Biologists interested in space exploration are consistently delegated to the back of the stellar tour bus, if we’re allowed on at all. We’re Luddites who harsh everyone else’s squee, you see. We keep pointing out that radiation is not kind to living tissue, whether gametes or neurons; that uploading to silicon chassis is not possible as an alternative to carbon bodies; that human babies cannot be hatched and reared by robots at planetfall; that living on extrasolar planets poses huge problems and dilemmas even if they’re quasi-compatible. And that since FTL and warp drive are and will always remain science fiction, we need to at least tackle, if not solve, some of these issues before we launch crewed starships for long exploratory or migratory journeys. This year, there were two non-news items in the domain that brought these matters once again to the fore.
The earlier of the two was the disclosure that “NASA scientists might achieve warp drive” based on Alcubierre’s theoretical concept (by using a Jovian weight’s worth of exotic matter as likely to exist as stable wormholes). Beyond its terminally wobbly foundation, the concept also doesn’t take into account that such folding of space would destroy nearby star systems (and almost certainly also the starship) via distortion of the local spacetime and/or massive amounts of radiation. It’s also unclear how the starship could be steered from within the “negative energy” or “tachyonic matter” bubble. This means that even if fast space travel were possible using this method, it would still take lifetimes to safely reach a planet within a system because local travel would by necessity be at sublight speed.
More recently came the non-news that radiation causes… brain malfunction, as if the term “free radicals” and “radiation damage” were not in the biomedical vocabulary since before I entered the discipline in the mid-seventies (let alone the in-your-face evidence of the Hiroshima and Nagasaki holocausts or the Chernobyl meltdown). Radiation, especially the high-energy portion of the spectrum, breaks atomic bonds directly and indirectly by producing free radicals. Free radicals start chain reactions: lines of descendants, each of which can damage a biomolecule. Radiation causes mutations in the DNA, which is bad enough, but it can also result in other errors: protein misfolding, holes in cell membranes, neuron misfiring. And although cells have several repair mechanisms to counter these insults, they have evolved for the radiation burdens of earth.
All these effects at the molecular/cellular level converge into two large rivers: for dividing cells, cancer; for non-dividing cells (most prominently gametes and brain neurons), death. Kill enough cells, past the brain’s ability to rewire and reroute, and you get neurodegeneration: if the most affected region is the substantia nigra, Parkinson’s; if the cerebellum, ataxia; if the hippocampus and parts of the cortex, Alzheimer’s; if the frontal lobe, frontotemporal dementia; if the Schwann cells of the myelin sheath, multiple sclerosis. Incidentally, radiation also affects electronic devices – something to keep in mind for even short interstellar journeys.
On earth, we are subject to a good deal of radiation from natural causes (radon, solar flares) as well as human-made ones (industrial, occupational, medical, airport X-ray machines). Cosmic radiation constitutes about 5-10% of our total exposure. That will be very different in space, where bombardment by galactic cosmic rays will be both chronic and acute. And whereas cosmic radiation on earth is moderated by the solar wind, the earth’s magnetic field and the layers of atmosphere, none of these protections will be present on a starship. Shielding options are inadequate or, like warp drive, sheer fantasy – which makes this risk one of the major showstoppers to star travel. The best candidate is the most low-tech: water.
Scientific papers that discuss these outcomes, from both inside and outside NASA, have been around since at least the early nineties. So what exactly is new in this study that is making the customary rounds in various space enthusiast sites and blogs? In a word, nothing. In fact it’s a bits-and-pieces study that reaches miniscule, non-surprising conclusions. The adage “labored as if for an elephant and brought forth a mouse” is particularly apt here. As for the originality of its discoveries/conclusions, it’s like hitting someone’s head repeatedly against a cement wall and concluding that such blows eventually cause, um, skull fractures.
At the same time, the authors of the study decided to gild their tinfoil lilies. They used a double transgenic mouse strain engineered to develop amyloid plaques of the Alzheimer’s-associated variety. Despite this loading of the dice, they saw changes in plaque size and numbers and in amyloid processing only in the male irradiated mice. Even the small shifts they saw are far less important than laypeople think: for a while now, the consensus in the field is that plaques may be neutral warehouses. In particular, plaques seem to be a sidebar for sporadic Alzheimer’s which is 90-95% of the disease cases. Many people have heavy amyloid plaque loads with zero cognitive impairment. As is often the case with mice studies, they subjected them to overwhelming amounts of the perturbing parameter (in this case, iron nuclei) that nevertheless represents a simplified subset of what they’d encounter in a real journey. Finally, they saw neither inflammatory microglial activation nor changes in amyloid clearance. They did see changes in a couple of behavioral tests, although in most of them the error bars overlap, which means “not statistically significant”.
The obvious experiment that might give remotely useful results would be to do such studies with a mouse strain that is not merely wild-type but aggressively outbred. However, that would still be superfluous, even if we set aside the limited usefulness of mouse models for human brain function. We already know what would happen during long interstellar journeys, and more or less why. I propose that we use the time and funds spent on irradiating guaranteed-to-develop-disease mice to develop effective, and preferably low-key, shielding. Radical-clearing drugs are also an option, although the favorite defaults bristle with their own host of problems (teratogenicity for retinoids, tumorigenesis for mitochondrial boosting). Like most complex problems, there are no silver bullets to counteract the iron-nuclei ones of galactic radiation. It will have to be done the hard, slow way – or not at all.
H White (2012). Warp Field Mechanics 101.
JD Cherry, B Liu, JL Frost, CA Lemere, JP Williams, JA Olschowka, MK O’Banion (2012). Galactic Cosmic Radiation Leads to Cognitive Impairment and Increased A? Plaque Accumulation in a Mouse Model of Alzheimer’s Disease. PLoS One 7(12):e53275