(Tom Merkle) writes:

[...]

After all, the quarantiners will say, if Nozomi can fail and plow into
Mars, possibly spreading earth bacteria, what's to prevent a Mars
return vehicle from doing the same thing to earth, resulting in
AAAAAAHHHH! The Andromeda Strain!

The result will raise the cost of Mars Sample Return for redundancy,
and realistically probably prevent it from happening for the
forseeable future.

Anything CAN fail, and there is currently estimated to be a 1%
probability of Nozomi hitting Mars if it continues on its present
course. Its controllers plan to try to lower this chance if (as seems
all but certain) attempts fail to get its power supply working to the
point it can power the heaters to thaw the frozen propellant to allow
Mars orbit insertion (and power the instruments to allow Nozomi to
perform any science). The chances of them doing this by using the small
(but still functional) mid-course correction engines are better than the
all-but-zero chance of them recovering the power supply, so the chance
of Nozomi hitting Mars is realistically less than that 1% estimate.

If Nozomi doesn't hit Mars, I don't forsee the Chicken Littles
succeeding in preventing a Mars sample return mission. Even if it does
hit Mars, the C.L.'s chance of success is, I think, not terribly great
-- I expect the space science community would be able to rally more
support that the C.L.s. IMHO, of course.