We humans are adapted to living on Earth, not in space. When astronauts return from the International Space Station they suffer the effects of microgravity or weightlessness such as loss of bone and muscle mass, balance disorders, loss of taste and smell, and vision problems from changes in eyeball pressure. While a spacesuit and the spacecraft itself provide protection from radiation, these measures are not perfect, and astronauts are still exposed to much higher radiation levels than on Earth. These raise the incidence of cancer, cataracts and damage to the immune system.
Some of the ill effects of space travel are temporary, while others are not, and the dangers are likely to increase with longer exposure. So, as preparations proceed to send humans on a journey to Mars that could last up to three years, it’s important to understand the long-term effects of space travel on the human body. Identical twin astronauts, Scott and Mark Kelly, proved the perfect subjects for such research, as identical twins start out life with the same DNA. While Scott spent almost a year on the International Space Station, breaking the record for consecutive time spent in space, Mark remained on Earth. So you might expect any changes in Scott’s DNA to be due to the effects of space travel during that time.
Now, two years after Scott’s return to Earth, there’s been a lot of hype in the media about the results of the study, including some inaccurate claims that extended time in space altered Scott Kelly’s DNA by 7%. DNA is complicated, and the results were clearly misconstrued. To give you an idea of how large a change 7% would be, human beings and cats have about 90% of their DNA in common, while humans and chimpanzees share about 96%. Furthermore, genetic variation among humans averages only about 0.1%.
To set the record straight NASA put out a statement explaining that there was no fundamental change in Scott Kelly’s DNA: “What researchers did observe are changes in gene expression, which is how your body reacts to your environment. This likely is within the range for humans under stress, such as mountain climbing or SCUBA diving. The change related to only 7% of the gene expression that changed during space flight that had not returned to preflight after six months on Earth. This change of gene expression is very minimal.”
What this means is that changes in the environment can affect whether particular genes are active or inactive, which in turn affects how the body’s cells read and react to the genes. We call such changes in gene expression epigenetic. However, these epigenetic changes do not involve changes to the underlying DNA sequence. So Scott and Mark Kelly are still identical twins, even though a small percentage of their gene expression has changed.
Some of the epigenetic changes observed were temporary, including changes in the length of Scott’s telomeres, the caps protecting the ends of chromosomes that decrease in length as people age. His telomeres lengthened during spaceflight but returned to their preflight condition within two days of his return to Earth.
Of more concern for the planned Mars mission are any long-term effects observed. Two years after Scott Kelly’s return to Earth changes persist in gene expression related to his immune system, DNA repair, bone formation, hypoxia (oxygen deprivation in body tissues) and hypercapnia (excessive carbon dioxide in the bloodstream). How long these changes persist remains to be seen, and could raise safety concerns for a future mission to Mars, currently planned for the 2030s.
Join the Springfield Stars Club on Tuesday, April 24th at 7:00pm at the Springfield Science Museum for a talk by Kenneth S. Thomas, author of “The Journey to Moonwalking,” a story of the effort, sacrifice and innovation required to allow the first humans to set foot on and explore the Moon. Thomas was a spacesuit engineer for 22 years, during which time he became an expert on Apollo spacesuit development. He has been a consultant to the Space History Department of the National Air and Space Museum since 1993. Thomas was due to speak at the February Stars Club meeting but had to postpone his presentation until now. Refreshments will be served, and the public is welcome. The meeting is free of charge for members, with a suggested donation of $2 per non-member.
Also, on Friday, May 4th at 7:30pm, the Stars Club and the Springfield Science Museum will host “Stars over Springfield,” an astronomy adventure for the whole family. Amateur astronomer Paul Cardone will give a talk on “Astrophotography at the NMNIGHTS-1 Observatory in New Mexico.” A fee of $3 for adults and $2 for children under 18 will be charged.
Copyright © Amanda Jermyn