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Most Earthlike exoplanet is uninhabitable

Kepler-438b – 470 light years from Earth – ranks highest on the Earth Similarity Index. But radiation from its violent parent star makes it uninhabitable.

Kepler-438b: The planet Kepler-438b is shown here in front of its violent parent star. It is regularly irradiated by huge flares of radiation, which could render the planet uninhabitable. Here the planet’s atmosphere is shown being stripped away. Superflares have energies roughly equal to or greater than 10^33 erg, about 10 times greater than the most powerful solar flare on record. They have been observed with energies up to around 10^36 erg - some 10,000 times the size of biggest solar flare.  Image credit: Mark A Garlick / University of Warwick

Kepler-438b: The planet Kepler-438b is shown here in front of its violent parent star. It is regularly irradiated by huge flares of radiation, which could render the planet uninhabitable. Here the planet’s atmosphere is shown being stripped away. Superflares have energies roughly equal to or greater than 10^33 erg, about 10 times greater than the most powerful solar flare on record. They have been observed with energies up to around 10^36 erg – some 10,000 times the size of biggest solar flare. Image credit: Mark A Garlick / University of Warwick

The planet Kepler-438b, 470 light years from Earth, is to date the exoplanet with the highest recorded Earth Similarity Index, a measure of how physically similar a planet is to Earth. But Kepler-438b is uninhabitable, researchers say. The planet’s atmosphere has been stripped away as a result of radiation emitted from its violent parent star, a superflaring red dwarf, according to new research published in Monthly Notices of the Royal Astronomical Society on November 18, 2015.

Although Kepler-438b is similar to Earth in both size and temperature, it’s closer to its star, a red dwarf, than the Earth is to the sun. Regularly occurring every few hundred days, the superflares from the star, Kepler-438, are approximately ten times more powerful than those ever recorded on our sun and equivalent to the same energy as 100 billion megatons of TNT.

While superflares themselves are unlikely to have 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.

Lead researcher, Dr. David Armstrong of the University of Warwick’s Astrophysics Group, explained:

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 serious damaging effects on the habitability of the planet.

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.

Discussing the impact of the superflares and radiation on the atmosphere of Kepler-438b, Chloe Pugh, of the University of Warwick’s Center for Fusion, Space and Astrophysics, said:

The presence of an atmosphere is essential for the development of life. While flares themselves are unlikely to have a significant impact on an atmosphere as a whole, there is another more dangerous phenomenon associated with powerful flares, known as a coronal mass ejection.

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. 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.

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Bottom line: According to new research published in Monthly Notices of the Royal Astronomical Society on November 18, 2015, the exoplanet considered most Earthlike, Kepler-438b, is uninhabitable due to radiation from its violent parent star. The planet’s atmosphere has been stripped away as a result of radiation emitted from the superflaring red dwarf, the study suggest.

Read more from the University of Warwick

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