[meteorite-list] It's Raining Rocks!

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Thu, 1 Oct 2009 15:31:02 -0500
Message-ID: <02F6EFF98A904F519E75DD72EBE6A459_at_ATARIENGINE2>

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.
Received on Thu 01 Oct 2009 04:31:02 PM PDT