Flagstaff, Ariz.– Our home solar system may be down by a planet with the recent reclassification of Pluto, but the number of giant planets discovered in orbit around other stars continues to grow. Now, an international team of astronomers has detected a planet slightly larger than Jupiter that orbits a star 500 light-years from Earth in the constellation Draco.
The new planet is especially noteworthy because it was identified by astronomers looking for transiting planets (that is, planets that pass in front of their home star) with a network of small, automated telescopes. The telescopes used in the discovery consist of mostly amateur-astronomy components and off-the-shelf 4-inch camera lenses. This is the third transiting planet found using telescopes similar to those used by many amateur astronomers.
The research team hails the discovery as the second transiting "hot Jupiter" found with the Trans-Atlantic Exoplanet Survey (TrES), an effort involving the "Sleuth" telescope at Caltech's Palomar Observatory in San Diego County, the “Planet Search Survey Telescope” (PSST) at Lowell Observatory near Flagstaff, Arizona, and the "Stellar Astrophysics and Research on Exoplanets” (STARE) telescope in the Canary Islands. The name of the planet, TrES-2, is derived from the name of the survey.
Unlike the mythological names associated with the solar system's planets, the newly discovered planet is known by "TrES-2" and passes in front of the star "GSC 03549-02811" every two and a half days.
The planet TrES-2 is also noteworthy for being the first transiting planet in an area of the sky known as the "Kepler field," which has been singled out as the targeted field of view for the upcoming NASA Kepler Mission.
“For a guy who has been working on the Kepler Mission in one way or another for the last 15 years, it's exhilarating to be involved in the discovery of the first transiting planet in Kepler's field of view!” said Edward Dunham, Lowell Observatory instrument scientist and a founding co-investigator of the TrES network. Using a satellite-based telescope, Kepler will stare at this patch of sky for four years, and should discover hundreds of giant planets and Earth-like planets. Finding a planet in the Kepler field with the current method allows astronomers to plan future observations with Kepler that include searching for moons around TrES-2. “Kepler will find lots of objects like TrES-2 in its quest to discover Earth-size planets orbiting other stars. However, I imagine that TrES-2 will be one of Kepler's first targets, and will be an old friend by the end of the mission,” Dunham said.
By definition, a transiting planet passes directly between Earth and the star, causing a slight reduction in the light in a manner similar to that caused when the moon passes between the sun and Earth during a solar eclipse. According to Francis O'Donovan, an Irish graduate student in astronomy at the California Institute of Technology, "When TrES-2 is in front of the star, it blocks off about one and a half percent of the star's light, an effect we can observe with our TrES telescopes,” said O'Donovan, lead author of the paper announcing the discovery in an upcoming issue of the Astrophysical Journal.
"We know of about 200 planets around other stars, but it is only for the nearby transiting planets that we can precisely measure the size and mass of the planet, and hence study its composition. That makes each new transiting planet an exciting find. And because TrES-2 is among the most massive of the nearby transiting planets, it sets a new limit to our understanding of how these gas planets form around stars," O’Donovan said.
“TrES-2 is among the largest and most massive transiting planets, but what makes it really interesting is that it crosses the face of its host star further from the disk center than any other known planet,” said Georgi Mandushev, Lowell Observatory research scientist. “This means that the Kepler space telescope will be able to measure properties of this planet which so far have been completely unknown for any extrasolar planet! We may be able to find out the tilt of the host star’s axis, whether the planet has moons or rings, whether there are other planets around that star, and much more! It is indeed a very exciting discovery!”
To look for transits, the small telescopes are automated to take wide-field timed exposures of the clear skies on as many nights as possible. When an observing run is completed for a particular field — usually over an approximate two-month period — the data are run through software that corrects for various sources of distortion and noise.
The end result is a "light curve" for each of thousands of stars in the field. If the software detects regular variations in the light curve for an individual star, then the astronomers do additional work to see if the source of the variation is indeed a transiting planet. One possible alternative is that the object passing in front of the star is another star, fainter and smaller.
TrES-2 was first spotted by the Sleuth telescope, which was set up by David Charbonneau, formerly an astronomer at Caltech who is now at the Harvard-Smithsonian Center for Astrophysics and is a coauthor of the paper. The PSST, which is operated by Georgi Mandushev and Edward Dunham (coauthors from Lowell Observatory), also observed transits of TrES-2, confirming the initial detections.
In order to confirm they had found a planet, O'Donovan and his colleagues switched from the 10-centimeter TrES telescopes to one of the 10-meter telescopes at the W. M. Keck Observatory on the summit of Mauna Kea, Hawaii. Using this giant telescope, they confirmed that they had found a new planet. O'Donovan said, "Each of us had spent countless hours working on TrES at that point, and we had suffered many disappointments. All our hard work was made worthwhile when we saw the results from our first night's observations, and realized we had found our second transiting planet."
The other authors of the paper are David Latham and Guillermo Torres of Harvard-Smithsonian; Alessandro Sozetti of Harvard-Smithsonian and the INAF-Osservatorio Astronomico di Torino; Timothy Brown of the Las Cumbres Observatory Global Telescope; John Trauger of the Jet Propulsion Laboratory; Markus Rabus, José Almenara, and Hans Deeg of the Instituto de Astrofísica de Canarias; Roi Alonso of the Laboratoire d'Astrophysique de Marseille and the Institute de Astrofísica de Canarias; Gilbert Esquerdo of Harvard-Smithsonian and the Planetary Science Institute in Tucson; Emilio Falco of Harvard-Smithsonian; Lynne Hillenbrand of Caltech; Anna Roussanova of MIT; Robert Stefanik of Harvard-Smithsonian; Joshua Winn of MIT; and Juan Belmonte of Instituto de Astrofisica de Canarias.
A computer-generated simulation of TrES-2 as seen from the night side, with its host star in the distance. The planet's home star is slightly bigger and hotter than the Sun, and is about eight times larger than the planet. TrES-2 is a gas giant, similar to our own Jupiter but somewhat bigger and more massive. Unlike Jupiter, however, TrES-2 is very close to its parent star and very hot. The star's radiation strikes the planet with roughly 800 times the intensity of the Sun's radiation at Earth. Credit: Jeffrey Hall, Lowell Observatory
Download a print-quality PNG of the above image [441 KB].
A computer-generated simulation of TrES-2 crossing (transiting) the disk of its host star. TrES-2 transits farther from the disk center than any other known transiting planet. The transit of TrES-2 causes a drop in the brightness of its home star of about one and a half percent. This slight dimming of the star's light was noticed and measured by the TrES researchers, who used the parameters of the transit to determine the planet's mass, size and other properties. Credit: Jeffrey Hall, Lowell Observatory
Download a print-quality PNG of the above image [95 KB].
In this 10-second computer animation TrES-2 is seen transiting the disk of its home star. The planet is visible at the start of the animation on the left, as a thin crescent. As it transits, the planet appears as a dark circle eclipsing part of the star's disk, and then again as a crescent on the right. In real life the transit lasts slightly less than two hours. Credit: Jeffrey Hall, Lowell Observatory.
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Lowell Observatory is a private, non-profit research institution founded in 1894 by Percival Lowell. The Observatory has been the site of many important findings including the discovery of the large recessional velocities (redshift) of galaxies by Vesto Slipher in 1912-1914 (a result that led ultimately to the realization the universe is expanding), and the discovery of Pluto by Clyde Tombaugh in 1930. Today, Lowell's 19 astronomers use ground-based telescopes around the world, telescopes in space, and NASA planetary spacecraft to conduct research in diverse areas of astronomy and planetary science. The Observatory welcomes about 80,000 visitors each year to its Mars Hill campus in Flagstaff, Arizona for a variety of tours, telescope viewing, and special programs. Lowell Observatory currently has four research telescopes at its Anderson Mesa dark sky site east of Flagstaff, and is building a 4-meter class research telescope, the Discovery Channel Telescope.
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