QUESTION:
We have heard that the Mars'96 was carrying Plutonium as a fuel.
Does Pathfinder also have Plutonium, and isn't that dangerous?

ANSWER from Donna Shirley on Decemebr 5, 1996:
Mars 96 was carrying a small amount (270 grams) of Plutonium, some to
generate electricity and some for heat.

Mars Pathfinder will carry a much smaller amount of Plutonium to keep the
rover from freezing at night.  The rover has about 3/10 of an ounce of
Plutonium in three containers, each about the size of a small 35mm film
cannister.  The Plutonium itself in each can is about the size of a pencil
eraser.  The cans are so well designed and rugged that they are tested by
being shot from a gun into a concrete wall without breaking open.

If you held one of the cans in your hand for an hour you would get about as
much radiation as from a normal chest x-ray.

In order for the Plutonium to hurt you it would have to vaporize, and you
would have to breathe the vapor.  Then, many years later, your chances of
getting cancer would be higher than otherwise.  But the chances of an
accident with Pathfinder releasing Plutonium vapor are so small that they
are a tiny fraction of the chance of your getting cancer just from normal
background radiation.

Donna Shirley
Manager, Mars Exploration Program