In the annals of space medical history, we will forever remember these as the mice that stayed behind.
"They are the model animal for immunology," space immunologist Millie Hughes-Fulford, Ph.D. said.
If Fulford sounds vaguely familiar, it's because almost 19 years ago, she rode the shuttle Columbia and became the 13th woman to visit space.
"It was the first dedicated medical mission," she said.
It was nine days of medical study aboard a laboratory in the payload bay -- nine days of probing why muscles lose mass, how the blood flows and experimenting with equilibrium.
For Fulford, this is really just a continuation from her 1991 mission. She's still asking the question why can't mankind travel a long way for a long way in space. We still face what she calls a couple of biological show stoppers.
"The T-cells and bone are the two tissues in the body more sensitive to gravity," Fulford said.
T-cells trigger the immune system, in weightlessness, they do not. Fulford treated those mice aboard the shuttle with a gene that, she hopes, might stimulate the T-cells when weightless. Such a discovery could have broad implications.
"We're talking about treating astronauts to have their immune systems wake up. And we might be able to activate the T-cells of people who are immune-suppressed on the ground," she said.
When the mice return, Fulford will compare blood samples with those that remained behind. She expects the space mice to be compromised, just as astronauts are.
"The big question is why do astronauts have immuno suppression? In Apollo, 15 of the 29 astronauts got sick either after their flights, or during their flights," Fulford said.
In short, if she solves this riddle, Mars becomes a real option -- a simple experiment of mice and men and women -- in space.