[meteorite-list] It's Raining Rocks!

[Sterling K. Webb]

No, not meteorites like Holbrook. And not on Earth.
On another planet altogether. The only flaw in their
reasoning (the computer model) is the assumption
of locked rotation with the star. As a body spirals in 
toward a much more massive body, it passes into
the period of 3:2 resonant locked rotation before
it gets down to the 1:1 resonant lock. The 3:2 lock
"catches it" and it never gets to 1:1.

The CoRoT-7b "year" is only 20 hours 24 min. long.
We used to assume Mercury always showed one face 
to the Sun, but like so many "obvious" things, it ain't 
necessarily so. If CoRoT-7b is in a 3:2 resonance like 
Mercury, its "day" would be 13 hours 36 min. long, 
which would keep the surface uniformly toasty, but
not as toasty as their model suggests.

It might be only 1500C. to 1700C. degrees on CoRoT-7b 
instead of the 2300 C their model suggests. Or, maybe it 
only rains rocks on hot summer afternoons...

Sterling K. Webb
----------------------------------------------------------------------

http://www.space.com/scienceastronomy/091001-rock-rain.html

On Alien World, It Rains Rocks 
By Andrea Thompson

On Earth, strange things, including frogs and fish, 
sometimes fall from the sky, but on a distant extrasolar 
planet, the weather could be even weirder: When a 
front moves in, small rocks rain down on the surface, 
a new study suggests.

The exoplanet, COROT-7b, was discovered in February 
by the COROT space telescope launched by the French 
and European space agencies. Last month is became 
the first planet outside our solar system to be confirmed 
as a rocky body - most other known exoplanets are 
gas giants.

The planet is nearly twice the size of Earth and about 
five times the mass of our world. Calculations have indicated 
it has a density about that of Earth's, which means it is 
likely made up of silicate rocks, just as Earth's crust is.

The planet is likely much less hospitable to life though, 
as it is only about 1.6 million miles (2.6 million km) away 
from its parent star - 23 times closer than Mercury sits 
to the sun.

Because the planet is so close to the star, it is 
gravitationally locked to it in the same way the Moon 
is locked to Earth. One side of the planet always faces 
its star, just as one side of the Moon always faces Earth.

This star-facing side has a temperature of about 4,220 
degrees Fahrenheit (2,326 degrees Celsius) - hot 
enough to vaporize rock.

So unlike the much cooler Earth, COROT-7b has no 
volatile gases (carbon dioxide, water vapor, nitrogen) 
in its atmosphere. Instead it's atmosphere consists 
of what might be called vaporized rock.

"The only atmosphere this object has is produced 
from vapor arising from hot molten silicates in a lava 
lake or lava ocean," said Bruce Fegley Jr., of Washington 
University in St. Louis.

To find out what COROT-7b's atmosphere might be 
like, Fegley and his colleagues modeled it. They found 
that COROT-7b's atmosphere is made up of the 
ingredients of rocks and when "a front moves in," 
pebbles condense out of the air and rain into lakes 
of molten lava below.

"Sodium, potassium, silicon monoxide and then 
oxygen - either atomic or molecular oxygen - 
make up most of the atmosphere," Fegley said. But 
there are also smaller amounts of the other elements 
found in silicate rock, such as magnesium, aluminum, 
calcium and iron.

The rock rains form similarly to Earth's watery weather: 
"As you go higher the atmosphere gets cooler and 
eventually you get saturated with different types of 
'rock' the way you get saturated with water in the 
atmosphere of Earth," Fegley explained. "But instead 
of a water cloud forming and then raining water droplets, 
you get a 'rock cloud' forming and it starts raining out 
little pebbles of different types of rock."

The exoplanet's atmosphere condenses out minerals 
such as enstatite, corundum, spinel, and wollastonite.

Elemental sodium and potassium, which have very low 
boiling points in comparison with rocks, do not rain out 
but would instead stay in the atmosphere, where they 
would form high gas clouds buffeted by the stellar wind 
from COROT-7.

These large clouds may be detectable by Earth-based 
telescopes. The sodium, for example, should glow in 
the orange part of the spectrum, like a giant but very 
faint sodium vapor streetlamp.

Observers have recently spotted sodium in the 
atmospheres of two other exoplanets.