Mariner 9 and the Viking orbiters were deliberately placed in orbits
around Mars where they would remain in space for at least fifty
years to kill off any stray microbes that might have hitched a ride
to avoid contaminating the planet when they do finally crash on it.
Maybe, just maybe, a future expedition could recover them for
study and exhibition, thus avoiding their touching the Red Planet
at all. Unless they are placed on Mars.
Can't say what the status or contamination protocols are for the
Soviet orbiters or the newest crop of similar vehicles.
BTW, is this the image you are referring to (scroll down 2/3 of the way):http://marsrovers.jpl.nasa.gov/gallery/pre.../20040311a.html
From the accompanying text:
It's a Bird, It's a Plane, It's a... Spacecraft?
Observing the sky with the green filter of it panoramic camera, the Mars Exploration Rover Spirit came across a surprise: a streak across the sky. The streak, seen in the middle of this mosaic of images taken by the navigation and panoramic cameras, was probably the brightest object in the sky at the time. Scientists theorize that the mystery line could be either a meteorite or one of seven out-of-commission spacecraft still orbiting Mars. Because the object appeared to move 4 degrees of an arc in 15 seconds it is probably not the Russian probes Mars 2, Mars 3, Mars 5, or Phobos 2; or the American probes Mariner 9 or Viking 1. That leaves Viking 2, which has a polar orbit that would fit with the north-south orientation of the streak. In addition, only Viking 1 and 2 were left in orbits that could produce motion as fast as that seen by Spirit. Said Mark Lemmon, a rover team member from Texas A&M University, Texas, "Is this the first image of a meteor on Mars, or an image of a spacecraft sent from another world during the dawn of our robotic space exploration program? We may never know, but we are still looking for clues."