New Worlds to Explore? Kepler Spacecraft Finds 750 Exoplanet Candidates

Article written: 15 Jun , 2010
Updated: 24 Dec , 2015


The Kepler spacecraft has found over 750 candidates for extrasolar planets, and that is just from data collected in the first 43 days of the spacecraft’s observations. “This is the biggest release of candidate planets that has ever happened,” said William Borucki, Kepler’s lead scientist. “The number of candidate planets is actually greater than all the planets that have been discovered in the last 15 years.”

This is an astounding amount of potential exoplanets from data taken during such a short period of time, however Borucki added that they expect only about 50% of these candidates to actually turn out to be planets, as some may be eclipsing binary stars or other artifacts in the data. But still, even half would be the biggest group discovery of exoplanets ever.

And the exciting part is that 706 targets from this first data set have viable exoplanet candidates with sizes from as small as Earth to around the size of Jupiter. The team says the majority have radii less than half that of Jupiter.

The Kepler team has found so many candidates, they are sharing. They will keep the top 400 candidates to verify and confirm with observations using other telescopes – with observations done by Kepler team members. And today they have released the other 350 candidates, including five potential multiple planet systems.

However, some astronomers are upset about this and think the Kepler team should release all of their findings from the first year, as is typically done with NASA data.

Kepler launched on March 6, 2009, and has been on the hunt for exoplanets. Of course, the holy grail is finding an Earth-like or Earth-sized planet, especially those in the habitable zone of stars where liquid water and possibly life might exist. In the spring of 2009 the Kepler Mission conducted high precision photometry on nearly 156,000 stars to detect the frequency and characteristics of small exoplanets. Kepler studied an area in the constellation Cygnus, looking for the small changes in light that would signal a planet passing in front of its star.

But it takes time to verify candidates and find out if they are actually exoplanets. Usually, confirming the transit of an extrasolar planet requires observations of three different transits. While NASA’s policy requires astronomers to release their data from NASA instruments in a year, the Kepler team has worked out an agreement with the space agency so they can keep a certain portion of their data until they actually have time to verify this huge amount of exoplanet data. Between launch delays of other telescopes, cloudy nights for Earth based telescopes, and viewing a part of the sky that is only visible from the ground from April until September, they haven’t had the observing time they needed to check out all their planet candidates. The extension of the deadline gives the Kepler team the time to make sure they have gone through and found all the false positives and other potential misinterpretations of the Kepler data.

Dennis Overbye in the New York Times has written an article that delves more deeply into this little controversy. What is propriety data, and what is public? It’s a tough argument either way: scientists who have put years of their life into building a spacecraft should have the time they need to verify their data. But others feel the science should be open and available, and a policy is a policy: the deadline for releasing the data is here.

Whatever your feelings on open or closed data (and the Kepler team is only getting an extra six months on just part of their data, by the way), you have to be impressed with the quantity of potential exoplanet finds. And Kepler still has at least two years left of observations.

Papers of interest:

Characteristics of Kepler Planetary Candidates Based on the First Data Set: The Majority are Found to be Neptune-Size and Smaller

Five Kepler target stars that show multiple transiting exoplanet candidates

Nancy Atkinson is currently Universe Today’s Contributing Editor. Previously she served as UT’s Senior Editor and lead writer, and has worked with Astronomy Cast and 365 Days of Astronomy. Nancy is the author of the new book “Incredible Stories from Space: A Behind-the-Scenes Look at the Missions Changing Our View of the Cosmos.” She is also a NASA/JPL Solar System Ambassador.

20 Responses

  1. Vanamonde says

    “My god…it’s full of…” PLANETS!!!

    i just could not resist. what a wondrous time for astronomy!

  2. Spoodle58 says

    I choked on the glass of water I was drinking while reading this headline.

  3. Molecular says

    If my calculations are correct, Kepler should find about 6,000 planets a year. So,since it’s launch, and up until the project is over, roughly 18,000 exoplanets will have been found. And, of those, 9,000 would turn out to be planets……..WOW!!!!

  4. Torbjorn Larsson OM says

    Planets, everywhere planets!

    Summing up their categories, they only score ~ 1 % frequency on current positives, IIRC the transit method should hit ~ 2-4 % of all planets from any POV. Hopefully that means there are systems that have planets further out, as ours.

    They do find neat statistics, like the 1/r^2 distribution (r = planet radius) – lots of Earth analogs out there!

  5. Uncle Fred says

    WOW! I nearly choked when I read this article’s title. If I understand this method correctly, there is only a 2-4% possibility of planetary detection per star? All this in it’s first year? JESUS!

    Best news I’ve heard all week.

  6. That’s the funny part. We all expect there to be a Gazillion planets out there, but we’ve been beaten back so often by Rare-Earth and other such theories that we’re rejoicing at confirming the expected…

    It’s like the talk about the missing Hydrogen on Titan.

    To me, if it turns out to be a previously unknown chemical reaction, it would be more incredible than if it turned out to be microbes… Since we’ve already SEEN microbes on Earth thriving in extreme conditions and eating up that sort of fuel… By all common sense, there SHOULD be microbes on TITAN. Yet, in the face of all religiously motivated doubters, confirming the expected counts as more incredible than discovering new chemistry.

    Shrug, and eyebrow-lift. Humans are so peculiar.

  7. Kevin says

    This is good. This is VERY good.

  8. Sirius_Alpha says

    @ Molecular

    It doesn’t quite work that way. Kepler will not find some value of planets per time because there is a finite amount of planets that are detectable. These 700 candidates are the planets with periods < ~40 days, which due to the mathematics behind transit probability, are probably the bulk of the planets that will be found.

    Additional planets that are found will have periods greater than this, but since they also have reduced transit probabilities, we won't find nearly as many of them.

    IIRC, it is expected that the mission will produce somewhere around a thousand planets.

  9. Torbjorn Larsson OM says

    Also, it hits me that there is then a following discrepancy between the ~ 350 expected true positives being the bulk, and the ~ 1000 original expected, by something like a factor 2.

    Not too bad considering the skewed statistics, but if it is a correct assessment, the fault is in the ‘wrong’ direction. Bummer!


    “Summary of The Expected Results

    Based on these assumptions and the capability of the Kepler Mission, we expect to to perform a census of planets with periods from days to a few years and to detect:

    Terrestrial inner-orbit planets based on their transits:

    * About 50 planets if most have R ~ 1.0 Re
    * About 185 planets if most have R ~ 1.3 Re
    * About 640 planets if most have R ~ 2.2 Re

    (Or possibly some combination of the above)
    * About 12% of the cases with two or more planets per system

    Giant inner planets based on the modulation of their reflected light:

    * About 870 planets with periods less than one week

    Giant planets based on their transits:

    * About 135 inner-orbit planets along with albedos for 100 of these planets
    * Densities for 35 of the inner-orbit planets, and
    * About 30 outer-orbit planets.”

    Yes, even considering the new fact that the small ones are the most numerous, bummer.

  10. Yes, basically, the closer in the planet, the higher the chance that it will transition the star from our POV.

    However, by the exact same token, statistically, every transitioning planet which is further out represents a larger population of non-transitioning planets.

    So we’re still ok, except that the Rare-Earthers will immediately point out that “see? there are far more uninhabitable planets out there than there are habitable ones!”, and when you point out the bias in the method of discovery, it will be same response as ever – “this is just conjecture. you haven’t PROVEN it yet”…

  11. Torbjorn Larsson OM says

    Ah, thanks SA and CEB for pointing out the source of the discrepancy. Still on target for ~ 2-4 % or so then, if making up for the sensitivity.

    @ CEB:

    Yes, I’m with you there, I think.

    People tend to confuse the result of evolution (which can be complex, say as measured by the number of traits or genes producing them), with the simplicity (well) of the process.

    The number of evolving populations AFAIK far outnumber the number of known catalysts (if not the number of possible reactions). Life started easily on Earth, as attested by the short period between aggregation and markers of life, which nicely counteracts the fact that we have but one sample to observe as of yet. The main factors for habitability can simply be availability of a liquid close to its triple point (so at least both liquid and vapor available) and a suitable temperature. (Abstracting Mendez’s theory for habitability.) Any lower reaction rates would be made up by a likewise stabler environment.

    That said, there is much we don’t know about the transition from probiotic chemistry to biological populations. “For lower temperatures, there [can] be OBSTACLES.” [Note found on edge of map for potential abiogenetic pathways besides a funny picture of a dragon.]

  12. raydekk says

    I wish they would publish the results faster, hopefully in an excel format and with a column representing the parent star.

    This way I can update my database and check them out in the 3D Galaxy Map.

  13. Freaky says

    Does anyone know why this part of the sky in Cygnus was chosen? I would hope because it was likely to find Earth-like candidates relatively close for a future visit (a few 10s of light years). Would seem pointless if candidates are 100s of light years away.

  14. TerryG says

    @Freaky From the kepler FAQ

    We need a region of the sky that is both rich in stars, and one where the Sun does not get in the way throughout the entire orbit of the Kepler spacecraft. Cygnus is far enough north of the plane of Earth’ orbit (the ecliptic) that the Sun will not encroach on Kepler’s view, yet is in a very star-rich part of our Milky Way galaxy. For additional information, read “ Target Field of View.”

  15. raydekk says

    Well Gamma Cygni is about 10.5 LY away, but Alpha Cygni is 1400 LY away…so grouping stars in constellations is quite inefficient compared to sectors.

  16. Member
    Aqua says

    Kepler’s ‘hit the ground running!’ Yas…..

  17. Greg says

    My first impression is that these guys are total hogs to keep the best half of thet dataset after the one year deadline. But then I realized that this covers only 43 days of data! Imagine how many positives there will be when it gets out to a few hundred days of data. They will probably be begging people to help them analyze their data in order to get it all done before they are too old to care anymore.

  18. Astrofiend says

    The Kepler team should be more than entitled to keep the data beyond a year. A year is NOT a very long time to analyse data and put out papers for even small/routine astronomical observations if there is a bit of work involved in the data reduction.

    As the article says, many of these people have invested many years of their life in this – it is only right that they get first slice of the pie without the vultures waiting in the wings to pick off the juicy bits first. All they have to wait is six more months. This mission will produce such vast amounts of data that it will be pored over for years to come. There will be plenty for everyone in the wash-up.

  19. TerryG says

    scientists who have put years of their life into building a spacecraft should have the time they need to verify their data

    There are points for and against. Since most feedback so far is in favour of Kepler mission scientists being allowed to extend the conventional one year deadline for publishing some results, here are some arguments against.

    1) If the Kepler mission is publicly funded, mission scientists do not own the raw data. Stick to the one year limit.
    2) It is appreciated that discovering/confirming exoplanets may take three transits which often entails a year or longer for observation, but scientific results are not accepted without peer review, therefore the independent verification process should opened up to other observatories at the earliest possible opportunity. Stick to the one year limit.
    3) The on-again off-again SIM, Dawn and SOFIA etc. risked cancellation when mission participants failed to seriously pick up the pace and get the job done. There is no place for the mind-set of spending “years of their life” on the development stages when lengthy delays will jeopardise the mission.
    The Kepler mission specialists have avoided unnecessary delays so far, so it would be disappointing to to see them suddenly start dragging their feet by exceeding the one year maximum delay for sharing all results. Stick to the one year limit.
    4) Mission scientists are compensated with a salary, possibly a performance bonus and the kudos of being associated with a leading project for these “years of their life”. That is enough for all other employees. Stick to the one year limit.

    Just presenting the counter case…

    In any event congratulations to the Kepler team for so many important and exciting discoveries. We need more missions like this. Well done.

  20. Aodhhan says

    Those who are upset about the Kepler team keeping data need to relax.

    Kepler team is sharing a lot of data. Since they put in the effort, allowing them to keep the 400 best targets is fair. Especially when they are sharing so many other areas which aren’t exactly dead. So take the time and work with the data they have released.

    NASA is sure to release the 400 they are keeping after they re-examine the data using other telescopes. Sure… they are more likely to find exciting and promising items in the data they are keeping, but they did do the WORK and research to get it. Why should someone else get all the glory when they dont do the majority of the work.

    So… be happy with the data NASA has released, and make the best of it. It isn’t like they are only giving out dead data. They have released excellent data in viable exoplanets to study.

    And here is the kicker… since it takes more than one year to realistically find and initially study exoplanets, NASA could have kept all the data for a couple of more years. However, they didn’t. They have released more than half of Kepler’s fidings for others to research. Quit crying because NASA is choosing to pick the cream of the crop to study.

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