Kepler's Early Results Suggest Earth-Like Planets Are Dime-a-Dozen

By Andrew Moseman | July 26, 2010 4:53 pm

KeplerCraftAlthough some publications glossed over the uncertainty in announcing the first findings of the planet-hunting Kepler mission, researchers say the overall point remains true: Earth-like planets (meaning that they’re small and rocky, not that they have aliens writing blogs about science) are not only not rare–they’re the most common type of planet in our galaxy.

The first intimations of this news came out a few days ago in reports like the Daily Mail’s, which blared that NASA’s planet-hunting Kepler mission had found 140 new planets that were like the Earth in size, and that worlds like our own could dominate the Milky Way. That claim came after a presentation now available to view online by one of the scientists behind Kepler, Harvard’s Dimitar Sasselov.

But Sasselov and colleagues responded to, trying to quell some of the excitement–or at least hedge on the exact magnitude of the find:

“What Dimitar presented was ‘candidates,'” said David Koch, the mission’s deputy principal investigator at NASA’s Ames Research Center in Moffett Field, Calif. “These have the apparent signature we are looking for, but then we must perform extensive follow-up observations to eliminate false positives, such as background eclipsing binaries. This requires substantial amounts of ground-based observing which is done primarily in the summer observing season” []

The trouble arose after Kepler scientists kept a tight lip on their findings. Last month, they announced that their first round of research had found around 700 exoplanet candidates. (For comparison, there are fewer than 500 confirmed exoplanets now). But the team refused to discuss the details of about half of those planet candidates, and those are the ones most like the Earth. Given the scientific cred at stake, they wanted to analyze and publish papers before releasing data to the public.

Sasselov says he wasn’t giving out new information that wasn’t already available in papers published last month, but in the conference video he’s pretty direct about the cosmic importance of the findings, whether or not they’re merely candidates.

At 8:15 into his 18-minute talk, Sasselov showed a bar graph of planet size. Of the approximate 265 Kepler planets represented on the graph, about 140 were labeled “like Earth,” that is, having a radius smaller than twice Earth’s radius. “You can see here small planets dominate the picture,” said Sasselov. Until now, astronomers’ exoplanet finds had been more like gas giant Jupiter than rocky little Earth [ScienceNOW].

So, yes, the astronomers need to conduct a battery of tests and analyses to make sure the signals they’ve seen truly are planets. Only five of Kepler’s 700-plus haul of candidates are officially confirmed now.

But that doesn’t mean we shouldn’t be excited. Sasselov says they should be able confirm 60 of these Earth-like candidates at the very least. And even that would change our picture of the galaxy, and mean that many more planets like our own are out there.

“Even before we have confirmed the planets among these hundreds of candidates, we can see statistically that the smaller-sized planets will be more common than the large-sized (Jupiter- and Saturn-like ones) in the sample,” Sasselov explained [].

As his slide says during the presentation: “The galaxy is rich in small, Earth-like planets.”

Related Content:
80beats: Kepler Telescope Spies Its First 5 Exoplanets, Including “Styrofoam World”
80beats: Kepler Sends Postcards Home: It’s Beautiful Out Here
DISCOVER: How Long Until We Find a Second Earth?
Bad Astronomy: Kepler Works!

Image: NASA

MORE ABOUT: exoplanets, Kepler
  • Rhacodactylus

    Nice, always good to see a figure in the Drake equation heading in a friendly direction!

  • Brian Too

    Maybe our solar system isn’t so atypical after all. That’s got to make the planetary formation theorists happy, or at least more comfortable. The exobiologists also get a big shot in the arm methinks.

    And yet there’s plenty of offbeat and edge case scenarios given what we’ve discovered so far. Do you get the feeling that there’s decades, nay centuries, of work in this? The Sloan isn’t even close to finishing the survey of all detectable galaxies…

    Then the stars…

    Then the planets…

    Then we need to try to detect life…

  • M Burke

    “…like the Earth in size…” != “Earth-Like”
    That’s like saying a donut is like a wheel… well, yeah, sorta.

  • Torbjörn Larsson, OM

    “That’s like saying a donut is like a wheel”

    Not really, since many characters will correlate (differentiated core, likely magnetic field for the same rotation rate, atmosphere pressure, and so on).

  • nick

    I think by earth-like they are referring to planets like Venus, Mercury, Mars and, of course, Earth – heck, many moons in our solar system could be considered earth-like planets except for the fact they orbit planets.

    I just think it’s sick that people can see so many trillions of stars and think “we are completely unique, no planets could possibly exist around them,” or, in the 15 or so years since we’ve actually found planets around other stars, think “well, we know there are a few other planets here and there but there couldn’t possibly be other solar systems like ours.”

    There is wayyyyyyyyyyyyyyy too much universe out there for there to not be planets like ours, and for there to not be life out there. The only question is when and how are we going to discover it, or will our species last long enough to make those discoveries. So far, so good…

  • gregorylent

    yogis have known this for centuries … astral travel is a concept because it is a reality

  • shiny hammer

    Did’ya hear about the new planet Kepler found called Pedantica? The dominant life form reproduces assexually. It seems they whine over the minutia of reproduction so much, they miss the bigger picture and can’t seal the deal.

  • pheldespat

    It’s been said above, but I think it’s worth repeating:

    “…Kepler mission had found 140 new planets that were like the Earth *in size*…”

    “…like the Earth *in size*…” != “Earth-Like”

    Venus is like the Earth in size, but it’s not very Earth-like. Mars is not much smaller either, but it isn’t very Earth-like.

    The Earth-like many people are thinking of is -more or less: a rocky planet, with liquid water, breathable atmosphere, magnetosphere, plate tectonics…

  • jim

    This is amazing. Millions of earth size planets in our galaxy alone. I think the numbers we see will blow everyone away.

  • Amos Zeeberg (Discover Web Editor)

    Good points about what Earth-like does and doesn’t mean. Maybe we’ll do a follow-up post on what the definition is and what can be inferred about planets that fall into that category, as Torbjörn mentions. Are you an astronomer of some stripe?

  • YouRang

    Discover Web Editor write: “….as Torbjörn mentions. Are you an astronomer of some stripe?”
    You don’t need to be an astronomer to recognize that they’re including inhospitable places like Venus, Mercury the Moon. If the zealots for atheism weren’t so intent on proving we’re not alone and that none of the planets in the universe harbor beliefs about gods, they wouldn’t go all wee-wee about religious arrogance of people other than themselves and wax so goo-goo about contact that hasn’t been made yet.
    On a technical note: I haven’t followed the details of what Kepler is doing very closely, but it seems to me that Kepler will have the opposite problem to the older planet detection methods–it will find inner rocky planets more than true Jupiter like planets (out at the edges of their respective solar system). I.E. it’s the innerness for which the planets are a dime a dozen.

  • Torbjörn Larsson, OM

    It’s been said above, but I think it’s worth repeating: “…like the Earth *in size*…” != “Earth-Like”

    “Earth-like” is a somewhat bad term, since people will read their own definition into it.

    For the purpose of the research discussed, it is the radius. (Transit method.) And as I noted, terrestrial planet radius correlates with many other characteristics.

  • Torbjörn Larsson, OM


    First, good idea.

    Second, I will assume that is directed to me.

    No, I’m not an astronomer, my background is in physics of electronics (PhD in semiconductor processing). But I’m interested in astronomy, also biology, up to the point that I’m currently enrolled in a course in astrobiology at the local university.

    The study material, and some access to professional astrophysicists and astronomers both, certainly helps to parse the science.

  • scribbler

    Someone correct me if I’m wrong but isn’t adding all these dead and “life impossible” planets to the formula systematically destroying conjecture about life in Space?

    I mean, until we at least find a single planet that can even theoretically support life as we know it, isn’t each planet added to the list that does not hold a possiblity of life adding to the indication that life isn’t likely?

    I’m not drawing any conclusions here and indeed caution not to. So far however there is only increasing evidence that the Earth is unique rather than the opposite. Of course more rocky planets MAY change that trend but they may very well place Earth in a more and more unique postion, may they not?

    As for the “vast number mean a thing must be true” line of thinking, I see no reason whatsoever that says that each and every planet out there except this one is a dead hulk. There is no science I am aware of that dictates that since life arose here that given infinite planets that it MUST arise again. More likely, perhaps but mandated, I think not at all…

    Pure and simple until we have proof of life elsewhere, all up to that point is at best educated speculation and at worst, uneducated speculation…

  • Kevin Heider

    For the record, Venus was probably much more Earth-like 2 billion years ago. Venus may even have had life before the Earth did. Venus always gets disregarded because it no longer has liquid oceans.

  • SpaceOddity

    I agree with the premiss of this article. I can understand that the Keppler crew is still careful about the exact findings, but it is still good news. If we assume that the validity of the method is equally distributed over the size of the candidates, the distribution itself stands as a result. Moreover, if double stars give false positives, the method is even slated towards finding more heavy planets than there really are…

    I am old enough to have lived in times that not all astronomers even were convinced there were planets beyond our solar system. Knowing the current methods that make it easy to find heavy planets, I was surprised to read that people were starting to think that heavy planets dominate the planetary systems. So I am really glad with this finding, and have little doubt that the result will stand under scrutiny. :)

  • William Patrick Haines

    If actual life bearing terestrial actually planets who would better the better choice for planetary ambassador Jimmy Carter Bill Gates or Howard Stern ?

  • Mo

    I don’t understand why this is so mind blowing. If it can happen here it can happen elsewhere. As to this somehow reducing our significance I don’t see the validity of that. If the argument is that we measure our importance based on being the most special in the cosmos, then it must be based on some form of belief system which would have a creator, which if all powerful would not need to wave a magic wand and create the Earth, but rather set the events in motion that play out exactly as they were planned, and the rules applied here will just as easily apply anywhere. Just because the liklihood of other civilizations grows does not imply that we are any less significant even if it were to be confirmed, because they would both be equally significant. It’s relative, and even if it were to be shown that we are not the most intelligent beings that doesn’t have any real impact on the belief systems in which this ideal stems from unless you are someone on the outside trying to analyze something you do not truly understand.

  • Norman Smith

    In the late sixties, fresh from my M.S. in Zoology, I was teaching General Science to eigth graders. I told them how we can detect exoplanets by observing light limitations when planets move across the face of their stars and the wobble of the star due to the effect of the gravity of the planet. I also told them that of all of the nearest stars they all wobbled. That was in 1967, 68, 69. Unfortunately I didn’t write it down anywhere except in my notes. I don’t even remember if I read it somewhere or made it up myself. At any rate, I know read that that was FIRST proposed in 1985, 86.

    I just wish I had pursued my Ph. D. before then and had written it all down.

  • Myron Gautreau


  • Conservatories Prices

    It’d be quite simple really to build a sustainable ecosystem in space, just follow some of jacque fresco’s design and you’ve got yourself a livable environment. It’s been a mystery for me why people find it hard to believe that there are planets that are livable out there besides our earth.

  • John Armstrong

    This is really a great news. I am in my 30’s and i would like to see few of the planets that have life in them before i die.. dont know whether it will be possible o not, but it will surely interesting to know!


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