The Viking Landings

July 4 1976: Viking 1 lands on Mars to analyse soil samples. Viking 2 follows on September 3 1976.

One of Viking's main goals was to search for life. Basic idea behind biological package:

scoop up a soil sample
add nutrients
search for oxygen, CO₂ -- the byproduct of life

Before launch, Viking experiments were tested in Antarctica, and verified that the Antarctic soil was lifeless. The package shouldn't give a false positive.

First results: oxygen! CO₂! life!! WOW!!!

It was quickly realized that these were chemical reactions, not biological reactions.

Think about the loss of water on early Mars --> H₂O dissociated, H escapes from atmosphere. But what happened to the oxygen? Oxidization of Martian surface -- oxygen locked into rocks. Any liquid added will cause oxygen and CO₂ to dissolve out.

rats... are we sure it can be done with chemical reactions alone?

verified in lab - a sterilized environment gave similar results under similar conditions

double rats... Viking showed no sign of life on Mars.

But waitaminnit! Recent studies showed that Antarctica has life. Whoops. Maybe Viking wasn't foolproof...

and then the Viking Orbiter took a picture of.....