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After Huntsville, a Red Dwarf Bonanza

Returning from Huntsville after the Tennessee Valley Interstellar Workshop, I was catching up on emails at the airport when the latest news about exoplanets and red dwarfs popped up on CNN. It was heartening to look around the Huntsville airport and see that people who had been reading or using their computers were all looking up at the screen and following the CNN story, which was no more than a thirty second summary. The interest in exoplanets is out there and may bode good things for public engagement in space matters. At least let’s hope so.

The workshop was a great success, and congratulations are owed to Les Johnson, Robert Kennedy, Eric Hughes and the entire team that made this happen (a special nod to Martha Knowles and Yohon Lo!). This morning I want to focus on the exoplanet news as a way of getting back on schedule, but tomorrow I’ll start going through my notes and talking about the Huntsville gathering. I’m hoping to have several articles in coming weeks from participants in the event on the work they are doing, and I have plenty of comments about the presentations, so the Huntsville coverage that begins tomorrow should extend into next week.

As to the exoplanet news, Courtney Dressing (Harvard-Smithsonian Center for Astrophysics) went to work on the Kepler catalog of 158,000 stars to cull out all the red dwarfs. She and the CfA’s David Charbonneau found that almost all of the identified stars were smaller and cooler than had been thought, which has the effect of lowering the size of the detected planets. An additional result is to move the habitable zone somewhat further in. The duo could find 95 planet candidates among these red dwarfs.


Image: This artist’s conception shows a hypothetical habitable planet with two moons orbiting a red dwarf star. Astronomers have found that 6 percent of all red dwarf stars have an Earth-sized planet in the habitable zone, which is warm enough for liquid water on the planet’s surface. Since red dwarf stars are so common, then statistically the closest Earth-like planet should be only 13 light-years away. Credit: David A. Aguilar (CfA)

Let’s pause for a moment on the analysis. Dressing and Charbonneau were comparing the observed colors of the stars to a model developed by the Dartmouth Stellar Evolutionary Program. The final sample in the study contained 3897 dwarf stars with revised temperatures cooler than 4000 K, and the revisions to stellar temperatures brought the stars down 130 K in temperature while reducing their size by 31 percent. The analysis proceeded to refit the light curves of the planet candidates to get a better understanding of their radii.

I wish I could have tracked the news conference live but was in transit at the crucial moments. Those of you who also missed it may want to check the archived version at the CFA’s site. The key point is on the opening slide: “Earth-like Planets Are Right Next Door.” Which is something of a stretch because we are talking about M-class stars where a planet in the habitable zone is probably tidally locked. Assuming (and it’s an open question) whether a benign climate for carbon-based life could exist on such a planet, it’s still an environment much different from the Earth, with a star that stays in the same position in the sky and night and day are endless.

Still, this is interesting news: The 95 planetary candidates imply statistically that at least 60 percent of red dwarfs have planets smaller than Neptune. Out of the 95, only three were close enough to Earth in terms of size and temperature to be considered ‘Earth-like.’ In other words, about six percent of all red dwarfs are found to have a planet like the Earth. 75 percent of the closest stars to the Sun are red dwarfs, leading Dressing to calculate that the closest Earth-like world is likely to be no more than 13 light years away. Again, this is for red dwarfs. The analysis of other stellar types like the intriguing G- and K-class stars Centauri A and B continues.

Here’s the payoff, from the paper. The authors have just noted that the high rate of habitable zone planets around nearby stars means that future missions designed to study these worlds will have plenty to work with::

Given that there are 248 early M dwarfs within 10 parsecs, we estimate that there are at least 3 Earth-size planets in the habitable zones of nearby M dwarfs awaiting the launch of TESS and JWST. Applying a geometric correction for the transit probability and assuming that the space density of M dwarfs is uniform, we find that the nearest transiting Earth-size planet in the habitable zone of an M dwarf is less than 29 pc away with 95% confidence. Removing the requirement that the planet transits, we find that the nearest non-transiting Earthsize planet in the habitable zone is within 7 pc with 95% confidence. The most probable distances to the nearest transiting and non-transiting Earth-size planets in the habitable zone are 18 pc and 4 pc, respectively.

I mentioned the G- and K-class stars Centauri A and B above, but I don’t want to leave the third element of the trio out, it being a red dwarf. The radial velocity work on Proxima Centauri continues, allowing us to constrain the size of possible planets usefully. This is not part of Dressing and Charbonneau’s study, but I’ll mention it here because it’s obviously germane. Using seven years of UVES spectrograph data from the European Southern Observatory, Michael Endl (University of Texas) and team have found no planet of Neptune mass or above out to 1 AU from Proxima, and no ‘super-Earths’ above 8.5 Earth masses in orbits of less than 100 days.

As to Proxima’s tight habitable zone (0.022 to 0.054 AU), no ‘super-Earths’ above about two to three Earth masses exist here. The habitable zone around Proxima corresponds to orbits ranging from 3.6 to 13.8 days, and you can see that we still have plenty of room for an interesting Earth or Mars-sized world around this closest of all stars to Earth. Adding more data points to what we already have on Proxima should gradually allow us to get to a better idea of what’s actually there.

But back to Dressing and Charbonneau’s red dwarfs. The three habitable zone candidates are Kepler Object of Interest (KOI) 1422.02 (90 percent Earth size in a 20-day orbit); KOI 2626.01 (1.4 Earth size in a 38-day orbit); and KOI 854.01 (1.7 times Earth size in a 56-day orbit). None of these are closer than 300 light years. The paper points out that while Kepler will need several more years of observation to detect Earth-size planets in the habitable zones of G-class stars (this is due to higher than expected stellar noise), the observatory is already able to detect Earth-size planets in the habitable zone of red dwarfs. We get not one but many transits per year and we have 1.8 times more likelihood of a transit than around a star like the Sun.

Thus we get this:

…the transit signal of an Earth-size planet orbiting a 3800K M star is 3.3 times deeper than the transit of an Earth-size planet across a G star because the star is 45% smaller than the Sun. The combination of a shorter orbital period, an increased transit probability, and a deeper transit depth greatly reduces the difficulty of detecting a habitable planet and has motivated numerous planet surveys to target M dwarfs…

Another advantage of M dwarfs is that confirming a planetary candidate is made easier because the radial velocity signal of a habitable planet here is considerably larger than that of a habitable zone planet around a G-class star. Given that the James Webb Space Telescope should be able to take spectra of Earth-sized planets in the habitable zone around M-dwarfs — and that it cannot do this for comparable planets around more massive stars — our first atmospheric readings from a habitable zone planet are probably going to come from these small red stars.

The paper is Dressing and Charbonneau, “The Occurrence Rate of Small Planets Around Small Stars,” to be published in The Astrophysical Journal (draft version online).


Comments on this entry are closed.

  • ljk February 7, 2013, 10:52


    The Physics arXiv Blog

    February 7, 2013

    SETI Study Of Habitable Exoplanets Draws a Blank For Jill Tarter

    The exoplanets of greatest interest show no sign of intelligent civilisations–so far

    The discovery of an ever-growing number of potentially habitable exoplanets brings an extra spiciness to the Search for ExtraTerrestrial Intelligence. For the first time, astronomers can direct the search towards these likely planets rather than aiming in hope towards the stars.

    Today, Jill Tarter, from the SETI Institute and of Contact fame, along with a group of buddies, reveal the results of their first directed search, carried out between February and April 2011.

    These guys pointed the Green Bank Telescope in West Virginia at 86 stars hosting exoplanets discovered by the Kepler space telescope. They chose their targets because they had exoplanets in the Goldilocks zone, had five or more exoplanets or had super Earths with relatively long orbits.

    Tarter and co looked at signals in the 1-2 GHz range, the region used by terrestrial mobile and cordless phones. In particular, they hunted for signals that cover no more than 5Hz of the spectrum since there is no known natural mechanism for producing such narrow band signals. “Emission no more than a few Hz in spectral width is, as far as we know, an unmistakable indicator of engineering by an intelligent civilization,” they say.

    The big challenge with these kinds of observations is to rule out the false positives generated on Earth. Tarter and co developed a technique based on the simple idea that a signal can only be interesting if it appears in the data while the telescope is pointing at the target star but not when the telescope is pointing somewhere else. “This excluded 99.96 per cent of the candidate signals,” they say.

    That left 52 candidate signals which Tarter and co then studied for signs of a terrestrial origin.

    Their conclusions are forthright. “No signals of extraterrestrial origin were found,” they say.

    There are some important caveats, however. In particular, is the question of how strong a signal the Green Bank Telescope can pick up.

    Tarter and co consider in particular the most powerful beam that humans could broadcast into space: the Arecibo Planetary Radar in Puerto Rico. They say that if such a beam were pointed towards Earth during their experiment, they would have spotted it at distances of up to 10,000 light years. Of course, the likelihood of such a happy coincidence is small.

    More advanced civilisations might have more power to play with and so be easier to see. In particular, civilisations that have harnessed all the energy from their star–so-called Kardashian Type II civilisations–ought to be easy to spot.

    The results allow the team to put important limits on the likelihood of Kardashian Type II civilisations. Tarter and co say that the negative result implies that the number of these civilisations that are loud in the 1-2GHz range must less than one in a million per sun-like star.

    That still leaves plenty of wiggle room. And the team points out that rapid improvements in the technology for sensing radio signals means that researchers ought to be able to tighten these limits significantly in the not too distant future.

    Ref: http://arxiv.org/abs/1302.0845: A 1.1 to 1.9 GHz SETI Survey of the Kepler Field: I. A Search for Narrow-band Emission from Select Targets

  • ljk February 7, 2013, 11:10

    Quoting the above post on SETI efforts to scan a handful of promising exoworlds:

    “More advanced civilisations might have more power to play with and so be easier to see. In particular, civilisations that have harnessed all the energy from their star–so-called Kardashian Type II civilisations–ought to be easy to spot.

    “The results allow the team to put important limits on the likelihood of Kardashian Type II civilisations. Tarter and co say that the negative result implies that the number of these civilisations that are loud in the 1-2GHz range must less than one in a million per sun-like star.”

    Kardashian? No wonder we can’t find any intelligent life out there! BTW, they meant Kardashev after the Soviet scientist who came up with the idea of progressive levels of technological civilizations (humanity isn’t even at Type 1 yet, while Type 3 utilizes the resources of an entire galaxy).

    This just shows how pervasive pop culture is in our society, to the detriment of much better things and our educational system in general. And this is from an MIT blog no less.

  • Harry R Ray February 7, 2013, 11:52

    A NOTE OF CAUTION! We went through this before two years ago when Barbara Rojas-Ayala came to the same conclusion for the same sample! As a result, Abel Mendez posted SIX KOI’s SIMILAR to KOI1422.02 on his PHL website. I contacted Ms Rohas-Ayala to warn her about a possible transet duration connundrum (i.e. the transet TIMES seemed a bit too LONG for the NEW stellar radii). Since then ALL SIX of these KOI’s have been DELETED from the PHL catalog. This may have been done due to vetting the stars and finding they are GIANT stars instead of dwarfs. I,for one, would like to know how Dressing’ analysis DIFFERS from Rojas-Ayala’
    On the other hand, I checked out this story on the Astrobio.net website , and saw a very interesting Graphic representation of KOI1422.02! It appears to be in the very farthest(i.e.,coldest) part of the habitable zone. HOWEVER, I do NOT believe this is the REVISED habitable zone from a recent posting. This means KOI1422.02 actually lies in the middle (or perhaps even the warm part of the zone.

  • Anthony Mugan February 7, 2013, 13:14

    Given the question of tidal locking, perhaps large moons (of larger planets) may be a possibility of exobiological interest around red dwarf stars?

  • Lord February 7, 2013, 13:18

    Would a planet with a large moon become phase locked? Would a planet at a high tilt do so?

  • andy February 7, 2013, 14:28

    Good point from Harry R Ray, it looks like they are not using the additional constraints provided by the transit duration on the stellar density in their modelling process, unlike for example this study of potentially-habitable Kepler planet candidates where this information is taken into account (among other things) when rederiving the stellar properties.

  • Mike February 7, 2013, 14:38

    What an interesting paper. As Kepler wasn’t designed to examine stars dimmer then 16th magnitude and is not optimized for near-infrared hence the Mdwarf target stars are mostly M0 to M1. Later sequence M dwarfs are much more numerous but they are too faint to be included in Kepler’s target list in significant numbers. Kepler was built for solar like FGK stars.

    This preliminary result of about 6% is interesting but I wonder how accurate it will prove considering the somewhat small and narrow range sampling of the M dwarf population. But still a good start for sure.

    This also strengthens the case for launching a TESS and or CHEOPs type mission. With CCD detectors optimized for visual deep red into the near-infrared to see stars with temperatures from 3900 K down to 2200K as these stars ( particularily the later Ms) emit most of their output in the infrared. Then we will find over the entire sky almost all transiting planets orbiting nearby red dwarf stars covering the entire rather wide range of M dwarf sizes and masses and brightness.

    This should provide a more robust percentage number of Earth-size worlds orbiting these most numerous of stars. It should also help firm up our ideas about planet populations and characteristics. It will also give the JWST a useful target list for spectroscopic studies of interesting planets found orbiting nearby stars.

    Could those tidally locked, flared and UV irradiated worlds have some kind of a biosphere that would produce indentifiable bio-markers in their atmospheres? Now that’s really interesting.

  • Bounty February 7, 2013, 16:07

    It’s interesting to picture a tidally locked planet’s water evaporating from one side and condensing on the other. If there were enough water, would this change the center of gravity, causing an ocasional rotation? Depending on wind (super sonic?) patterns, would ice buildup lopsided on the dark side around where it gets cold. Would an ice mountain squeeze out more snow against a (super sonic?) wind. Imagine those wind carved ice canyons.. So many posibilities.

  • Wojciech J February 7, 2013, 16:21

    It is interesting to see statistics emerging regarding possibility of Earth like planet near our Sol system. I believe a month ago there was a paper which among other things postulated high probability of Earth like planet to be within 100 light years.

  • Aleksandar February 7, 2013, 16:23

    Now if only propulsion for star-flight would follow suite…

    I’ve sent a plea for correction on that tech-review article. It’s so entertaining to read about the Kardashian type II civilizations :) (as opposed to Kardashev type II; this Freudian slip is telling a lot).

  • Wojciech J February 7, 2013, 16:24

    “Today, Jill Tarter, from the SETI Institute and of Contact fame, along with a group of buddies, reveal the results of their first directed search, carried out between February and April 2011.”
    I really doubt anyone believes in the possibility of another civilization emerging so close to our own(as mentioned target area in the area), and within the same time(give or take one milion years).
    SETI really should start switching to different search methods…

  • Dispatcher February 7, 2013, 16:35

    It would seem probable that rocks will be found in the hab zones of many M dwarfs. While that would seem well, its already been noted that many of these may be tidally locked to their stars. Habitable moons of these worlds might escape the locked effect, as someone pointed out.

    Another consideration is the fact that a good percentage of the M stars are variable (which may be problematic for life at such worlds). Of these, a significant percentage have been identified as flare stars (UV Ceti being archetypical). Flare stars definitely pose problems for their planets; occasionally bathing them with hard radiation at higher than typical levels.

    I think it will be seldom that we find planets in M star hab zones which possess days as well as years, and which have escaped the radiation wrath of their stars.

    In any case, the results should be interesting.

  • Phil February 7, 2013, 19:16

    I really think its time everyone stopped using the term ‘tidally locked’ so…errr loosely. Given Mercury’s situation in our own family of 8 planets, surely many of these close in worlds will be ‘locked’ in other than 1:1 resonance. What that exactly says about their habitability I dont know, but at least in press conferences an attempt should be made to make it clear that the Moon analogy doesnt near cover the range of possibilites a close in M dwarf planet might face.


  • jkittle February 7, 2013, 22:14

    I would be really careful about extrapolating from these numbers. We do not have very many positives yet -all of the arguments are extrapolated from just a small number of tentatively identified “earthsized planets in the HZ” Also note that as we look at red suns near our solar system, things get most interesting ( for us!) when we look at stars closest to earth… but again as we shrink that sphere of what we mean by “close” the number of stars shrink. When we are talking about 6% of say, 50 stars , the statistical fluctuations go crazy. we might be talking about 3 ( on”average” ) or the actual number may be zero or say 6 or even some probability of more than 6. at this point. we need to actually LOOK at the closest stars. it is not hard to imagine we will get the results of the closest 500 star in the next decade.
    A Live example…when I am engineering bacteria, on average about 5 to 10% of the bacteria we initially select actually have the engineered change.. so we pick at least 24 to 48 independent clonal lines to analyze. Recently we had about 120 candidate clones… we picked 24 and from those we got 3 good ones… but they were numbers 21, 22 and 24. Had we picked 20, we would have thought the experiment a failure!

  • Neil S February 7, 2013, 22:38

    I just want to know what “45% smaller than the Sun” means. Aside from questions of whether we’re measuring diameter or volume (or I suppose mass or even surface area) there’s the question of what “45% smaller” means.

    I’ve seen “twice as small” used in situations where it must have meant “half as big”. Following that logic “45% smaller” would mean 1/0.45 or 2.22… times as big. From the context I’m sure it doesn’t mean that. Or it could mean 1 – 0.45 = 0.55 times as big. But if it means that why not say so? Surely “55% as large as” is at least as meaningful as “45% smaller than”. And I have the feeling I’m missing whatever the author really meant.

    Anyone here know what the author really meant?

    And why are we now using such confusing language for simple ideas?

  • Thomas Hackney February 8, 2013, 2:44

    Having picked up our first handful of sand on the beach we begin sifting the grains through our fingers. How poignant is that?

    “Astronomers have found that 6 percent of all red dwarf stars have an Earth-sized planet in the habitable zone, which is warm enough for liquid water on the planet’s surface. Since red dwarf stars are so common, then statistically the closest Earth-like planet should be only 13 light-years away.”

    Thirteen light-years could take us 150 years just to get there. Frankly, robot probes don’t do it for me, though they would be cheaper and less dangerous than a manned probe, needless to say. Our work is cut out for us either way, though. But heck, a starship (space ark) is still my choice, even if a “few” technical problems remain.

    The best hard sci-fi book on this subject might be Martin Caidin’s book, EXIT EARTH. Before he died, Caidin was a friend and client, so I guess I’m biased on this score, but if there’s a better and “harder” book available I’d certainly like to know its title and author.

  • Daniel February 8, 2013, 3:17

    Not entirely on the subject, but I was wondering, if we can send information by using lasers to the Moon, why can’t we (at least try to) send information to the nearest stars using the same technology – instead of sending probes. Or something looking like a laser. It would take only 4 years to get there.

  • Anthony Mugan February 8, 2013, 10:59

    Just a thought on the SETI related comment. I can’t help but feel that this sort of radio based SETI is heroically hopeless.
    If we take the current range of estimates of potentially habitable worlds as being between 2% and 12% of the number of stars then this suggests 6-32 billion potentially habitable planets (in round terms) in the galaxy. Most of these are considerably older than earth by an average of 1.85 billion years, and with some up to 5 billion years older than earth if Linneweaver’s 2000 paper is still the best one to use for this.
    If the probability of an advanced civilisation emergining on any given world is extremely low (lets say < one in a billion within the past 5 billion years) then we could potentially be unique in the galaxy, if few survive the difficult early technological phase that we are currently in. In that case we won't hear anything. As the probability gets up to around one in a billion in five billion years the numbers of advanced ETCs emerging in the galaxy at some point in the past five billion years begins to rise to numbers were it becomes difficult to presume they will have all destroyed themselves.

    We have discussed before that if a civilisation achieves the ability for interstellar travel they are likely to become almost indestructable (except perhaps if the come up against an even more advanced civilisation). In that scenario the galaxy should have been fully explored by the first such ETC to appear, probably billions of years ago. This scenario would require something like the zoo hypothesis to make sense of the great silence.

    I struggle to imagine what level of technology a billion year (+) old civilisation would attain. It is pretty clear that we are not at the end of physics (quantumn non- locality, concsiousness etc etc.). If they exist they appear not to be using radio to communicate, as half a century of SETI makes clear.

    This could sound like a council of despair. Perhaps on the outer limits of our current theories their may be concepts that, in a few cases, eventually pan out and may give us clues as to other ways to pick up evidence. One thought that has occurred, although this may not be robust (just an idea to float) is, if they are not using radio that may suggest FTL travel or signalling may be possible. Our early theories on such topics might be an area to look for signals or perhaps even detecting physical objects in movement, but others will be far more informed than I about all that.

  • ljk February 8, 2013, 12:42

    Daniel said on February 8, 2013 at 3:17:

    “Not entirely on the subject, but I was wondering, if we can send information by using lasers to the Moon, why can’t we (at least try to) send information to the nearest stars using the same technology – instead of sending probes. Or something looking like a laser. It would take only 4 years to get there.”

    It is called Optical SETI, and while we humans have not attempted such a means of communications yet with other stars, more advanced beings may have done so. There are some Optical SETI programs underway, though like most SETI these days they are sporadic in nature.

    Start here for lots of information on the subject:


    We should not disparage on Radio SETI just because we think the more sophisticated types of aliens would have stopped using it ages ago. Radio is one of the cheaper and easier ways to communicate across the stars despite its limitations.

    Since current SETI is really designed to look for beings who at least think and behave similarly to humanity, Radio SETI is all the more plausible. We can talk about fancy gamma ray and neutrino methods of galactic communication, but they are much harder to do and I am pretty certain that the operators of the neutrino observatories on this planet are not looking for alien messages in their data.

  • andy February 8, 2013, 15:59

    And why are we now using such confusing language for simple ideas?

    Because English lends itself well to ambiguity, even when you are trying to be precise. Maybe we should go back to German or Latin for scientific discussions…

  • Thomas Hackney February 8, 2013, 16:03

    At 45 meters asteroid DA14 will pass Earth at a proximity of 21,000 miles, making it a record. Tungusta was 30-40 meters. The extraterrestrial object will perform its fly-by of Earth on February 15, the day after Valentine’s day. A fitting cosmic rejoinder, perhaps, to NASA’s recent NEAR mission to the 21 mile behemoth, “Eros.” And funny, though, that Shoemaker-Levy 9 should happen to include twenty-one, by George!, large fragments to help mark the 21st century. A comet for each century!

  • FrankH February 8, 2013, 16:12

    @Phil – Exactly; “tidally locked” can mean a resonance other than 1:1

    The Hill sphere of a planet orbiting very close to its primary (basically, a planet in a red dwarf’s HZ) may be too small to allow a big moon.

  • ljk February 8, 2013, 16:22

    Wojciech J said on February 7, 2013 at 16:24:

    “I really doubt anyone believes in the possibility of another civilization emerging so close to our own (as mentioned target area in the area), and within the same time(give or take one milion years).”

    Why do you say this? Are you assuming that an alien intelligence and any society that may emerge from it would progress in a linear fashion similar to ours, or linearly at all? Do you expect them to METI us or send a vessel?

    Such hypothetical beings could probably say the same about us and assume we do not exist because we are not chatting or visiting, either. And we know why we aren’t doing it, and it has little to do with ability compared to will and interest from the general populace (that group includes the politicians and purse string holders).

    “SETI really should start switching to different search methods…”

    What methods exactly and where will the funding and resources come from? The ATA is barely holding its own with handouts and everyone else is operating sporadically and even on a token level as far as I am concerned.

    People criticize SETI (and METI even more) as if there is some version of S. R. Hadden from Sagan’s Contact waiting in the wings ready to fund such a project to the max.

    The problem is that SETI is barely past the red-headed stepchild stage these days (is that PC to say?) and many mainstream scientists still look upon it with the same disdain that they hold for UFOs. Ironic considering that science is supposed to be about posing hypotheses and searching for the predicted facts via empirical evidence.

    We don’t have a starship fleet ready to ply the galaxy, or even an observatory on the lunar farside or in high Earth orbit, so we go with what we have, which is better than doing nothing and almost guaranteeing we will never find any ETI or even ETnonI. No, I don’t expect a silver saucer to land on the White House lawn.

    You can blame the current bad economy if you want to, and it is partly to blame, but a lot of SETI’s inability to rise above comes from an uneducated and apathetic (and scared) public and leaders who are far more concerned about keeping all the money and power for themselves than trying to advance humanity into the Cosmos.

    Either this changes and we start growing up and expanding as a species, or asking for a better and different kind of SETI will be like asking for a better type of warp-driven starship: Neither will happen and eventually society will degrade to where no one can make them even a remote reality.

  • Rob Henry February 8, 2013, 18:58

    I have being thinking a lot recently about a topic tangentially breached by Phil and FrankH. Giant planets in the traditional HZ of an M star would have a slim region between Hill sphere and Roche limit. If they formed in situ, wouldn’t this tend to concentrate all their leftover material into a single moon? And wouldn’t the combination of two strong tidal forces make it impossible to avoid tidal heating by becoming 1:1 locked.

    What I’m seeing is a moon with Io’s activity, but with the mass and ice of all the Galileans combined. A planet with a Mercury-like 3:2 spin resonance around an M star’s HZ would have similar activity, also due to the much higher tidal forces.

    With all the volcanic gas being emitted from these worlds, avoiding a run away greenhouse effect might be the problem, not the (mainly) icy surface freezing over, So we might HAVE to place living examples of such worlds at the limits of the traditional HZ JUST to avoid a runaway greenhouse.

    Of cause they could never entirely freeze out as long as those tidal forces were strong enough to promote that high level of geological activity, so the new HZ would extent right out to the limits were tidal heating is to low to melt through a substantial fraction of the surface ice.

  • Thomas Hackney February 8, 2013, 19:37

    LJK and Wojciech: I am one who believes in the “possibility of another civilization emerging so close to our own and within the same time.” Any technological civilization beginning, say, a billion years ago would have probably explored, if not colonized, most or all of the Milky Way by now. We should not assume. however, that such an intelligence would necessarily contact us as equals. We would probably not be equals. We would more likely be observed from a distance, like some sort of interesting primitive intelligent life. This is to say, they may be driven by a consciousness not easily detected, much less understood, by mere mortal men, and moving in mysterious ways its wonders to perform.

  • coolstar February 8, 2013, 23:29

    This work by Dressing and Charbonneau ties directly into a previous paper discussed here by John Johnson’s exoplanet lab at Cal Tech (Johnson was the “external” commenter at the press conference) on Kepler 32. Johnson mentioned Dressing’s work very favorably during his Newton Lacy Pierce prize talk at the recent AAS meeting. A conclusions of the Kepler 32 paper was that the great majority of close in planets around M dwarfs formed MUCH FURTHER OUT (beyond the frost line), and then migrated in. Thus, while an eta-earth of 0.06 for M dwarfs seems like a fairly large value, it may well be that while these planets are earth sized, they are very far from being Earth LIKE (there’s no current evidence that they’re rocky). One way to know for sure is to wait for the next generation of radial velocity spectrographs to get masses and thus densities of transiting exoplanets around M dwarfs. Masses and densities might actually come sooner from TTV studies of the multiple planet Kepler systems. Johnson’s prize talk is very good and is available to members at AAS site, and should eventually migrate to being publicly available (at least I believe that’s the policy).
    Oh, there’s no reason to believe the planets listed by Dressing and Charbonneau are false positives as the vetting now being done by their group and by Johnson’s is very good and has led to the discovery of some very interesting systems. Note that the “desizing” of late type stars in the Kepler catalog has nothing to do with K & M dwarfs in close binaries being apparently around 10% larger than predicted by models. Finally, the “45%” smaller means what you would expect, the radii are 55% of the input catalog values ( which leads to the transit depth being 3.3 times larger than for a G star, as Paul quoted).

  • coolstar February 8, 2013, 23:39

    Phil and FrankH: for the closely packed M dwarf systems (as closely packed as dynamically allowed, apparently) “tidally locked” really does mean a 1:1 resonance as the eccentricites required for other resonances would make the systems dynamically unstable on short timescales. Eccentric systems cannot be in 1:1 resonances (I think it was Piet Hut who first showed that) while low eccentricity systems can’t be in any other resonance. Of course, other resonances are allowed for single planet systems, but it’s very hard to explain how such systems can have high eccentricities, since the timescales to circularize the orbits are short.

  • Thomas Hackney February 9, 2013, 4:09

    LJK, you quoted: “SETI really should start switching to different search methods…”

    I’ve been telling NASA-Ames that for almost 20 years, much to its annoyance. (I have numerous responses.) The best investigation methods are always based in intuition as much as science, and for the best results, its always best to go old school. Science often enough falls short of being detective work, throwing out all manner of objective data, unproven intuitions or even common sense as irrelevant. When you knock at a door with no bell, no knocker, not even a door handle, and a face rises out of the wood, like a swimmer from the depths breaking the surface of the water — not a human face, mind you, but one full of emotions — then yawns slowly before fixing you with its emerald eyes, as if in suddenly recognizing you, you’re not talking radiowaves, okay? The technical bias becomes just too much and not enough at the same time.

  • Tarmen February 9, 2013, 8:12

    I hope we don’t find any evidence of real live ET at any stars of any kind within a hundred lightyears of us. They’d be older than us, maybe very very old. If they detect us in their backyard they might treat us as an upstart weed, rather than a peer. I actually expect that they would be so old as to be dead. So, I would hope to find ET artifacts, rather than ETs.

  • Daniel February 9, 2013, 11:29

    Good news! The possible habitable planet around a M dwarf at 13 light-years can be imaged for the E-ELT

    It’s seems that with E-ELT ever no-transit Earth-size planets in HZ of Red Dwarf at 10 pc will be imaged

    Direct Imaging of Habitable Exoplanets with ELTs


  • Thomas Hackney February 9, 2013, 17:22

    Tarmen: If there was something to fear from them I think we would have felt these effects by now, but since we haven’t I don’t think we have any idea what we’re missing.

  • andy February 10, 2013, 11:39

    Exomoons in the habitable zone around low-mass stars suffer from the problems of strong stellar tides (i.e. the same reason the planets would otherwise end up locked).

    According to Heller (2012) “Exomoon habitability constrained by energy flux and orbital stability“, stars below ~0.2 solar masses probably cannot host habitable exomoons thanks to the tidal heating being sufficient to trigger a runaway greenhouse effect, and for stars below ~0.5 solar masses there can still significant effects (e.g. if the satellite has non-zero orbital eccentricity).

    Even without this consideration, giant planets are rare in the habitable zones of low-mass stars anyway.

    Really I don’t see that exomoons offer any advantages at all for mitigating the issues facing habitability for M-dwarf systems. Then again, so far it doesn’t look like tidal locking is necessarily fatal for habitable conditions.

  • xcalibur February 10, 2013, 16:11

    As for SETI and the Fermi Paradox: it’s clear that there is no situation out of the Halo game series in our neighborhood. But there are many other possibilities.

    First of all, the Milky Way is one of numerous galaxies. Even if we’re the only intelligent species in the galaxy, there could be plenty of ETI in the Universe at large.

    Second, we haven’t comprehensively observed everything in the galaxy. The region opposite the galactic core is relatively unknown, and the rest is incomplete.

    Third, not all ETI must be highly advanced and star-faring. They might turn inward towards virtual reality rather than outward to the stars. They might be closer to our level of technology. And so on.

    Fourth, there can be distance in time as well as space. It is entirely possible that our first contact with ETI will be in the form of abandoned ruins and artifacts from a long-vanished species.

  • xcalibur February 10, 2013, 16:23

    As for planets being locked in a spin-orbit resonance (assuming that’s the correct term):

    this would present some interesting surface conditions and issues for habitability. I’m certain that we could adapt to this, though. I’m not aware of any computer models for an earth-like planet in a 1:1, 2:1, or 3:2 resonance, but I imagine there would be strong wind systems present.

  • Rob Henry February 10, 2013, 16:29

    Andy, I already noted that exomoons would probably have to be on the extreme outer limits of the traditional HZ to avoid a runaway green house. I was postulating that, as long as frictional heating is sufficiently high that the crust remains very thin, and with many holes to the ocean, a snowballearth would be avoided, and so this new HZ could be pushed out much further.

    A thick ice crust would lower the potential for either photosynthesis or utilisation of high energy chemicals generated in the atmosphere. If we take the mystery of the H2 that seems to be disappearing into the surface of Titan, react it with ethane, and scale it to the light intensities of Ceres, we already have about 250W of bioenergy per square kilometre, which is a quarter of a million times greater than a ecosphere fed by hydrothermals on Europa could have. In my opinion we are starting to get close to bioactivity levels where we can contemplate intelligent life arising, and so these would be HZ’s is its truest sense.

  • Ronald February 14, 2013, 20:20

    ljk: maybe Kardashian referred to Kim K. Wishful thinking. I would love to get a signal from her.

  • Thomas Hackney February 16, 2013, 5:16

    That DA14 is “astronomically unrelated” to the meteorfall in Russia the same day is of course is reminiscent of the Peekskill meteorfall, Oct. 6, 1992. The media and even some scientsts said it was a Draconid because the Draconid meteor shower just happened to be at its apex on that day. Draconids arrive from the North, seeming to hail from the northern circumpolar constellation, Draco the Dagon. But the Peekskll meteor was NOT a Draconid1 (it was a sporadic), for the simple reason that it arrived from the South, travelling South to North. So we’re talking about a happy coincidence here. (right! uh-huh)

  • Thomas Hackney February 16, 2013, 5:17

    Correction: Oct. 9, 1992 (not Oct. 6) sorry…

  • Ronald February 17, 2013, 13:51

    Another question, with regard to Kepler: how is Kepler doing right now? I mean after the very disturbing recent news. Have things been restored?

  • andy February 18, 2013, 14:26

    @Ronald: Last I heard, Kepler was back to science mode.

    Mission Manager Update 29th January 2013

  • Ronald February 18, 2013, 18:07

    andy, thanks, that is very good news, let’s hope scientific workhorse Kepler keeps functioning well from now on for the rest of its extended mission.

  • Ronald February 18, 2013, 19:11

    Further to the publication quoted by andy above, Heller even goes so far to state:
    “Deleterious effects on exomoon habitability may occur up to ~0.5M_sun. Although the habitable zone lies close to low-mass stars, which allows for many transits of planet-moon binaries within a given observation cycle, resources should not be spent to trace habitable satellites around them. Gravitational perturbations by the star, another planet, or another satellite induce eccentricities that likely make any moon uninhabitable.”

    And other studies, such as the above-mentioned Kepler-32 paper by Swift et al., indicate that giant planets are quite rare around M dwarfs, only about 1% occurrence. The same paper also indicates that planets are rather scarce around M dwarfs anyway, about 1-2 per star.

  • andy February 25, 2013, 17:44

    Apparently there was an error in the paper. The estimate of potentially habitable planets around M dwarfs is now 15% as opposed to 6%.

    The most probable distance to the nearest habitable planet has been decreased from 4 parsecs (=13 light years) to 3 parsecs (=10 light years).

    The Occurrence Rate of Small Planets around Small Stars (v2)

    We corrected an error in the code that calculates the number of stars for which a given planet could have been detected. The stellar parameters, planet parameters, and fraction of stars with planets did not change significantly. However, our estimate of the occurrence rate of habitable-zone, Earth-sized planets increased.

  • Harry R Ray March 13, 2013, 11:28

    WHAT DID I TELL YOU! Kopparabu’s REVISED HZ estimates put KOI1422.02 RIGHT IN EARTH’S POSITION in the HZ! He ALSO ADDS KOI2626.01 and KOI1686.01 to the mix in the middle and cold part of the HZ respectively(check out his RECENT paper on this)! I will NOW dare to characterise KOI1422.02 as a hot (but NOT steamy “water world” due to the fact that it is the third farthest out planet in a 3 planet system, and therefore, is almost certainly composed of a higher ratio of lower density material than earth. KOI2626.01 is a slightly cooler wersion of earth, and KOI1686.o1 is a MUCH HYPOTHESIZED “EYEBALL EARTH” if (and only if) 1. it hsa a huge water ocean, and;2. there is a very high amount of tidal heatiog going on in the rocky interior.