When scientists
want to understand something they will often use an experimental
“unit” and a control “unit”. And when studying something if
you have a second copy around then you can control for more kinds of
factors. And when it comes to people identical twins are the closest
you can get to a second copy.
Genetically they
are the same, so you can rule out genetic differences. Though
identical twins can still be very different. This is one way that
scientists can determine when something has a genetic basis rather
than some other. Nature versus nurture. Combine that with the overall
similarity of identical twins and you have a nearly perfect way of
comparing effects.
So when Scott Kelly
went up to the International Space Station at the end of March, NASA
was lucky enough (or far sighted enough) to pick someone with an
identical twin. In fact Scott's brother Mark was an astronaut flying
on four Space Shuttle missions before he retired. (Mark Kelly is also
the husband of Gabrielle Giffords, the congresswoman that survived
the assassination attempt back in 2011.)
So Scott Kelly is
going to be up on the International Space Station for a year. And he
and his brother will be examined to see what affect the long stay in
space has on his body. There are know issues such as bone loss. But
they are going to look at psychological effects, immunological
effects, how long periods in space affect vision, and many other ways
that space could impact the human body. Taking strong advantage of
the twin as a control.
One of the benefits
of such a study on the long term impact of space travel on a human
body is in planning for trips to Mars. Even with no restriction on
the amount of fuel, it takes hundreds of days to get from the Earth
to Mars. And all that time in space will affect the astronauts making
the trip. So knowing ahead of time what can and will happen to the
astronauts is essential in forming a reasonable plan for getting
people to Mars. So the opportunity to have a twin study for these
effects is far too good to pass up.
Sadly one thing
they won't be able to control for is diet. Scott is going to be
limited to “space” food, while Mark will have a normal earthbound
diet. That alone could be a significant psychological impact. I know
I'd have trouble with that.
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