Red Dwarf Stars Aren't So Deadly to Planets After All
The most populous stars in the galaxy might be the norm for life.
Recent evidence suggests the most common stars in the galaxy might not be as deadly to life on nearby rocky planets as we thought, which could mean more planets beyond our solar system with conditions amenable to life, according to a forthcoming study in the Monthly Notices of the Royal Astronomical Society, which was also shared to a preprint server.
This could flip the script on planetary life orbiting red dwarfs.
Red dwarf stars' flares probably miss nearby exoplanets entirely
Red dwarf stars, which are also called M dwarfs, make up roughly 75% of all stars in our galaxy. They're far smaller and cooler than the sun, and, lacking the internal layers that stars like our sun (or G-type) stars possess, the tiny red dwarfs spin fast enough to trigger cataclysmic magnetic activity, like flares. Flares happen when stellar magnetic fields are twisted and stretched until they "snap" back into their initial position, flinging high-energy radiation out into space in the process. In the past, astronomers thought this radiation could strip nearby planetary atmospheres, precluding the possibility of life.
Planets thought to orbit in a life-friendly habitable zone around red dwarfs were especially vulnerable, since they need to orbit extra-close to receive enough light for water to remain in liquid form on the rocky crust. But the recent study from Ekaterina Ilin of the Leibniz Institute for Astrophysics Potsdam, in Germany, has revealed new evidence that suggests flares aren't as destructive to such planets, after all. Analyzing data from NASA's Transiting Exoplanet Survey Satellite (TESS), Ilin's team searched for M-dwarf superflares that persisted for longer than the rotation period of the host star. Surprisingly, they discovered that all of these flares happened at high latitudes, which means they ejected from the poles, upward and downward, instead of outward toward orbiting planets.
High-altitude flares on red dwarfs are likely the norm
This breaks with conventional flares observed on our sun, which typically burst outward from its equator. Contrasting with this local model, the deadly radiation from M dwarf's high-latitude flares would miss potentially life-harboring planets entirely, leaving their fragile atmospheres intact. The team of scientists studied the light curves of M dwarfs because they show how a star's brightness grows or diminishes over time. When flares begin, there's a noticeable spike in the brightness of the star, and, since the flares last longer than the star's rotational period, Ilian and the team can track a rotational fingerprint that betrays the precise location on the globe of the star.
For the M dwarfs under study, the flares were ejected between 55° and 81° in latitude, much farther than would have been possible on the sun, where they typically happen within 30° of the solar equator. While Ilin's team only discovered four high-latitude-flaring M dwarf stars, another scientist named Cynthia Froning, who wasn't part of the study, suspects this has wider ramifications, according to a report from Sky and Telescope. If flares were equally likely to happen at any latitude, the research team would have seen them occur closer to the equator, where solar ejections could endanger nearby life. There was a mere 1 in 1,000 chance that every observed red dwarf flare happened at high latitudes, which means this is probably the norm for M dwarf flares, which in turn ups the chances for life to live and grow on nearby exoplanets.