Twins in Space: What Happens when we Live in Zero Gravity?


Mark Kelly: “What do we look like? Well I look like him and he looks like me - you know, two regular guys from New Jersey” - except identical twins Scott and Mark Kelly are anything but regular. The 51 year old NASA astronauts are the only siblings to have ever travelled in space and they’re about to conduct a unique study into the effects of long-term human spaceflight as Scott and mission partner, cosmonaut Mikhail Kornienko, complete a 341 day stint aboard the International Space Station - the longest ever by a US astronaut - whilst Mark stays earthbound.

The “Year in Space” mission that blasted skywards on a Soyuz rocket on Friday 27th March offers an extraordinary opportunity to gain insight into the remarkable effects of long-term spaceflight on the human body. With Scott weightless whilst orbiting the Earth once every 90 minutes and Mark presumably sat at home with his feet up watching TV, it is certain that the radically different environments will yield many interesting differences, not only in physiology, but also in psychology over the year-long period.

By comparing these effects on ostensibly the same genetics, NASA and a vast group of international collaborators hope to significantly develop our currently limited knowledge of how the human body reacts to spaceflight over residences greater than six months. This research in turn will feed into the planning of future six to eight month duration flights to Mars, serving to improve the health and care of future “Marstronauts”. On top of this, it could also lead to breakthroughs in aiding the recovery of long-term bedbound patients back on Earth. .


The human body, sculpted over millennia under the influence of gravity, behaves very differently once the concept of “up” and “down” is removed. It is well known that bones and muscles degrade as the astronauts float about the ISS, without the need for their legs to support the mass of their bodies, which is why exercise is a key part of an astronauts daily activities. However, this is not the only effect. One third of astronauts develop eyesight problems after months in space. Current thinking suggests that this is caused by fluids shifting into the upper body once freed from the confines of gravity. On top of this, the immune system is also affected, with symptoms similar to that of ageing seen in a study conducted with mice in a simulated microgravity environment.

As part of the Twins Study NASA will conduct 10 investigations to be carried out on Scott and Mark in their respective environments. Physiological tests will seek to understand how muscles and organs such as the heart and brain react to spaceflight. Behavioural studies will determine how perception, reasoning, decision making and alertness are affected. Microbiology studies will see how differences in diet and stressors affect the twins guts and molecular studies will look at the way genes are turned on and off, as well as how the contents of various biological samples differ. All in all the brothers can expect to be prodded, poked, weighed, measured, scanned and generally harassed for the sake of science for the duration of the mission.

Of course testing one set of twins won’t provide a definitive set of answers to the plethora of questions surrounding the matter of human spaceflight, but it’s a promising move in the right direction, paving the way for a healthy and happy journey for the ambitious proposed human mission to Mars in the 2030’s.

#Physics #Space #AdamHarris

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