Gliese 15Ab: The Closest Known Super-Earth?

Saturday, September 13, 2014

Gliese 15Ab: The Closest Known Super-Earth?

Gliese 15Ab: The Closest Known Super-Earth?:

An artist’s rendering of the newly discovered exoplanet OGLE-2013-BLG-0341LBb (far right) orbiting one star (right) of a binary red dwarf star system, from an Earth-type distance of approximately 0.9 Astronomical Units away. Image Credit: Cheongho Han, Chungbuk National University, Republic of Korea

An artist’s conception of the view from an exoplanet orbiting one star in a binary red dwarf system. Image Credit: Cheongho Han, Chungbuk National University, Republic of Korea

Our solar neighborhood is rich with planetary systems. Within 20 light-years we’ve detected sizzling gas giants and rocky planets orbiting closer to their host star than Mercury orbits the Sun.

Astronomers have now added one more to the list, and this one — a super-Earth dubbed Gliese 15Ab — ranks as one of the closest known exoplanets, circling its host star only 11.7 light-years away.

Gliese 15 is a binary system, with two cool, dim red dwarfs orbiting each other. Although red dwarfs are the most common type of star in the galaxy, they’re so intrinsically faint that not a single one (including the closest star to the Sun, Proxima Centauri) is visible to the naked eye.

Although Gliese 15A might appear faint from Earth, it is overwhelmingly bright compared to its barely reflective exoplanet. So unfortunately we can’t easily see the exoplanet directly. But it does leave an imprint on its host star. Its small gravitational tug makes Gliese 15A wobble ever so slightly as both orbit a mutual center of mass, known as the barycenter.

The star’s movement is then imprinted on its spectrum. As Gliese 15A moves away from the Earth, its spectral lines stretch to redder wavelengths. But as it moves toward the Earth, its spectral lines compress to shorter wavelengths.

The radial velocities for Gliese 15Ab. Image Credit: Howard et al.

The change is minute. But the Keck 10-meter telescope, with an extremely high-resolution detector, can see such small changes. And from this tiny wobble, Andrew Howard and colleagues calculated that the planet is 5.35 times the mass of Earth and orbits its star in only 11.44 days, making it a hot super-Earth. And remember, it’s only 11.7 light-years away.

A handful of other planet candidates have been found that are closer, but all — including Gliese 15Ab — have yet to be confirmed by other research teams. In the long run, it may turn out that this hot super-Earth is the closest planet to our pale blue dot. Then again, it may not. That’s how science works.

Nonetheless, Gliese 15Ab might prove to be an exciting target for one of the new planet imagers that came online within the past year.

The findings will be published in the Astrophysical Journal and are available online.

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The National Aeronautics and Space Administration (NASA) is the United States government agency responsible for the civilian space program as well as aeronautics and aerospace research. President Dwight D. Eisenhower established the National Aeronautics and Space Administration (NASA) in 1958 with a distinctly civilian (rather than military) orientation encouraging peaceful applications in space science. The National Aeronautics and Space Act was passed on July 29, 1958, disestablishing NASA's predecessor, the National Advisory Committee for Aeronautics (NACA). The new agency became operational on October 1, 1958.

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The Oxford English Dictionary defines a UFO as "An unidentified flying object; a 'flying saucer'." The first published book to use the word was authored by Donald E. Keyhoe. The acronym "UFO" was coined by Captain Edward J. Ruppelt, who headed Project Blue Book, then the USAF's official investigation of UFOs. He wrote, "Obviously the term 'flying saucer' is misleading when applied to objects of every conceivable shape and performance. For this reason the military prefers the more general, if less colorful, name: unidentified flying objects. UFO (pronounced Yoo-foe) for short." Other phrases that were used officially and that predate the UFO acronym include "flying flapjack", "flying disc", "unexplained flying discs", "unidentifiable object", and "flying saucer". The phrase "flying saucer" had gained widespread attention after the summer of 1947. On June 24, a civilian pilot named Kenneth Arnold reported seeing nine objects flying in formation near Mount Rainier. Arnold timed the sighting and estimated the speed of discs to be over 1,200 mph (1,931 km/h). At the time, he described the objects' shape as being somewhat disc-like or saucer-like, leading to newspaper accounts of "flying saucers" and "flying discs". In popular usage the term UFO came to be used to refer to claims of alien spacecraft. and because of the public and media ridicule associated with the topic, some investigators prefer to use such terms as unidentified aerial phenomenon (or UAP) or anomalous phenomena, as in the title of the National Aviation Reporting Center on Anomalous Phenomena (NARCAP).

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Photos of Nature | Nature Photography What is The Universe

Saturday, September 13, 2014