October 8, 2016

Team finds ‘alien’ microbe that feeds on cosmic rays

Nearly all organisms on Earth require carbon, oxygen, and sunlight to survive, but the discovery of an unusual microbe that thrives deep within a South African gold mine has experts wondering if living organisms might have adapted to survive on seemingly uninhabitable planets.

In research published this week in the Journal of the Royal Society Interface, Dimitra Atri, an astrobiologist and computational physicist at the Seattle, Washington-based Blue Marble Space Institute of Science, proposes that rogue planets located too far away from a host star to benefit from their life could potentially be home to life that feeds off of cosmic radiation.

According to Science Magazine and Popular Science, Atri’s hypothesis is based on the existence of the rod-shaped bacterium Desulforudis audaxviator, the so-called “gold mine bug” that live at depths of nearly three kilometers in an environment devoid of light and oxygen. Instead of using energy from the sun to survive, the microbe feeds off radioactive uranium found in the depths of the mines calls home, indicating that such adaptations are possible.

Audaxviator “really grabbed my attention because it’s completely powered by radioactive substances,” Atri explained to Science. “Who’s to say life on other worlds doesn’t do the same thing?” He added that it “can’t be ruled out that life like this could exist” in other corners of the universe, and that somewhere, organisms are using cosmic rays to thrive.

Mars deemed the most likely candidate to support such life

Here on Earth, living organisms typically gather the energy they need through photosynthesis (the process of collecting energy from sunlight and using it to convert water and carbon dioxide into food, common in plants and some bacteria) or by feeding off of plants or animals to acquire the energy that those organisms have already converted and stored.

In D. audaxviator’s case, however, it draws energy from the radioactivity of rocks located deep in the mines where it lives, according to Science. As the element decays, radiation from its nuclei break down sulfur and water molecules, producing molecular fragments like  hydrogen peroxide that are excited with internal energy.

The bacteria gathers those molecules, drains the energy that they contain, then releases them, using most of the energy to power its internal and reproductive processes and the rest to repair damage caused by the radiation itself. In his new study, Atri argues that an extraterrestrial life form could use a similar system, but instead of harnessing energy from uranium, it would take radiation from energetic particles known as galactic cosmic rays (GCRs).

GCRs are everywhere – including here on Earth. However, our atmosphere and magnetic field prevent most of them from affecting us on the surface. That’s not necessarily the case on planets such as Mars, which are more susceptible to GCRs due to their thin atmospheres and the lack of magnetic fields. Atri believes that these rays could reach the surface of some worlds with enough energy to power small, simple organisms similar to the “gold mine bug.”

As part of his research, he conducted a series of simulations that confirmed that even a small but steady shower of GCRs would be sufficient to provide enough energy to keep a microbe alive on most planets in the solar system (Earth excluded). He went on to suggest that Mars would be the best candidate to support such life, due to its rocky Earth-like composition and the likelihood that it contains at least trace amounts of water.


Image credit: NASA