NASA Twins Study Confirms Preliminary Findings

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. Researchers are looking at the effects of space travel on the human body. (Credits: NASA)

Editor’s note: NASA issued the following statement updating this article on March 15, 2018:

Mark and Scott Kelly are still identical twins; Scott’s DNA did not fundamentally change. What researchers did observe are changes in gene expression, which is how your body reacts to your environment. This likely is within the range for humans under stress, such as mountain climbing or SCUBA diving.

The change related to only 7 percent of the gene expression that changed during spaceflight that had not returned to preflight after six months on Earth. This change of gene expression is very minimal.  We are at the beginning of our understanding of how spaceflight affects the molecular level of the human body. NASA and the other researchers collaborating on these studies expect to announce more comprehensive results on the twins studies this summer.


The Twin Study propelled NASA into the genomics era of space travel. It was a ground-breaking study comparing what happened to astronaut Scott Kelly, in space, to his identical twin brother, Mark, who remained on Earth. The perfect nature versus nurture study was born.

The Twins Study brought ten research teams from around the country together to accomplish one goal: discover what happens to the human body after spending one year in space. NASA has a grasp on what happens to the body after the standard-duration six-month missions aboard the International Space Station, but Scott Kelly’s one-year mission is a stepping stone to a three-year mission to Mars.

If the results of the Twins Study are like a play, Act 1 began at NASA’s Human Research Program (HRP) 2017 Investigators’ Workshop (IWS), where the ten teams presented their preliminary findings. Reports included data on what happened to Scott Kelly, physiologically and psychologically, while he was in space, and compared the data to Mark Kelly, as a control subject on Earth. The 2018 IWS is Act 2, where findings from 2017 were corroborated, with some additions. Researchers also presented what happened to Scott after he returned to Earth, again while making comparisons to Mark. Act 3 will be debuted later in 2018 when an integrated summary publication is expected to be released.

By measuring large numbers of metabolites, cytokines, and proteins, researchers learned that spaceflight is associated with oxygen deprivation stress, increased inflammation, and dramatic nutrient shifts that affect gene expression.

After returning to Earth, Scott started the process of readapting to Earth’s gravity. Most of the biological changes he experienced in space quickly returned to nearly his preflight status. Some changes returned to baseline within hours or days of landing, while a few persisted after six months.

Scott’s telomeres (endcaps of chromosomes that shorten as one ages) actually became significantly longer in space. While this finding was presented in 2017, the team verified this unexpected change with multiple assays and genomics testing. Additionally, a new finding is that the majority of those telomeres shortened within two days of Scott’s return to Earth.

Another interesting finding concerned what some call the “space gene”, which was alluded to in 2017. Researchers now know that 93% of Scott’s genes returned to normal after landing. However, the remaining 7% point to possible longer term changes in genes related to his immune system, DNA repair, bone formation networks, hypoxia, and hypercapnia.

Increasing mission duration from the typical six-month ISS mission to one year resulted in no significant decreases in Scott’s cognitive performance while inflight and relative to his twin brother Mark on the ground. However, a more pronounced decrease in speed and accuracy was reported postflight, possibly due to re-exposure and adjustment to Earth’s gravity, and the busy schedule that enveloped Scott after his mission.

For additional detail on preliminary findings, visit NASA Twins Study Investigators to Release Integrated Paper in 2018. All of these findings are being integrated and summarized by the research teams; researchers are also evaluating the possible impact that these findings will have on future space travel beyond low Earth orbit. The next step for Twins Study investigators is Act 3, as referenced above. An integrated summary paper will be published later this year. A series of smaller papers grouped by related research areas will also be released.

The Twins Study has benefited NASA by providing the first application of genomics to evaluate potential risks to the human body in space. The NASA Twins Study also presented a unique opportunity for investigators to collaborate, participating in a team approach to HRP research.

Observations guide development of future hypotheses. Research from the landmark Twins Study will inform NASA’s Human Research Program studies for years to come, as NASA continues to prioritize the health and safety of astronauts on spaceflight missions.

NASA’s Human Research Program (HRP) is dedicated to discovering the best methods and technologies to support safe, productive human space travel. HRP enables space exploration by reducing the risks to astronaut health and performance using ground research facilities, the International Space Station, and analog environments. This leads to the development and delivery of an exploration biomedical program focused on: informing human health, performance, and habitability standards; the development of countermeasures and risk mitigation solutions; and advanced habitability and medical support technologies. HRP supports innovative, scientific human research by funding more than 300 research grants to respected universities, hospitals, and NASA centers to over 200 researchers in more than 30 states.

  • therealdmt

    The mustache guy should grow a goatee for these pictures

  • JS Initials

    WOW!!!! We have a REAL starman!!…David Bowie was right.

  • JS Initials

    OK! Time for me to be serious! We have milksop wimpy scientists who claim it is too dangerous to send people to Mars on a 3 year mission, because of cosmic radiation. i have a humble set of solutions that involves crew discipline, spending half or two-thirds of their time journeying to and from Mars in a 7.5 foot-deep times 7 foot diameter ‘cubby hole’ surrounded by a stainless-steel container (one millimeter thick) electroplated with lead and filled with water one foot deep. No more than 8 tons of water required. Do the math! …In addition, the water-filled cubby hole shell will be encased in a thick layer of hydrogen-rich plastic. In fact it may be a good idea to encase the entire Mars-bound mothership with hydrogen-rich plastic. I believe these methods will reduce radiation level exposures by more than half.

  • ThomasLMatula

    How dare you recommend a practical engineering solution! Don’t you realize is more fun, and profitable (in terms of government grants and academic publications) for NASA to research this problem for the next decade or two. Note how they make a point of nearly 300 grants going out to 30 states? That makes a lot of Congress Critters happy.

    And don’t forget that one key mission of the LOP-G is to do research on this problem of enabling astronauts to reach Mars. That a $40 billion dollar project you are endangering. Money that will make a lot more Congress Critters happy.

    Yes, this illustrates well why NASA is really not in the human exploration business anymore. It’s in the business of spending money in as many Congressional Districts as possible to ensure Congressional support.

  • JS Initials

    Thumbs up for your reply. LOL.

  • duheagle

    Carbon fiber composite isn’t quite as hydrogen rich as, say, high-density polyethelene (HDPE), but it’s gotta help if the whole spaceship is made out of the stuff as SpaceX is doing with BFR-BFS.

  • Michael Vaicaitis

    I think the radiation exposure risk may be somewhat overstated, in fact, it’s highly plausible that an increased radiation dose from travelling to and from Mars could well turn out to actually be beneficial to human health. Being subjected to radiation below some threshold level (difficult to pinpoint that threshold level and it may be highly individual) actually produces statistically lower cancer rates and generally lowers all cause mortality – it seems that the radiation is destroying more pathogen/toxin problems than is causes. Basically, Earth-bound populations living in higher background radiation locations, and many people who have received more than average medical radiation, are statically less prone to many diseases, including cancers. The dna damage (supposedly/potentially leading to cancers) of prolonged (as in lifelong for some populations) low level radiation has been greatly overblown. It has been recently estimated that every cell in your body experiences some 10,000 single strand DNA breaks every day (caused by just the chemical environment of a properly functioning body), i.e. human bodies repair 10,000 x ~50 trillion dna breaks every day of your life. Living organisms have evolved to have extraordinary self-repair mechanisms.

    Using a carbon fibre hull, perhaps together with your hydrogen-rich materials would all but eliminate the secondaries associated with metal hulled spacecraft, and greatly reduce the worst effects of the cosmic ray bad boys. With that said, some sort solar storm shelter would likely be a sensible, but even that is really just a matter of strategic cargo (including water) storage.

    I don’t mean to entirely dismiss the quite plausible risks of increased radiation exposure from interplanetary travel, especially from those fast moving cosmic “ray” particles, but EM and even particle radiation risk is far from fully understood and has been severely hampered for decades by the pseudo-science of Linear No Threshold. The health risks of prolonged spaceflight are more likely to come from low-g, as is implied by Scott’s rapid return to normal functioning upon his return. Which highlights the biggest unanswered question facing potential Martian (or lunar) colonists: is 0.37g enough to return humans travellers to normal health?, and then inevitably some colonial years down the line, will there be any disastrous developmental issues for babies conceived and born at .37g?.

  • Aegis Maelstrom

    Here where I live at least one high-ranked tenured professor of nuclear physics wages his war against LNT model using similar arguments (eg. data from regions with high ambient radiation etc.).

    Nevertheless, LNT is the theory in power. Finding something better requires not only persuasion but also a good theory how much is safe *as I believe some radiation shielding is needed*.

    Other risks remain valid as well, eg IIRC people in space experience a significant reduction of their cognitive capabilities. There is a plethora of things which can just go wrong (TM)…