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Re(3): MARTIAN PALEOBIOLOGISTS - NYET!



Date: Fri, 23 Aug 1996 10:35:42 -0700
From: seale@dimensional.com
Subject: MARTIAN PALEOBIOLOGISTS - NYET!

Terry Colvin / David Portree wrote:

> The next two robot probes to Mars are NOT sterilized. Several Soviet probes
> of the past also were not sterilized. When I raised this issue with some NASA
> sample analysis people immediately after the public announcement that
> possible dead martian life had been found, I was told that sterilizing these
> probes was not an option, because it would double their cost.

This is true, but not the complete picture.

The next probes to Mars are not sterilized, but they are "cleaned"
with alcohol, and given bioassays to make sure their load of spores
is below some critical level (don't know the numbers off-hand).  The
logic behind this is that given our current understanding of the
Martian surface chemistry (highly oxidizing, lots of UV), anything
that goes to Mars on a lander won't survive far from the spacecraft.

Essentially, bioburden is limited, not eliminated.  The plan for
future landers is to sterilize only those spacecraft that carry
life sciences payloads (to eliminate the chance of a "false positive"
reading).

Again, the logic for this is that most scientists feel life could
not currently develop / spread on the surface of Mars.  Any
sufficiently-small amount of bioburden on a lander will only "pollute"
a small area around the lander (mostly under it -- sheltered from
the ambient UV flux).  Anything that blows beyond that gets fried
in pretty short order.


> ...The plan is to launch small, low-cost
> ($150 million) probes to Mars at each launch opportunity (about every two
> years). .... The first two,
> Mars Global Surveyor (an orbiter) and Mars Pathfinder (a lander with a tiny
> rover) are due to launch in November and December, respectively.

For what its worth, future probes in the series will be even cheaper.
In particular, the 1998 probes are slated to come in at $50 million
each (not including science or launch costs).

Eric Seale
----------------------------------------------------------------------
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