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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


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  • (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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