Powerful radiation made most Earth-like planet uninhabitable

The most Earth-like planet ever found could have been made uninhabitable by vast quantities of radiation from superflares ten times more powerful than those recorded on the Sun, a new study has found.

The atmosphere of the planet, Kepler-438b, is thought to have been stripped away as a result of radiation emitted from a superflaring Red Dwarf star, Kepler-438, researchers said. Regularly occurring every few hundred days, the superflares are approximately ten times more powerful than those ever recorded on the Sun and equivalent to the same energy as 100 billion megatonnes of TNT. While superflares themselves are unlikely to have had a significant impact on Kepler-438b s atmosphere, a dangerous phenomenon associated with powerful flares, known as a coronal mass ejection (CME), has the potential to strip away any atmosphere and render it uninhabitable.

The exoplanet Kepler-438b is to date one with the highest recorded Earth Similarity Index (a measure of how physically similar a planet is to ours). It is both similar in size and temperature to the Earth but is in closer proximity to the Red Dwarf than the Earth is to the Sun. "Unlike the Earth's relatively quiet sun, Kepler-438 emits strong flares every few hundred days, each one stronger than the most powerful recorded flare on the Sun. It is likely that these flares are associated with coronal mass ejections, which could have had serious damaging effects on the habitability of the planet," lead researcher, Dr David Armstrong of the University of Warwick's Astrophysics Group, said.

"If the planet, Kepler-438b, has a magnetic field like the Earth, it may be shielded from some of the effects. However, if it does not, or the flares are strong enough, it could have lost its atmosphere, be irradiated by extra dangerous radiation and be a much harsher place for life to exist," said Armstrong. "The presence of an atmosphere is essential for the development of life," Chloe Pugh, of the University of Warwick's Centre for Fusion, Space and Astrophysics, said. "Coronal mass ejections are where a huge amount of plasma is hurled outwards from the Sun, and there is no reason why they should not occur on other active stars as well," she added.

"With little atmosphere, the planet would also be subject to harsh UV and X-ray radiation from the superflares, along with charged particle radiation, all of which are damaging to life," said Pugh. The research was published in the journal Monthly Notices of the Royal Astronomical Society.