Did you ever go on the Gravitron ride at a show or fair? The ride spins faster and faster, and all of a sudden the floor falls away but you don’t fall with it. You remain pinned to the wall by forces three times that of normal gravity. It’s fun, unsettling, and for some, guaranteed to result in puking. Fortunately, whether you lose your lunch or not, the effects are short-lived. But what happens when your body experiences extremely high (and low) levels of gravity over longer periods, as is the case for astronauts? We know spaceflight is not kind to human bodies. With the help of a set of identical twins, NASA is busy trying to understand more about how our bodies respond to living in space.

Identical twin astronauts Mark and Scott Kelly are helping NASA understand the effects of spaceflight on our bodies. Image credit NASA via Flickr.

There’s not a lot of gravity in space

Whether you’ve been on the Gravitron or not (and incidentally, you can buy your own Gravitron for US$55,000), chances are you know what I mean by gravity. Gravity is the force that causes every object to pull every other object towards it. Remember Isaac Newton and the apple that supposedly fell on his head? In space, people and objects appear to be weightless. Contrary to popular belief that there is no gravity in space, there is actually a small amount of gravity everywhere in space and the correct term is microgravity.

On the upside, astronauts grow up to three percent taller when in space. Without gravity compressing the disks between the bones of our backs, our spines lengthen. On the downside, we’ve known for a long time that human bones and muscles waste away in microgravity. Our bones need to be stressed to stay strong – that’s why we are told to do weight-bearing exercise to avoid osteoporosis.

NASA Astronauts spend about two and a half hours a day exercising to try to minimise these wasting effects. And of course these have to be special space exercises given that a dumbbell of any weight is still effectively weightless in space. But even with all that exercise and osteoporosis medication, an astronaut’s leg bone will still lose about 10% of its mass during a six-month stay in space. It seems exercise alone isn’t enough.

It’s not only bones and muscles that lose condition and age prematurely. Recent research showed that at the same time as the bones age, the immune system also ages. B cells are particularly important cells in our immune systems: they produce the antibodies we need to fight infections. B cells are produced in bone marrow in long bones like our leg bones and it seems as bones lose mass, their ability to produce B cells also declines.

Not just in your head

Other parts of our bodies have a tough time during space travel too. Astronauts who previously had 20/20 vision are returning to Earth and discovering they need glasses. Close monitoring of astronauts’ eyes in space has shown that in some astronauts, the rear of the eyeball becomes unnaturally flattened and in most, there is bulging in the optic nerve. These are both deformities that can cause permanent vision problems.

If that isn’t enough, exposure to high-energy cosmic rays can have all sorts of bad effects on your body such as an increased risk of cancer and reduced mental performance. Suffering from a hazy brain can’t be good when you’re in space and may be required to make snap life-and-death decisions.

And there are still other issues. Astronauts suffer sleep deprivation; it can’t be easy to sleep for ’normal’ periods when in space, sunrise and sunset alternate every 45 minutes. Most astronauts also report gaining much less pleasure from the food they eat. It’s not surprising space travel is also known to cause feelings of long-term isolation and depression.

Enter the twins

One of the issues scientists have in trying to fully understand the effects of space travel on humans is that all astronauts are genetically different. This simple fact makes it harder to generalise about the physical consequences of life in space. How could we overcome this problem? Ideally, you’d have many sets of identical twins, in each case, both trained astronauts who could undergo simultaneous missions – one in space and one on earth.

Unfortunately we don’t have lots of such twins, but we do have one set!

Mark and Scott Kelly provide the perfect opportunity to deepen our understanding of humans in space. Scott is currently spending one year living aboard the International Space Station, while Mark spends the same period on Earth. Scientists will take blood, saliva, urine and poo samples from the brothers before, during and after the year and also carry out psychological and physical tests. They plan to study a whole variety of aspects of human health, as it is influenced by space travel.

 Will we really colonise Mars?

Fortunately it seems unlikely I’ll be employed as an astronaut anytime soon (or be rich enough to afford a space joy flight). So none of this is a problem for me personally.

But people planning on living out their days on Mars might want to reconsider. Arriving on Mars and not being able to walk, see or think well doesn’t sound ideal.

Perhaps we’d do better to look after our own planet rather than assume we can successfully inhabit another.

Dr Kevin Fong puts it best:

Space isn’t an environment we’ve evolved to survive in.

Links and stuff

• Six everyday things that happen strangely in space
• Commercial space travel: a new frontier for health in The Conversation
• Mixed up in space – audio from NASA
• NASA’s twin study
• Sciencecasts video: Separated at Launch
• Mark and Scott Kelly putting Einstein’s twin paradox to the test – in The Guardian

Radio on demand

 This post accompanies a radio segment on Triple R’s Breakfasters program on Wednesday 13 May 2015.