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Small Planets Confirm Kepler’s Capabilities

The planetary system around Kepler-37, some 210 light years from Earth in the constellation Lyra, had its place in the media spotlight yesterday, although it will surely be a brief one. But it’s heartening to see the quickening interest in exoplanets that each new discovery brings. Will the interest continue? In the Apollo days, public enthusiasm reached a frenzy as we moved toward the first lunar landings, then plummeted. What the media see as the big event in exoplanetary science is the discovery of a terrestrial world around a star like the Sun. Let’s hope there is no similar letdown afterwards.

After all, we’re getting close, and discoveries like those announced yesterday remind us that Kepler can find very small worlds indeed. Kepler-37b lays claim to being the smallest planet yet found around a star similar to the Sun, similar in this case meaning a G-class star with a radius about three-quarter’s of the Sun’s. The new planet is just a bit larger than our Moon, as the image below shows. The world is assumed to be rocky and, with a 13-day orbit, its surface temperature is probably in the range of 700 K.


Image: NASA’s Kepler mission has discovered a new planetary system that is home to the smallest planet yet found around a star like our sun, approximately 210 light-years away in the constellation Lyra. The line-up above compares artist’s concepts of the planets in the Kepler-37 system to the moon and planets in the Solar System. The smallest planet, Kepler-37b, is slightly larger than our moon, measuring about one-third the size of Earth. Kepler-37c, the second planet, is slightly smaller than Venus, measuring almost three-quarters the size of Earth. Kepler-37d, the third planet, is twice the size of Earth. Credit: NASA/Ames/JPL-Caltech.

As you can see from the image, we have three new worlds all told, all of them orbiting at a distance less than Mercury’s distance to the Sun. Kepler-37c orbits the star every 21 days, while Kepler-37d, probably a Neptune-class world, orbits every 40 days. A fourth candidate, identified as KOI-245.04 in the most recent Kepler planet catalog, is now disregarded, thought to be the result of random noise, starspot activity on Kepler-37, or instrumental artifacts.

Variable starlight can confuse transit detections, particularly of tiny worlds like Kepler-37b. Fortunately, Kepler-37 is both bright and quiet, allowing the methods of asteroseismology to be brought into play. The oscillations caused by sound waves generated beneath the stellar surface appear as a flickering of the star’s brightness. These measurements are tricky to observe in smaller stars, but making them allows the team to calculate the radius of Kepler-37 to a three percent accuracy. That, in turn, gives us accurate readings of the planetary radii in the system.

All of this is good news, for it implies that Kepler will be able to find Earth-sized planets in longer orbits around Sun-like stars. Once we begin finding them, is the public going to get exoplanet fatigue just as it lost interest in the Moon after Apollo? Astronomer John Johnson (Caltech) takes note of the possibility in this article in the Los Angeles Times:

“I don’t think anyone would have been taken seriously if they had said, before Kepler launched, that we’d find planets as small as Mercury,” he said. Mercury is slightly larger than Earth’s moon.

The telescope has revolutionized astronomers’ notions of our galaxy as a place that must be “teeming with rocky planets” that seem to be “a natural outgrowth of star formation,” he added.

Indeed, Kepler has been so prolific that many space enthusiasts have become blasé about exoplanet discoveries just as scientists are closing in on finding truly Earth-like worlds, Johnson said.

“Every one of these detections was unimaginable in 2008,” he said. “Every one of these is super-important.”

The paper is Barclay et al., “A sub-Mercury sized exoplanet,” published online in Nature 20 February 2013 (abstract).


Comments on this entry are closed.

  • Harry R Ray February 21, 2013, 11:22

    You are right about this “record not lasting long! In a previous comment, I mentioned KOI1422. If Courtney Dressing’s revised radii are RIGHT, one of the planets in THIS system is SMALLER than the moon! ALSO, the most recent KIC12257548.o1 radius estimate is also moon sized.

  • Michael February 21, 2013, 12:59

    If they can see planets that small it won’t be long before they can tease out the details of a moon in orbit around one.

  • Rob Flores February 21, 2013, 14:19

    Well, I guess it may be possible to get an estimate on how common
    large extra-solar moons are. I welcome a chance to test out my
    suspicion that Migrating or Original planets at orbits where gravitational
    effects of the central are strong, are so rare that we can rule out finding
    a habitable moons orbiting them.

    But maybe the angular separation of a moon and planet is not
    something that Kepler spacecraft can resolve, the article does not mention it

  • Wojciech J. February 21, 2013, 14:54

    As somebody pointed out once, the problem with Apollo was that there were no aliens on the Moon. To a public it’s a quite boring place.
    Potential to detect alien life and civilizations probably will create some interest(although I have no illusions that it will be overwhelming).
    Another aspect should be the costs which probably will be lower.
    Interestingly it seems that people at NASA are at least conceptually envisioning imagining exo-Earths after 2030.


    We will see what comes of it.

  • Joy February 21, 2013, 15:34

    What the hoi polloi think is and always has been irrelevant. The masses have no influence on politics or economics. They have always been and always will be more interested in the Kardashians than the possibility of Cardassians. What matters is whether the ruling elite develop a philosophical interest in astronomy or see a potential profit in space development. The first possibility would require our owners to imagine a cosmos greater than themselves, not a happy prospect for narcissistic sociopaths. The second possibility requires a positive return on investment in industrial space development, something that is still elusive in the 56th year of the space age.

  • Enzo February 21, 2013, 17:10

    “Will the interest continue?”

    Not if people keep announcing planets in the habitable zone that :
    1) Are not in the habitable zone in the first place. I have seen heaps of these.
    2) They are too massive (5-10 Me or more) not to likely have an atmosphere so deep that the concept of habitability becomes very speculative.

    I would start to get excited when something of 2-3 Me or less is found in the habitable zone (really HZ not just outside, on the edge, etc.). Even then, the effect of the atmosphere cannot be discounted as Earth’s atmosphere is suspiciously thin compared to what a planet with the same mass can have (Venus).
    I believe that some of the newest Kepler candidates, once confirmed, might fit the bill.

  • NS February 21, 2013, 18:09

    “The masses have no influence on politics or economics.”

    So much for democracy…

  • Dmitri February 21, 2013, 18:24

    Funny, the picture of Kepler 37-d reminded me Gliese 581c. Jokes aside we actually have a song made after the announcement of the planet was made. It was well arranged and raised to a hit status. The song is about reaching the far reaching goals (in life) depicted w/ imaginary Nature of Gliese 581c.

    Maybe we are a bit ahead of others. Can’t recall mainstream pop groups sing about the far away heavenly bodies unless they want to woo a babe.


    Laura – 581c http://www.youtube.com/watch?v=8PilONE2FjA

  • Tarmen February 21, 2013, 18:29

    @Joy . Our political leaders do indead see value in space. That is why 4 great powers have each deployed their own arrays of positioning satellites in high orbits. US has the GPS. EU has the Galileo. China is building one now. And Russia has an array of them also. These 4 GPS networks are profitable in more ways than one. They are vital military assets for each of the four. Who can doubt that military rivaly will spur mankind ever ‘higher’ to Luna and on past? The race started with V-2 rockets and the Atomic Bomb in the world war. The prize is immense.

  • Ronald February 21, 2013, 20:20

    @Enzo: I agree; a G-star (or something just bordering on it, F9, K0/1), a planet of 0.5 – 2 Me, and smack in the HZ.
    And preferably in our immediate galactic neighborhood (say, up to about 70 ly).
    Then we will get really excited. And there will be sufficient incentive, and funds, for great new space-based platforms.

  • Daniel February 22, 2013, 10:38

    This discovery of moon-size planet Kepler-37b was possible because the Kepler-37 star It’s very quiet, bright and 210 light-years for such record detection,don’t expect such kinds moon-size detection for all star in the Kepler field of view,expect for the Red dwarfs on the Kepler field because of it’s small size of course

  • Daniel February 22, 2013, 11:10

    Sources from my comment before:

    “We uncovered a planet smaller than any in our solar system orbiting one of the few stars that is both bright and quiet, where signal detection was possible,”



    Lucky strike
    Barclay said it was a bit of luck that allowed his research team to detect Kepler-37b from an extremely tiny signal. The star is relatively bright and doesn’t have a lot of activity on its surface such as star spots and flares that could cause other variations in brightness. Such phenomena would make it more difficult to detect the dimming caused by planets.

    “For most stars we are not so lucky,” Barclay added.

    While it’s hard to extrapolate how common planets this size are from a single sample, he said, “the fact that we found one around one of the very few stars that we could find one is suggestive that small planets may be very common.”


    So as we can see is the star proprieties that allow the detection of such small planets and not the Kepler capabilities of itself, in other stars in the Field will be harder,because they are very noise,and this why Kepler Mission need a least till 2016 mission to detect Earth-size planet around sun types stars habitable zone, don’t expect moon-size planets be detect around Sun type of star often,like I’ve said maybe for M dwarf star is possible,and in Kepler-37 itself can have small planets or who Knows planets with moons detect by Transit further out in long orbits from the star.

  • lurscher February 22, 2013, 14:46

    i hope it doesn’t sounds too emotional what i’m going to say, but i’m going to say it:
    We will go to the stars.

    stay tuned!

  • andy February 22, 2013, 15:13

    The telescope has revolutionized astronomers’ notions of our galaxy as a place that must be “teeming with rocky planets” that seem to be “a natural outgrowth of star formation,” he added.

    Really? Because the impression I’m getting is of a galaxy teeming with mini-Neptunes…

  • Tarmen February 22, 2013, 17:16

    Hmmmmm… I wonder if any of the millions of species now still living on this planet may have extra terrestrial origin. Q – Would there be any survivals of a wholesale alien attempt at eco-forming this rock a million years ago, or a billion years ago? Maybe an odd gene? An insect gene or a family of bugs with no pre-history ? Perhaps the dna surveys may unveil an ancient colonial survival of an overal ET failure.
    A lot of water under the bridge.

  • spaceman February 22, 2013, 17:58

    What I took away from one of the articles on this important discovery is that although it may be too early to determine the occurrence rate for small telluric planets in the Kepler data set, the fact that one was found around a star that lends itself– due to being “quiet” as opposed to “active”– to the detection of tinier planets indicates that perhaps the planet mass function does not actually drop off below 1-2 earth radii. As it stands right now, the Kepler team is still not sure if the observed drop off in planet counts below 1-2 earth radii is due to an actual fall off in small planet numbers or just that planets below this size are, as yet, undetectable around the majority of Kepler stars which have been found, on average, to be significantly noisier than anticipated. So in a way this discovery of a very small rocky planet around a star quiet enough for the detection of a very small rocky planet around it lends tentative support to the notion stellar noise is responsible for the observed drop off in planet counts– rather than a true drop off in planet counts below 1-2 earth radii. It just seems strange in light of the core accretion paradigm, as well as the dominant trend observed during the past 20 years of planet hunting, that nature would produce greater numbers of larger super-earth terrestrials and mini-Neptunes than it would smaller sub-earth terrestrials. Could it be that these smaller worlds were produced in vaster numbers only to be kicked out of their respective systems by the bigger guys? I don’t know, but it will be interesting to see how this plays out as the mission continues to collect more data…

  • xcalibur February 23, 2013, 15:06

    Really? Because the impression I’m getting is of a galaxy teeming with mini-Neptunes…

    My impression is that there is a huge variety of exoplanets and solar system arrangements out there. I believe lopsided results are caused mostly by selection bias, and the picture will be filled out more completely over time.

    I’m more optimistic than ever about finding exo-earths within 100 light years. The discovery of potential destinations in the cosmos will fuel greater interest and speculation in starflight. In particular, a confirmed habitable exo-earth will make a major impact and become a cultural icon.

    Even as we advance, there are still greater goals, of course. I think it will be some time before we start getting data on exomoons around gas giants.

  • GaryChurch February 25, 2013, 0:11

    “But it’s heartening to see the quickening interest in exoplanets that each new discovery brings. Will the interest continue? In the Apollo days, public enthusiasm reached a frenzy as we moved toward the first lunar landings, then plummeted.”

    If we can travel at around .25c in the next century (my best guess) then it will take close to a thousand years to travel 210 light years. If we detected a living second Earth would we launch such a mission? Would a black hole starship be able to function for ten centuries?
    Maybe in a century we will know- or maybe we will be extinct.

    “-a positive return on investment in industrial space development, something that is still elusive in the 56th year of the space age.”

    Hi Joy,
    Hopefully this is “the year of the comet” and the public will finally realize we are an endangered species as long as we only live on Earth. Please take a look at my take on when the space age started and give me a critique if you have the time;

  • Wojciech J February 26, 2013, 20:14

    Gary, it is unlikely that we would be able to travel directly to planets that would require more than 100 years of travel. At least using technology known to us now.
    A 100 year travel still allows a two-generational ship. Anything beyond this will require advanced techniques such as genetic modification that for example would allow long-term sleep or hibernation without aging etc. Or post-biological existence. Sending embryos would require an advanced AI capable of bring them up(unless a one man raising whole generation scenario is envisioned-Fred Saberhagen wrote about this once)
    I don’t see it happening in the next century.

  • GaryChurch February 27, 2013, 17:48

    “-unlikely that we would be able to travel directly to planets that would require more than 100 years of travel. At least using technology known to us now.)

    The only technology missing is revivable cryopreservation and IMO this will eventually be perfected; it does not break any laws of physics and basically consists of freezing without generating ice crystals. Why no money is being spent on it is a mystery. Probaby human beings are too stupid to survive.
    We could go this century if we could freeze humans. Next century we may be able to create small black holes and these are the most likely star drive. Again, there does not seem to be any laws of physics to overcome and no unobtanium required.

  • coolstar February 28, 2013, 0:13

    That paper was incredibly frustrating to read as Nature’s “rules” precluded the DOZENS of authors (everyone remotely associated with Kepler wanted in on this one) from even mentioning the star’s spectral type! (or temperature). It seems to be, from the size and mass, a late G or very early K star…..

  • Dmitri March 6, 2013, 5:52

    So, there is no place like backyard of your home galaxy. The more you dig the deeper you see what lies megaparsecs away. Turns out Europa has active ocean water circulation with the surface and Io’s sulfurus geysers rain down on the Europe’s surface. Beside earth-like planets we should not exclude moons, but that makes things a bit too complicated. And depth of Europe’s ocean is considered around 100 km. Pretty nifty staff.


  • ljk April 8, 2013, 10:46

    Dead Star Warps Light of Companion Red Star, Astronomers Say

    Apr. 5, 2013 — NASA’s Kepler space telescope, in concert with Cornell-led measurements of stars’ ultraviolet activity, has observed the effects of a dead star bending the light of its companion red star.

    Full article here: