Stellar superflares from young red dwarfs may make conditions uninhabitable on fledgling planets, according to the new results of the Habitable Zones and M dwarf Activity across Time (HAZMAT) survey.
An artist’s impression of a habitable exoplanet orbiting a red dwarf. Image credit: Sci-News.com / NASA.
About 70% of the stars in our Milky Way Galaxy are red dwarfs — small, low-surface temperature main-sequence stars with a spectral type of K or M.
Most of the Galaxy’s habitable-zone exoplanets — planets orbiting their stars at a distance where temperatures are moderate enough for liquid water to exist on their surface — likely orbit these stars.
In fact, the nearest star to our Sun, a red dwarf named Proxima Centauri, has an Earth-mass planet in its habitable zone.
However, young red dwarfs are active stars, producing ultraviolet (UV) flares that blast out so much energy that they could influence atmospheric chemistry and possibly strip off the atmospheres of fledgling planets.
“The goal of the HAZMAT program is to help understand the habitability of planets around low-mass stars,” said HAZMAT principal investigator Dr. Evgenya Shkolnik, a researcher at Arizona State University.
“These low-mass stars are critically important in understanding planetary atmospheres.”
Using the NASA/ESA Hubble Space Telescope, Dr. Shkolnik and colleagues examined the flare frequency of 12 red dwarfs in the 40-million-year-old Tucana-Horologium moving group.
“Getting these data on the young stars has been especially important, because the difference in their flare activity is quite large as compared to older stars,” said study first author Dr. Parke Loyd, also from Arizona State University.
The team detected 18 superflares, which are 100 to 1,000 times more energetic than when the stars are older.
One of these events, dubbed the ‘Hazflare,’ was more energetic than the most powerful flare from our Sun ever recorded.
“With the Sun, we have a hundred years of good observations,” Dr. Loyd said.
“And in that time, we’ve seen one, maybe two, flares that have an energy approaching that of the Hazflare.”
“In a little less than a day’s worth of Hubble observations of these young stars, we caught the Hazflare, which means that we’re looking at superflares happening every day or even a few times a day.”
Could superflares of such frequency and intensity bathe young planets in so much UV radiation that they forever doom chances of habitability?
“Flares like we observed have the capacity to strip away the atmosphere from a planet,” Dr. Loyd said.
“But that doesn’t necessarily mean doom and gloom for life on the planet. It just might be different life than we imagine. Or there might be other processes that could replenish the atmosphere of the planet. It’s certainly a harsh environment, but I would hesitate to say that it is a sterile environment.”
The results will be published in the Astrophysical Journal.
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R.O. Parke Loyd et al. 2018. HAZMAT. IV. Flares and Superflares on Young M Stars in the Far Ultraviolet. ApJ, in press; arXiv: 1810.03277
