Excellent news! Purple dwarfs blow their superflares from the poles and save their planets from destruction
The only known life in the universe lives on a medium-sized rocky planet orbiting a medium-sized yellow star. That makes our planet a little unusual. While small rocky planets are common in the galaxy, yellow stars are not. Smaller red dwarf stars are much more typical and make up about 75% of the stars in the Milky Way. Because of this, most of the potentially habitable exoplanets that we have discovered orbit red dwarfs.
If everything is in balance, then one would expect that dwarf red planets would be the most likely to harbor life. But not all things are created equal. Red dwarfs can be much more active than sun-like yellow stars. They can emit enormous solar flares and powerful X-rays. And since red dwarfs are much cooler than the sun, planets must orbit them very closely to be potentially habitable. All of this paints a bleak picture for life on dwarf red planets. A red dwarf would likely erode the atmospheres of nearby planets and destroy any life these worlds could harbor. But a new study finds that things may not be as bad as we thought.
The planets of Trappist-1 orbit their star very closely. Photo credit: NASA / JPL-Caltech
The team used data from the Transiting Exoplanet Survey Satellite (TESS). While the main objective of the TESS mission is to study exoplanets traversing their stars, the TESS survey also provides data on star eruptions. So the team went looking for the stellar torches of the Red Dwarfs. From this they could determine the latitude of solar flares on the star. They found that the distribution of the flares on red dwarfs is very different from that of our sun.
Solar flares generally occur within the equatorial region. Because of this, the energy and particles of these flares can hit planets in the inner solar system. This last happened in 1859 with the Carrington Event. But the earth’s strong magnetic field protects us well. If such an event occurred today, it would disrupt our electronic infrastructure, but it would not threaten earthly life as a whole. If the earth orbited the sun much closer than Mercury, such a flare would be much more dangerous.
It was widely believed that red dwarfs also emit flares from their equatorial regions, but this new study found that the largest flares tend to appear near the poles of the star. The red dwarfs they observed all appeared above the 60th parallel. Their sample size was small so they couldn’t rule this out as a coincidence, but if further observations support the trend, that’s good news for red dwarf planets. This means that most of the flares are deflected out of the orbital plane and potentially habitable worlds are spared from an apocalypse.
Relation: Ilin, Ekaterina, et al. “Huge white light flares on fully convective stars occur at high latitudes.” Monthly Announcements from the Royal Astronomical Society 2021.