QUESTION:
It is clear that the MPF must slow down to safely land on Mars. But why is
there a planetary protection requirement which limits the impact velocity to
less than 1000 ft/sec? This requirement is stated in the description of the
trajectory correction maneuvers.

How many pieces of hardware litter the Martian surface? I know that there is
Viking I, Viking II, Pathfinder, Soujourner, and a Russian probe. Are there
any others? Also, regarding the Russian probe, I heard that there were
concerns that it was not properly sterilized. What concerns are raised by
microbes traveling to Mars?

ANSWER from Pieter Kallemeyn:
The requirement you're talking about is meant to further reduce the
contamination of Mars from parts of the vehicle in the unlikely event of a
crash landing. It specifically states that at any time during cruise, there
should be a less than 0.1% chance that the spacecraft will impact Mars at a
velocity greater than 1000 ft/sec. This, of course, assumes that we have
lost control of the spacecraft completely at some point along the way to
Mars, which is itself an unlikely event. This requirement affects how we
execute the first two midcourse maneuvers.

-- Pieter Kallemeyn, Mars Pathfinder Navigation Team Chief

ANSWER from David Dubov:
There are internationally accepted guidelines that NASA has adopted as rules
that govern the number and distribution of Earth "spores" (bacteria or other
biological contaminate) that we can sprinkle (intentionlly or otherwise) on
the surface of another planet (or moon) believed to have had the potential
of harboring life in the past or present.

The two Viking landers were sterilized in a large oven and then encapsulated
just before they were rocketed to Mars. This means that there were minimal
concerns about the spacecraft inadvertantly crashing onto the Martian
surface and spraying Earth spores everywhere. Baking the Viking spacecraft
was considered very controversial in its day however. The builders were very
concerned that the high temperatures would damage or degrade the materials
used in the construction. On Pathfinder we were very reluctant to bake the
whole spacecraft. Instead, we opted for baking bits and pieces (low gain
antenna, parachute, etc.), and cleaning the rest (wiping or immersing in
cleaning solvents).

The end result is that the outside of Pathfinder is clean to within the
allotment set by the international guidelines (we know this because we were
continously taking bio-assays to count the bugs). But what if we
inadvertantly put it onto a collision course with Mars and then somehow lost
control of the spacecraft? Wouldn't the Earth-bacteria sealed on the inside
escape onto the surface when it crash landed?

We don't know, but we could avoid the issue altogether by putting the
spacecraft on a collision course in the first place. By keeping the
trajectory near the edge (limb) of Mars we could make sure that, if the
spacecraft is lost control of, either it misses Mars altogether, or crash
lands with a velocity slow enough so it doesn't spew the bugs all over the
surface. Of course, this won't happen!

ANSWER from Donna Shirley on August 4, 1997:
There are also at least two Russian landers which were sent in 1971.  Both
Russia and the U.S. are signatories to a Planetary Protection protocol which
lays out groundrules for protecting the planets from terrestrial microbial
contamination.  For instance, Pathfinder and Sojourner were carefully
cleaned and tested to make sure that spores were not carried to the surface. 
Mars Global Surveyor will be in an orbit which will ensure that it will not
contact the surface for at least 50 years.

Donna Shirley