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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."
"the temperature on its sun-facing side is around 4220 degrees Fahrenheit." For anyone using the SI, this is about 2327 degrees Celsius
While this is really cool if correct, one needs to understand that this isn't by any means a slam dunk.
Well, it does come quite close to being a "slam dunk".
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.
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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.
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http://www.sciencedaily.com/releases/2009/09/090930165038.htm
No, because it's still a closed system. The solid contents of the planet are continually moving towards the sun (the freshly-deposited rock is always pushing the older rock towards the hot side via gravity) But the overall center of gravity of the planet never changes position relative to the star since the momentum of the solid part of the planet is counteracted by the momentum of the atmosphere moving in the opposite direction. So the planet itself always stays the same distance away from the star.
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BTW....this is related to the process that is thought to occur on most tidally-locked rocky planets. They likely do not have atmospheres, since it entirely sublimates on to the cold side of the planet. When the atmosphere freezes out on the cold side, it reduces the atmospheric pressure on the cold side, which causes the atmosphere on the hot side to flow to the cold side, repeating the process until the entire atmosphere is gone. But in this particular case, the 'atmosphere' is getting continuously replaced through evaporation of the planet itself. This process is also one of the reasons why planets around red dwarf stars may be unlikely, since the planet has to be close to the star to receive enough energy from it, but being that close to the star increases the likely-hood of it becoming tidally locked with the star.
Since Kelvin is indicated just by the K, no degree sign, there should be no need to post the degree sign. "Degrees Kelvin" is a misunderstanding of the system of units.
Not a sentence!
With the rain of pebbles it might never form a hard crust but instead be a ball of semi-loose material with a liquid core. There would probably be a "hard" concrete like layer but nothing on the order of tectonic plates so it may be able to form into a sphere rather rapidly constantly shifting so that the shift isn't as noticeable. You might not even see earthquakes there, as the rain would cause more than enough vibration that the underlying shifting of the inner planet would be lost in the noise.
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There are several planetary detection methods and 'transit' is indeed one of them.
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