We are experts working on The Twins Study to learn how NASA spaceflight affects the human body. Ask Us Anything!

What information was found that was most surprising and unexpected? Also, what were some concerns if any found?

For the epigenetics portion of the study, we thought we would see very large differences in DNA methylation in Scott during his mission compared to Mark, but actually we found that there was more variability in Mark! This makes sense when you think about the fact that Mark experienced a more variable environment (seasonal changes, more varied diet, etc) than Scott did on the space station. - Lindsay Rizzardi

For the microbiome study, we were pleasantly surprised by how well maintained the diversity of the gut microbiome was in space. With a limited diet and limited contact with other people, we anticipated a decline in diversity, and did not see it. -Martha Vitaterna

why did you think his gut microbiome would diminish after being in space? Just curious as it seems that without any interactions with competing micro organisms, the microbiome would stay relatively intact? or am I totally off base?

To be clear, I expected the number of species to decline, not the number of microorganisms. I thought that without the steady introduction of new microorganisms from the environment-- meeting new people, going new places, eating new food, etc.--that if any gut microorganisms went extinct in space, they would not be replaced. It sounded reasonable, but is not what we saw.

On the other hand, we did see shifts in the composition of Scott's microbiome while in space that then returned to a more pre-flight state when he returned, so it isn't that the microbiome didn't change. It just didn't change as I had expected it to.
-Martha Vitaterna

Speaking of gut microbiomes, are astronauts screened for pathogens before flight? It would be a nightmare trying to disinfect the ISS for C. difficile.

I'd think that the medical exams the astronauts receive would prevent someone with C. difficile from flying. -Martha Vitaterna

For the gene expression data and cell-free DNA component, we saw a larger number in the second half of the mission, and also the spike in mtDNA in the blood was completely unexpected. - Chris Mason

What was the hardest part about returning to Earth? Was it disorienting having to deal with gravity again?

Physically I would say the swelling in my legs was the worse part of returning to gravity. I could feel the blood rushing out of my head into my legs. My legs swelled like water balloons.

-Scott Kelly

Was this only when standing up or would there be swelling and pain even when laying down as well?

It was due to gravity, so sitting was worse than lying down and standing worse than sitting.

-Scott Kelly

Is there any solution to that, like squeezing your core or arms or something?

I wore the tight leggings that you see many NBA players wear. That helped a little. Mostly it was the tincture of time.

-Scott Kelly

Also, the largest cognitive changes were not observed in-flight, but after Scott returned to Earth. Re-exposure to gravity certainly played an important role, but also re-adjusting to a hectic life with lots of science experiments and media events may have contributed. - Mathias Basner

The difficulty in returning from space varies between people and progressively resolves over time. In the first few hours, neuro-vestibular issues and blood pressure regulation are problematic. Over the first 24 hours, these problems become less. Other issues depend on what level of effort you try to exert (decreased muscle strength, reduced exercise capacity, etc.). How long it takes to recover depends how long you were in space, what countermeasures your performed in space, and how much you participate in the postflight rehab program.

SMC

The biggest changes you can see in the metabolomics and expression data, especially look at Supp. Fig 8 from the paper. For example C-reactive protein went up >4,000%.

I’m curious on this too! Do astronauts need to rewire the brain when it comes to being back on earth with gravity? I always see this video of an astronaut who keeps dropping stuff midair as if he has forgotten that he now is dealing with gravity.

I only felt the desire to float things in front of me after my first flight, which was only eight days. I think the longer you are in space, the more you feel that you are no longer in space when you return so the propensity to drop things diminishes.

-Scott Kelly

Hello everyone! I just wanted to thank you all for working on this study and providing us with such a landmark scientific case that I had the pleasure of following along with for the last 4 years. Scott you’re an inspiration and I’m so glad I got to witness those 340 days along with you.

My question is out of all of the experiments conducted on the twins during the Year in Space, what was an experiment whose results strayed furthest from your hypothesis?

Thank you!

For the telomeres investigation, the observation that Scott had longer average telomere length during spaceflight was exactly the opposite of what we hypothesized. susan bailey

Awesome! Thanks for all the research into stuff like this and making knowledge greater! I don't really know what to ask other than maybe, what's the one thing you always want people to know about space or space travel in general? Any misconceptions maybe?

One thing that I would want most people to know is that NASA is still participating in human spaceflight. I am amazed when I go around the country and people think that NASA stopped flying people to space when the Shuttle retired. We now have 18 years of a continuous presence in space on the International Space Station. And you can go online to find the times when ISS is passing overhead so that you can see it!

SMCL

Well those are two different questions. The first thing is that we as a species are capable of doing some pretty incredible things if we put our minds and resources to it and work together as a team. The second, regarding the misconceptions , is that living in microgravity is all fun. Floating is fun, but the fluid shift to your head is not. It also makes just about everything we do harder.

-Scott Kelly

Were there any major or minor psychological effects that were noticeable in the year study? Did you study the brain or neurons to see if there were any changes in the body? I’m curious if there were any psychological or neuropsychology related changes in the body when it comes to earth vs space.

Scott and Mark performed a cognitive test battery specifically designed for astronauts on a regular basis. We did not see a major change in cognitive performance during the second half compared to the first part of the mission. However, we saw a more relevant decrease in cognitive performance after return to Earth, and this persisted until 6 months after Scott's return. This seems to be congruent with his own experience, as just reported by him during the press conference. - Mathias Basner

As far as space colonization or far afield missions, has there been any study or conjecture about fetal development in zero G? Specifically brain function, development, I wonder if it's possible to raise a child in space

There have been mice born in space, so we know it's possible, but anything beyond that we don't know yet. - Chris Mason

As an avid space enthusiast and twin myself, i have so many questions!

What kind of disclosure was necessary to make the twins aware of the potential dangers of this study?

Have there been any unexpected dangers or hazards we have found from this study so far?

What are the next steps for research in this field?

How does your team control the near infinite variables between the lifestyles of the twins?

1. As with a lot of human research, there were genetic counselors talking to the twins, to discuss the findings with them, and any potential ramifications.
2. Some of the changes that persist even 6 months after return are potentially hazardous. We found some cytokines whose levels rose only after return and continued to stay elevated 6 months after return.
3. Next steps - study more astronauts in a similar manner, and see if any findings from Scott are seen in a larger population of astronauts.
4. We do not. In essence, we are looking for differences between a 'regular' Earth lifestyle, and a space lifestyle, which includes increased exposure to radiation, microgravity, the stress of takeoff and landing, but also changes in diet, habitat changes etc.

-- Tejaswini Mishra

Regarding the near infinite variable question, this is one of the interesting aspect of the study. Instead of classically comparing astronaut and controls, we were sampling the astronaut and control very frequently so that any change can be compared to its own baseline. It is not perfect as indeed you cannot be sure that something else happened coincident to the space travel by change, but it makes it very unlikely. If something changes exactly in synchrony with when the flight started and returned to baseline when it ended, the most likely explanation is space travel especially if in the other twin and other subject the same variable is very constant over time. This is a new “personalized” design that is going to be used more and more in the future and is very powerful to see what is changing within an individual. We anticipate this kind of deep and constant monitoring of human physiology will be more and more done to detect disease, changes etc in human medicine. It was ideal for this study as we don’t have 100s astronauts to work with! Emmanuel Mignot

Great questions! Definitely the next steps are MORE DATA! We need data from additional astronauts on long-duration missions to confirm our findings. As far as the huge number of environmental variables.....this obstacle will also be overcome with additional astronauts. These uncontrolled variables are why we still cannot say that the changes observed were CAUSED BY spaceflight, but were associated with the space environment. - Lindsay Rizzardi

For the gut microbiome team, our next steps for research in this field is to study the microbiomes of mice. We can have many more genetically matched individuals, and match the lifestyles and diet between the space and ground controls. -Martha Vitaterna

Thank you for your great questions. The next steps would be to collect more data from similar assessments from additional astronauts and control subjects and assess if the findings are consistent with our initial findings. Francine Garrett-Bakelman

Which of the changes you observed are reversible (as in effect starts wearing off after time back on Earth)? and which were irreversible?

Most metabolic changes returned to preflight levels as well. One striking finding was the increased APOB/APOA1 ratio that only went up significantly in the last 6 months inflight. The APOB/APOA1 ratio is a better predictive marker for stroke than even cholesterol levels(!). So first we were concerned, but then we looked at Scott's return time points. The good news for Scott and hopefully for other astronauts in the future, is that APOB/APOA1 levels came back down to normal. -- Tejaswini Mishra

We expect that most of the adaptations to spaceflight are reversible. NASA continues to follow the health of the astronauts for many years after their last spaceflight to understand the long-term healthy implications of weightlessness.

SMCL

The cognitive decline we observed after Scott returned to Earth were protracted, i.e., performance was still decreased 6 months after he returned. Unfortunately, we did not measure cognition further out. - Mathias Basner

The DNA methylation changes we observed during spaceflight returned to normal upon return - so great news there! - Lindsay Rizzardi

Almost all (>91%) of the gene expression changes - Chris Mason

The changes in the gut microbiome composition that we observed seem to reverse upon return to Earth. Scott's gut microbiome after the flight was more similar to his microbiome before flight than during flight. -Martha Vitaterna

Most genes that had altered expression during spaceflight returned to baseline levels upon landing. There were some genes which stayed perturbed during the 6 month follow up, but we think some of these changes can be attributed to changes in behavior and life style before the mission, while onboard the ISS, and after landing. - Cem Meydan

As someone who deals with back pain everyday and the only relief I get is when I'm in water. Would I be pain free in space, like I am in water?

Hard to say. Interestingly, many astronauts experience back pain during the first days of their mission, when their spine extends due to the microgravity. - Mathias Basner

How brutal are spacewalks and how long does it take someone to recover after doing one? I saw some astronauts on twitter talking about it being a marathon.

Are there differences in muscle recovery in a low/no gravity environment? Thanks!

Pretty brutal. You are in the spacesuit for nearly twelve hours. The work itself is like running a marathon from a metabolic perspective. It's type two kind of fun. Type one is the roller coaster, fun while you're doing it. Type two is the kind of fun that's fun when you're done. People have done them with a few days recovery time. I would say a week to ten days between spacewalk is preferred. Probably longer, if possible.

-Scott Kelly

Several days usually separate each EVA in which a specific astronaut would participate. If several spacewalks are scheduled in a short amount of time, different crewmembers are scheduled for each one.

One might assume that people would recover more quickly without the effects of gravity (reduced muscle loading), this has not been specifically tested. Because this a challenging environment, there also should be time given for the crewmembers to mentally recover and plan for their next event.

well, how does it affect the human body? what have your findings been so far

Because the human body is well adapted to living in a gravity field, we expect that all of the body's systems will be affected to some degree. The body adapts to the decrease in loading (e.g., muscle, bone), loss of hydrostatic gradients (e.g., cardiovascular system), altered neuro-vestibular inputs, etc. We have a wealth of information from shorter missions than Scott's 340 days in space, but only 4 have been in space longer than Scott and Mikhail. But this is the first time that we have done such an integrated study from DNA to physiological and cognitive function.

SMCL

How will your findings help improve the possibilities of someday humans can travel to other planets?

A mission to Mars will take unprecedented time (currently projected at ~1,000 days), and only 4 humans have spent consecutively more than 1 year in space. The interdisciplinary TWINS study was a first important step to help better characterize the potential risks inherent to long-duration inter-planetary spaceflight. - Mathias Basner

These data give us a very good baseline for studying future astronauts, and any changes we see here can be referenced for Mars missions and other work.

Are there any negative effects of being in a zero gravity are for prolonged amount of time? Say you got stuck in space(I know this chance is very very small) for say 10 years what would it do to your body.? Then say you get to come back to earth would the gravity affect your body or would you quickly be able to adjust?

There are a number of concerns with being in space for prolonged periods of time. From the performance standpoint, without the proper countermeasures, muscle strength declines, cardiac mass is reduced, bone mass is lost, neuro-vestibular control is altered, etc. And in space beyond low Earth orbit, there is the concern for radiation exposure that may magnify these problems. A spacecraft with radiation shielding and the facilities to prevent deconditioning is important for our long missions. How it takes to recovery from spaceflight depends upon how long your are up there (takes longer to recover the longer you are in space) and how deconditioned you become.

From the data we have so far, the adaptation seems to be continual (6x more genes changing in second half of flight), so I would expect this would also be true for longer missions. It took Scott about 8 months to adapt to the 1-year missions, so longer missions may take longer. - Chris Mason

Scott how did it feel to be slightly taller than your brother for a few days?

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Did you try to play one-on-one with him after getting back from space?

I stretched an inch and a half in space. Gravity pushed me back to my normal height of 6 foot 6 when I returned to Earth. Immediately. I bet when we go to bed and wake up in the morning we are a little taller - while lying down.

- Scott Kelly

Will you be sending more twins into space to continue the research? Is it better to study the effects of space having a twin on earth vs any other astronaut without a control subject?

While it was fantastic to have twins for this study, as NASA moves forward with more long-duration missions it will be nearly as good having more astronauts participating so we can compare to Scott and see if his results are consistent in all astronauts. - Lindsay Rizzardi

How did you got those samples back to earth? This must be logistically challenging. Big compliments!

The samples were collected on the ISS, loaded into a Soyuz (that was delivering supplies), the Soyuz lands in Kazakhstan (Russia), gets put on a plane to Houston, gets driven to the lab at Johnson Space Center where some poor researcher was waiting (frequently at an awful time in the middle of the night). - Lindsay Rizzardi

There is a good summary of this here: https://www.theverge.com/2019/4/11/18306653/scott-kelly-blood-earth-logistics-nasa-twins-study-international-space-station

At what point in your life/career did you start calling yourselves experts? I feel like no matter how versed in a subject I become I could never call myself an expert because I know there is more to learn than I am aware of

Someone else called us experts...the trick is to never call yourself an expert :-). - Chris Mason

How would you expect the human body to react to the conditions of mars after a year? How would you help prevent or dilute some of these conditions?

The estimated radiation on the surface of Mars would be around 232 mSv, and Scott had 146 mSv during the mission, so we think it would be similar, but more radiation would come from the actual trip to get to Mars (no planet to shield you). A 3-year mission there and back would be about 1200 mSv. - Chris Mason

Would we expect to see more drastic effects if the duration of the stay was longer?

It's really too soon to say. We definitely found the majority of our changes occurring in the later half of the flight. We really need to collect more data from more astronauts to get a better picture. - Lindsay Rizzardi

This is really hard to say, as we have very little information on how humans react to being exposed to the spaceflight environment for extensive periods (only 4 humans have spent consecutively more than 1 year in space). This is why the TWINS study was an important first step to increase our knowledge base on how humans react to prolonged stays in space. - Mathias Basner

How does NASA prepare astronauts psychologically? Has there been any cases aboard the ISS that could be similar to cabin fever?

Astronauts (and their families) have psychological support before, during, and after a space mission. Also, groups of astronauts train in so-called space analog environments that share a lot of the features of space flight (e.g., isolation, confinement, extreme environment). This helps them prepare psychologically for the real mission. - Mathias Basner

How many of these changes could be avoided if there was some form of artificial gravity present?

You would expect that "replacing gravity" would go a long way to preventing many of the issues with spaceflight but other concerns remain, including confinement (small space), radiation, living in a closed environment, and distance from Earth (for exploration missions).

If I wanted to pursue a career in astrobiology, or something similar in the field, how could I approach that? I am an undergrad in college and the things you all work on right now just seems so out of grasp. Thank you!

Keep helping with research and joining work in labs. Be proactive and write up your results and publish papers to build a baseline of knowledge that you can draw from. Be curious! - Chris Mason

Do men and women react differently to zero gravity?

So far women seem to be less affected by eyesight issues, but our sample sizes are very small so we don't really know yet.

- Chris Mason

This is an area of specific inquiry for NASA. Unfortunately the number of women who have flown in space so far is small but you can see that is steadily increasing with the selection of the last few classes of astronauts.

Was there a considerable difference between the cells of Scott and Mark and how they function?

We saw differences in the proportion of cells, and the activity of the genes in immune cells, indicating greater activity as a big difference. - Chris Mason

Specifically regarding the telomeres findings, does the existence of longer telomeres caps in space (I’m not entirely sure how they work, please excuse me) basically assure the human race of living longer in extraterrestrial environments?

I do not think that going into space is the "fountain of youth". Upon Scott's return to Earth, his telomeres shortened very rapidly, and over the following months stabilized, but he still had many more short telomeres after spaceflight than before.. so perhaps there is always a price to pay :) susan bailey

Scott Kelly, what's your favorite space memory?

That's a tough one, landing the space shuttle, landing in the Soyuz, doing spacewalks, seeing earth from space the first time perhaps, but if I had to choose only one thing I would say the first few seconds after the solid rocket motors lit on my first flight into space in 1999. 7 million pounds of thrust- in an instant.

-Scott Kelly

What is an experiment you wish you could have conducted but were not able to due to time or resources?

That's a tough question to ask a scientist. There are always are more questions to ask, and each answer usually makes you hungry to learn more.

This study pushed the envelope for technology and resources to perform these tests in space. Future studies will extend our capabilities even further.

I wish that we could have directly measured telomerase activity during spaceflight. Hoping this might be possible on future missions. susan bailey

So how does this information bode for longer term space missions in the future? To Mars and beyond

Mostly good news, atleast as far as spending a long time in low gravity goes. Going from ISS to Mars means we worry more about ionizing radiation, but on the flip side we might worry less about the effect of gravity. With Mars, you are spending more time in <1G, but a lot of that is at Mars gravity, and some of it (the travel time) will be in microgravity. We have have seen that being in microgravity for ~1year did not lead to any serious bad news for Scott. What remains to be seen is what are the effects of increased radiation that would come with a trip to Mars, and is there a difference between 1 year, and 2-3 years in < 1G. -- Tejaswini Mishra

It is mostly good news for future long duration missions - overall, the human body is remarkably adaptable to the space environment. susan bailey

Will the data be publicly available, so other unexplored hypotheses can be tested?

-- Boris

Yes - the data can be requested from NASA. - Chris Mason

Please see the "Data and materials availability" section of the paper for instructions. - Francine Garrett-Bakelman

How does the gene expression changed in space? Does gene alteration occur?

Yes, we saw significant changes in gene expression during flight, especially genes related stress and immune system activity. - Cem Meydan

Most genes were increasing in their expression, especially for DNA repair, but many also decreased. - Chris Mason

Was there any increase seen on mutation rate due to the radiation from being in space?

At the chromosomal level (Bailey lab), we saw and increase in inversions over time. At the single-base level, we are still looking at this. - Chris Mason

Are you required to draw blood on the ISS or is everything sample wise taken on land before and after? If yes, do you take the blood yourself and is it tested up in the station itself?

As a researcher working with NASA for the first time, I had the exact same questions! What is possible onboard the ISS, and what is not? Can we do standard experiments in space? Luckily, NASA has spearheaded many advancements in this area. Blood does get drawn on the station, and astronauts are trained phlebotomists! Here is a Youtube video of ESA astronaut Tim Peake drawing blood in space - https://www.youtube.com/watch?v=mUuRzZbM4uY.

There is also a centrifuge, all-important for centrifuging the blood samples after collection. There is equipment for pipetting to transfer small volumes of liquids from one container to another (which describes A LOT of molecular biology, unless you are using robots), and there is a -80C refrigerator for storing the samples and keeping them frozen. You can find what facilities are available onboard the ISS here: https://www.nasa.gov/hrp/elements/issmp/facilities

For the Twins Study, the samples were analyzed once they got back down to Earth, since there were many assays that needed to be performed, and the precious samples had to be divided between all the investigator teams.

-- Tejaswini Mishra

Hello, NASA team!

I'm in the process of making a video discussing the issues that might arise when we eventually try to colonize Mars. You guys mostly focused on the health effects of no gravity, but what health problems might arise from living in a low-gravity environment like Mars? I'm especially curious about the effects that low gravity might have on any babies that might be born on Mars in the future.

Thanks!

In addition to the ~3/8 gravity on Mars, the planet rotates on its axis at a different speed than Earth. A Martian "sol" is longer than an Earth day. Our biological clocks are evolved for a 24-hour day, not a 24.6-hour day. Humans would have to delay their internal clock each day (rather than advance as they do on Earth), and this could have significant effects on clock-controlled biological processes. -Martha Vitaterna

One bit of good news is that it would be 36% of the gravity of Earth, so the body's re-adjustment should not be as difficult. - Chris Mason

My dad who's a pilot asks if their sleep patterns changed at all, and whether that affected their performance I general?

We did not study the sleep patterns specifically in this mission but sleep is indeed disturbed mostly too short because the astronauts schedule is very tight and busy. They are often sleep deprived as a result and typically sleep only 6.5 hrs instead of 7 hr recommended. Emmanuel Mignot

Do you foresee any extrapolation of this data for the earth-bound general population? Anything useful from the cognitive decline that can be used in understanding the disease course of dementia?

It is hard to extrapolate in a 1:1 fashion, as spaceflight has so many unique environmental stressors. However, chronic stress in general is prevalent on Earth as well, and some of our findings may thus translate to individuals in these stressful situations on Earth. - Mathias Basner

What are some differences between Mark and Scott that might influence the final results of your studies? How do you think they'll affect the validity of the outcomes?

Also thank you for conducting these studies and furthering our understanding of how humans are affected by spaceflight!

Nature and nurture... Scott and Mark are not only identical twins, but they share a lot of the same history (e.g., both were Navy test pilots and Mark was also an astronaut). So in every aspect, Mark was the perfect "control" for Scott. - Mathias Basner

You are so welcome! It was a privilege and an honor :)

In the paper, we describe a host of baseline differences between Mark and Scott, which are absolutely important to know. However, to discover spaceflight-associated changes in Scott, we were benefited by the longitudinal nature of our study design. I mentioned this somewhere below - studied over time, most humans are more similar to themselves across different biomedical research study paradigms (transient and chronic illnesses, diet perturbations etc.). So, it actually really helps to have multiple data points from Scott himself, and we can say with a lot of confidence that the changes we saw in Scott were definitely associated with spaceflight. Of course, to extrapolate the findings to a general population, we do need to perform similar longitudinal profiling in other astronauts, i.e. conduct a study with a larger sample size. -- Tejaswini Mishra

Given that commercialized space travel will likely pose a whole new challenge to medicine someday (potentially soon), will you be able to extrapolate the data to show how space travel may affect different age groups, specifically a younger demographic?

Not at this time; additional studies assessing similar biological features we measured in different age groups will be needed in order to address this question. thank you for asking. - Francine Garrett-Bakelman

What is the next step after those 340 consecutive days ? A longer mission ?

I think step one is getting more data on more astronauts on 1-yr missions. We need to confirm our findings to know if what we saw in Scott happens in all astronauts and determine what a realistic range of responses to long-duration spaceflight is. Then we can design countermeasures to prevent adverse effects and THEN think about longer missions. - Lindsay Rizzardi

How would you compare DNA of two people? Are you looking only at certain parts of DNA or did the whole sequencing of genes?

Thank you for your question. We do not currently have data to report from DNA assessment in the form of whole sequencing; this is beyond the scope of the study being published in Science tomorrow. - Francine Garrett-Bakelman

What measures were taken to make sure the twins were physically identical before the study began? I’m assuming being identical twins doesn’t account for muscle mass, body fat, etc.

We cannot impose these types of constraints on our study participants, so what we do is to gather these measurements at multiple time points and ask how much did one twin change compared to another. While they may start out at slightly different places (different baseline measurements), we can see if the amount of change over time is greater or in a different direction in Scott during his time in space than in Mark on Earth. - Lindsay Rizzardi

twins

One interesting observation from other research is that if you analyze human molecular profiles over time, you will see that people are usually more similar to themselves than to others. This of course makes sense, but it also holds true when you compare people with transient or chronic illnesses, or during diet perturbations. Our lab works on trying to understand a the personal molecular baseline for human participants, and that has been the most striking finding so far, is that you are always more similar to yourself. Your genome defines the context for your molecular profiles, and, your lifestyle, diet etc. are the more dynamic factors that really affect your molecular profiles. Still, with all that, often the biggest component of variation is the inter-individual component :) And that has also been the power of this study, that we were able to have Mark be the genetic control, but also they both gave us samples periodically throughout the study. Longitudinal profiling with a larger sample size of individuals will really help us understand how much people vary over time, how much is natural variation, and how much is associated with a perturbation or lifestyle change or spaceflight. --Tejaswini Mishra

How intensively were microbiomes monitored during this study?

Were there any surprising or significant changes in these microbiomes over time and especially after Scott returned to Earth that are worth mentioning?

The gut microbiome was monitored by metagenomic sequencing of material from fecal samples obtained at nine time points from each twin. These included samples before, during, and after the one year mission so that we could evaluate how each twin's microbiome changed over time. We identified bacteria, viruses, and fungi (but mostly bacteria).
Both twins had high diversity (many different species) throughout the whole study, and NO decline in diversity was associated with space in Scott. However, the composition of Scott's microbiome did shift during space, but returned to more closely resembling his pre-flight composition after he returned to Earth. -Martha Vitaterna

Thank you for your response, Dr Vitaterna!

How surprised were you and the team when no decline in microbiome diversity was observed as Scott was in such a secluded and controlled environment? Were any preemptive steps taken to ensure Scott's microbiome would remain intact during the flight?

What changes were associated with the mentioned shift?

Also were there any significant changes related to the viruses Scott was carrying such as his total viral load?

The decline in diversity was the ONE prediction I was comfortable making as to an effect of spaceflight. So I, at least, was pretty surprised.

I think the maintained diversity indicates that the NASA food science folks have provided a varied, healthy diet despite the constraints.

One way the change in the microbiome was obvious was if you look at the ratio of the bacterial phyla Firmicutes and Bacteroidetes. These account for the vast majority of the microorganisms in the GI tract. During spaceflight, the F:B ratio significantly increased and stayed elevated. Note that both beneficial and pathogenic bacteria are found in both phyla, so it can't be taken as a "good" or "bad" shift. This F:B ratio then dropped back to pre-flight levels upon return to Earth. -Martha Vitaterna

How the gene expression changed! Any news about those "space genes" everybody reported about? What have been surprising for real?

We do still see some genes active from spaceflight even 6-months later, and they are involved in DNA repair, so we think the body is still adapting from the time in space. - Chris Mason

I can find nothing in the report regarding height; as someone who doesn't fit in his car in the morning but does in the afternoon, I would like to know how much of an effect microgravity had on height?

As the spine extends in microgravity, astronauts height typically increases slightly during a space mission, but will return to pre-flight levels quickly after return to Earth. - Mathias Basner

What do you think of the germs they found on the ISS?

And also- were you observing for any specific changes related to cytokines or interleukin expression?

Yeah! One striking finding was that we saw changes in a pro-inflammatory cytokine, IL1RA spiking really high, days after Scott landed. And it actually was followed by what looked like a feedback anti-inflammatory response from a different cytokine, CCL2. Scott reported a skin rash right after landing, so those cytokine spikes could be associated with inflammation from the skin rash.

In addition we saw 19 cytokines elevated before launch and in space, that went down after return. And a separate set of 31 cytokines that went up after return, and stayed elevated even 6 months after return.

-- Tejaswini Mishra.

Are efforts underway to test the twins paradox?

Since the ISS is in low earth orbit, not traveling at the speed of light relative to us, the effect of time dilation is very minimal - only a few milliseconds. The telomeres study addressed the question of spaceflight associated aging by way of assessing telomere length dynamics (changes before, during, and after flight in both Mark and Scott). Scott did not return younger, and in fact despite longer telomeres in space, had many more short telomeres after flight than before. Susan Bailey

What major differences, if any, can still be observed today?

We would need to do more studies, since we only went out to 6 months post-mission.

- Chris Mason

What interesting plans for follow up studies are in the works now as a result of what you've learned?

Additional missions and measures are planned here: https://www.nasa.gov/1ym - Chris Mason

Did you guys analyze Gene expression changes while Scott was still on the ground as a control?

As for epigenetic changes, was methylation the only variable tested for or was it more comprehensive?

We measured DNA methylation both pre and post-flight to compare with measurements from Scott's time on the ISS. We compared the ISS data to those taken before and after to see what changed and if it persisted - Lindsay Rizzardi

yes, indeed we measured pre-flight gene expression levels and used that as a reference for the analyses performed. - Francine Garrett-Bakelman

Yes, we collected samples and gene expression data from both twins from approximately 6 months before the launch to 6 months after landing. These samples collected on the ground from Scott were used as a baseline. We also utilized the data from his identical twin Mark during the same period to see how much variability there is in gene expression patterns for a person on Earth during the ~25 month period to put our findings into perspective. - Cem Meydan

Just DNA methylation for now - more work is ongoing to infer chromatin state from the cell-free DNA. -Chris Mason

Hi! How did you assess the effects of radiation doses on the twins and what did you find? Does the body show particular adaptations to high/prolonged radiation levels in space ? Thanks!

The biggest adaptation from the view of gene regulation is that more genes increase in response over time to such changes. Also, the DNA damage levels from the Bailey lab shows that it keeps increasing over time. - Chris Mason

We assessed chromosome aberrations - a well established signature of radiation exposure - in the twins. Such structural rearrangements also provide evidence of a DNA damage response (also seen in Dr. Mason's study). Certainly, frequencies of translocations (rearrangements between chromosomes) and inversions (rearrangements within chromosomes) were elevated for Scott during spaceflight - consistent with his exposure to space radiations. Inversions were particularly informative, and they stayed elevated post-flight, suggestive of on-going genomic instability. susan b

What if any effects of microgravity changes have on the limbic system? any changes to testosterone levels? any marked stress changes that have been noticed?

We will participate in more 1-year missions over the next few years where we will, in addition to cognitive testing, do functional neuroimaging in astronauts before and after the mission. This will hopefully give us critical insights into which areas of the brain, as the limbic system, are primarily affected by long-duration spaceflight. - Mathias Basner

Other than gravity, what are other elements that are present on the space station can't be studied from a simulated pod on Earth?

Although the space station is still within Earth's magnetic field, radiation exposure on the ISS is higher compared to Earth's surface. It will be much higher on a mission to Mars when we venture out of Low Earth Orbit (LEO). Also, due to microgravity, all surfaces of a spacecraft can be used in-flight, which makes it very hard to study issues related to spacecraft habitability on the ground. - Mathias Basner

How do you shower?

In microgravity? You don't. It's strictly wet towels only... - Mathias Basner

What is telomeres ? How does the change occur and what differences did it create in Scott Kelly, physically ?

Telomeres are the ends of our chromosomes that shorten as we age - and with a variety of lifestyle factors like stress and environmental exposures to things like air pollution, UV and ionizing radiations. sb

What do you think are the next challenges to tackle with this data in hand? Changes to any protocols, or future studies you want to do because of this?

Doing more sequencing in space or zero gravity would help make the measures more real-time. Some of this has been shown here:

https://www.nature.com/articles/npjmgrav201635

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and here:

https://www.nature.com/articles/s41598-017-18364-0

- Chris Mason

Ideally, future studies will allow astronauts to not only draw their own blood samples (which they do now) but also separate and freeze down the specific blood cell types we need for epigenetic analysis. By being able to do this, we can get more samples that don't have to be coordinated with a Soyuz resupply! Having to get "fresh" blood samples was a challenge for this study, but we did it! <48 hours from blood draw on the ISS to the lab in Houston! - Lindsay Rizzardi