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SETI Looks at Red Dwarfs

When it comes to astrobiology, what we don’t know dwarfs what we do. After all, despite all conjecture, we have yet to find proof that life exists anywhere else in the universe. SETI offers its own imponderables, adding on to the question of life’s emergence. How often does intelligence arise, and if it does, how often does it produce civilizations capable of using technology? Even more to the point, how long do such civilizations last if they do appear?

We keep asking the questions out of the conviction that one day we’ll start retrieving data, perhaps in the form of a signal from another star. It’s because of the lifetime-of-a-civilization question that I’m interested in a SETI search focused on red dwarf stars. True, M-dwarfs have a lot going against them, as Centauri Dreams readers know. A habitable planet around an M-dwarf may be tidally locked, which could be a showstopper except that some scientists believe global weather patterns may make at least part of such planets habitable.

Flare activity is always an issue on younger M-dwarfs, though it’s possible to conceive of this as an evolutionary spur, and we can’t rule out life’s ability to adapt to extreme circumstances. But despite all these unanswered issues, my interest in these stars draws primarily from two main points. First, they are the most common stars in the galaxy, comprising perhaps as much as 80 percent of the total. That gives us a huge number of candidates for life and potential civilization.

And while we can’t say how long civilizations live, not being sure if we ourselves will survive, we can take heart from the idea that if enough of them come into being, at least a few may get past whatever culture-shredding ‘filter’ they encounter to move into a serene maturity. Here red dwarfs truly stand out, because they live so much longer than any other stars. Every red dwarf that has formed in the universe is still there, and we can expect such stars to live for trillions — not billions — of years.

I like the odds, but I’m also trying to imagine what a civilization would look like a billion years after the emergence of tool-making. Or five billion. If a culture can survive for aeons, it will have mastered issues of conflict that plague us daily and much else besides. Surely a mature species long past emotional and technological infancy would want to know about its neighbors. Would such a culture reach out to others, if only to exchange notes? Or would it have moved into realms of philosophy and thought that make all this irrelevant?

We’re deep in imponderables here, but all we can do is look and listen. Thus I was pleased to see that the SETI Institute is initiating a search using the Allen Telescope Array that targets red dwarf stars. As the Institute’s news release explains, we now believe that somewhere from one-sixth to one-half of red dwarfs have planets in their habitable zones, which is a percentage that may be comparable to stars like the Sun, and for all we know at this point, may exceed it.


“Significantly, three-fourths of all stars are red dwarfs,” notes SETI Institute astronomer Seth Shostak. “That means that if you observe a finite set of them – say the nearest twenty thousand – then on average they will be at only half the distance of the nearest twenty thousand Sun-like stars.”

That, of course, means that we have a larger population of stars whose potential signal to us would be stronger. The SETI Institute is drawing on a target list of 20,000 M-dwarfs compiled by Boston University astronomer Andrew West, one that will incorporate new data as it is collected by missions like TESS, the Transiting Exoplanet Survey Satellite, slated for launch next year. Using the ATA’s 42 antennae, the red dwarf survey will take two years to complete, working in several frequency bands between 1 and 10 GHz. Says Institute scientist Gerry Harp:

“Roughly half of those bands will be at so-called ‘magic frequencies’ – places on the radio dial that are directly related to basic mathematical constants. It’s reasonable to speculate that extraterrestrials trying to attract attention might generate signals at such special frequencies.”

My assumption is that as resources become available (never an easy matter), SETI will search broadly through the various stellar types — we can’t know what we’ll find until we look. But it’s heartening to find a SETI attempt specifically turning to a category of star that has generally received little attention. It may well be that a race that is deep into philosophical maturity will have moved beyond beaming signals to other stars. It may, for all we know, have moved beyond biology! But let’s keep up the search and learn as much as we can about the small red stars that pepper the cosmos and may, if in any way habitable, hold clues about life’s emergence.


Comments on this entry are closed.

  • Ron S March 31, 2016, 13:28

    “…what we don’t know dwarfs what we do.”

    Nice pun.

    “Roughly half of those bands will be at so-called ‘magic frequencies’ – places on the radio dial that are directly related to basic mathematical constants. It’s reasonable to speculate that extraterrestrials trying to attract attention might generate signals at such special frequencies.”

    It’s also true that at sub-GHz frequencies, where most of our high-power communications take place, is less detectable because of the higher cosmic noise. That is, poor signal-to-noise ratio (SNR) for a given transmitter power. Above 10 GHz you pretty much need to get the antenna into space because of atmospheric absorption. Again, poor SNR.

    I sometimes wonder whether the focus on 1 GHz to 10 GHz is due to motivated reasoning.

  • djlactin March 31, 2016, 13:34

    M stars are not all alike. Very old red dwarfs (1st gen, maybe 2nd) would have formed in a epoch in which elements > Li were almost absent. I think such conditions would preclude evolution of life, and possibly even of planets. Perhaps SETI should examine M stars from later generations, if they can be identified as such.

  • Alex Tolley March 31, 2016, 13:36

    I think one thing we would need to know is how common life is around red dwarfs. If we found it common, then there is a greater likelihood that intelligent, technological life could have emerged. If however, it turns out that red dwarfs are poor abodes for life, then perhaps ETI is best looked for elsewhere.

    I’d love to see a decent survey, like Kepler, in my lifetime of likely living planets, even if the spectrographic bio signatures are not unequivocal.

    Even if ETI is vanishingly rare (perhaps we are unique). living worlds with multicellular life might be much more common, and would make fascinating targets for interstellar probes.

    Unlike “unobtanium” mining on Pandora, the value of biology on alien worlds might be vast. Just as Weyland-Yutani wanted “alien” specimens for their biowarfare programs, the value of biology for humans might be quite extensive for many fields of science.

    Yes, it would be much easier to communicate with friendly aliens, but I think that direct examination with our probes may be extremely productive. Robotic probes doing field studies on a number of worlds would provide a firehose level of scientific data for us, offering new insights and discoveries that could keep our whole world occupied for generations.

  • Ashley Baldwin March 31, 2016, 13:38

    M dwarf habitability is the great battle ground of exoplanet science. But still dominated by simulation without detailed observation. Lots of evidence of nastiness both pre main sequence and indeed often for billions of years after . Proxima , similar age or older to Sol still flares though there are many much quieter ,older stars such as nearby Wolf 1061 with a terrestrial mass planet in its Hab zone .

    For every simulation that pours cold water on their potential for life a counter theory springs up immediately . Wolf 1061 c has a 7 % chance of transiting . If you hope for anything , hope it does. If so it will be a top target for 6.5m JWST’s transit spectroscopy “hit list” ( circa 250 systems if all goes well ) which thanks to Hubble and Spitzer is a technology that has refined quickly. Better for assessing M dwarfs than direct imaging due to their close in planets and a far wider bandwidth too to look for various bio signatures or other interesting “spikes” . Relatively high resolution for Super Earths and even Earth mass planets . Just waiting to pick up TESS and maybe K2 targets .

    Whatever spectroscopic results we find from transiting exoplanets can only be informative and interesting and will I think prove once and for all whether they are potentially habitable even if we doesnt finds signs of life immediately .

    Even a thin Earth mass atmophere in any close in M dwarf planet shows that they can outlast CMEs and flares and transit spectroscopy has already developed to a point that it can determine planetary rotation rates to see if it is true that all habitable zone planets are tidally locked or if the methods put forward by which they can avoid this do indeed apply.

    Never mind long lasting life, many M dwarfs older than Sol may only just be entering their long habitable stage but certainly the older ones ( significantly so compared to Sol) present a good target for SETI. One thing is for sure , if we do find life around an M dwarf it’s going to be incomprehensively alien though .

  • Michael March 31, 2016, 14:44

    My big concern with RD’s is the long luminous contraction phase which could make inner worlds in the HZ bone dry. There is also the deep gravity well these worlds find themselves in, techaliens will find it very difficult to get out of. Remember as the mass of the star falls the luminously shrinks at a steep rate leaving worlds in need of a hell-of-lot of delta V to get out of, it is a serious amount. The flare activity and it can be colossal may also place limits on the time they could spend traveling away from a protective planetary field.

  • Daniel Högberg March 31, 2016, 16:13

    If there are any civilizations out there the reason we dont see any evidence is because of technology. When you can live out all your fantasies, all your dreams and create your own universe in virtual reality there is no need to go to the stars. The VR-world will go from crude to indestinguishable from the real thing in a very short time and everyone will go in never come out, the best drug in the world.

  • DJ Kaplan March 31, 2016, 16:41

    @Alex Tolley, I agree that the discovery of “space bugs” will be fascinating and revolutionary, and to my mind, much more likely in our lifetimes.

    It’s worth remarking that it’s also easier to find exoplanets around smaller stars such as red dwarves.

  • PW March 31, 2016, 20:53

    I know Red Dwarfs go for a long time.
    Otherwise, they don’t fascinate me much.
    To be close enough to stay warm, you’re tide locked.
    On top of that little problem, they are as prone as any star type to flares.

    Me personally, I would stay with what we know works. Yellow dwarfs that harbor planets with seasons. They can be difficult with flares also.

  • Moebius April 1, 2016, 3:06

    In my opinion, if aliens have moved beyond biology, something that I think is very probable – humanity might do the same in a few centuries (we already developed quite advanced bionics) – it is very unlikely that we can detect them at all. They probably miniaturised themselves at a point where we wouldn’t be able to notice them even if they were a few meters away. Their lifespan might be practically infinite, and they could probably switch their robotic bodies to sleep mode to save energy during thousands of years to travel to other star systems. They wouldn’t need to go fast, they wouldn’t require enormous amounts of energy or giant lasers to go elsewhere in the universe, they could do it simply by using small ion engines and waiting in stand-by mode for hundreds of thousands or even millions of years until they reach their destination. Their fleets in transit would look to us just like some interstellar dust. As their artificial bodies would be able to work on any planet whatever its atmosphere is composed of, even well outside of the HZ or in the vacuum of space as long as they have enough solar power or any other source of energy, they wouldn’t need to have a noticeable impact on a planet’s atmospheric composition and their worlds would look uninhabited and completely inhospitable to biological life from our point of view.

  • Michael Spencer April 1, 2016, 7:31

    “Roughly half of those bands will be at so-called ‘magic frequencies’ – places on the radio dial that are directly related to basic mathematical constants. It’s reasonable to speculate that extraterrestrials trying to attract attention might generate signals at such special frequencies.”

    I’ve wondered about this preoccupation with “magic frequencies”- maybe somebody trying to attract attention would use them, but more likely they are busy with their lives and not thinking about others. Just as we are doing.

  • Harry R Ray April 1, 2016, 10:11

    Paul Gilster: Please log on to the http://www.voxcharta.org website ASAP and scroll down to the astro-ph#44 entry: “Pi in the sky” by Ali Frolop, Douglas Scott. Is this an April Fools joke(I DOUBT it because it was uploaded on 3/31, NOT 4/1)and: IF NOT; could it mean that KIII(OR HIGHER) civilizations could be COMMUNICATING via ANOMALIES in the CMB?

    • Paul Gilster April 2, 2016, 14:49

      Interesting paper, Harry. This is the first I have heard of it, but I’ll give it a closer read in the next few days.

      • djlactin April 3, 2016, 8:09

        If you check out the later references in the list, the authors lose their straight face!

  • Michael April 2, 2016, 12:11

    I have posted this before, but some RD’s will eventually glow blue!


  • Simon G. Farmer April 2, 2016, 22:12

    I had a dream that I was on a planet around an M-class. As I looked around at the alien plants, and the red star overhead, all the plants suddenly contracted or curled up – and I understood it to mean that they detected the precursors of a flare and went into protective mode. After the flare they unfurled their tentacle/fern like leaves.