In the search for “potentially-habitable” extrasolar planets, one of the main things scientists look at is stellar activity. Whereas stars like our own, a G-type (G2V) yellow dwarf, are considered stable over time, other classes are variable and prone to flare-ups – particularly M-type red dwarf stars. Even if a star has multiple planets orbiting within its habitable zone (HZ), the tendency to periodically flare could render these planets completely uninhabitable.

According to a new study, stars like our own may not be as stable as previously thought. While observing EK Draconis, a G1.5V yellow dwarf located 110.71 light-years away, an international team of astronomers witnessed a massive coronal mass ejection that dwarfed anything we’ve ever seen in our Solar System. These observations suggest that these ejections can worsen over time, which could be a dire warning for life here on Earth.

The study, which appeared in the December 9th issue of the journal Nature Astronomy, was led by Dr. Kosuke Namekata, a researcher at Kyoto University, the National Astronomical Observatory of Japan (NAOJ) and the National Solar Observatory (NSO). He was joined by researchers from CU Boulder’s Laboratory for Atmospheric and Space Physics (LASP), the Nishi-Harima Astronomical Observatory (NHAO), the Tokyo Institute of Technology, the Graduate School of Advanced Integrated Studies in Human Survivability, and multiple universities.

Stellar flares could threaten life on red dwarf planets. Credit: NASA/ESA/D. Player (STScI)

Their study explores a stellar phenomenon known as a “coronal mass ejection” (CME), aka. a solar storm. These ejections, which occur with our Sun regularly, often accompany a stellar flare (or sudden and bright burst of radiation). When they happen, CMEs send clouds of extremely hot charged particles (aka. plasma) at extremely high velocities into space. While Earth is protected from charged particles by its planetary magnetic field, a CME could cause significant damage if it hit Earth head-on.

Astronauts in orbit would be exposed to lethal radiation levels, satellites would be disabled, and Earth-based infrastructure (like electrical grids) would be knocked out. Earth has experienced several powerful geomagnetic storms over time, the most well-known example of which was the Carrington Event in 1859. Several such events have occurred in Earth’s history and are usually several thousand years apart.

While studying EK Draconis, the research team observed evidence that superflares may become worse for Sun-like stars over time. As co-author Yuta Notsu (LASP) explained in a recent CU Boulder Today press release:

“Coronal mass ejections can have a serious impact on Earth and human society. This kind of big mass ejection could, theoretically, also occur on our sun. This observation may help us to better understand how similar events may have affected Earth and even Mars over billions of years.”

Artist’s impression of a flaring red dwarf star, orbited by an exoplanet. Credit: NASA, ESA, and G. Bacon (STScI)

The research builds on previous research by co-author Yuta Notsu, who was joined by many of the researchers who conducted this latest study. They showed how young Sun-like stars experience frequent superflares that are tens to hundreds of times more powerful than solar
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