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Wolf 1061c: A Nearby Habitable Zone Planet?

At no more than 14 light years away, Wolf 1061 gains our attention with the discovery that this small red dwarf hosts three planets, in orbits of 4.9, 17.9 and 67.2 days respectively. Of particular interest is Wolf 1061c, which appears to be within the habitable zone, defined here as the region in which it would be possible for liquid water to exist on the surface, and potentially life. Wolf 1061c has a mass at least 4.3 times that of Earth, with inner planet Wolf 1061b coming in at 1.4 times that mass. Wolf 1061d is calculated to be at least 5.2 times Earth’s mass.

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Image: The Wolf 1061 system, with the habitable zone depicted in green. Credit: University of New South Wales.

One thing Wolf 1061 reminds us is that red dwarf stars are good targets for radial velocity studies. For one thing, such stars have low levels of luminosity, which means their habitable zones are small and planets within them are in close orbits. Such planets create a stronger, more detectable signature for instruments using Doppler methods, a fact that is intensified by the typically low mass of the star. The paper on this work adds that M-dwarfs also show sharp molecular absorption features and typically have slow rotation speeds.

The current work, led by Duncan Wright at the University of New South Wales, is based on data from the HARPS spectrograph (High Accuracy Radial Velocity Planet Searcher) installed on the European Southern Observatory’s 3.6m telescope at La Silla. Long-term monitoring data on more than a hundred M-dwarfs is found within the HARPS database. 148 HARPS spectra for Wolf 1061 are available here, taken over a period of 10.3 years. Wright and team have found a more precise way to extract Doppler signals from the HARPS data reduction software (DRS) by creating a custom mask generated from within the data for the star.

The template is, in other words, custom-built for the particular star under study, with details supplied in the paper. For our purposes, the results for the two outer planets stand out. From the paper:

The 17.867 d planet is of particular interest because it is of sufficiently small mass to be rocky and is in the habitable zone of the host M dwarf star. The probable outer planet at 67.274 d resides just on the outer boundary of the habitable zone and is also likely rocky. These planets join the small but growing ranks of potentially habitable rocky worlds orbiting nearby M dwarf stars.

Sky_area_near_Wolf_1061

Image: The sky area in the constellation of Ophiucus near the red dwarf star Wolf 1061 which includes the impressive, but unrelated, star cluster Messier 107. Wolf 1061 is 14 light years away. Credit: The “Aladin sky atlas” developed at CDS, Strasbourg Observatory, France.

But we may be able to deploy other tools besides radial velocity, for the paper argues that the strong Doppler signals may be supplemented by transits, considering how short the orbital periods of these planets are. The transit probabilities are listed as 14 percent for planet b, 5.9 percent for planet c, and 2.6 percent for planet d. These would be transits that are detectable from ground-based telescopes given the transit depths the authors estimate, which would make Wolf 1061 an excellent target for projects like MEarth (a robotic observatory on Mt. Hopkins, AZ) and MINERVA (MINiature Exoplanet Radial Velocity Array, also on Mt. Hopkins).

The paper is Wright et al., “Three planets orbiting Wolf 1061,” to be published by The Astrophysical Journal Letters (preprint).

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Comments on this entry are closed.

  • Andrew LePage December 22, 2015, 13:53

    For readers interested in some more background on Wolf 1061 and the prospects for the habitability of Wolf 1061c, check out the following:

    http://www.drewexmachina.com/2015/12/19/habitable-planet-reality-check-wolf-1061/

  • RobFlores December 22, 2015, 14:10

    More like this , to stimulate the public’s imagination and goad (as someone mentioned awhile) a mega billionaire to fund the planning of a long range
    manned flight with the intent to colonize. That Harps may yet detect the
    holly grail of Earth like planet. I regret not visiting La Silla in Chile when this ex-patriot was travelling close by.

    Yes, this sounds like a habitable world, but it’s a bottom of the barrel
    catch. I imagine liquid water runs there at 101+ centigrade only because the Atmospheric pressure is probably close to double Earth’s Milibars at sea level. Nice place to slow cook a lobster though.
    This world appears to be in the hottest possible HZ. If it does have a substantial atmosphere then I suspect there are no Ice caps of any type.
    The day/night side atmospheric rebalancing must be incredibly violent
    since that sun side is really hot. Does a world like this with a 1.5 RE (aprox) mean stronger hurricane like winds compared to something smaller?

    Must say, this tendency of New discovered Terrestrial to be RE 1.4 + is
    quite unsettling. Overall it seems that for multiple planet systems discovered so far, RE 1 or within 10% of that seem scarce.

  • Michael December 22, 2015, 14:49
  • FrankH December 22, 2015, 16:18

    Andrew, good article. I think that the PR press machine is hyping this world. Assuming that the mass and radius are a minimum, depending on inclination, this planet has surface gravity of over 1.6 times Earth. It’s also just at the right mass and temperature to (probably) hold on to significant amounts of hydrogen. This isn’t a place I would consider habitable. It may not be a mini-Neptune, but it certainly isn’t a New Earth.

    @Michael – with a surface temperature of 3380K, Wolf 1061 is hardly “red”; a standard incandescent bulb temperature is 2700K.

  • Brett December 22, 2015, 17:30

    Habitable M-dwarf planets seem vanishingly unlikely to me. Even if it’s one of the bigger M-dwarf stars and relatively “quiet” in terms of flares, it’s still going to be roasted in the pre-main sequence phase of the star.

  • Ronald December 23, 2015, 7:21

    I agree with Brett, in that the relevance of M dwarfs for habitable planets is probably grossly overstated: superflares, tidal locking, and moreover, such narrow habitable zones (HZ), that, although M dwarfs are by far the most common stars, the total area of HZ is not more than that of all G stars combined.

  • Michael December 23, 2015, 10:33

    @FrankH December 22, 2015 at 16:18

    ‘@Michael – with a surface temperature of 3380K, Wolf 1061 is hardly “red”; a standard incandescent bulb temperature is 2700K.’

    Strangely when I look at it close up it is orange as it should be.

    An issue or one of many I have with Red dwarfs is the long luminous contraction phase, Wolf 1061 d would have had a better chance of holding onto any water during this phase and now if it has a thick enough atmosphere it would be better placed for life to develop even if just outside the HZ. Although planet d for a period would have been too hot for life moons could have sheltered organisms within their crusts and could have been ‘chipped off’ later to land on the cooler planet to propagate.

    @Ronald December 23, 2015 at 7:21

    ‘I agree with Brett, in that the relevance of M dwarfs for habitable planets is probably grossly overstated: superflares, tidal locking, and moreover, such narrow habitable zones (HZ), that, although M dwarfs are by far the most common stars, the total area of HZ is not more than that of all G stars combined.’

    Although there are many issues with habitability around red dwarfs the HZ also extends down into the planets and moons. If there are more red dwarfs than G types, as there is, it follows that there is more HZ real estate around red dwarf stars than G types.

  • Harry R Ray December 23, 2015, 10:35

    What amazes me about this system is that it is NEARLY identical to the Gliese 581 system, but WITHOUT the Neptune! As a result, I therefore PREDICT the following: ONE, in just a few months, ANOTHER planet hunters group will combine the HARPS data with their own and CIRCULARISE the rather eccentric orbits of the two outer planets and the unknown eccentricity of the inner one, and; LO AND BEHOLD, two or three NEW planets will pop out of the data(one or two 2-3 earth mass ones in the CONSERVATIVE habitable zone and a 6-8 earth mass one considerably farther out from the Gliese 581d analog. TWO: In a year or so, a paper will be published stating that only the two INNER planets are REAL, and that everything else is a result of stellar activity). THREE: In 2-3 years, ESPRESSO will FINALLY RESOLVE these controversies ONCE AND FOR ALL, AS WELL AS the controversies surrounding Alpha CentauriB, Gliese 667C, HD40307, Tau Ceti, and Kaptyan’s Star! As for transits: MOST, ASAP!

  • Eniac December 23, 2015, 11:12

    Ronald:

    moreover, such narrow habitable zones (HZ), that, although M dwarfs are by far the most common stars, the total area of HZ is not more than that of all G stars combined.

    You do not say how you define “narrow” and “area”, but surely you understand that width in AU or geometric area in AU^2 are not appropriate measures. What seems a fairly appropriate measure is the ratio between geometric width and radius. If I am not mistaken, by this measure the HZ of a red dwarf is not at all narrower than that of brighter stars.

    The ultimately proper way to define the “area” of the HZ is by the percentage of all planets falling inside it. For that you have to take the probability distribution of planets by distance into account. I would not expect this measure to assign a smaller value to red dwarfs, either, but that is hard to know for sure.

  • Ashley Baldwin December 23, 2015, 14:28

    I think that M dwarfs make up by far the biggest main sequence group of stars and especially in the local neighbourhood. As M dwarfs go Wolf 1061 is a a very “quiet” ,old example ( ironically helping make RV spectroscopy signals more than likely correct) One hundred days rotation period etc etc.
    Life on any planet around an M dwarf will be nothing like that on Earth or indeed any other planet. That is for sure . We are talking from a sample of one . Who knows what is possible. There are as many theories that allow for habitability around such stars as there are those saying not . Pre main sequence EUV or not . What we should be reflecting on is why we don’t have more ways of assessing such planets in interesting systems on our doorstep than RV spectroscopy and transit photometry . False positives are still an issue but with increasing familiarisation of what is still a relatively new and very difficult technique , the rate will fall and with the eventual introduction of astrometry and direct imaging all characterisations of planets will be built around multiple approaches. It may even be that Wolf 1061’s planets will be amongst the first if the system is close enough for confirmation via Gaia’s first data set and it does indeed have regular transits that TESS can pick up and JWST or the ELTs use for transition spectroscopy . For “d” some residual “greenhouse ” hydrogen in the atmosphere of a planet on the edge of the conservative habitable zone may even help extend it as described by Seager et Al. Unlikely if exposed to such a prolonged EUV battering during pre ZAMS but maybe the increased tectonics of a larger terrestrial planet will help with constant replenishment of a secondary atmosphere instead as well as acting as a protective shield against radiation even in the absence of a magnetic field . All bets are still on. And why not ?

  • RobFlores December 23, 2015, 15:29

    If the M dwarf is several billion years old, and the Planet is that close to the primary, wouldn’t most of Hydrogen envelope be gone by now. I understand the high gravity would slow things, but as an example the Earth lost most of it’s hydrogen very rapidly. Even a slow gas leak at 1061C would have an impact, especially with a hot atmosphere. The in this tide locked world the transfer of gasses from hotter to cooler night regions would give ample opportunity for Mr H2 to break out as it where.

  • Michael December 23, 2015, 16:19

    @Ashley Baldwin December 23, 2015 at 14:28

    ‘For “d” some residual “greenhouse ” hydrogen in the atmosphere of a planet on the edge of the conservative habitable zone may even help extend it as described by Seager et Al. Unlikely if exposed to such a prolonged EUV battering during pre ZAMS but maybe the increased tectonics of a larger terrestrial planet will help with constant replenishment of a secondary atmosphere instead as well as acting as a protective shield against radiation even in the absence of a magnetic field . All bets are still on. And why not ?’

    I would think with that mass (5.2 e) holding onto hydrogen would be fairly easy thing to do. As for the colder region of the HZ it may not be that cold as snow gets less reflective as the wavelength gets longer. I also believe this planet lies outside of the tidal lock danger zone and more likely to have a magnetic field. But all is not lost as you have said about the secondary atmosphere through potential crustal turn over. I would tend to believe life is more probable on planet d than the other inner worlds.

    http://www.intechopen.com/source/html/9541/media/image1.png

    http://www.intechopen.com/books/advances-in-geoscience-and-remote-sensing/automated-detection-of-clouds-in-satellite-imagery

  • Ronald December 23, 2015, 18:50

    @Eniac December 23, 2015 at 11:12
    I agree with you that a good measure would be the chance of a planet being inside the HZ.
    How that compares for M dwarfs and G stars I am not yet sure. Remain of course the issues of flares and tidal locking.

  • Michael December 24, 2015, 6:18

    Here is an interesting article on Red dwarfs habitability looking into the effects of U.V. It does not look that bad at all.

    http://www.as.utexas.edu/astronomy/education/spring02/scalo/heath.pdf

  • Ashley Baldwin December 24, 2015, 17:33

    This system , one way or another , is potentially one of the most interesting discovered to date , and critically , so nearby . If confirmed, good timing too. The author emailed into “Drew ex Machina” and confirmed that it is an unusually quiet M dwarf so it may be that either ESPRESSO and/or Gaia can confirm and improve on these findings and better still with a bit of transiting luck ,TESS and JWST will help characterise them. Hydrogen envelopes , barren , airless cores , mini Neptunes , Terrestrial Super Earths perhaps even crazy “Habitable evaporated cores .” Who cares ? One way or the other even in the next few years we may yet learn more about exoplanetary science from This star and its ” system “than we’ve learnt so far . Bad or good , we haven’t heard the last of Wolf 1061. Fingers crossed.

  • Terry Moseley December 25, 2015, 19:52

    Remember that the mass figures are all MINIMUM masses – they could be considerably higher. Another factor is that if the c and d planets are rocky, and so massive, they may well have considerable internal heat: that could be bad for the ‘c’ planet, but boost the surface temperature of ‘d’ to within the liquid water range if it has some insulating atmosphere.
    On the other hand, M dwarves are prone to very violent flare activity!

  • Ashley Baldwin December 26, 2015, 17:37

    Looking up Gaia’s performance stats, although a figure of 24 micro arc second precision is given this is an average. For brighter ( nearer) stars with magnitudes between 6 and 12 this figure climbs to 8 micro arc seconds for stars within ten parsecs or 32 light years. That is sensitive enough to pick up “Super Earth” planets ( 10 micro arc seconds ) especially around the nearest stars like Wolf 1061 ( magnitude 10.10) . (An Earth mass planet needs 1 micro arc second precision or less) . Whether that will confirm any planets around the star is touch and go but if so it will give the inclination and as per msini, thus the exact masses.
    If Gaia however continues with even more visits per star over an extended “secondary” mission ,this accuracy will increase further which will help increase precision especially for the smaller nearby stars as any planets will give a larger lateral displacement . An often forgotten fact about Gaia ,which we are constantly reminded will find thousands of gas giants , is this significant extra precision for a small cohort of close “brighter” stars, especially for smaller stars with planets in wider orbits which further helps astrometry unlike Doppler spectroscopy or transit photometry . Even Proxima falls into the “brighter ” class at magnitude 11 and could yet have planet/s detected in this way too.

  • Janw Pool December 28, 2015, 6:10

    I am especially interested in what mass a planet at a distance of 0.12 – 0.16 AU has to be to remain undetected at the current capabilities… If I understood correctly, there is a tendency to fill ‘gaps’ between planets with another one. And the space between c and d looks like a gap to me.

  • Harry R Ray December 28, 2015, 10:16

    Janw Pool: The paper states that the “c” planet has an ECCENTRICITY of ALMOST 20, and that the “d” CANDIDATE planet has an eccentricity of just over 30! If this is true, then there can be NO stable planet in the 0.12-0.16 AU gap. If, however, the orbits are CIRCULAR(please read my ABOVE comment), then there is a very good likelyhood of at least one “conservative habitable zone” planet residing there.

  • andy December 28, 2015, 15:32

    The paper states that the “c” planet has an ECCENTRICITY of ALMOST 20, and that the “d” CANDIDATE planet has an eccentricity of just over 30!

    Actually it provides two orbital solutions: one with free eccentricities for the c and d planets, one with circular orbits. In the free eccentricity solution, the error bars need to be considered: for planet c the value given is 0.19±0.13, which is merely 1.5σ away from zero so is not an especially significant value. For planet d the value is 0.32±0.16, which at 2σ away from zero is slightly more significant but still compatible with circularity. The values of reduced-χ² for the eccentric versus the circular fit are very similar so there doesn’t appear to be much in it.

    More data are needed to constrain the planetary eccentricities to the point where anything definitive can be said.

  • Andrew LePage December 31, 2015, 12:15

    @Janw Pool December 28, 2015 at 6:10

    I think it remains to be seen if there are any stable orbits between planets c and d especially given their rather substantial minimum masses of 4 or 5 times that of Earth. That being said, Wright et al. did not include an analysis of detection limits in their paper and it is not a trivial matter to figure that out. But, my best SWAG given what I’ve seen in the paper is that a planet with a minimum mass on the order of an Earth mass would probably have been detectable in the data if it has an orbital radius of 0.12 to 0.16 AU… but don’t quote me on that.

  • Mike Fidler January 6, 2016, 6:03

    New funding in 2016 budget;
    Wide-Field Infrared Survey Telescope (WFIRST): The Omnibus includes $90 million for WFIRST-AFTA and instructions that it should be moved into Phase-A in January. This is 5.4 times the NASA request for WFIRST!

    https://thespacereporter.com/2016/01/former-spy-satellites-will-search-dark-energy-exoplanets/

    http://astronomicaltelescopes.spiedigitallibrary.org/issue.aspx?journalid=166&issueid=934639

  • Stan Erickson January 8, 2016, 16:11

    Am I the only person who thinks the term habitable for liquid water planets is very inappropriate? I wouldn’t care if someone came up with a new word or hybridized two or anything, as long as the media didn’t use ‘habitable’ in such a misleading way.

  • Harry R Ray January 10, 2016, 14:42

    Paul, Andrew LePage, ANYONE! Can anybody tell me what’s going on with HEC? The latest revision has FINALLY been posted, and, lo and behold, it has Wolf 1061 c in the CONSERVATIVE list of potentially habitable exoplanets! The REASON for this is that the Teq(K) is 223 instead of the MUCH HIGHER VALUE stated in the paper! WHAT GIVES? But that’s not the REAL stunner! The K2 list of potentially habitable planet CANDIDATES has EPIC 203823381.01 listed as follows: Radius(Re);0.7: Teq(K); 203: Orbital period (days); 8.3: DISTANCE(LIGHT YEARS); 10!!!!!!!! I have NOT been able to CROSS-CORELATE the designation in more well-known catalogs(i.e. Gl-Gj, Wolf, Ross, etc) CANN ANYONE HELP ME OUT HERE?

  • Mike Fidler January 10, 2016, 19:45

    The RA and Dec for EPIC 203823381 put it in southwest Ophiuchus near Antares and it is listed K2 campaign 2, magnitude 13.47 and flagged as possible giant. It would have to be a M7V dwarf at 10 light years – still looking for reference to distance, nothing listed at that distance in Ophiuchus.

  • Mike Fidler January 11, 2016, 5:46

    EPIC 203823381 = UCAC 327-080293 and 2MASS 16283288-2447550

    Found on: http://archive.stsci.edu/k2/epic/search.php

    Also found on Sky Chart / Cartes du Ciel with the UCAC4 catalog V2 – Equator -30/+22.5 added.

    Still nothing on distance?

  • Harry R Ray January 11, 2016, 10:26

    Mike Fidler: THANKS! It not only is a POSSIBLE giant, it HAS TO BE ONE! The PARALLAX at a distance of 10 ly would be SO OBVIOUS that it would have been catagorized as one of the ten stars nearest the sun DECADES AGO! Now all that remains is to resolve the Wolf 1061 c Teq(K) issue.

  • Harry R Ray January 11, 2016, 11:59

    Mike Fidler: Very interesting co-incedence here: Wolf 1061 is ALSO in Ophiuchus(Right Ascension: 16h 30m 18.1s, Declination: -12 degrees, 39′, 45”)! Now I wonder if it was ALSO in the K2 field AT THE SAME TIME EPIC203823381 was? If you know, please post. If you don’t know, post the CO-ORDINATES here so I can get a sense of how close the two co-ordinate sets are to each other.