In 2015, a clone will spend a year on the International Space Station while his doppelg盲nger remains on Earth. Mark and Scott Kelly, the only identical twins who are also astronauts, have volunteered themselves for study, creating a unique opportunity to disentangle the health effects of space from those of genetics.
鈥淲e have the best ground control you could dream of,鈥� says of the Baylor College of Medicine in Houston, Texas, who is helping NASA with the experiment. The question of space health is especially timely as several human trips to Mars are currently being discussed.
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Last year, Scott Kelly was chosen to take part in the first one-year mission aboard the ISS, double the usual stay, along with Russian cosmonaut Mikhail Kornienko. Then last week NASA announced a twist: his brother Mark will be monitored on Earth throughout.
, chief scientist of NASA鈥檚 human research programme, says the brothers came up with the idea: 鈥淚 was discussing plans with Scott and he said, 鈥榟ow about the twins angle?鈥欌�夆��
Researchers will have access to blood and saliva samples from both twins taken before, during and after Scott鈥檚 trip to the ISS, along with assessments of their vision, sleep patterns and cardiovascular activity. NASA will also measure both twins鈥� bone mass before and after the mission.
Tilted beds
Such data could help determine how genetics affects the health problems seen in space, including loss of bone and muscle mass and vision issues, all caused by low gravity, plus an increased risk of cancer from cosmic radiation and sleep problems while in space.
It鈥檚 not the first time twins and space research have collided. of the University of California, San Diego, previously asked 15 sets of twins to lie in angled beds for a month.
The lack of activity, combined with the downward tilt of their heads, which simulates the effect of microgravity on bodily fluids, produces reductions in cardiovascular activity and bone and muscle mass similar to those seen in astronauts. One twin in each set was asked to regularly exercise lying down, while the other remained stationary. The results revealed the extent to which exercise could slow the loss of cardiovascular fitness.
NASA doesn鈥檛 have the luxury of sending hundreds of people to space, so one weakness of the Kelly study will be the sample size of one. at the Department of Twin Research, King鈥檚 College London, points out that epigenetic changes, which arise due to exposure to environmental factors, can create variations in gene expression between identical DNA sequences. So twins only have a one in three chance of having the same disease. 鈥淯sing one as a predictor of the other only works when you鈥檝e got lots of them,鈥� he says.
Twin paradox
Another factor is that both Kellys already have extensive space experience. 鈥淚deally one would never have flown, but that鈥檚 not the hand we were given,鈥� says Charles. 鈥淭he only twins we have access to are both astronauts.鈥�
Still, once Scott has finished his year long sojourn, he will have spent much more time in space than Mark (see diagram), who retired in 2011 to aid the recovery of his wife, congresswoman Gabrielle Giffords, who was shot that year. Comparing the effects of short versus long space trips could be interesting, perhaps revealing whether bone mass loss worsens with each trip.
Some may also delight in the fact that the Kelly study will be the strongest test yet of the twin paradox posed by Albert Einstein. It states that a twin on a round-trip journey aboard a fast-moving spacecraft will return to Earth younger than the one who stayed home, thanks to relativity. The ISS orbits Earth at 7.71鈥痥ilometres per second, so Scott will age roughly 10 milliseconds less than Mark over the year. 鈥淚 don鈥檛 think our equipment is sensitive enough to pick up that difference,鈥� says Charles.
This article will appear in print under the headline 鈥淚t鈥檚 ground control for astronaut twins鈥�
