Kepler Discovers 6-Planet Exo-Solar System

Article written: 2 Feb , 2011
Updated: 24 Dec , 2015

Using data from the Kepler space telescope, scientists have discovered a horde of six planets orbiting a sun-like star, approximately 2,000 light years from Earth. This is the largest group of planets detected so far around another star. The planets in this newly found solar system are relatively small – they range from 2.3 to 13.5 times the mass of the Earth – and are amazing mix of rock and gases. All six planets are crowded within an orbit the size of Venus’ orbit around our Sun; however, the inner five are closer to their star than any planet in our solar system.

“This is a surprisingly flat and compact system of six transiting planets,” said Jack Lissauer, co-investigator on the Kepler mission, speaking at a press conference on February 2, 2011. “The five inner planets are especially close together, something we didn’t think would happen for worlds of this size. This discovery forces us to go back and look at formation models of planets.”

Lissauer added that the close proximity of the six worlds around the star — now called Kepler 11 — also means that the planets are perturbing each others’ orbits. While having a multi-planet system makes it difficult to untangle the signals from each planet, it has the added benefit of providing more information about each of the worlds.

“In a system where the planets are tugging on one another, that means we can weigh the planets,” Lissauer said. “We have found they are low density planets; some are fluffy, sort of like marshmallows. But they are not all gas, so maybe like a marshmallow with a little hard candy at the core.”

Lissauer was incredibly enthusiastic about the discovery.

“We really were just amazed at his gift that nature has given us,” he said. “With six transiting planets, and five so close and getting the sizes and masses of five of these worlds, there is only one word that adequately describes the new finding: Supercalifragilisticexpialidocious.”

Kepler finds planets by using the transit method. The planets’ orbits are edge-on as seen from Earth, so when they pass in front of their star they block a small portion of its light. That dip in brightness is what Kepler detects.

Lissauer explained the animation (seen at the top of this article): “This is the view of Kepler, and it looks like a very special clock, one with six hands moving at six different rates, and we interpret this as six planets orbiting near the same plane. Then, you can see how it might look face on. This is the most compact system of planets every discovered by any technique anywhere.”


The time between transits provides the orbital period. To determine the planets’ masses, the scinetists analyzed slight variations in the orbital periods caused by gravitational interactions among the planets.

Lissauer said the five close inner bodies tug on one another’s orbit, and sometimes the pull can retard the transit time by 10-20 minutes.

“The timing of the transits is not perfectly periodic, and that is the signature of the planets gravitationally interacting,” said Daniel Fabrycky, a Hubble postdoctoral fellow at UC Santa Cruz, who led the orbital dynamics analysis. “By developing a model of the orbital dynamics, we worked out the masses of the planets and verified that the system can be stable on long time scales of millions of years.”

Five of the planets’ orbital periods are all less than 50 days, and the sixth planet is larger and farther out, with an orbital period of 118 days and an undetermined mass.

Kepler-11 is a sun-like star around which six planets orbit. At times, two or more planets pass in front of the star at once, as shown in this artist's conception of a simultaneous transit of three planets observed by NASA's Kepler spacecraft on Aug. 26, 2010. Image credit: NASA/Tim Pyle

Finding a large multiplanet system has many people wondering when Kepler will discover an Earth-like world. The scientists on the panel today estimated it will take three years of Kepler data to find another Earth.

“No one is more eager to get to the point of an Earth-like planet than the Kepler team,” said Douglas Hudgins, Kepler program scientist. That will require at least 3 years of Kepler data and painstaking follow-up observations from ground-based before those types of discoveries will emerge from the data.”

Hudgins reminded everyone that the first 15 years of exoplanet searches from ground-based observing produced about 500 planets, and that last year the Kepler team announced 750 exoplanet candidates from just the first three months of Kepler observations. With the release of more Kepler data today, there are now more than 1,200 planet candidates.

“The key thing to remember about every planet candidate,”Hudgins said, “ is that every time we see in data evidence of a signal, there is required analysis and follow-up data and observations to determine it is actually planet and not something masquerading as a planet.”

Translation: this takes time and won’t happen overnight.

But with the release of more data, the Kepler team said they wants to harness the horsepower of the whole planetary community, as well as citizen scientists to scour through the data. The Planet Hunters program from Galaxy Zoo has been a successful project that allows anyone to contribute the science of finding extrasolar planets.

The public has made over 1.3 million classification using just the first 30 days of publicly released Kepler data,” said Debra Fischer, professor of Astronomy at Yale University who heads up the Planet Hunters project. “We are really excited and appreciative that NASA and the Kepler mission has essentially quadrupled the amount of public data with the early release of their latest data.”


11 Responses

  1. Torbjorn Larsson OM says

    Oh wow! Keepler at it!

  2. Niolator says

    Great! If there are so many planets close to the star it could mean thaat there are aa lot of undetected planets further out. Think, a system with around 15-16 planets would be cool.

  3. DrFlimmer says

    So, we may get a planetary system that looks like that in Firefly. Hopefully, no Reavers are around for a party…

  4. Don Alexander says


    I’ll read that paper [i]pronto[/i].

    Also, the lead author is named Lissauer, not Lassauer.

  5. William928 says

    I loves me some Kepler! Keep it coming! Perhaps the 3 year estimate for and earth-like exoplanet can be compressed. Can’t wait.

    • Manu says

      No, if by earth-like you mean orbiting at an earth-like distance from a sun-like star: you need 3 observed transits for confirmation, hence 2+ years.

  6. HeadAroundU says

    A couple of days ago 90 planet candidates and 42 eclipsing binaries candidates got released. All of them found by planet hunters like me.

    I have 5 planet and 3 binaries candidates so far. I checked around 5000 stars.

  7. HeadAroundU says

    Abstract. On 1 February 2011 the Kepler Mission released data for 156,453 stars observed from
    the beginning of the science observations on 2 May through 16 September 2009. There are 1235
    planetary candidates with transit like signatures detected in this period. These are associated with
    997 host stars. Distributions of the characteristics of the planetary candidates are separated into
    five class-sizes; 68 candidates of approximately Earth-size (Rp < 1.25 R!), 288 super-Earth size
    (1.25 R! < Rp < 2 R!), 662 Neptune-size (2 R!, < Rp < 6 R!), 165 Jupiter-size (6 R! < Rp < 15 R!),
    and 19 up to twice the size of Jupiter (15 R! < Rp < 22 R!). In the temperature range appropriate
    for the habitable zone, 54 candidates are found with sizes ranging from Earth-size to larger than
    that of Jupiter. Five are less than twice the size of the Earth. Over 74% of the planetary
    candidates are smaller than Neptune. The observed number versus size distribution of planetary
    candidates increases to a peak at two to three times Earth-size and then declines inversely
    proportional to area of the candidate. Our current best estimates of the intrinsic frequencies of
    planetary candidates, after correcting for geometric and sensitivity biases, are 6% for Earth-size
    candidates, 7% for super-Earth size candidates, 17% for Neptune-size candidates, and 4% for
    Jupiter-size candidates. Multi-candidate, transiting systems are frequent; 17% of the host stars
    have multi-candidate systems, and 33.9% of all the candidates are part of multi-candidate

  8. Dark Gnat says

    I wonder how these planets gravitationally affect each other, being so close.

  9. William928 says

    @ Manu: See today’s article. I know, I know, there’s still significant confirmation that needs to be done, but still, pretty exciting!

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