Red Dwarfs Have Teeny Tiny Habitable Zones

Article written: 11 Jan , 2008
Updated: 26 Dec , 2015

As space telescopes get larger and more sensitive, the search for Earth-sized worlds surrounding other stars is about to get rolling. But astronomers are going to need to know where to look. A team of researchers are working on a survey of nearby stars, calculating the habitable zones around them. When the search begins, astronomers are going to want to study these regions.

The Research Consortium on Nearby Stars (RECONS) is a survey using relatively small telescopes to study the habitable zones in the nearby stars. The team uses measurements of various stars brightnesses at optical and infrared wavelengths matched with their distances to get a sense of the stars’ habitability.

After gathering together a big list of potential candidate stars, the researchers can then categorize stars by size and temperature to find ones that might harbour life.

“Once we have good values for the temperatures and sizes of the nearby stars, we can estimate how hot planets will be at different distances from the stars,” explains Justin Cantrell, a Doctoral Candidate in Astronomy at Georgia State University. “We consider those stars that would have surface temperatures suitable for liquid water to be in the traditional habitable zone.”

The researchers were looking for habitable zones around red dwarf stars, which can be 50-90% smaller than the Sun and much cooler. The comprise 70% of the stars in the Milky Way, but they’re harder to spot because they put out less light.

They were surprised to learn that these red dwarf stars have tiny habitable zones. When they added up the habitable zones of 44 red dwarf stars nearby the Sun, they found they didn’t add up to equal the habitable zone of a single Sun like star.

So even though these red dwarfs are common, they’re not great candidates for life. Earth-type stars would need to be perfectly positioned in their tiny habitable zones to be good candidates for life.

Original Source: Georgia State University News Release

17 Responses

  1. Fabio Knopf says

    “[…]they’re not great candidates for life. Earth-type stars would need to be perfectly positioned[…] ”

    I think it is “Earth-type planets “? You mean rocky planets?

    By the way, you do a remarkable job. Really. Thank you so much!

  2. The Fool says

    Do you know what percent of the stars in our galaxy are similar to the sun? Thats too bad that the red dwarfs have such small habitable zones it reduces the amount or chance of life in the galaxy by a good bit.

    The Fool

  3. maxim says

    Exoplanets dwarfs. Habitable zones live the galaxy.

  4. alfonso padilla says

    i wonder if there is any possiblitiy that a moon around one of these big gas planets harbor life?

  5. Frank Winkler says

    “Nearby Stars”, What is the definition of “Nearby Stars”.
    How many Light-Years away are they.
    If we find Life on “Nearby Stars”, what impact will it havev?
    I believe it will have a huge effect on some scientific theories.
    However, will it really make a difference to scientifice research? Other than astronomy?
    Interlectually its incredibly exciting.
    However are the other effects even the interlectual ones way exagerated? Perhaps for selfish reasons such as funding of research.

  6. Greg says

    Red dwarfs are the most common type fo star in the galaxy. They are more numerous and much longer lived since they burn their fueld much more slowly than larger stars. As a result they generate less radiation and heat and therefore teh habitable zones are smaller. They are too dim to be seen without powerful telescopes unless they are very close by. Life can exist around a large moon around a gas giant in the habitable regions of these stars.

  7. To “The Fool”:

    As far as sun like stars go, we have no further to look than our nearest (triple) companions, Alpha Centauri.

    As far as “an exact” match, I remember one star being hailed called HIP 56948 (Google it for more info).

    Either way, I wonder, what about blue stars? Are they more/less favorable for habitable planets than our regular sun?

  8. RUF says

    “Habitable zones” can be increased if planets have massive greenhouse effects, or a shell of ice over an ocean. Also, life can exist at the bottom of oceans around vocanic vents.

    This doesn’ take into considereation the fact that water may not be needed for alien life. This insistance on liquid water for life is tiresome.

    What about crystaline life-forms? Remember “alien” means “alien.” We may not even recognize alien life when we see it.

  9. RUF says

    What if life is found on Europa? It is not in Sol’s “Habitable zone.”

  10. passerby says

    But it’s apparently in Jupiter’s hab zone.

    The Hab Zone is simply the distance at which water will be liquid due to temperature from solar radiation. As was mentioned, there are other things that can affect whether water can be liquid, like albedo and greenhouse and heck, even gravitational mucking. But we don’t completely understand whatall goes into MAKING things like greenhouse.

    Earth itself was very inhospitable for a long time. Only single-celled organisms could survive. A little closer or farther from the sun, and they might not have.

    If Venus or Mars were ever habitable, it didn’t last long enough for life to really take hold. There might still be something in either place, as Life can be rather tenacious. At most, we will find bacteria there. I suspect we’ll find lots of bacteria, and that it will all be related, to whatever extent can be detected from something that evolves in hours or days rather than millenia or megayears.

    The big question is, will we ever find complex life, and complex life has a fairly narrow band of tolerances, and this is what Hab Zone will come to mean when bacteria is discovered all over the place.

  11. Ed Oleen says

    “Red Dwarfs have Teeny Tiny Habitable Zones”

    On behalf of red dwarfs everywhere, some of whom are my best friends, I wish to complain of their being stereotyped. You wouldn’t call a tall people basket-ball players, would you?

    And anyway, what research has been done to measure the mean size of red dwarf habitable zones, or to determine the statistical significance of any difference in size between their habitable zones and those of white dwarfs or those of normal people of any color.

    If you are talking about the habitable zones and temperature of stars, I would remind you that stars, in general, like, fer example Britanny Spears, are HOT HOT HOT.

  12. Nick Mascall says

    It may also be worth pointing out another inhospitable characteristic of small stars – they seem to be significantly more prone to major flares and large-scale luminosity variations.

    Small habitable zones are bad enough. Fluctuating, fast-moving habitable zones are much worse.

  13. andy says

    Why exactly is this a surprise? If you scale anything up or down, for the smaller scales, it will end up smaller. For habitable zones you scale by the square root of the luminosity of the parent star, so obviously for a low luminosity you get a small zone.

    However, nature seems to like logarithms. If the planets in planetary systems are spaced approximately logarithmically, this isn’t so much of a problem, since you get more planets close to the star (in fact, scaling the habitable zone does not change its width on a logarithmic scale). In fact both Gliese 876 and Gliese 581 have two planets each which are in or close to the habitable zone.

    So all-in-all, a bit of a non-story.

  14. Ray says

    Great article Fraser. Most astronomers don’t want to limit themselves to the obvious in their quest for ET life forms. I would prefer to reduce the search to the most likely prospects. Research in space isn’t just limited to the search for life. There is much to learn about phenomena that has nothing to do with a life. We know of at least one yellow star that supports life on a nearby planet so yellow stars are the obvious place to start looking. There is virtually no chance of any life developing on a dwarf star yet alone surviving there. Rule out the bright stars too, they have a nasty temper. The notion of a rocky planet orbiting a gas giant isn’t feasible either; the tidal effect keeps the same face toward the giant and creates a day that is many Earth days long (for example 28 days on our moon) and makes for a long cold night. Gas planets produce a huge shadow but they provide high reflectivity too. I’d rule the thought out too.

    Finally, binary star systems are common but not likely to be hospitable to life on any planet that orbits one of them. Young yellow stars aren’t good candidates either, they need to be more than 3 billion years old, preferably in the 4-5 billion year range to be the most stable. This reduces the number of stars to no more than 1 in 100 that are worth looking for habitable planets around. The odds of a planet – one to maybe three times the size of Earth being in the habitable zone are let’s say 1 in 10. I don’t know. I’m not claiming that my numbers are accurate, but if only one in a thousand stars had the potential of life, that would still be more than a million sources of life in our galaxy. Now that is exiting! Spread them out through the arms of the galaxy and hundreds of them could be in “near spaceâ€? by my definition. I suspect that the term “nearâ€? has probably changed a lot in our life time as the number of large telescopes and optical arrays increased.

  15. Tony says

    By the same token, hotter brighter stars will have larger habitable zones, though their shorter lifespans will preclude the development of complex life forms, before they go BANG! :oP

  16. superalien says

    why do alien life forms need water???
    you cant tell that looking only at one plant!
    you cant know for sure there arent life on ploto or even neer the core of the moon!
    maybe on other stars life will need liquid iron and helliom to survive and they will like your old roller mouth (for the computer) and they will be more involved then us
    forgive me for bed spelling im not a native english speaker

  17. Bruce says


    We don’t know of course if some alien life forms might exist that have no need for water – but the problem is that we don’t have any examples available to know what chemical reactions they might use. On the other hand we do know of at least one example of a family of life-forms that do require water, and we understand a good deal about their chemistry. (“At least one” because there is still some debate about whether life on Earth evolved only once – the majority view – or multiple times).

    So granting that some other life forms might exist, how might we detect them? We have a pretty good idea that if we observe molecular oxygen (O2) on another planet, it’s likely to be the result of photosynthesis from water-based organisms. What do we look for in order to detect non-water-based life? Since we don’t have an example, we don’t know – except to look for “unusual” spectra that we can’t explain any other way. It will most likely be many centuries (if ever) before we will be able to detect alien life directly, say by detecting signals from intelligent beings or actually being able to image the effects that alien lifeforms might be having on their world. We should be able to get spectra from those worlds much sooner.

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