Why going into orbit sends cells haywire
Space is not a very hospitable place. There is no air. Depending on whether you are in sunlight or not, it is either freezing cold or roasting hot. There are subtler hazards, too. Even when provided with oxygen and a stable temperature by their spacecraft, astronauts seem to sicken the longer they spend away from Earth.
Spending time in orbit, for instance, causes bones and muscles, including the heart, to waste away. Astronauts on the International Space Station (ISS) spend several hours a day exercising in an attempt to fight this enfeeblement, with only partial success. Levels of radiation beyond Earth’s protective atmosphere and magnetic field are higher than on its surface, which may increase the risk of cancer.
A report published on October 22nd by the Guy Foundation, a British non-profit interested in the links between physics and biology, adds some new potential health hazards for astronauts to worry about. The report draws on several strands of emerging research to argue that long-duration spaceflight, or living on other planets, might be even more difficult for humans than had been assumed.
The main concern is the damage space travel seems to do to mitochondria, components found in almost every cell that produce the energy that powers the rest of the cell. In 2020 a group led by Willian da Silveira at Queens University in Belfast, and including researchers from NASA, found that spaceflight causes dramatic shifts in how mitochondria work. They suggested this could explain many health problems seen in astronauts, from immune-system difficulties to cardiovascular issues. The new report suggests astronauts face something that looks like “accelerated ageing”, and that this is associated with the disruption of cellular energy production.
The report floats several potential causes for the malfunctioning mitochondria. Some are well-grounded in existing science: radiation can damage cells directly, for instance. Others are more speculative. Free-fall is one potential villain. The report presents emerging evidence that the drag of Earthly gravity may be important for various cellular processes. Even the lights in spacecraft come in for examination. These currently do not reproduce the full spectrum of sunlight, particularly infra-red radiation. Sunlight is known to govern the body’s sleep-wake cycle, and may affect other bodily functions too.
The researchers also note one emerging question in cellular biology: whether the influence of Earth’s magnetic field might be an important factor for the chemical reactions upon which mitochondria rely to produce energy. Neither Mars nor the Moon, two possible places for establishing space colonies, possesses a magnetic field like that of Earth.
More data would help: although astronauts are examined by medics on their return from space, there have been few long-term studies. One solution, the researchers say, might be to run multi-year animal experiments in orbit. Other data will be harder to generate. If lack of gravity is a problem, is the gravity on the Moon (about a sixth of that on Earth) enough to fix it?
Some problems might be fixable via engineering. Lunar bases could be built underground to shield them from radiation, and lighting tweaked to make it more sun-like. A more drastic approach would be to tweak the humans rather than their habitats. Sir Martin Rees, an astronomer and former president of the Royal Society, has long argued that Homo sapiens is constitutionally unsuited for space travel, and that genetically engineering a new subspecies—Homo spaciens?—might be a better way to colonise other worlds.
This article appeared in the Science & technology section of the print edition under the headline “The wrong stuff” (Oct 30th 2024)
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