These new planets are young enough that they are still glowing from heat leftover from their formation which took place approximately 60 million years ago (fresh out of the oven by astronomical standards). Since these planets take hundreds of years to orbit their host star, directly measuring their masses is not immediately possible ... we have to wait.
In the meantime, theoretical models of planetary interiors and atmospheres can be used to infer many of their properties. This type of analysis is greatly aided by the ability to take pictures of the planets orbiting HR 8799, allowing us to peer straight down into their atmospheres and measure what the conditions are like. Comparing the predictions from theory to the observed brightness across a broad range of wavelengths tells us that these planets are respectively about seven, ten, and ten times the mass of Jupiter and about 20 percent to 30 percent larger than Jupiter in diameter. The planets could be slightly more or less massive depending on their exact age.
"Knowledge of the age of HR 8799 is critical for linking the observed luminosities of the planets with their masses," commented co-author Travis Barman, an astronomer at Lowell Observatory. "The older (or younger) the planets are the more (or less) massive the planets will be. Detailed comparison with theoretical model atmospheres confirms that all three planets possess complex atmospheres with dusty clouds partially trapping and re-radiating the escaping heat."
For theorists like Barman, HR 8799 is a gold mine, allowing broad tests of predictions for planet formation, evolution, and atmospheric physics. The most exciting discoveries about these new planets are certainly still to come. Now that each planet can be individually imaged, plans are underway to take the first spectra of young planets which will allow us to study in detail their chemical compositions, cloud structures, and thermal properties.
This work appears today in Science Express and in an upcoming issue of Science.
Partial support for this work was provided by NASA to Lowell Observatory through grant NNX07AG68G S03 from the Origins of Solar Systems program and by a generous allocation of computing time at the NASA Advanced Supercomputing facilities. Support for this work was also provided by the Mount Cuba Astronomical Foundation.
René Doyon – Département de Physique and Observatoire du Mont Mégantic, Université de Montréal, Montréal, QC
About Lowell Observatory
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 20 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 more than 75,000 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, in partnership with Discovery Communications.
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