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posted by Fnord666 on Thursday July 13 2017, @05:33PM   Printer-friendly
from the twice-as-bright dept.

Exoplanets that orbit a star that is part of a multiple star system may have lower densities than previously estimated:

In the search for planets similar to our own, an important point of comparison is the planet's density. A low density tells scientists a planet is more likely to be gaseous like Jupiter, and a high density is associated with rocky planets like Earth. But a new study suggests some are less dense than previously thought because of a second, hidden star in their systems.

As telescopes stare at particular patches of sky, they can't always differentiate between one star and two. A system of two closely orbiting stars may appear in images as a single point of light, even from sophisticated observatories such as NASA's Kepler space telescope. This can have significant consequences for determining the sizes of planets that orbit just one of these stars, says a forthcoming study in the Astronomical Journal by Elise Furlan of Caltech/IPAC-NExScI in Pasadena, California, and Steve Howell at NASA's Ames Research Center in California's Silicon Valley.

[...] Previous studies determined that roughly half of all the sun-like stars in our sun's neighborhood have a companion within 10,000 astronomical units (an astronomical unit is equal to the average distance between the sun and Earth, 93 million miles or 150 million kilometers). Based on this, about 15 percent of stars in the Kepler field could have a bright, close companion -- meaning planets around these stars may be less dense than previously thought.

[...] In the new study, Furlan and Howell focused on 50 planets in the Kepler observatory's field of view whose masses and radii were previously estimated. These planets all orbit stars that have stellar companions within about 1,700 astronomical units. For 43 of the 50 planets, previous reports of their sizes did not take into account the contribution of light from a second star. That means a revision to their reported sizes is necessary.

At least 5 of the 50 studied exoplanets could have a substantially lower density than previously reported. NASA cartoon explaining the problem.

This study examined exoplanets that orbit one star, but there are also circumbinary planets that orbit two stars.


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  • (Score: 0) by Anonymous Coward on Thursday July 13 2017, @06:36PM

    by Anonymous Coward on Thursday July 13 2017, @06:36PM (#538789)

    The third panel of the comic shows two stars with markedly different spectra. It should be possible to work out from that difference which star(s) a planet is occulting.