QUESTION:
Could Hubble see the Mars Global Surveyor and Pathfinder if it was aimed at
them?

ANSWER from Mike Malin on May 28, 1997:
Both spacecraft are very small and very faint, but it is just barely within 
the ability of HST to see light reflected from them, if one makes a few
favorable assumptions.  When Mars Observer was lost, calculations were
made that showed that light reflecting off of the gold-and-plastic thermal
blankets was just bright enough to be very near the limit visible to HST
when Mars was closest to Earth.  "Just bright enough" means that, for a 10 hour
exposure, the spacecraft signal and the background noise would be about
equal (this means the spacecraft would be very, very, very difficult, but
not impossible, to see).  For all practical purposes, however, the Pathfinder
and MGS are not visible now, since they are smaller than Mars Observer, and
the distance to them is larger than the closest approach distance between
Earth and Mars.

Mike Malin