The first pictures of not 1, not 2, but 3 planets orbiting a star

A team of astronomers used the Keck and Gemini North telescopes on Mauna Kea in Hawaii to discover three planets in orbit around the young star HR 8799. Christian Marois (the lead author of a paper to be published in Science) and his collaborators developed an advanced computer processing technique that helped separate the planets from the much brighter light of the star. HR 8799 is located about 130 light-years from Earth and is just visible to the naked eye in the constellation of Pegasus. 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.

Source: Lowell Observatory