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posted by martyb on Friday December 04 2015, @12:36AM   Printer-friendly
from the still-leaves-a-lot-of-exoplanets dept.

Over half of the gas giant "exoplanets" spotted by the Kepler telescope may actually be explained by other astrophysical phenomena, such as binary stars and brown dwarf stars:

It's always exciting when Kepler discovers a new exoplanet, and it's generally assumed that there is a relatively low chance of a false positive. But according to a new study, there may be a much higher rate of false positives than we thought with regard to gas giants, possibly up to 55%.

In the study, astronomers from Instituto de Astrofísica e Ciências do Espaço examined a sample of 129 gas planets detected by Kepler through the transit method. The transit method involves extrapolating the existence of a planet from the periodic dimming of a star's light emission that is presumably caused by an exoplanet's orbit. They found that approximately half of them weren't planets at all; rather, the light's dimming was caused by some other astrophysical phenomenon.

Gas giants are particularly vulnerable to false positives, as they can easily be imitated by eclipsing binaries. Eclipsing binaries are binary star systems aligned with the observer's (in this case, Kepler's) line of sight, which causes the larger star to block the light from the smaller. The researchers found that 52.3% of the gas giants were actually eclipsing binaries, while 2.3% were brown dwarfs, or a "failed star" between gas giants that doesn't have enough mass to fuse hydrogen to its core.

Also at the Institute of Astrophysics and Space Sciences.

SOPHIE velocimetry of Kepler transit candidates XVII. The physical properties of giant exoplanets within 400 days of period

Original Submission

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  • (Score: 2) by bzipitidoo on Friday December 04 2015, @12:58AM

    by bzipitidoo (4388) Subscriber Badge on Friday December 04 2015, @12:58AM (#271638) Journal

    Astronomers have been pretty conservative about declaring that data that suggests the existence of an exoplanet is not caused by something else. This is only one possibility they check before announcing. It can take years, waiting for multiple transits or wobbles, before they feel the evidence is compelling enough to be sure a planet is causing the observed phenomena.

    So I don't know about this article that suggests they got it that wrong. Over half? Really? If true, pretty bad, sloppy astronomical work. Perhaps planet hunting got turned into a competition, with rival teams racing to announce first. Maybe that could explain how over half the results are false positives. Or, maybe the article is full of crap. After all, we recently had the sensationalist speculation that the odd fluctuations in intensity of a recently examined star could be caused by megastructures built by an alien civilization. I'm reserving judgment.

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  • (Score: 0) by Anonymous Coward on Friday December 04 2015, @01:05AM

    by Anonymous Coward on Friday December 04 2015, @01:05AM (#271642)

    Given the nature of their report you would think they would be more conservative in the claims:

    We confirm that giant planets receiving a moderate irradiation are not inflated but we find that they are in average smaller than predicted by formation and evolution models. In this regime of low-irradiated giant planets, we find a possible correlation between their bulk density and the Iron abundance of the host star, which needs more detections to be confirmed.

    Really? They can't even see these gas giants, they see cyclical fluctuations in light intensity from stars.

    • (Score: 2) by HiThere on Friday December 04 2015, @03:49AM

      by HiThere (866) on Friday December 04 2015, @03:49AM (#271688) Journal

      You thought that had better evidence? We could get it, but it would cost a lot more that funding sources have been willing to spend. I once saw a proposal that would give really good evidence. A Neptune orbit telescope (for the cold) with a 5-mile diameter mirror. (You could build it out of flat mirrored segments.) That would give you enough resolution to see clouds in motion, possibly in planets in the Magellanic Clouds.

      Even better use a pair of them with an optical link so you could calculate distance by parallax rather than using various inferred measures of distance.

      But as I said, this would be a mite expensive. It would clearly need to be a totally automated system, so you need to design it for repair, but at that distance from the sun it wouldn't need a liquid helium cooler to handle Infra-red.

      Well, that's unrealistic. Nobody's going to fund that before we have a serious space industry. So most of astronomy is done working long chains of inference, often with several weak links. E.g., ever hear of the kind of super-nova called the "standard candle"? How do you know the supernova you're looking at is the right kind of supernova? By inference. Unfortunately, there are other quite similar events that are hard to tell apart. So that's a weak link. Parallax would be much better, but for some purposes even Neptune's orbit is too small a diameter of separation. (The big bang is a long distance away, so when you're looking at things near it, desolution gets difficult. [Actually the big bang happened everywhere if it happened anywhere, but when you're looking back in time you're effectively looking a long distance measured by how much the light has diverged.])

      Caution: I am not an astrophysicist or cosmologist. Don't depend on this comment for anything expensive. But I'm pretty sure everything's right.

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  • (Score: 2) by darkfeline on Friday December 04 2015, @05:36AM

    by darkfeline (1030) on Friday December 04 2015, @05:36AM (#271701) Homepage

    You can't really blame them though. We are talking about trying to detect things extraordinarily far away. No, farther than that. No, even farther than that.

    We're talking about distances where a slight vibration would make an Earth-bound telescope point at a different galaxy.

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  • (Score: 2) by cubancigar11 on Friday December 04 2015, @09:05AM

    by cubancigar11 (330) on Friday December 04 2015, @09:05AM (#271738) Homepage Journal

    Even with >50% false positives, there are too many planets that the chance of an alien life form is still exciting.

    • (Score: 0) by Anonymous Coward on Friday December 04 2015, @09:13AM

      by Anonymous Coward on Friday December 04 2015, @09:13AM (#271741)

      The alleged false positives are for gas giants, which wouldn't be supportive of life anyway. As far as I can see, they don't claim false positives on the smaller rocky planets, which are the ones which possibly bear life.