Buzz Aldrin on the moon in 1969, photographed by first-on-the-moon astronaut Neil Armstrong (NASA)


When Buzz Aldrin became the second man to ever walk on the moon, his lunar escapades, along with those of Neil Armstrong,  were a cause of national and pretty much global joy, wonder and pride.   That the mission was hazardous was self-evident — from launch to the ad-lib and hair-raising landing on the moon, to return to Earth– but the nation and certainly the astronauts were more than ready to take the risk.

A half century later, Armstrong has passed (at 82 from complication of cardiac surgery)  but Aldrin is still writing books and proposing plans to reach Mars. Their time in space may well have changed their lives and views of the world, but it did not seem to affect their basic health.

But the two were in space for only eight days and so were not exposed to the long-term effects of solar radiation, microgravity and isolation that are now under intense study.  Because the next generation of astronauts who may be going to the moon and beyond will be going for much longer periods of time and so will face a wide range of potential problems that weren’t considered major issues in Apollo or even later days.

Much has been learned since Apollo, however, and some of it raises new risks and new problems.  And that’s why the just-released Twin Study of the health comparison of long-staying International Space Station astronaut Scott Kelly and his ground-based twin brother Mark Kelly has been eagerly awaited.

Now that we know somewhat better what to look for in terms of more subtle damage that can come from long stays in space, what are the dangers and how serious are they?

Identical twins, Scott and Mark Kelly, are the subjects of NASA’s Twins Study. Scott (left) spent a year in space while Mark (right) stayed on Earth as a control subject.  It was Scott Kelly’s idea to have he and his (former astronaut) brother serve as subjects of the extensive research into the effects of space travel on the human body. (NASA)

“Given that the majority of the biological and human health variables remained stable, or returned to baseline, after a 340-dayspace mission, these data suggest that human health can be mostly sustained over this duration of spaceflight,”  the study concludes.

Published in Science, the intensive study was led by Francine E. Garrett-Bakelman,  a physician and PhD  now working as an assistant professor of Biochemistry and Molecular Genetics at the University of Virginia.  The final results are largely in keeping with the preliminary findings released  over the past year.

This is the good news that many experts and supporters of human space exploration have focused on.  Given the proper precautions, long durations in space do not seem to have overt negative health implications.

There are, however, some pretty substantial “buts” associated with the conclusion, and they contribute to what make the study different from many previous ones.  As the paper concludes:

“Given our results, it is expected that astronauts conducting exploration-class missions could experience risks from mitochondrial dysfunction, immunological stress, vascular changes and fluid shifts, and cognitive performance decline, as well as alterations in telomere length, gene regulation,and genome integrity.”

We’ll go back to look at what these risks might entail, but the study authors properly make the point that the Kelly in space was actually not in deep space — only 240 miles above the Earth — and so was not exposed to the much higher levels of radiation that exist beyond the protection of our Van Allen belt.


A cutaway model of the Van Allen radiation belts with the ISS shown deep inside them. The radiation belts are two donut-shaped regions encircling Earth, where high-energy particles, mostly electrons and ions, are trapped by Earth’s magnetic field. They form protective shields that keep all that is beneath safe — or relatively safe — from the harm that can come from high-energy radiation. (NASA)

The radiation load for astronauts traveling to Mars, for instance, would be at least five times greater than in the space station, and the exposure would by significantly longer.

Solar and cosmic radiation is known to damage human DNA, with myriad possible harms including the development of cancers.  Radiation can  also be hazardous to the heart and can harden and narrow arteries as well as hinder the production of new brain cells. The risks all build up over time exposed.

So in a teleconference about the study’s findings, many of the participants stressed that the Kelly twins study does not give any definitive answers about the effects on astronauts who might be flying to Mars or living for long times on the moon.

The study suggests that the human body can adapt to space and can overcome many of the ill effects of life in deeper space with a return to Earth.  While using the experience of Scott Kelly to predict the health of a future deep space astronaut is certainly useful, it is also, to some extent, comparing apples and oranges.


Scott Kelly and Russian cosmonaut Mikhail Kornienko on their 300th day on the ISS. (NASA)

Putting all this aside for a moment, here are some of the known significant effects of life in space for astronauts who stay there for more than a short time:

  • As a result of being in a zero-gravity environment, fluids in the body tend to rise upward in the body in ways they don’t on Earth. This can have effects on the cardiovascular system, on cognitive abilities, and perhaps most commonly on the eyes.  A constellation of minor to significant symptoms now called spaceflight-associated neuro-ocular syndrome, or SANS, has been found in numerous astronauts. Scott Kelly experienced SANS during flight and was found to have “significant diminutions” in cognitive abilities after landing.


  • On a molecular level, astronauts and others exposed to higher levels of radiation experience structural abnormalities in their chromosomes, and Scott Kelly did as well. In particular, the inversion of chromosomal fragments caused by radiation can lead to chromosome transformation, with potentially harmful longterm consequences. The expression of DNA-repair genes in Scott Kelly remains high after returning to Earth.


  • Researchers paid great attention to the telomeres on the twin’s chromosomes, which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes. A decline in the robustness of telomeres is associated with aging. The telomeres on Scott Kelly’s chromosomes mostly lengthened during his time in space, but shortened to some extent on return and some remained shortened.

The human chromosomes here are grey and are capped by white telomeres. (U.S. Department of Energy Human Genome Program)

In addition to the results of the Twin Study, Science also published a commentary by Markus Löbrich and Penny A. Jeggo of (respectively) the Radiation Biology and DNA Repair, Darmstadt University of Technology in Germany and the Genome Damage and Stability Centre, at the University of Sussex in the United Kingdom.

Their assessment of the potential long-term hazards was more concise and somewhat more concerning, and so I’ll include their overall conclusions at some length.  They write here mostly of travel to Mars, but the radiation environment on the moon is similar:

“The observed effects reported by Garrett-Bakelman et al. are arguably broader and more pronounced than might have been expected, particularly for the more (ionizing radiation)-specific responses such as genomic instability, persistently up-regulated expression of DNA damage response genes, and cognitive function decline.

But the more microgravity-specific alterations in the neuro-ocular system and severe vascular physiology changes could also potentially couple with the known impact of (ionizing radiation) on cataract formation and cardiovascular diseases.

Both pathologies are known to arise at significant rates in people who have been exposed to radiation doses above ~500 millisieverts. (mSv) Such exposure levels, although not encountered during the 1-year ISS flight, will be received during travel to Mars, where the dose rate exceeds that on the ISS by about five-fold, and total dose estimates range up to 1000 mSv .

Consequently, during Mars travel, the spectrum of biological effects will shift, placing more weight on IR-induced effects and those reacting synergistically with the microgravity responses. To understand the details of such shifts and their long-term consequences will be important for future studies and the development of countermeasures. Undoubtedly, the study by Garrett-Bakelman et al. represents more than one small step for mankind in this endeavor.”

NASA has proposed as many as five additional long-duration ISS astronaut health studies to better determine what health effects to expect and how they might be addressed while in space.


Artist rendering of a moon base. (NASA)

NASA “travel poster” for Mars. (NASA)

The astronaut health issue has taken on a greater urgency, of course, because of plans and hopes to send astronauts to the moon to set up a colony and later to Mars.

The moon project has become a high priority for  NASA and the Trump administration, with a tight time-table proposed to have an American astronaut land on the moon by 2024.  Many in the space community consider the date to be overly optimistic for reasons of both hardware and funding, but the push forward does reflect the view of some that the time has come to begin to set up a permanent base on the moon.  Mars, in this scenario, would come later.

One of the aspects of the moon project that I find sobering — with its proposed long-term stays in worlds where there is no Van Allen belt protection from harmful radiation — is that we won’t have firm answers about the dangers to astronauts before they set off.   This will make it more difficult to come up with the proper shielding techniques and equipment.

As is often said, exploration always involves risks and nobody would be going to the moon or Mars (or up Mt. Everest) who doesn’t accept them.  Fair enough.

But despite the impressive work of the Twin Study and the numerous reassuring conclusions from it, the fact remains that astronauts will be going for potentially long stays into radiation and microgravity environments that are far from fully understood.