The atmosphere of Kepler-438b is thought to have been stripped away as a result of radiation emitted from the planet’s violent parent star, says a team of scientists led by University of Warwick astronomer Dr David Armstrong.
Kepler-438b is shown here in front of its violent parent star, Kepler-438. Image credit: Mark A. Garlick / University of Warwick.
Kepler-438b is 1.2 times larger than Earth and orbits its parent star, Kepler-438, once every 35.2 days.
The star, also known as KOI-3284 or KIC 6497146, is a red dwarf located in the constellation Lyra, approximately 470 light-years away. It is smaller and cooler than our Sun.
According to Dr Armstrong and co-authors, Kepler-438b is regularly irradiated by huge flares of radiation, which could render the planet uninhabitable.
“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,” Dr Armstrong said.
While superflares themselves are unlikely to have a significant impact on Kepler-438b’s atmosphere, a phenomenon associated with flares – a coronal mass ejection (CME) – has the potential to strip away any atmosphere.
“It is likely that these flares are associated with coronal mass ejections, which could have serious damaging effects on the habitability of the planet,” Dr Armstrong 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,” added team member Dr Chloe Pugh, also of the University of Warwick.
“The likelihood of a coronal mass ejection occurring increases with the occurrence of powerful flares, and large coronal mass ejections have the potential to strip away any atmosphere that a close-in planet like Kepler-438b might have, rendering it uninhabitable.”
“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”.
“If the planet, Kepler-438b, has a magnetic field like the Earth, it may be shielded from some of the effects,” Dr Armstrong said.
“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.”
The findings will be published in the journal Monthly Notices of the Royal Astronomical Society, but have been published on arXiv.org ahead of time.
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D.J. Armstrong et al. 2015. The Host Stars of Kepler’s Habitable Exoplanets: Superflares, Rotation and Activity. MNRAS, accepted for publication; arXiv: 1511.05306
