The reality of a man-made colony in space is becoming more plausible every year. Both private industry and government institutions are combining their collective genius to tackle the substantial engineering challenges associated with building human habitats on these completely alien environments. Many see space colonization as inevitable, like homesteading the American West with a twist; however, the implications of living in an environment without earth's gravity have yet to be fully explored and present unique-unavoidable challenges to extraterrestrial habitation.
Mars, with only 38% of the gravity that is experienced on earth, has been of particular interest for forward thinkers and space-exploration optimists. Elon Musk, the visionary billionaire and SpaceX founder, has been quoted as saying “I want to die on mars, just not on impact,†and the company Mars One is planning to send up to four people to Mars each year, starting in 2024.
Despite the obvious challenges of a Martian colony—no air, no food, no water and way too much radiation—there are less-obvious biological implications associated with living in microgravity (a fraction of the gravity experienced on earth).
Unsurprisingly, having evolved in earth's gravity, much of normal human physiology is adversely affected in long periods of microgravity. The most famous physical phenomenon associated with microgravity is known as spaceflight osteopenia, or the loss of bone density due to prolonged space travel. The cause of this osteoporosis is poorly understood yet can be somewhat managed with a strict workout regimen.
Less well known is the crippled immune response of those living in microgravity environments. For example, greater than 50% of astronauts coming back from Apollo or Skylab missions experienced illnesses, such as skin and urinary tract infections, that are not typical of healthy individuals. While the exact mechanism of this phenomenon is not yet apparent, the lab of Millie Hughes-Fulford at the University of San Francisco has been on the forefront of research on microgravity immunosuppression. In both simulated microgravity experiments and experiments aboard various space missions, the Hughes-Fulford lab has identified a major decrease in T-cell activation. T-cells, arguably the most important cells in the adaptive immune system, are integral to fending off pathogens or identifying tumors that cause disease. Through a number of genetic tests, they were able to identify many dysregulated markers in the T-cells exposed to microgravity. For example, Tumor Necrosis Factor (TNF), a central cell-signaling molecule involved in a host of immune responses, experienced a 15-fold reduction. T-cell transcription factors, proteins that influence which genes are expressed, have been linked to many of the impaired immune problems, though it is not well understood how microgravity is causing their down regulation.
Some solutions to offset the microgravity have been suggested in the past. If each structure were built as a centrifuge, constantly rotating, artificial gravity would be attained by the centrifugal force. While this may sound ridiculous, the idea has actually been floated for decades and culminated in the CAM, Centrifuge Accommodation Module, being built by the Japanese Aerospace Exploration Agency (JAXA) and commissioned by NASA as an add-on to the international space station. Far from being a perfect fix, there are fundamental problems with a centrifuge structure; namely, a person's feet would experience more gravity than their head, leaving them feeling particularly light-headed.
Alas, some interesting questions remain. Would humans be able to withstand living for years in microgravity? Are chronic infection and osteoporotic bones able to be overcome or would they be endemic in an extraterrestrial community? Would someone that lives on Mars ever be able to come back to earth (technology permitting) after having lived in microgravity for so long?
For now, it seems that biological barriers to healthy human space habitation present obstacles to Elon Musk's blissful retirement in his Martian vacation home.
References:
- http://www.space.com/16871-how-big-is-mars.html
- http://www.theguardian.com/technology/2013/jul/17/elon-musk-mission-mars-spacex
- Peter R. Cavanagh, Angelo A. Licata, and Andrea J. Rice (June 2005),Exercise and pharmacological countermeasures for bone loss during long-duration space flight,Gravitational and Space Biology18 (2): 39–58, PMID 16038092
- Gueguinou, N., Huin-Schohn, C., Bascove, M., Bueb, J. L., Tschirhart, E., Legrand-Frossi, C., Frippiat, J. P. (2009) Could spaceflight-associated immune system weakening preclude the expansion of human presence beyond Earth's orbit? J. Leukoc. Biol. 86, 1027–1038.
- Hawkins, W. R., Ziegleschmid, J. F. (1975) Clinical aspects of crew health. In Biomedical Results of Apollo (NASA SP 368) (Johnston, R. Diet- lein, L. Berry, eds.), C. NASA, Washington, DC, USA, 43–81.
- Chang T. T., Walther I., Li C-F., Boonyaratanakornkit J., Galleri G., Meloni M. A., Pippia P., Cogoli A., Hughes-Fulford M. (2012) The Rel/NF-κB pathway and transcription of immediate early genes in T cell activation are inhibited by microgravity. J. Leukoc. Biol. 92, 1133–1145.
- http://www.spaceref.com/iss/elements/cam.html
Patrick Griffin is an undergraduate Genetics major at the University of Georgia. He enjoys cycling, science, and eating donuts, though not necessarily in that order, and once solved a Rubix Cube in under a minute. Follow him on Twitter: @patrick_griffN or contact him via email: pgriff10@uga.edu
