X-rays on Earth-like planets may end alien life

Intense X-ray radiation could eliminate the possibility of alien life on many Earth-like planets, by stripping away the ozone layer and rendering them uninhabitable, a study has found. Astronomers now know of around 4,000 planets in orbit around other stars. A handful of these are both Earth-sized and in the habitable zones of the stars they orbit, where the temperature is right for liquid water.

However, many candidate Earth-sized worlds are in orbit around red dwarf stars, much smaller and cooler than our own. To be in the habitable zone, the planets need to be much closer to their stars than we are to the Sun.

The problem, however, is that red dwarfs can produce significant X-ray emission, and often have large flares of radiation and eruptions of particles in so-called coronal mass ejections (CMEs). To try to assess the risk, researchers at the Thueringer Observatory in Germany are intensively monitoring low-mass stars where flares might take place.

In February, they observed a giant flare from the star AD Leo, located 16 light years away in the constellation of Leo. AD Leo has a giant planet orbiting three million kilometres away (fifty times closer than the Earth to the Sun), and it may have Earth-sized worlds further out in its habitable zone. Their initial results suggest the giant planet was unaffected, and that unlike similar events on the Sun, the radiation flare was not accompanied by a CME.