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Earth-Sized Planets Widespread in Galaxy

Plenty of interesting news is coming out of the American Astronomical Society meeting in Long Beach CA, enough that I’ll want to spread our look at it out over the next few days. I want to start with Geoff Marcy’s investigations with grad student Erik Petigura at UC-Berkeley, the two working in tandem with Andrew Howard (University of Hawaii) on the question of Earth-sized planets and their distribution in the galaxy. But I can’t help noting before I begin how science fictional all these exoplanets are starting to seem as each day brings a new paper or announcement.

For me, science fiction has always been as much about landscape as it is about science, and exoplanets are the ultimate exercise in imagining exotic places. When exoplanet announcements were still new and we had only a small catalog of these worlds, I would find myself pondering each and thinking about what it would be like to orbit one, or stand on it. Now we’re getting hard data on potentially habitable places that evoke the compelling artwork on the covers of SF magazines I’ve read over the years. People gripe about not having flying cars or humans in the outer system, but to me the future I’ve lived into is every bit as provocative as the one that used to be portrayed in the pages of Astounding or Galaxy.

I spent yesterday afternoon thinking about the upcoming presentation of Marcy’s team at the AAS. They’ve created a new structure within which to analyze Kepler photometry for transiting planets, applying their algorithm to a sample of 12,000 G and K-class stars that were chosen because they are among the most photometrically quiet of Kepler’s targets, and thus best suited for the detection of small planets. The work focused on close-in planets with orbits between 5 and 50 days, Earth-sized worlds that are at the margin of detectability within the Kepler data.

The results show that about 17 percent of all Sun-like stars have planets in the 1-2 Earth diameter range orbiting close to their host stars — here we’re talking about distances within about 0.25 AU, which places these worlds well inside the orbit of Mercury. The team also extrapolates from its results that the fraction of stars having planets of Earth size or a bit bigger orbiting in Earth-like orbits may be as high as 50 percent. Both findings follow from the researchers’ analysis of how often planets of a particular size appear, as Andrew Howard notes:

“Our key result is that the frequency of planets increases as you go to smaller sizes, but it doesn’t increase all the way to Earth-size planets — it stays at a constant level below twice the diameter of Earth.”

In other words, there are more small planets than large ones, with perhaps one percent of stars having planets the size of Jupiter, while 10 percent have planets the size of Neptune. But Petigura’s work goes farther than this, suggesting that the increase in planets as size decreases stops when we get down to planets of about twice Earth’s diameter. The numbers then remain the same until we reach planets the size of the Earth, beyond which this analysis ends. That’s a finding that leaves plenty of room for Earth-like worlds in abundance throughout the galaxy.

Petigura’s work was clearly key for the project because it was he who developed TERRA (Transiting ExoEarth Robust Reduction Algorithm), a program through which the UC-Berkeley team fed 12 quarters of Kepler data. Petigura wanted to find out how many Earth-sized planets Kepler was missing, their faint signals lost in the ‘noise’ of a transit lightcurve. Measuring the fraction of planets Kepler wasn’t seeing, the team was able to extract 119 Earth-like worlds ranging from six times Earth’s diameter all the way down to a planet the size of Mars. Thirty-seven of the team’s planets had not been identified in the previous Kepler work.


Image: The fraction of Sun-like stars having planets of different sizes, orbiting within 1/4 of the Earth-Sun distance (0.25 AU) of the host star. The graph shows that planets as small as Earth (far left) are relatively common compared to planets 8.0x the size of Earth (similar to Jupiter). For example, 7.9% of Sun-like stars harbor a planet with a size of 1.0-1.4 times the size of Earth, orbiting inward of 1/4 the Earth-Sun distance (closer than Mercury’s distance from the Sun). There are increasing numbers of planets from 8x the size of Earth down to 2.8x Earth. Remarkably, the number of planets smaller than 2.8x Earth is approximately constant with planet size, down to the size of our Earth. The gray indicates the planets discovered in this study, and the orange represents the correction applied to account for planets the TERRA software would miss statistically, typically about 20%. Credit: Image by Erik Petigura and Geoff Marcy, UC Berkeley, and Andrew Howard, Institute for Astronomy, University of Hawaii.

This study takes us another step along the way to a major exoplanet goal. Getting a sound estimate of the fraction of Sun-like stars bearing Earth-sized planets in the habitable zone — eta Earth — is tantalizingly close, and the paper on this work points out that its 12,000 stars will be among the sample from which this estimate is drawn. The Berkeley team homes in on close-in planets as a way of studying planet frequency in relation to size, the assumption being that estimates of habitable zone ‘Earths’ will tighten as we get further data. From the paper:

Our key result is the plateau of planet occurrence for the size range 1–2.8 RE for planets having periods 5-50 days. With 8 years of total photometry in an extended Kepler mission (compared to 3 years here), the computational machinery of TERRA— including its light curve de-trending, transit search, and completeness calibration—will enable a measurement of [eta Earth] for habitable zone orbits with extended mission photometry.

All in all, the team estimates that uncertainties in detection mean that Kepler misses about one in four big Earth-sized worlds, a figure this work now corrects. Planets larger than Earth in this category may often turn out to be more like Neptune than Earth, with a rocky core surrounded by helium and hydrogen — planets like these may, in close orbits, be water worlds with vast oceans and no exposed land surface. But the UC-Berkeley work gives us plenty of reason to think that rocky worlds like Earth within stellar habitable zones are going to be anything but rare.


Comments on this entry are closed.

  • Wojciech J January 8, 2013, 14:25

    Looking forward to more news from AAS meeting. What we are starting to see, even if it isn’t clear yet, is that a breakthrough in astronomy is emerging. Year by year the exoplanet research is becoming more important with its discoveries. I hope that it will give a strong impulse for a mission observing our closest neighborhood and follow up in form of direct imagining telescopes.

  • Tom B January 8, 2013, 15:19

    Agreed, as time goes on this just gets more and more interesting. Makes one wonder as to where we will stand with our research in say five years.

  • Rob Flores January 8, 2013, 15:33

    Very heady stuff. You have to look at the positives. For while, early
    planet hunting there was the posibilty of alot of Jovians, and not so many
    Terrestrials. While Jovians maybe great for fueling ships, it certaintly is
    nice that heavy metals are easly gathered on planets on these new solar systems.

    It’s sounds as if we have a reasonable chance at detecting 1-4 Earth
    analougues when all the analysis is done. How close an analogue is the
    magical questions isn’t it. an E-size World with an avg equatorial temp of 25C-35C. with rotation between 18-30 hours. Sofar I haven’t heard anything regarding Orbital Eccentricity mentioned. I assume it can be
    derived. I would be usefull to know if our very ordered Solar system is

    I know they have ruled out large population of Jovians close in to the stars being analyzed by Kepler. But does that mean that they are More or Less likely to possess Jovians at the range of 4-20 AU

    Hope they aren’t meeting at the Queen Mary.(great history site but leaky creaky site)

  • Eric January 8, 2013, 16:30

    And the amazing news keeps on coming, week by week. This is a wonderfully exciting time to be alive.

  • Zen Blade January 8, 2013, 16:34

    Bam! I kind of feel like telling no one in particular “I told you so”.

    The exciting part of this is how long until we have “Earth” candidates out there. Within the next year or two would be my novice’s estimate, but I’d love to hear from someone more knowledgeable about how long it will be.

    Once a definitive candidate has been found, I think that’s when real interest in space from the general public will begin to pick up again. The idea of imaging (and imagining) an Earth planet out there. I’d love to see some advancement on the solar system-sized (or something similar, I forget the precise specifications) telescopes where space crafts are present at various locations to create a gigantic lens (correct interpretation?) that would be capable of visualizing planet-sized (or continent-sized) bodies in the galaxy.

    Anyways, tally ho!

  • Mike January 8, 2013, 16:45

    I certainly hope Kepler keeps working for at least 4 more years. We already have almost 4 years worth of data. Improved and clever data analysis of the existing Kepler data base might eventually provide the answers to our questions regard eta-Earths but it will be much better to get 8 or more years total worth of observations.
    Also I have some doubt about the indicated rarity of Jovians worlds. Even single transit detections of cold Jovians might give us a little better understanding of their numbers. Another good reason to hope Kepler stays healthy.
    What wonderful things we have to debate and argue over. When I was young I never thought we would have our hands on this kind of knowledge. I thought we would have to send star ships to learn about exo-worlds. Something that was clearly far in the future I thought. Well the star ships probably are still. Is this partly what you meant Paul when you mentioned the science fictional feel to the AAS news?
    This taste of the future leaves me greedy for more. I would love to see a biomarker hunter mission launched in my lifetime. Well, who wouldn’t?

  • GaryChurch January 8, 2013, 19:08

    Wojciech is reading this right.
    Finding living worlds with space telescopes is the next big frontier that will appeal to the public. After the first blue or green or whatever planet is imaged people will go nuts over this stuff.

    Once imagery is available the race will be on to find the “Closest Earth.” And finally when this planet is identified then serious discussion about sending people there will begin.

    Technology being where it is then a beam propelled Bernal Sphere several miles in diameter and slowed down up arrival (after centuries) by H-bombs will be proposed- and may fly by the end of this century.

  • Rob Flores January 8, 2013, 19:15

    Okay some calculations to get an idea of the scope of things.

    Via Kepler info, I was able to determine that Kepler looks at
    an square of 15 deg of the sky and is capable of detecting transits from 300-3100 Ly. 2800 Ly depth of detection. Converted Degs to Ly to ge the size of sides the rectangle view area, (at mid point of detection range)

    This tranlates to roughly to 14,049,280,000 CU LY. Basically
    2240 Ly x 2240 Ly x 2800 LY

    Here is the average distance between Earth Twins based on the assumed number of twins in the Kepler field of view including all planets, transiting
    as well non-transiting. Avg dist normalized to a regular CUBE of 2,412 Ly.

    1 twin = 2400 Ly Avg. dist
    10 twins = 1120 Ly Avg dist
    100 twins 519 Ly Avg Dist. (one Kepler twin detection would suggest
    this, but it’s not a rigid stat. unless we somehow got extra lucky)

    500 earth twins 304 Ly Avg Dist. ( this is what 5 Kepler twin detections would tend to)

    1000 Earth Twins 241 Ly Avg Dist. (Gold Rush, this means our closer
    Sun like stars MIGHT have a habitable planet. Somebody else do the
    statistics. I hate Stats.

    Obcourse the issue of what is a twin of Earth is fungible. Suffice it to say, that if you were on such a planet at the equator you would only need a breathing mask, plus land and water as part of the geography.

  • joy January 8, 2013, 19:21

    The one caveat is whether the 12% of Kepler stars which are photometrically quiet have planetary systems which are statistically representative of the entire Kepler sample. I would assume probably yes …

    Once again, had Kepler not been conceived, designed, funded, and flown, the exoplanet field would likely has languished for a decade or longer. Kudos to all involved with Kepler. Hope this lights a fire under the astronomy community to fund planet imagers!

  • Ronald January 8, 2013, 21:22

    More fascinating Kepler news concerning planets and in particular earth-sized planets!
    Note that the fact that planet abundance per size class does not keep increasing all the way down to the smallest classes can also be attributed to the size classes being so unequal: toward the smaller sizes they become narrower. If we take similar size classes, or even logarithmically similar (1-2, 2-4, 4-8), we see a continued increase in planet abundance toward smaller sizes.
    The sentence “119 *Earth-like worlds* ranging from *six times Earth’s diameter*” (emphasis by me) can’t be right, though it was in the original paper as well.

    The really spectacular conclusion is the statement that “the fraction of stars having planets of Earth size or a bit bigger orbiting in Earth-like orbits may be as high as 50 percent”.
    That implies an Eta Earth of some 50%!!!
    How amazingly different from very conservative previous estimates (such as by Catanzarite & Shao).

    As I mentioned in another recent comment, it would be so interesting not just to have ‘planet size class distributions’, but also ‘planets per orbital period distributions’ for different size classes and planet types. In other words, extrapolations to wider orbits. But other than the above-mentioned very promising statement about Earth-size planets in Earth-like orbits, it may still be a bit too early for reliable extrapolations like that.

  • joy January 8, 2013, 22:00

    Continuing the refinment of what is an “earth twin”. We would be thrilled for Kepler to find an earth radius, earth mass planet in a 225 day orbit around a sun like star — Oops, that one is Venus! And most of these Kepler super earths are likely much less earth like than that.

    Agree with what Rob Flores calculated. I would suspect that the nearest world which is move-in ready for farmers and real estate agents is hundreds of LY away. However the nearest world with liquid water on the surface is likely to be much closer than that, even though it might lack any dry land. For this century, it will be all about gathering knowledge with telescopes.

  • Stan January 8, 2013, 22:35

    Add to the Earths in habitable zones an even more exciting possibility: Jovians in habitable zones with two or more Earth-size moons.

    If we saw another big blue and green Earth rising out there every night, we would have sent a colony there a LONG time ago, and by now we would be a serious space-faring civilization. Even without an Earth for a moon, most of our ancient civilizations were obsessed with the workings of the night-time sky to the point where they invented mathematics. With an Earth up there, they might have had the incentive to develop the other sciences as well.

    In any case, if these systems would eventually catalyze space colonization, they would then catalyze science in general as well. And vice versa. It may be unending: Each moon might fill in when the other slacked off. These may be the main centers of galactic colonization.

    It will be interesting to see if Kepler can find any.

    Thanks to whomever brought up this possibility here on Centauri Dreams a while back.

  • coolstar January 8, 2013, 22:50

    If eta-earth really is close to 0.5, the there should be, very roughly, about
    0.01*0.5*12000 = 60 earth analogs in this sample. Given that these are the quietest solar type stars and were chosen because of that (about as quiet as the mission was designed for, more or less), then the odds are we’d already have good data (at least 3 transits) on at least a handful of these systems (and perhaps many more). Nobody would wait for 6 transits if they already had 3 good ones to announce the single thing Kepler was designed to do.
    Thus my conclusion is that eta-earth, unfortunately, is no where NEAR 0.5. An eta-earth of just a few percent, as argued by Catanzarite and Shao, is entirely consistent with no earth analogs yet being found.

  • GaryChurch January 8, 2013, 23:49

    We should be launching a telescope that masses about twice as much as the Webb every 3 or 4 months. We just need an HLV like the SLS and some DOD money.

    I think ten or twelve stationed at L2 could be combined into a decent planet imager. But I know about as much about telescopes as Eniac knows about space radiation so I am shooting in the dark here.

  • coacervate January 9, 2013, 0:24

    I wish to echo Joy’s second point and suggest if you agree, please let your representatives know about that. For me, Kepler came as a wonderful surprise days before it was launched. I had no notion that this approach could work. What other wonders await discovery if we only take the chains off the creative minds in our midst…Was it Rutherford who said “We didn’t have much money so we had to think” ? More candles, less darkness! May we all endorse investing in deep thought as essential lube for the wheels of progress?

  • A. A. Jackson January 9, 2013, 8:03

    I went to the Jan. AAS meeting in Austin last year , there were so many EXO planet and EXO moon sessions I lost track.
    The numbers went up then and now up again, I expect them to go up again!
    I remember when the skeptical used to put the fraction of those stars that have planets at 1.
    I fully expect that by the end of the decade the average number of planets that can potentially support life per star that has planets (Goldilocks zone) will be known too.
    Copernicus strikes again!

  • Jason January 9, 2013, 10:27

    Rob, not sure why you are trying to find the volume of a cube, but per my email conversation with Alan, and Engineer working on the project, the total volume of the search area is 1.3BLy^3:

    V = 1/3 (s^2 x h)
    if s = length of the side of the base and h is height of the pyramid.

    Since field of view is about 10 degrees square, s is approximately h (tan 10), so

    V ≈ 1/3 h^3 x (tan 10)^2 ≈ 1/3 x 5000 x 5000 x 5000 x 0.176^2 ≈ 1.3 billion cubic LY

    I was maily curious how much volume in the form of a sphere Keplers search area would fill. It comes to around 680Ly^3.

  • Wojciech J January 9, 2013, 14:26

    Zen Blade-the term you are searching for is hypertelescope

    Mike January 8, 2013 at 16:45
    ” certainly hope Kepler keeps working for at least 4 more years. We already have almost 4 years worth of data”
    As I understand the current results are from data till March 2011, so there is a lot more already downloaded that needs to be analyzed. But further years would be good. Also as far as I remember Kepler originally was basically dedicated to answering if exoplanets exist in meaningful numbers at all-due to distance it doesn’t answer questions about our closest neighbors which are most interesting

    GaryChurch January 8, 2013 at 19:08
    “” Finding living worlds with space telescopes is the next big frontier that will appeal to the public. After the first blue or green or whatever planet is imaged people will go nuts over this stuff.”
    That is my hope as well. While I am too realistic to expect revolution, I hope that direct image of an alien biosphere(even if only continents with vegetation cover for example) will gradually give more impulse to space efforts.Certainly not one that will make governments spend 10’s of percents to space programs, but even doubling of today’s numbers would be good. And there is always a slight hope-however slim-that direct imagining will succeed where radio SETI has failed.

    joy January 8, 2013 at 22:00
    “Agree with what Rob Flores calculated. I would suspect that the nearest world which is move-in ready for farmers and real estate agents is hundreds of LY away”
    I think that most of readers here after countless studies of possible colonization efforts in far, far future(certainly not within this century) know that alien biospheres probably will never be subject of colonization(too much effort to destroy too much value), the minimum requirement would be an asteroid field in other system-of which there are plenty it seems.

  • Daniel January 9, 2013, 16:08

    Copernicus go Strike Coolstar with his pessimism Like always he is…Kepler mission is not at end yet,and Earth-size planets in Hz is very hard to detect in the Kepler field due the Stars on the filed are very active,very noise,there is a lot of hard work to detect a Earth-size in HZ.

    Skepticals Always broke the face in the wall on the end of the day.
    They put too much faith on simulations, but forget that is a lot of observation to do yet,and normally the observation always find something that challenge the simulations in the exoplanet field is full of examples,Like,existence of other planetary system are rare (I remember long time ago Skepticals saying that the solar system form in a very rare stellar collision hypotheses the most “likely explanation” for many on the time),Hot Jupiter,circumbinary planets,planets around neutron stars,planets in binary systems,planets in globular clusters (like PSR 1620-26b in M4 globular cluster) etc.

    Or sometimes like Coolstar,Ronald (on the Kepler-32 post about M dwarf planetary system in the galaxy) and other…jump to conclusion without wait the full data,and take conclusions for there preliminary data, ever if the data start point for something different from what they expect

    I just wait and expect for detection of Earth-size moons around Jupiter-size planets be confirm by Observation, specially if there is many of Gas giant-Earth-size moons in the galaxy , to see what the Skepticals go to say,I know what they go to do,they go to try new simulations, because the old one like always don’t explain what is been observed,like they did for explain the existence of hot hot Jupiter,with planet migration.

    What I want say with all this is that does not help make a premeditate pessimistic view of something that is not yet been observable ,specially with incomplete data and only by computer simulations,a fully good simulation need more observation,and Kepler I believe will be capable of this like the scientist of the project say in 7-8 years,so just not is time to jump to conclusions.

  • Daniel January 9, 2013, 16:11

    ” like always” is wrong statement of mine, “like many time” would be more appropriate

  • FrankH January 9, 2013, 16:14

    A Jovian in a habitable zone may make for good sci-fantasy, but in reality it’s probably the worst possible scenario:

    A jovian planet would have formed past the snow line and its moons will be mostly ice & rock. It’s very unlikely that a Jupiter sized planet will have moon’s larger than Mars.

    Move a jovian planet into a warm HZ and that icy, Mars sized moon will melt. Since its mass will be much lower than an equivalent sized rocky world, it’s escape velocity will also be much lower. The Mars sized moon will quickly become an ex-parrot – a smaller, airless rocky world.

    About the only way to get an Earth-sized (0.75 – 1.25 Earth mass, just to be conservative) moon around a migrating jovian is via capture, as the jovian barrels in. While possible, it’s not likely. A more reasonable result is that the Earth planet will impact the jovian or it will be sent into the inner system or ejected.

  • coolstar January 9, 2013, 18:12

    FrankH has made that observation before, and very few people seem to be listening. This is too bad because he’s almost certainly correct! The discovery of exo-moons will be exciting, but the number of habitable worlds they’ll add is very likely to be inconsequential.

  • Stan January 9, 2013, 18:54

    Thanks, FrankH

  • Rob Flores January 9, 2013, 19:17

    Just to point out, some differing assumtions, since I was off by one order of magnitude compared to your calculations on cubic volume.

    Okay, I found the Field of view value of 15 degrees on this site, .
    http://kepler.nasa.gov/cgi-bin/ra2pix.pl .
    You used 10 Degs I used 15 degs 125% more area
    My depth of detection was off probably too. From nasa website.
    600 Ly to 3,000 Ly. 2400 Ly depth and over statement by 35% by me.

    If I take the cube root of YOUR result 1.3B Cu ly you get =
    a box 1,091 Ly on each side. ( I prefer boxes to illustrate distribution.

    Recalculating for 500 total Earth Twins in Keplers field of view (inc. non transiting potential planets. 1.3 ^9 / 500 = 2,600,000 cu Ly (we should detect 5 twin earths with Kepler field of view, if this is the most prevalent result).
    Taking the Cube Root of this We get an average distance of 137 LY.
    Pretty good.

    There will be much gnashing of teeth if Kepler detects ZERO
    Twins of earth It will mean the closest Earth twin is more than likely a couple hundreds of LY away, on the average. In this scenario I would consider it wonderous luck to find one at less than 300LY.

    Using 15 degrees of FOV, I get a CU LY of 7.02^9

  • Wojciech J January 9, 2013, 19:46

    ” It’s very unlikely that a Jupiter sized planet will have moon’s larger than Mars.”
    Plenty of planets that were discovered in HZ are larger than Jupiter.

  • jkittle January 10, 2013, 10:07

    It should be possible to build a relativley inexpensive scope with the ability to scan the ENTIRE SKY from orbit. This oule have perhaps 16 to 32 mounted 50 megapixel cameras with relatively modest lenses eachwith exagerated Field of view. mount each at the corners of a ccube and pointing in divergent directions. This all-seeing instrument( ISIS?) would continuously cover the entire sky and take in all the major star systems within say 1000 ly and be able to monitor for kepler like trasitions. thus we could identify all the start systems nearby wit edge- on planet systems, making it easwier to study these ojbects ( a lof o the kepler systems are pretty far away. ) It is now not about the sensitivity of the detectors, just the dynamic range.
    Heady times… this type of data whets the appetite for more! the Kepler team is amazing.. I do fear the instrument platform is failing before the next five yeras are out ( bad gyros)

  • Ronald January 10, 2013, 13:43

    jkittle: if your proposed transit scope would observe all stars up to 1000 ly, it would then cover almost 4.2 billion cubic ly and some 8 million stars, assuming a reasonable 0.002 stars per cubic ly.
    So, even going to only 500 ly would already include some 1 million stars in the survey, and to 300 ly (isn’t that about our Local Bubble?) still over 200,000.
    Nice idea!

  • Ronald January 10, 2013, 14:01

    Just joining the habitable exomoon duscussion: although I tend to agree with FrankH with regard to gias giants in the HZ mainly being bad news and also pointing out to Wojciech J that super-Jovians are actually rather rare, I want to make reference to an interesting recent study, by Heller and Barnes in Astrobiology: Exomoon habitability constrained by illumination and tidal heating.
    There is a complete PDF of the article accessible.

    They distinguish a circum-planetary “habitable edge”. To be habitable, moons must orbit their planets outside the habitable edge.
    And conclude about two studied planets: “If either planet hosted a satellite at a distance greater than ten planetary radii, then this could indicate the presence of a habitable moon”.

    They do treat the issues of formation of massive satellites and harmful radiation near a gas giant.

  • Mike January 10, 2013, 15:32

    To jkittle, what you’re describing sounds a lot like CHEOPs or TESS. Now if only the funding is secured. Especialy if these instruments are optimized for the near infra-red so as to observe the entire M dwarf sequence more completely.
    Kepler ( as intended) can and should give us a very good understanding of planet populations around solar-like stars (at least for the inner part and HZ of the systems) but the small number and only early part of the M dwarf sequence in Kepler’s target list means that for red dwarfs the survey results will be somewhat shaky.
    Considering that most stars in our galaxy are red dwarfs and most of them are much smaller then .5 solar masses that is why I think an all-sky transit survey optimized for the entire stretch of the M dwarf sequence is required to improve our knowledge of planet populations hosted by all types of galactic disk main sequence dwarf stars. From F through G and K ( Kepler) to M ( Super TESS or superCHEOPS). That’s the vast majority of stars.
    Now if you want to know about planets around all the very nearest (30 light years) stars then it’s time to restart the Space Interferometry Mission.
    The transit method will not detect most of the nearby stars’ planets.
    Imagine having an atlas of all the nearby stars listing their planets with known orbits and masses. Information essential for next generation atmospheric analysers or planet imager missions. This info is going to be very difficult for ground based instruments to obtain. Particularly for smaller planets in wider orbits. I think SIM is still what’s required to get that job done.
    But where’s the money coming from? Perhaps George Lucas would like to be remembered in the coming centuries long after his space operas are forgotten. The Lucas SIM planet finder! He can name all the newly discovered planets! Why not? As long as it gets the mission launched. Us astronomical beggars can’t be too choosy in these difficult economic times.
    Anyone know George Lucas’ email address?

  • jkittle January 10, 2013, 17:16

    Mike ; the European space scope GAIA will be able to track the proper motions of nearby stars with high accuracy but this will not be very sensitive to transits. it surveys the whole sky but onelyover a series of pictures over time. a continous surveillance would record a different set of events. We actually have the technology to to an ISIS without any stretch. would be decent for NEO’s too. it is just not sensitive to faint or dark objects, like the infrared one would be. it would not be hard to have it extend down to 1 micron which is just below the visible range . I recently posted on a Different mission for a soupped up WISE telescope to do that. thanks !

  • Rob Flores January 10, 2013, 18:09

    Agree trying to get a better handle on Red dwafs, up to 50% solar mass.

    I hold the view that generaly planets around M stars are Hostile to the emergence of life. But we need to know what percent of M of these are quiescent in terms of flares, to get a handle on the size of the possible exceptions. Even if only 10% of M stars are well behaved that
    will push the average number of planets suitable for life way up.

  • Ronald January 10, 2013, 20:04

    great idea: Lucas, and Spielberg, Gates, …

  • Etienne January 11, 2013, 14:52

    Great news! Looking forward to living long enough to see wonders!

  • Jim C January 11, 2013, 18:03

    Rob, I think Jason’s figure of of 1.3 billion cubic light years for the Kepler ‘search volume’ is a bit off the mark.

    Taking 3000 ly as the outer limit, that’s a volume of 1.13×10^11 cubic ly (4pi/3 x 3000^3). Subtract the inner sphere with radius of 600 ly results in a volume of 1.12×10^11 for all space around us between 600 and 3000 ly out. The Keper field of view is 105 square degrees square – thats 0.25% of the sky. So the Kepler search volume is 0.25/100 x 1.12×10^11 = 280 million cubic light years. Equivalent to a cube 654 ly on each side.

    Using your 500 earth twins figure within the Kepler volume gives us 82 light years as the average distance between earth twins.

    But wait, there are absolutely tons of stars within this search volume that Kepler doesn’t monitor, especially the M class ones and perhaps the fainter ones to us. On the other hand the field of view was chosen partly because it had a lot of stars.

    In terms of estimating the average distance from us to the nearest earth twin I guess a better method would be to understand the distribution of classes of stars in our area and allocate figures proportionally from the chosen Kepler stars.

  • spaceman January 13, 2013, 1:17

    It is also worth noting that the high false positive rate for giant planets found by SOPHIE last fall was recovered by the most recent analysis of Kepler data by David Charbonneau et al. Here is a quote from the paper which was accepted for publication in the Astrophysical Journal:

    “Another estimate of the false positive rate
    for giant planets was made recently by Santerne et al.
    (2012), from a subsample of KOIs they followed up spec-
    troscopically. They reported that 34.8±6.5% of close-in
    giant planets with periods shorter than 25 days, tran-
    sit depths greater than 0.4%, and brightness Kp < 14.7
    show radial-velocity signals inconsistent with a planetary
    interpretation, and are thus false positives. Adopting the
    same sample restrictions we obtain a false positive rate of
    29.3 ± 3.1%, in good agreement with their observational
    result. This value is significantly larger than our over-
    all figure of 17.7% for giant planets because of the cut
    at P < 25 days and the fact that the false positive rate
    increases somewhat toward shorter periods, according to
    our simulations (see Sect. 6.1)."

  • ljk January 14, 2013, 18:06

    A golden age of exoplanet science

    Last week astronomers met in California to discuss the latest discoveries in the field, and the study of extrasolar planets was front and center. Jeff Foust reports on the wealth of exoplanet discoveries that are giving scientists new clues about how common planets, and potentially Earth-like ones, are in the galaxy.

    Monday, January 14, 2013


  • Ronald January 17, 2013, 19:52

    Ref. ljk’s article “A golden age of exoplanet science”, two remarkable quotes:

    – “70 to 90 percent of stars have planetary systems. Almost all Sun-like stars have a planetary system”.

    But also on M dwarfs:

    – “based on existing data, there should be 0.06 planets in the habitable zone per small star. That means there is, with 95% confidence, an Earth-like planet within 31 parsecs of our Sun”.

    I am sorry, but that conclusion I do not logically see, unless the reporting is wrong. A planet in the HZ is not yet an earthlike planet. Ok, most planets around M dwarfs are small to medium-sized. But 6% of M dwarfs with any kind of planet in the HZ does not seem like a whole lot to me.

  • Holger January 18, 2013, 16:59

    @Ronald: “6% of M-dwarfs with any kind of planet in the HZ ” would be few indeed. But you could reach the claimed conclusion if you additionally assume e.g. that 10% of those planets are Earthlike (i.e. eta_Earth=0.006 for M-dwarfs): There should be some 10,000 M-dwarfs within 31 parsecs (most probably still undiscovered), so this would give an average number of about 0.006*10,000 = 60 Earthlike planets within that distance – thus certainly more than one at 95% confidence.

    But of course 31 parsecs is still a big distance; I would rather hope for a “second Earth” within 5-10 parsecs.

  • Thomas Hackney January 22, 2013, 3:21

    Since M-class dwarfs are both numerous and long-lived I wonder if some sort of life might have had time to develop on some of their planets. We know that life as we know it developed almost immediately around a 4.8 billion year old G-type star, but what about around a 10 billion year old M-type star where life can take its sweet time getting started? With Goldilocks having so many choices and so much time to look around you have to wonder. Maybe the life there is not “life as we know it” but something rather different. Maybe instead of being self-replicating it is eternal — it simply grows and grows. Such a lifeform would essentially take over or become the planet, maybe even developing a form of intelligence. Instead of taking only a few hundred million years to develop, Mr. Murphy’s weird cousin (if life can happen, it will) could provide Goldilocks with a comfortable bed in which to lie in several billion or more years. Hey, stranger things have probably happened, somewhere, and what more likely place could there be for this than on a planet revolving around an M-class dwarf? Just wondering. Again.