When searching for totally novel forms of life, one of the most basic rules of thumb is: look up. But one researcher from the Blue Marble Space Institute says that rather than searching far-away planets for new forms of life, we might be able to find some right here at home, simply by looking down. Deep down.
Dimitra Atri's new hypothesis paper, published earlier this month on the arXiv preprint server, argues that there might exist life that could be powered entirely by high-energy cosmic rays—and that we might be able to find such life right here on Earth. Hypothetically, of course.
But the idea isn't actually quite as out-there as it might first appear. Prior studies have found deep subterranean bacteria that they suggest have evolved to live off the energy released by the radioactive decay of substances like uranium. These bacteria find oxygen highly toxic, and instead make use of hydrogen (H2) created when high-energy particles released by these decaying radioisotopes impact water molecules in the surrounding rock.
This allows the bacteria to power themselves totally independent of the surface world, and that makes them fundamentally distinct from all other forms of life. From bacteria to plants to human beings themselves, all life was previously thought to run off the photosynthetic energy captured by plants—by eating the plants, by eating the animals that eat the plants, or simply by making use of high-energy molecules like O2 that are released in the process of photosynthesis.
"If we dig deeper, in more regions, we could find a life-form which thrives just on this cosmic radiation," Arti hypothesized
Atri told Motherboard that his hypothetical life-form would work on much the same basis, but that the radioactivity which creates the crucial hydrogen supply could be generated by cosmic rays just as readily as radioactive decay. He would know; much of his prior research has focused on theorizing the effects and quantifying the amount of cosmic-ray energy available to particular populations. The paper's core claim is that muons could generate a livable amount of hydrogen several kilometers deep.
"If we dig deeper, in more regions," Atri said, "we could find a life-form which thrives just on this cosmic radiation." His paper also discusses the possibility of more direct use of cosmic rays, in which a life form could absorb rays with pigments like melanin, but such a mechanism has not yet been found in nature.
The H2 referenced in this case is actually the tertiary product of cosmic rays—the high-energy particles released by supernovae and other violent astronomical events. These super-charged cosmic particles (mostly protons travelling near the speed of light) impact molecules in the Earth's upper atmosphere and destroy them, producing high-energy muons, among other things. Muons have only weak interactions with regular matter and it takes a lot to bring them to a halt—a property that makes them particularly useful for things like seeing through heavy shielding and, according to Atri, creating life-powering molecules several kilometers below the surface of the Earth.
"This can happen anywhere, on Europa or any other place," Atri said. "Because it doesn't need any photons, you don't have to be tied to any star." His hypothesis suggests that life could even exist even on so-called rogue planets hurtling through deep space, desolate and alone.
This isn't the only recent paper theorizing new forms of power for life; as NASA prepares to search more widely for life on Mars, Atri says these sorts of theories will be essential. finding it not just on Earth-like paradise planets, but on virtually any body, virtually anywhere in the known universe.