-discovered exoplanet COROT-7b has an unusual form of precipitation: rocks. Because it orbits so close to its sun, the temperature on its sun-facing side is around 4220 degrees Fahrenheit. That's hot enough for rocks to vaporize — not unlike water evaporating on Earth. And, like Earth, when the vapor cools in the upper atmosphere, it forms clouds and begins to rain. But instead of water, COROT-7b gets a shower of pebbles."

Comments

Related to the current poll ?

[slashmatteo]

"the temperature on its sun-facing side is around 4220 degrees Fahrenheit." For anyone using the SI, this is about 2327 degrees Celsius

Let's not exaggerate

[slyborg]

Some hyperbole here.

The Castle Bravo test shot (http://en.wikipedia.org/wiki/Castle_Bravo) was one of the largest thermonuclear detonations ever, with an estimated yield of 15-22 MT. The blast crater from Bravo was 2000m in diameter and 75m deep. Assuming it was square because I'm too lazy for math today, that's about 300,000 cubic meters. Assuming that this was blasted in solid granite (http://www.allmeasures.com/Formulae/static/materials/32/density.htm) you get about 780k metric tons.

However, most of this material wasn't vaporized, it was pulverized by the shock wave and propelled as a solid into the mushroom cloud. The actual quantity of material melted I wouldn't hazard to estimate, but it was a small proportion of the overall material excavated.

Much as in the "it's raining rocks!" planet, this precipitation would be much closer in form to dust, not "pebbles". One of the reason that water on earth comes in larger forms is that the water molecule has a charge, and will aggregate electrostatically. I don't think that would be true of this silicate cloud.

Re:Not unusual

[Chris Burke]

The parent raises a good point. How do we know the rock comes back down to the surface as a solid? Why doesn't it rain lava?

I'm going to make an educated guess, and say it's in the same way we "know" that it rains any kind of rock at all -- because that's what the simulations said. It says they even varied constraints based on not knowing exactly what the composition of the planet is, but they kept ending up with the same basic result.

So it all comes down to how good the simulation model is. It's possible it's inaccurate in a way that it is right that there is rock-based precipitation, but that it's in liquid form, but I certainly have no idea.

Oops

[justthinkit]

The planet is tidally locked. Just stay on the dark side of the planet. The equilibrium temperature there is 59F -- not bad at all.

This star-facing side has a temperature of about 2600 degrees Kelvin (4220 degrees Fahrenheit). That's infernally hothot enough to vaporize rocks. The global average temperature of Earth's surface, in contrast, is only about 288 degrees Kelvin (59 degrees Fahrenheit).