A study at the Carnegie Institution for Science considers the use of naturally occurring space weather observatories orbiting the early orbits of at least 10% of M dwarfs.
We know that most M dwarf stars (smaller, cooler, and fainter than the Sun) host at least one rocky Earth-sized planet. Most of them are inhospitable, too hot to contain liquid water or atmosphere, or frequently hit by stellar flares and strong radiation.
But stars can still provide interesting laboratories for understanding how they shape the environments in which their planets reside.
Luke Buuma, who led the study, explained, “Stars influence planets through light, both through optical observations, which we are good at, and through space weather, such as solar wind and magnetic storms, which is more difficult to study at long distances.”
Tracking the complex movements of M dwarf stars
Bouma, in collaboration with Moira Jardine from the University of St Andrews, focused on a strange type of M dwarf called a complex periodic.
These are young stars, rapidly rotating, and observations have shown that their brightness repeatedly decreases. Astronomers weren’t sure whether these dips in brightness were caused by star spots or by material orbiting the star.
“For a long time, no one knew what to make of this strange little change in darkness,” Buuma said. “But we were able to demonstrate that they can tell us something about the environment just above the star’s surface.”
Bouma and Jardine answered that question by creating a “spectroscopic movie” of one of these complex periodic variable stars. They demonstrated that they are large clumps of cold plasma trapped in the star’s magnetosphere, forming a donut-shaped torus.
How DIP becomes a space weather observatory
Bouma explained: “Once you understand this, the dimming phenomenon ceases to be a strange little mystery and becomes a space weather observatory.
“The plasma torus gives us a way to see what’s concentrated in the material near an M dwarf, how it’s moving, and how strongly it’s influenced by the star’s magnetic field.”
Bouma and Jardine estimate that at least 10% of type M dwarfs may have such plasma features early in life. Therefore, these space weather observatories could help astronomers learn a lot about how particles from stars contribute to planetary conditions.
Next steps in torus research
Next, Buma hopes to find out where the material in the torus comes from: the star itself, or an external source.
Bouma concluded as follows: “This is a great example of a serendipitous discovery, something we never expected to find, but one that gives us a new window into understanding the relationships between planets and stars.
“We don’t yet know whether planets orbiting M dwarfs can support life, but we are confident that space weather will be an important part of answering that question.”
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