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To Mars and Beyond

By Koh Wanzi - 31 Aug 2019

What happens to the human body in space?

Image Source: NASA

What does space do to the human body?

But even if we pull off amazing feats of engineering and devise a flawless system to get humans to Mars, there’s still one very pesky problem. The human body just wasn’t built to exist for long periods in a zero-gravity environment bombarded by cosmic radiation. 

“The NASA Twins Study: A multidimensional analysis of a year-long human spaceflight” is a cross-disciplinary study of the long-term effects of space on the human body. The study was just published in the April 2019 issue of Science, and it is a one-of-a-kind study, conducted on identical twin astronauts Scott and Mark Kelly. Scott Kelly spent an entire year aboard the International Space Station between 2015 and 2016, while his twin Mark remained on Earth as a control. 

Over the course of 25 months, the brothers submitted to the collection of a multitude of biological samples, in addition to a battery of cognitive and physical assessments. The idea behind the study was to determine what exactly happens to the human body after prolonged periods in space, and by extension, assess the dangers of long-term space habitation.

The ISS is in Low Earth Orbit, so astronauts are still protected by the Earth's magnetic field. (Image Source: NASA)

The answer is pretty simple. The human body does not like space. As adaptable as we are, cosmic radiation wrecks havoc on our DNA, leading to scary changes that scientists are only beginning to understand. Scott Kelly lived in space for a year, and it’s difficult to extrapolate what would happen to Mars colonists who would be exposed to far more radiation. What’s more, the ISS orbits low enough to still be protected by Earth’s magnetic field, even if the astronauts are exposed to more radiation than someone on Earth because they’re above the planet’s atmosphere. 

A crew journeying to Mars would have to contend with eight times more radiation than Scott Kelly. While the study ultimately concluded that it was still possible to sustain human health for a year-long spaceflight, longer space missions are an entirely different ball game, and round trips to Mars could take up to three years

Radiation by the numbers
  Effective radiation dose (mSv)
Estimated Mars mission (3 years) 1,200
1945 Hiroshima A-Bomb 200
Skylab 4 (87-day mission orbiting Earth at 473km) 178
ISS mission (up to 6 months orbiting Earth at 353km, solar maximum) 160
Scott Kelly's year-long mission 146.34
ISS mission (up to 6 months orbiting Earth at 353km, solar minimum) 80
Apollo 14 (9-day Moon mission) 11.4
Space Shuttle 41-C (8-day mission orbiting Earth at 460km) 5.59
1 year on Earth 3
Full-body CAT scan 1.1
X-ray 0.11

 

What is Galactic Cosmic Radiation (GCR)?

GCR is a type of ionizing radiation that mostly comes from outside our solar system, but still within the Milky Way galaxy. Ionizing radiation can blast through substances and alter them. It has been described as an "atomic-scale cannonball", so you can imagine the damage it brings about.

Specifically, GCR comprises heavy, high-energy ions of elements that have had their electrons stripped away. They travel at nearly the speed of light, and can cause ionization of atoms as they pass through a spacecraft or an astronaut's skin. Often, these high-speed particles are shot out into space by the magnetic fields of supernova remnants. Astronauts on the ISS have even reported seeing flashes of light light up their field of vision when their eyes are closed, the result of radiation impacting on their retinas.

 

Twisted chromosomes

Space sure did a number on Scott’s DNA. Sections of his chromosomes were inverted or translocated, which possibly ended up affecting gene expression as well. The study found that over 10,000 genes in Scott’s genome were activated in space, no doubt a response to stressors like lift-off and zero gravity.

And even though 91.3 percent of these genes whose expression changed in space returned to normal within six months of Scott returning to Earth, a full 811 genes never did. More worryingly, these genes existed in different cell types and were almost all involved in DNA repair and immune function. If humans are to survive for long in space, these genes will be crucial to protecting us from radiation. Cells that cannot repair DNA damage are prime fodder for mutations to accumulate and give rise to cancer and heritable diseases.

 

Shortened telomeres

Telomeres are the caps that protect the ends of our chromosomes from deterioration. They shorten as our cells divide, and when they get short enough, the cell simply stops dividing and dies, which is what eventually leads to aging and death.

Oddly enough, while Scott’s telomeres lengthened onboard the ISS – likely because of the recommended exercise regime – they rapidly shortened within 48 hours of returning to Earth, perhaps a result of the stresses of reentering the atmosphere and landing. Most of his telomeres regained their baseline levels eventually, but things were never quite the same. Scott now has significantly fewer telomeres overall and higher numbers of critically short telomeres, and telomere loss may eventually make astronauts more susceptible to cancer and other diseases associated with old age.

 

Visual deficits

Before space travel (left) and after. (Image Source: American Academy of Ophthalmology)

Up to 40 percent of the astronauts who have lived on the ISS have suffered some sort of damage to their eyes. NASA isn’t completely sure how this happens, terming it “spaceflight-associated neuro-ocular syndrome”, or SANS. The condition is characterized by optic disc edema, globe flattening, choroidal folds, and other structural changes. Some astronauts also develop cotton wool spots, which appear as fluffy white patches on the retina.

The most common problem is probably globe flattening, where what we think of as the eyeball essentially becomes less round at the rear-end. It’s thought to be a result of fluid build up and increased intracranial pressure, which end up squishing the eyeballs and flattening them.

 

Poorer cognitive performance

Mark and Scott Kelly (right) are identical twin astronauts who took part in a study to examine the long-term effects of spaceflight. (Image Source: NASA)

Space also affected Scott Kelly’s brain. He did worse on cognition tests even six months after returning home, responding more slowly and making more mistakes. The findings were slightly odd, since Scott’s performance actually increased in space before declining sharply upon return. Obviously, the limitations of the study – the sample size of 1, for instance – make it difficult to attribute reasons to this decline. 

It’s entirely possible that Scott was simply less motivated once he was back on Earth, but there could also be more insidious mechanisms at work. Either way, it’s concerning, since any crew landing on Mars will need to be ready to tackle more challenges. 

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