The investigation of exoplanets has advanced significantly during the last ten years. There are now 4,201 verified extrasolar planets, and there are another 5,481 candidates awaiting confirmation.
Because they seem to be the most probable location where rocky (also known as Earth-like) planets may be discovered orbiting inside the star's habitable zone, M-type red dwarf stars have been a focus of exoplanet research in the middle of all this (HZ).
Red dwarf stars are not always strong prospects for having habitable planets, however. Consider GJ 887, one of the brightest M stars in the sky, which is home to a planet system with two (perhaps three) planets.
GJ 887 was always assumed to be steady and quiet, but recent study by astronomers from Arizona State University suggests that it may not be as stable.
It was recently determined that GJ 887 (also known as Lacaille 9352), which is situated just under 11 light-years from Earth, has two Super-Earths with orbits that bring them near to or within the star's HZ.
Similar results suggested that the star was rather "boring," meaning that it was less likely to have flare-ups than other red dwarf stars, which was excellent news for the star's habitability.
Recent publications of the team's results in the Research Notes of the American Astronomical Society (RNAAS).
Parke Lloyd, an astrophysicist with ASU's School of Earth and Space Exploration (SESE), served as the study's principal investigator. Evgenya L. Shkolnik, also a leader at SESE, as well as scientists from the University of Colorado Boulder and the Naval Research Laboratory Space Science Division also contributed to the study.
The scientists used historical Hubble Space Telescope data, which was used to conduct their study and track GJ 887 in the ultraviolet.
They discovered that the star flashed hourly, defying earlier conclusions based on information from NASA's Transiting Exoplanet Survey Satellite (TESS), which revealed that there were no discernible flares throughout the length of 27 days of nonstop monitoring.
In contrast to many more recent space observatories, Hubble is better suited to searching for flares in the UV band, which was the crucial step. This enabled their team to conclude that GJ 887 was in fact "boring," as Shkolnik outlined:
"Knowing that monitoring stars in the typical optical spectrum, like the TESS mission does, doesn't even begin to give the whole picture is exciting. Only UV measurements, like those from the Hubble Space Telescope, can properly explain the harmful radiation environment of these worlds."
These results are especially depressing since they show once again that red dwarf stars, the most prevalent stars in the Universe (representing 75% of stars in the Milky Way alone), tend to bombard host planets with dangerous radiation.
This has made them an important component in humanity's hunt for habitable exoplanets along with their propensity to host rocky planets, like Proxima b or TRAPPIST-1's seven planet system.
Red dwarfs are not only prone to flare-ups, but they can also be deceitful in their methods. They may often release flares that are only visible in other wavelengths, despite the fact that they may look quiet in visible light (as GJ 887 demonstrated).
Each flare will result in a bombardment of fast-moving particles that might remove the atmosphere from an orbiting planet since UV photons have a lot more energy than visible light photons.
According to Shkolnik, "a star's ultraviolet emission is truly an important, if yet unsolved, jigsaw piece to our knowledge of planet atmospheres and their habitability."
Although essential, astronomers presently lack the resources to carry out these investigations. Fortunately, there are plans to change this by sending missions that can cover the gap.
The Star-Planet Activity Research CubeSat is a CubeSat mission that ASU is spearheading the construction of (SPARCS). This satellite will provide scientists UV observation time, with Shkolnik serving as the mission's lead investigator.
They will be able to see flares originating from M-type stars and gauge their frequency and strength, giving them information about the likelihood that life may develop on these exoplanets.
"M stars are playing those dice significantly more than any other form of star," said Loyd, "assuming the origin of life on a planet is more or less a roll of the dice."
Additionally, as previous studies have shown, red dwarfs' propensity to flare up need not always result in any planets surrounding them being barren and lifeless. In reality, it has been discovered that a favourable environment and cloud cover would provide a window for the emergence of life.
This implies that planets like Proxima b, which circles the red dwarf star Proxima Centauri and is closest to our Solar System, might really support a stable environment and life on its surface!
On the other hand, it's certainly plausible that the planet is a "water world," with seas that are inconceivably deep. The only way to learn is to continue monitoring, and maybe one day send an expedition there.
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