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Far Ultraviolet Flares an Issue for M-dwarf Planets

SPARCS is the name of a CubeSat-based space mission out of Arizona State University, the acronym standing for Star-Planet Activity Research CubeSat, with astronomer Evgenya Shkolnik as principal investigator. The idea here is to look at ultraviolet flare activity on M-dwarf stars, a wavelength about which we could do with a great deal more information. The plan is to target specific stars that will be observed continuously over at least one complete stellar rotation, which could be anything from five to forty-five days.

That this is a good idea is borne out by what we are learning about GJ 887, also known as Lacaille 9352 and known to be orbited by at least two planets. Located in the southern constellation of Piscis Austrinus, the star has the fourth highest known proper motion, with parallax measurements indicating it is a bit less than 11 light years from the Sun. It is one of the brightest M-dwarfs in our sky. When TESS (Transiting Exoplanet Survey Satellite) fixed its gaze on GJ 887, it found no detectable flares over 27 days of continuous observation.

Which goes to show how much older data can help us. Fellow ASU astronomer Parke Loyd worked with Shkolnik and co-authors from the University of Colorado, Boulder and the Naval Research Laboratory (Washington DC) to demonstrate on the basis of Hubble Space Telescope data that GJ 887 is anything but a quiescent star. In fact, its flares occur on an hourly basis, the spikes in brightness showing up only at ultraviolet wavelengths. The paper on their findings has been published as a Research Note of the American Astronomical Society. Says Shkolnik:

“It is fascinating to know that observing stars in normal optical light (as the TESS mission does) doesn’t come close to telling the whole story. The damaging radiation environment of these planets can only fully be understood with ultraviolet observations, like those from the Hubble Space Telescope.”

Image: Violent outbursts of seething gas from young red dwarf stars may make conditions uninhabitable on fledgling planets. In this artist’s rendering, an active, young red dwarf (right) is stripping the atmosphere from an orbiting planet (left). Credits: NASA, ESA and D. Player (STScI).

At an estimated age of 3 billion years, GJ 887’s lack of detectable flares and scarce rotational variability is belied by the Hubble findings, an indication that atmospheric erosion is a serious concern for the two and possibly three planets we thus far know about. We’re now learning that flare activity in the far ultraviolet (FUV) may be a feature of numerous M-dwarfs. Here is part of the paper’s Figure 1, illustrating how GJ 887 looks at these wavelengths.

Image: Archival far-ultraviolet (FUV) data of GJ 887. Top panel: The FUV spectrum of GJ 887. Credit; Loyd et al.

The authors note that X-class solar flares, major events that can trigger long-duration radiation storms, are almost always accompanied by coronal mass ejections, and add that far ultraviolet flares with equivalent durations occur every few hours on other M-dwarfs across a wide range of emission levels and ages. The paper continues:

GJ 887’s similar rate of FUV flares strengthens the possibility that all early to mid M stars share the same FUV flare frequency distribution (FFD) when cast in equivalent duration. This universal M-star FFD implies that most of the molecule-splitting FUV photons M-star planets receive could be delivered in short, intense bursts that are not captured by sparse and brief FUV observations (Loyd et al. 2018a).

The paper speaks of the need to account for the “hidden UV lives” of M-dwarfs, whose radiation may have a great deal to say about photochemistry, heating and evaporation in the atmosphere of orbiting planets. At GJ 887, we may be looking at a system whose planets lost their atmospheres through erosion from such flares long ago. The goal of the SPARCS mission is to provide the extended observing time needed to extend our knowledge of flare activity on the most common type of star in the galaxy.

The paper is Loyd, “When ‘Boring’ Stars Flare: The Ultraviolet Activity of GJ 887, a Bright M Star Hosting Newly Discovered Planets,” Research Notes of the AAS Vol. 4, No. 7 (20 July 2020) (full text).


Comments on this entry are closed.

  • Geoffrey Hillend August 28, 2020, 15:50

    Although an M dwarf exoplanet’s original atmosphere could in potential be completely lost by solar wind stripping and erosion from flares, there is still the possibility of some kind of volcanism and an atmosphere especially with an close to Earth sized exoplanet.

    • Bruce D Mayfield August 28, 2020, 23:53

      That’s right, and in addition to outgassing from volcanism there could be accretion from comets. Large mass helps, but a long duration magnetic field would still be needed for a RD planet’s atmosphere/ocean to rebuild after the star’s flaring tappers off.

    • Michael Fidler August 29, 2020, 5:03

      Plus replenishment from the cometary cloud around these stars. One problem that should be investigated is how large the Oort type comet cloud is and how long it may supply water to these planets. Looking at the results from ALMA around Proxima Centuria, it shows two rings that may be made up of comets.

      The other problem is we have no real idea of where on the surface of red dwarfs the Far Ultraviolet Flares form. Red dwarfs are fully convection where solar type stars are radiative near the core and convective on the outer zone:
      The Sun’s flares and coronal mass ejection (CME) develop north and south of the suns equator closer to the poles as the 11 year sunspot cycle starts. They reach maximum some 5 to 6 years later and are much closer to the equator of the sun. Red dwarfs may be like a boiling pots of water and flares and CME’s cold be near the magnetic poles of the star. Hopefully SPARCS may be able to clarify the situation but just as earth is not effected by CMEs and flares near the sun’s edge, planets around red dwarfs may miss the radiation from these storms. We are dealing with a different beast in red dwarfs then from the sun. Take a look at Jupiter, clouds near the equator form bands till you look near the poles where they form large vortices. Jupiter’s south pole:
      Jupiter’s north pole:

      • Michael Fidler August 29, 2020, 10:10

        Carrington Event still provides warning of Sun’s potential 161 years later.


      • Michael Fidler August 31, 2020, 4:11

        There is another situation that could be causing the UV flaring in red dwarfs in the same matter as Io and Jupiter. A earth to super earth iron core planet in a close orbit such as around GJ 887/Lacaille 9352 b would have a strong magnetic field and create a huge Io type flux tube that connects to the Red dwarf. This may cause both regular sunspot type flares plus UV flares and CME’s in the polar regions of the star. This may protect the other planets in the system GJ 887 c and d from the stellar storms and atmospheric erosion.

        This schematic of Jupiter’s magnetic field shows the Io plasma torus (red), which is filled with energetic charged particles, and Io’s flux tube (yellow-green), which connects Io to Jupiter’s upper atmosphere like a giant umbilical cord, spawning auroras near the poles of the planet.

        • wdk September 6, 2020, 12:46

          The Io and Jupiter illustration provided appears apt. At the very least, it shows how complicated the situation can be. At first mention or read, it reminds of how bombarded the surface of Io has been by charged particles – and deficient in many volatile materials as a result, not habitable as generally understood.

          Also it distinguishes the situation of Io from the other Galilean satellites. Magnetosphere flux elsewhere does not vanish, but it is still intense.

          Still, looking at the result, why does all this flux channel to Io?
          Not that I would like it better otherwise, but why isn’t the phenomenon repeated? Is it not that Ganymede has the largest magnetic field of the four satellites? And how about Amalthea? It’s close in and reddened by weathering from charged particles too.

          It is fair to say that the Jupiter system has many parallels to what we see or might find among red dwarf stellar systems, but some features of G stars might be worth considering too. Say if the sunspot cycle from northern to southern hemisphere reflected a reversal in polarity or reduction in intensity, would that mean that a torus would die down, reverse direction or re-attach to a different orbiting body? I don’t know anything about red dwarf sunspots, but I enter it as a consideration on this overall question: can an HZ be established close to a red dwarf?

  • Robert Flores August 28, 2020, 18:31

    I am trying to Imagine how a primitive single celled alien life, could survive, on a planet orbiting a flaring M dwarf. The main issue is atmosphere bleed off, plus H20 Dissasociation. Assuming a planet is tide locked, it will still lose most the dark side H2O too while it retains an atmosphere to transfer heat. On Earth, we have places deep in the crust where water is trapped by geological events, being removed from the water cycle. This oasis combined with chemical reducing single-celled organisms come to mind. But even this type of life is limited in duration due finite energy source for the microorganisms. When we explore these M-dwarf orbiting planets in the far future and examine their geological strata, I am sure the geological record will show than any microorganisms will turn out to have existed for only a few hundred million years.

    • Andrei August 31, 2020, 9:28

      You said it in your first sentence, it is hard to imagine life to get started at all under circumstances like the ones found on a world like this. Even less how it could develop into higher life forms.
      Now that we know these planets are very common, I can imagine the very rare case where the planet had enough gas and water from the start that it had enough volatiles to bleed off and then had the luck of a primary that develops into one unusually quiet red dwarf.
      Finding such a world will be finding a needle in a haystack, but such an oasis world can not be completely ruled out – from the data we got right now it’s still going to be a very rare case though. And if it got a moon, it might even have rotation. So lets keep looking. :)

  • Robin Datta August 29, 2020, 1:49

    Any complex organization approaching biological life needs a means of receiving messages (serving as “blueprints”) of sufficient complexity from prior generations, and transmitting them to future generations. Each unit of information would be represented by a moiety, and all the moieties must maintain an organization decipherable in each generation. The more complex the organism, the larger the “blueprint” needed (although in many instances the size of the genome may exceed such expectations).

    The larger the blueprint, the more susceptible it will be to disruption by radiation, heat, chemicals, etc. The demands of abiogenesis may be more fastidious than those of evolved and adapted descendants.

    However, the presence of alien simple life forms or their remains elsewhere would suggest that they are ubiquitous. And as has been suggested, in such a case, the absence of advanced forms with interstellar travel and megastructures might indicate a Great Filter still ahead of us.

  • Ryan Carthy August 30, 2020, 19:09

    Hasn’t it already been determined that the Trappist-1 planets (for example) have significant atmospheres? If this is true then UV flux this high on these kind of stars isn’t insurmountable.

  • ljk August 31, 2020, 9:21

    Planets Close to Their Host Stars May Be Habitable, but There’s a Catch

    A dusty atmosphere will increase the chances of life existing, but also make it harder to find.

    By Dirk Schulze-Makuch


    JULY 15, 2020

    In a new study published in Nature Communications, Ian Boutle from the University of Exeter in the U.K. and his British colleagues showed that mineral dust can increase the habitability of Earth-like exoplanets, especially those that are tidally “locked,” meaning that they always keep the same face toward their host star.


  • Laintal September 4, 2020, 6:24

    Hi Paul

    I was just reading these two

    The High-Energy Radiation Environment Around a 10 Gyr M Dwarf

    Utilizing a Database of Simulated Geometric Albedo Spectra for Photometric Characterization of Rocky Exoplanet Atmospheres

  • wdk September 9, 2020, 20:44

    Coincidentally, had reason to review Zeeman lines and stellar magnetic fields. It seems like Hale and Babcock 80 to 100 years ago pioneered the work with identifying splitting lines in solar spectra and isolating the phenomenon to inside and outside of sunspots. Then the work went on with the brighter stars. Babcock created a catalog. White dwarfs and
    neutron stars are shown to be intensely magnetic …

    Now what about red dwarfs? If the magnetic fields could be characterized – and probably are already – then maybe we can assess the direction of or correlate conditions of flare activity – in or out of assumed orbital plane.