In article <1994Jul20.220444.18261 at news.cs.brandeis.edu> story at binah.cc.brandeis.edu writes:
>What processes give rise to comets.
Comets can be thought of as left over junk from stellar formation. The best
model, mostly based on spectral analysis of cometary tails is that a comet
is a matrix of frozen water, CO2, methane, ammonia, dust & stones
(silicates). C,N & O are produced in older stars. As these stars go nova,
they spew out their contents, which can form the above components as they
cool. Where large concentrations of silicates and metals occur, you get
rocky planets like Earth, Venus, Mars, Mercury or Pluto, or you get asteroids. Where there are concentrations of ammonia & methane, you get gas giants
like Jupiter, Saturn, Uranus & Neptune. Small bits of this stuff can
accrete to form comets.
> Are they formed catastrophically
Given the above, I would say so! Given how fragile comets appear to be, I
don't think they can form by accretion, although someone may be able
to correct me on this point. I'm pretty sure that the result of a collision
between two comets would be a bunch of small comets. Therefore, the best
way to think of them would be as frozen droplets of condensed gasses.
>and would any life survive this?
Typically, the answer is probably not. Stars that 'live' long enough for
life to evolve are small like the sun. They go through a red giant phase
that should fry any life on earth-like planets, prior to contracting
into white dwarf stars that will eventually go nova. While it is not
impossible that the shock wave from a nova might carry along with it
the remnants of life from an earth-like planet, the chances seem
dubious, at best.
>kand why would one expect life on space stuff?
I dunno, why?
>Finally, a virus as I understand it is not a free living organism. So
> to postulate space viruses one must presumably postulate "higher" cells
> as well, out there.
Correct. Viruses are completely dependent on cell hosts for replication.
>I'm very sceptical that a bit of the very simplest amino acids on a ball of
>cometary ice is evidence for life in even the weakest sense.
>I'd go along with that.
Brian Fristensky |
Department of Plant Science | A question is like a knife that slices
University of Manitoba | through the stage backdrop and gives us
Winnipeg, MB R3T 2N2 CANADA | a look at what lies hidden behind.
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