Everyone is curious about space now that NASA astronaut Scott Kelly has returned to Earth after spending nearly a year aboard the International Space Station with Russian cosmonaut Mikhail Kornienko. What happened to his height? What do astronauts do when they're bored? What do researchers hope to learn from his 340-day space odyssey?

NASA scientists took to Reddit for an AMA to answer well, anything. Participants included NASA’s Chief Scientist for the International Space Station Julie Robinson, Associate Manager for International Science for NASA’s Human Research Program John Charles, Nutritional Biochemistry Laboratory Manager for NASA’s Human Research Program Scott M. Smith, NASA flight surgeon Dr. Shannan Moynihan, and strength and conditioning coach Bruce Nieschwitz.

You can read the full transcript, but here are some of the most interesting points:

How long does it take for astronauts to walk properly again after landing back on Earth?

Astronauts usually begin walking soon after landing. As they begin to readapt to gravity, we see a change in the way they perform all physical tasks, including walking. Some take longer depending on the level their balance and coordination... Astronauts go through a 45-day reconditioning program with the Astronaut Strength, Conditioning and Rehabilitation group where all the physical deficits are addressed. But most astronauts walk pretty normally within a few days.

When will Kelly lose the extra height that he gained from being in space? Or is that a permanent physical change?

As soon as Scott returned to gravity and stood up, gravity began to compress his spine again. Most likely, he is already back to his pre-launch height.

Does this process tend to be painful for the astronauts, and if so is the pain experienced more on orbit as their spines decompress or when they return to 1g/Earth gravity and their spines recompress?

Some astronauts do experience back pain when they get to space and upon return. We are learning more with studies such as this.

While speaking, do Kelly and Kornienko communicate in Russian or English? Are they both fluent in each?

The astronauts on orbit speak both Russian and English, and sometimes communicate in one language and sometimes in the other.

What does it feel like returning to Earth after so long?

I have heard from crew at landing that the first things they notice are the breeze and the smell of the earth ... they love it! Then they start noticing how their body feels in gravity again ... heavy and a little off balance for some.

What's something that really surprised you during your research?

One of the most surprising results was that about three years ago, we discovered that some (not all) astronauts were having permanent vision loss in space. We hadn't noticed the pattern until we had multiple long-duration missions on the space station!

Have you guys been able to pinpoint what's causing the vision loss?

We think the shift of fluids to the brain causes the optic nerve to swell and press on the back of the eye, literally causing the globe (eyeball) to flatten!

I read about the vegetables grown aboard the ISS. Did the environment they grew in affect their nutritional content or taste? How does a microgravity environment affect plant growth?

Feedback from the crew was that the taste was great! And growing them up there was a favorite activity.

What were the main findings from Kelly's year in space mission?

From the perspective of NASA's Human Research program, that mission is not yet over just because the flight has landed. We have weeks, even months, of data collection continuing post-flight. Also, some of the blood samples are still on ISS and won't be back for analysis until May. So far, the main findings are that Scott Kelly looks great, and year-long missions are not the limit, and it was successful largely because of the close coordination between the Russians, the U.S. and all the partners.

Can I ask why the astronauts are usually given a piece of fruit or a cucumber to eat as they begin their initial health checks when they return to Earth? Why fruit or cucumber and not that pizza slice they've been dying for? ;)

Trust me, the pizza comes soon enough! Its a very popular choice for their first meal while we are traveling back to the U.S. The green apples at landing are a Russian tradition. We are also out in the desert, so portable tasty items are good.

What sort of physical and mental toll does one year in space have on a person?

As far as physical stress, astronauts in microgravity will experience a number of losses in areas of bone mineral density, muscle mass and strength, cardiovascular endurance, balance and coordination and many more. NASA has developed countermeasure systems to counteract the physical effects of microgravity through exercise.

I noticed that they had to be carried from the Soyuz capsule. How long did it take them to regain their 'Earth legs'? Did their legs 'tingle' as they were regaining strength?

It's the Russian plan to carry the crew immediately after they land because sometimes they can somewhat off balance. "Earth legs" come back pretty quickly — usually within a few days for most.

Mark and Scott KellyFormer astronaut Mark Kelly is taking part is NASA's Twins Study with his brother, Scott, who just came back from nearly a year in space. (Photo: NASA/Robert Markowitz)

What experiments will Scott and Mark Kelly still have to participate in during the 'aftermath' of the year in space? What do you hope to learn from them that will help with the journey to Mars?

The same experiments as in-flight: muscle function, cardiovascular stress using fluid shifting, blood draws, psychological testing. Everything we learn will be specifically applicable to planning and then doing the Mars missions.

How much choice do the astronauts get over what food they get to eat in space? Obviously it all needs to be part of a balanced diet, but is there much leeway in their personal preferences/dislikes?

In essence, they can eat whatever they want — from the space food system, which repeats about every eight days. They also get a set of "preference" containers to augment nominal food supply (amounts to about 10 percent of their intake). We track what they eat, and make recommendations, but it is a bit like sending your kid to school with a lunch box. :)

What is the most important psychological research being done right now at NASA? How far do we still have to go in that area of study? How will we care for the minds of the crew members who travel to Mars?

The three major topics are behavioral medicine (what happens to an astronaut during spaceflight), team (how do groups of people work together effectively in stressful, confined environments) and sleep/circadian rhythm studies.

What are most valuable insights that will come from the project? And what is the impact of having this knowledge on future missions?

One thing that I think is really important is understanding the behavioral and psychosocial effects of a longer mission. We know that crew members get ready to come home at the end of their mission. It's a form of "senioritis" we sometimes call the "third quarter effect." As missions get longer, the impacts of being away from your family and isolated from people are expected to be bigger. Scott participated in several studies of performance to get scientific data on this issue.

Could virtual reality help improve the physical and, in particular, mental well-being of astronauts who are in space for so long and, if so, how?

Possibly! We are just beginning to test virtual reality: [Learn more about those tests here.]

I've always wondered if/how space alters sleep cycles? Whether changes in duration happen among the astronauts or maybe more frequent but shorter sleeping times, etc. Bonus question: Do you still get a 14:30 sleepy effect that is so common? Thanks!

Great question. We do keep an eye on that since the environment is different than what we are used to on Earth. Good sleep hygiene, lighting, and consistent schedules can help. The crew is pretty busy at 14:30 in their day, so I haven't heard many reports on that effect on ISS.

Scott Kelly on the ISSKelly returned home March 1 from nearly a year about the International Space Station. (Photo: NASA)

Does living in space for a longer period have an effect on brain activity?

That is one of our studies. Scott and other astronauts and cosmonauts have volunteered to do some simple mental and physical tasks (not so simple, maybe — adding numbers, recognizing shapes in different orientations, etc.) while inside a MRI so the actual regions of the brain involved in the task can be visualized and measured.

Which areas of the body do you expect Kelly to have suffered the greatest decrease in bone density? How long after returning to Earth are scientists able to see an increase in bone density again?

Bone loss is primarily in the lower half of the body — spine and legs. We see biochemical changes reflecting return to gravity almost immediately, but bone growth takes time. Our estimates from four- to six-month Mir and ISS missions is that it takes two to three times the length of the mission to recover bone. The great thing about this mission is that we have no idea what happens with crewmembers on one-year missions.

What were some of the biggest problems encountered during the year in space?

One of the biggest challenges we had was not in space, but in our support from Earth. We had several cargo launches that didn't make it and we had to replan the research a lot. The crew was doing great, but we had to be really smart to keep the research and support cargo flowing. Helps you think about how much harder a Mars mission would be logistically.

What kind of music would be suitable for an astronaut on his/her journey to Mars?

Without a doubt, the Foo Fighters would be a great choice! Check out Scott Kelly's Spotify playlist "Songs of a Year in Space" for some of his favorite jams.

What kind of activities would the astronauts do on their journey to Mars?

A Mars mission will probably never be boring. The astronauts en route to Mars will be doing lots of physical exercise, continuing mission training, in-flight simulations with VR and other capabilities. There will always also be cooking, laundry, housekeeping and maintenance on the spacecraft. When they finally get to Mars, they will be busy almost every day with in-depth studies of the surface features, plus all of the above. The trip back to Earth will also be busy with the same activities plus debriefings and report-writing. Anybody who is bored on a Mars trip must be ignoring lots of important activities!

After whatever research is conducted, what recreational activities do you typically engage in?

Astronauts report enjoying spending time in the cupola of the space station (it's like a large bay window), and watching the Earth and taking pictures. There is also a large screen available for viewing movies, and crew members often gather together for a movie night when time allows.

After being in space with no gravity, then returning to space at 4 or 5 Gs, did they black out during the return trip? Vomit? (is that why some were greeted with towels?)

Nope, no blacking out. Sometimes astronauts can have nausea and vomiting when they return, but in Scott's case, he looked great. The towels are always there to wash their faces. It can get pretty warm in the capsule, and it just feels good.

Mary Jo DiLonardo Mary Jo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.