In article ,
randyj wrote:
...the surface of Mars may have become geologically
stable a 10s or 100s of millions of years before Earth. Life could have
arisen there first and infected Earth.

Wouldn't that be more likely, rather than earth infecting Mars,
or is it possible for meteor transfer to go outward in the solar system?

There's no particular inward/outward bias -- one direction is pretty much
as easy as the other. What does matter is that it's much easier to get
rocks *off* a small planet with weak gravity and a thin atmosphere.

Mars is a particularly favorable case. Getting a rock off Venus or Earth
is quite difficult, requiring a very large impact, something that happens
very seldom nowadays. Most of the rocks of planetary origin in the inner
solar system are from Mars or the Moon.

(Mercury is a minor contributor -- the problem there is not that outward
transfers are hard, but that a rock from Mercury has to get a *long way*
outward without encountering the Sun first. Mercury is very deep in the
Sun's gravity. We have one unusual meteorite which *might* be from
Mercury, but nobody can be sure -- we don't have surface data from Mercury
to compare it against.)
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |