Narrator: This is astronaut
Scott Kelly back in 2015.
For 340 days, he circled Earth
inside the International Space Station,
the longest any American has
ever spent in space at once.
Meanwhile, someone with the
same face, body, and DNA
was back on Earth: his
identical twin, Mark Kelly.
Scott and Mark are the only
twin NASA astronauts in history.
Separated by 250 miles of space and sky,
the twins participated
in a groundbreaking study
unlike anything NASA
had ever tried before.
The mission: discover long-term effects
of space on the human body.
And now, four years after Scott
Kelly launched into space,
we have the full results,
which confirm that, yes,
a crewed mission to Mars is possible.
Bakelman: To me this is very reassuring
and really suggests that...
longer-term travel is a possibility.
Narrator: NASA is trying
to put humans on Mars
in the 2030s, but even if
it had the rocket technology
to visit today, there's
still one major obstacle
standing in the way: our bodies.
Because traveling to
Mars will be the longest
crewed space mission in history,
lasting for over a year,
and while NASA has tested in-depth
how the isolation will affect our minds
with missions like HI-SEAS,
it has little information
about what space travel
will do to our bodies.
That's where NASA's twin study comes in.
News Anchor: Astronaut Scott
Kelly will try something
no American has ever done before.
This spring, he will leave for a mission
and spend a year in space.
Narrator: Over the course of that year,
Scott gathered all kinds
of data about himself.
He drew blood, collected urine,
and took cognitive tests.
And back on Earth, his twin brother,
the perfect human control,
did the exact same thing.
Then, in 2016, Scott
returned home to Earth
where scientists studied him
for another six to nine months.
And now, finally, four
years after Scott's launch,
researchers have published
the full results,
and here's what they found.
For one, there were
signs of radiation damage
in Scott's chromosomes.
Those are the structures in
our cells that contain DNA.
Bailey: We know that radiation
causes or will induce
these chromosome aberrations,
or rearrangement of the chromosomes.
So essentially it breaks the DNA.
Narrator: And on a longer
mission, say to Mars,
more of those DNA breaks could build up.
Bailey: And that can contribute
to genomic instability.
Narrator: Which could lead
to diseases like cancer.
The year in space also
activated thousands of genes
in Scott's genetic code, something similar
to what can only happen in
extreme environments on Earth.
That's because many of these genes
are linked to our immune system.
Bailey: When we get into
stressful situations,
or we have an injury, or we get sick,
the immune response kicks in.
And the way it does that is
it turns the genes on that it needs.
Narrator: Bailey was part of a group
that also looked at structures
in the twins' cells called telomeres.
Telomeres are caps at
the end of chromosomes
that help protect our DNA from damage,
and as we age or are
stressed, they shrink.
That's why Bailey figured
that Scott's telomeres
would shorten during his year in space.
He wasn't just aging, but he was exposed
to all kinds of stressors
from cosmic radiation
to zero gravity, and pretty
much everything in between.
But she was wrong.
From what researchers could tell,
Scott's telomeres
weren't shorter in space.
They were significantly longer.
Bailey: I don't know
what's going on in space.
We imagine things like, "Oh,
they're just having such a grand time."
You see 'em floating around.
They all look real happy
while they're up there.
A dream come true.
But it's just, I just don't think
it's the fountain of youth.
Narrator: One explanation is that Scott
had a healthy regimen on the ISS
replete with exercise and
nutritious astronaut food.
But Bailey says longer
telomeres are more likely
yet another signal of
stress or even injury.
Radiation, for example,
might have triggered
the production of stem cells,
which can renew damaged
structures in the body,
and those cells inherently
have longer telomeres.
So one major takeaway from the study
is that space is, well, stressful.
But all that stress was
short-lived for Scott,
and for the most part, his body
actually returned to normal
after landing back on Earth.
Within 48 hours, his telomeres
were short once again,
and after six months, more than 90%
of those activated genes turned back off,
and nine months out, there was less damage
in his chromosomes,
which means that none of the changes
the researchers observed was
immediately life-threatening.
Bakelman: To me what
that means is that people
can be in space.
They can be there for a year,
maybe longer, we don't know.
Even though we're not born in space,
our bodies figure it out,
and they're able to function.
Narrator: Taken altogether,
that's great news for NASA
or for anyone else hoping
to send humans to Mars.
Swanton: I definitely think
they're gonna be possible.
Narrator: That's Dr. Charles Swanton,
a cancer biologist at the
Francis Crick Institute
in Britain, who wasn't
involved in the study.
Swanton: What I can't
predict at the moment
is the impact on human health
and reproductive potential.
Narrator: He acknowledges
that a yearlong trip to Mars
isn't the same as a year on the ISS.
There'd be more radiation, for example.
But, following the twins study,
he and the researchers
have far more confidence
than ever before that
we're going to get there.
