QUESTION:
If you need a heat shield to get into the earth and if Mars has the 
same atmsophere wouldn't a meteor melt before it gets to Mars.  Why 
would there be so many meteors on Mars?

ANSWER from Jeff Plescia on February 12, 1997:
You need a heat shield when re-entering the Earth's atmosphere
in a spacecraft to protect the spacecraft from the frictional heat
of the atmosphere. Without the heat shield, things would get very hot.
The heat shield gets hot too, it just has properties which allow it to
absorb and reject the heat.

Meteors also get heated when they enter the atmosphere. Most of
them burn up, the shooting stars you see at night. But something
does not have to be very large to make it through the atmosphere
all the way to the surface. A piece of iron the size of a baseball will
make it to the earth, a rocky object a couple of feet across will make it
as well. The outer parts of it will be burned away, but something will
get to the ground.

Many spacecraft which do not have heat shields re-enter the earth's
atmosphere and the wreckage makes it to the ground. It's burned and
bent, but pieces do get to the surface - Skylab crashed in Australia
and the recent Russian Mars 96 mission crashed in the western
pacific. The heat shield only keeps it cool enough to get to the ground
in one piece.

Many of the meteorites from Mars (and the moon) never make it to
the ground on the Earth, most burn up in the atmosphere. But the ones
that are big enough will get through.