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Two Planets Around Nearby Gliese 887

Red dwarf stars have fascinated me for decades, ever since I learned that a potentially habitable planet around one might well be tidally locked. Trying to imagine a living world with a sun that didn’t move in the sky was the kind of exercise that I love about science fiction, where playing with ideas always includes a vivid visual element. What kind of landscapes would a place like this offer to the view? What kind of weather would tidal lock conjure? Stephen Baxter’s novel Proxima (Ace, 2014) is a wonderful exercise in such world-building.

Thus my continuing interest in the splendid work being done by RedDots, which takes as its charter the detection of terrestrial planets orbiting red dwarfs near the Sun. You’ll recall that this is the team that discovered Proxima Centauri b, a star under increased scrutiny of late as other potential planetary signals are examined. RedDots also gave us Barnard’s Star b and has found three planets around the red dwarf GJ 1061.

Now we learn about a system of super-Earths orbiting nearby Gliese 887, which is the brightest red dwarf in our sky (as per RECONS, the Research Consortium On Nearby Stars). More massive than the Earth but smaller than the ice giants in our system, the two worlds may or may not be rocky — this is radial velocity work, so we have only minimum mass figures to work with. The minimum masses reported in the paper in Science are 4.2 ± 0.6 and 7.6 ± 1.2 Earth masses (M). My guess is that these planets are more like Neptune than Earth, but we’ll see.

The RedDots team found the two planets using the HARPS spectrograph at the European Southern Observatory in Chile. There is also an unconfirmed signal with a period of roughly 50 days, possibly a third planet of a similar mass, but note this: “We regard the third signal at ~50 days as dubious and likely related to stellar activity.”

Lead author of the paper is Sandra Jeffers (University of Göttingen), who notes the opportunity this system provides astronomers for follow-up work. The two planets have orbital periods of 9.3 and 21.8 days respectively and circle a star that is about 11 light years away. A space-based observatory might be able to tease out their reflected light. From the paper:

GJ 887 has the brightest apparent magnitude of any known M dwarf planet host. This brightness, combined with the high photometric stability of GJ 887, exhibited in the TESS data, and the high planet-star brightness and radius ratios, make these planets potential targets for phased-resolved photometric studies, especially in emission. Spectrally resolved phase photometry has been shown to be sensitive to the presence of an atmosphere and molecules such as CO2.

Image: Dr Sandra Jeffers. Credit: University of Göttingen.

The team believes that the star has few starspots:

The TESS variability can be explained by one starspot, or a group of starspots, with a total diameter of 0.3% of the stellar surface, indicating that GJ 887 is slowly rotating with very few surface brightness inhomogeneities.

And that’s interesting because it implies a lower value for the star’s stellar wind, which could cause planetary atmospheres to erode and, if strong enough, conceivably strip them altogether. Thus the likelihood that there may be atmospheres on these planets, which renders them interesting potential targets for the who-knows-when-it-will-fly James Webb Space Telescope.

Image: Artist’s impression of the multiplanetary system of newly discovered super-Earths orbiting nearby red dwarf Gliese 887. Credit: Mark Garlick.

The paper is Jeffers et al., “A multiplanet system of super-Earths orbiting the brightest red dwarf star GJ 887,” Science Vol. 368, Issue 6498 (26 June 2020), pp. 1477-1481 (abstract).

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{ 13 comments… add one }
  • Mike Serfas June 30, 2020, 14:32

    The suggestion of a large sunspot on a small star is interesting. With the Sun, we always thought of sunspots as having a trivial effect, appearing when the Sun is actually brightest; but in articles like https://phys.org/news/2020-06-giant-star-betelgeuse-dimming.html we are seeing notions of sunspots that swallow half a star, as if during some previous eclipse the lazy villagers had failed to use their pots and pans to scare off the dragon.

    When we place a large magnetic convection shelter on the surface of a small star, is it time to start wondering? If you go to Wikipedia their phase diagram of carbon shows a line between liquid and solid from the triple point headed out toward infinite temperature. I found a couple of old papers that read that way, one with the suggestion of a metallic phase, but most seem to believe the line doesn’t really go much above 5000 K. Still, the phase diagram might bear annotation: “here there be dragons!”

    So when we have a small cool star with a big cool spot… just maybe it is possible to find a place middling deep beneath the surface, not too hot, with a wonderland of precipitated solid carbon in its countless allotropes, conducting and insulating, doped with a bit of nitrogen and oxygen, interacting with ceaselessly changing magnetic fields to harvest unlimited amounts of electrical energy? As possibilities for extraastral ? life go, that would be outright conventional. What sort of diamond-skinned fire-breathing beast do you suppose might fly around guarding these spots? :)

    • wdk July 1, 2020, 11:49

      Mike Serfas,
      When you mentioned the metallic or degenerate phase of hydrogen, it did remind me that red dwarf stars, brown dwarfs and gas giant planets experience that state as you dig your way down to the center – and G types main sequence stars like the sun do not. And since Gliese 887 is a rather bright RD, it makes me wonder: does it resemble the sun more than the typical RD – and does that have anything to do with the size and depth of its metallic hydrogen envelope? I don’t have a quick answer to that; maybe someone else does. But with two planets of several Earth mass ( taking into account maybe 40% more than the nominal what with doppler estimates), there is great likelihodd of considerable entrapment of volatiles simply due to planetary escape velocities.

      Then, there is the question of magnetospheres. It is logical or likely that the planets orbit synchronously, unless something periodically disturbs
      their equilibrium states ( fluid or sediment buildups?). Given how odd and unpredictable magnetospheres are in the solar system, it might not be out of the question for these planets to have magnetospheres – and that could cause some deflection of RD flare events.

      In effect, it is hard to predict whether these two planets have too little or too much atmosphere and ocean. They could be very interesting examples of separately shaken martinis.

      • Mike Serfas July 1, 2020, 16:19

        I’m not familiar with metallic hydrogen in red dwarf stars, but I know it is widely believed to be present in brown dwarfs. Maybe cooler spots on red dwarfs could have this also, which would certainly make the chemical basis of a hypothetical ecosystem more interesting!

        Actually, the source I found was talking about metallic carbon – http://cds.cern.ch/record/691793/files/project-note-78.pdf Looking into it further, I found a reference about diamond and “BC8”, something which occurs at even higher pressures (?!), both with a melting point around 8000 K at immense pressures. https://ui.adsabs.harvard.edu/abs/1997PhPl….4.2011H/abstract There are more recent sources for carbon remaining solid at 6000 K at least: https://www.researchgate.net/figure/Phase-diagram-for-carbon-D-diamond-G-graphite-CNT-carbon-nanotubes-L-carbon_fig1_307085281 How it would interact with the surrounding hydrogen is another question…

        As a matter of sci-fi, the notion of a sunspot even conceivably having solid carbon-based organisms around sounds like a lot of fun. From the first days of radio, people have been complaining about the sunspots trying to communicate with us and fouling up their reception! :) A conductive carbon organism would surely have intimate interactions with the magnetic fields of its local spot. Such an organism might have a different sense of time a bit like in Forward’s “Dragon’s Egg”. What if someone designed and aimed a large antenna to communicate with a specific sunspot … and started getting answers? It might be good to set this one in the 1950s.

        • Robin Datta July 4, 2020, 5:23

          Prior to the microscope the ubiquity of the microbial world was unimagined and unknown.

          Careful parsing and deciphering might well resolve the cacophony of electromagnetic noise in the universe into massive bandwidths of conversations. Or perhaps the equivalent of nerve signals between parts of brains across interstellar distances.

          If the sources were within red dwarves themselves, chemical-biologic life could be considered by them to be truly ephemeral and hence ignored.

        • wdk July 4, 2020, 12:26

          Mike Serfas,
          Thanks for the reply and the lead on that issue. Checking around, and perhaps in acknowledgment of what you said, it does appear that convective heat transfer through large portions of the radius of RDs is responsible for their long life. Had
          there been radiative transfer, the hydrogen fusion fuel would have been cut off from the core due to buildup of fusion products, and the trillion year lifetimes of M dwarfs would not be possible. So hence, there would not be much room to hide
          a metallic hydrogen segment similar to a gas giant or brown dwarf.

          This picture seemed to build up over decades. Osterbrock had a paper in 1953 suggesting as much. Though looking at a Red Dwarf characteristic summary in Wikipedia, it is noted that this picture applies to RDs less massive than .35 solar mass. What kind of corner turns after that…?

          • Mike Serfas July 6, 2020, 19:17

            Metallic hydrogen really is useful in speculating about red dwarf ecosystems, because of the typical gas-giant issue of needing to stay aloft. There are speculations that metallic hydrogen could be a room temperature superconductor ( https://phys.org/news/2019-03-superhydrides-approach-room-temperature-superconductivity.html ) just as there are some indications that graphene may be superconductive over 500 K ( https://www.reddit.com/r/Physics_AWT/comments/5j5mkd/superconductivity_above_500_k_in_conductors_made/ ). If we’ve come from a few kelvins to that sort of temperature, why not go hog wild and speculate about superconductors in sunspots? Superconductor plus magnetic field leaves us with magnetic levitation, and metallic hydrogen helps in being very light though not so light as plasma. A process of (at least) “chemical selection” might accumulate such compounds at a long-lived starspot.

            The magnetic fields of starspots offer some protection from convection – how much I don’t really understand, and I don’t know how much the corona illuminates the sky above them. The core of the Earth is probably about as hot as the photosphere of the Sun, so if only in concept a few thousand miles of insulation could leave you with a starspot cool enough for afternoon thunderstorms. Sunspots are said to be planet-sized and can be detected 60,000 km beneath the Sun’s surface before they are visible to the eye ( https://www.nasa.gov/mission_pages/sunearth/news/sunspot-breakthru.html ). So we seem to have enough tools here, given a whole lot of optimism, to build a framework for some sort of solid object to be found in a starspot. Pending further data, we might take as many liberties as our imaginations allow.

            It should be noted that in one way red dwarf stars are not as friendly as the Sun, having half the mass but half the radius so twice the Sun’s 28g surface gravity. On the other hand red giants like Betelgeuse, with 887 times the radius of the Sun, have only something like 0.04% of Earth’s gravity, which is bad for the bones, even if those giant starspots might promise some cool scenery. The red subgiants I looked up have higher than Earth gravity; it would take some digging to find one at a comfy 1 g. There’s something of a lack of online resources evaluating stars for human colonization. :)

  • Enzo July 1, 2020, 8:25

    I have Proxima from Baxter and I haven’t talked myself into reading it yet. I never finished Ark, even though I was almost captive on a 24 hours flight from Sydney to Rome when the only alternative was the entertainment system of the plane (sigh). I didn’t even get to the point when they leave earth. I just couldn’t. Paul’s remark that Proxima “is a wonderful exercise in such world-building” makes me want to try it but, at the same time, bad memories hold me back.
    Mayne someone can give me a word of encouragement or at least let me know how much I have to go through before I get to the “world building” bit.

    • Paul Gilster July 1, 2020, 9:54

      Enzo, I really enjoyed Proxima, but then, I also enjoyed Ark. But hey, we all have our own taste in these matters, so perhaps readers here can suggest some other such exercises in world building that will be more to your liking.

    • Simon July 3, 2020, 13:35

      I may have just read one story-line* of proxima, but then read all of and really enjoyed the sequel, Ultima.
      *I skipped the flashback storylines of humans, but read about the aliens history and the present storyline humans

  • Spaceman July 1, 2020, 11:11

    Does anyone know if the RedDots campaign is looking for planets around the two “nearby” red dwarf stars Ross 154 and Ross 248 (each of these stars is approximately 10 light years away from our solar system)?

  • Michael Lorrey July 1, 2020, 14:42

    given the correlation of our own sun’s variability with Jupiter/Saturn orbital dynamics, I would not rule out a planet in that 50 day slot, it could easily be a jovian whose influence would explain the large size of the sunspots.
    as for JWST, when is NASA going to put its foot down and demand fixed price with performance penalties of Northrup Grumman.???

  • laintal July 1, 2020, 20:23

    Hi Paul

    “Red dwarf stars have fascinated me for decades” Yes me too that’s why your site here has really captured my interest again.

    I’m still reading proxima and I really enjoyed Nemesis
    https://en.wikipedia.org/wiki/Nemesis_(Asimov_novel)

    Great post and an interesting Planets

    • ljk July 2, 2020, 12:36

      While it may be problematic if native life forms can arise on worlds around red dwarf stars, the incredible longevity of these suns and the high possibility that their systems contain no potentially problematic natives may make them highly desirable to advanced interstellar-capable ETIs looking for resources, a place to dwell, and who knows what else.

      Although fictional, the Orion’s Arm site gives us some ideas as to how post-Singularity Artilects and other advanced species might utilize red dwarf systems. In any event, this alone may make them suitable targets for SETI if we can catch their technological activities and noise.

      https://www.orionsarm.com/eg-article/476465c5b3138

      https://www.orionsarm.com/eg-article/4703bf9ef0270

      We just have to keep thinking outside the box in order to succeed.

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