HR 8799 is home to the first planetary system ever detected by direct imaging. Its three known planets, designated HR 8799b, c, and d, are all gas giants estimated at 7 to 10 times the mass of Jupiter. The overall architecture of the system is reminiscent of our own solar system, since the giant planets are located at great distances from their star, leaving plenty of room for smaller planets closer in. But the scale of HR 8799's system is much larger than the Sun's: Its three planets orbit at distances of approximately 25, 40, and 70 AU from their star, and their orbital periods are estimated at 100, 190, and 460 years respectively. By comparison, Jupiter orbits at only 5 AU form the Sun, Saturn at 9.5 AU, and Uranus at 19 AU. But HR 8799 weighs in at one and a half times the mass of the Sun and is five times more brilliant. As a result the radiation absorbed by its giant planets is comparable to that of Saturn and Uranus.
HR 8799 is a young star, approximately 60 million years old, and is surrounded by a thick disk of gas and dust. In 2007 and 2008 astronomers took images of the star with the Gemini and Keck telescopes in Hawaii. They focused on the region inside the inner edge of the disk, where they assumed the debris had been cleared by the gravitational action of orbiting planets. By observing in the infrared range they hoped to take advantage of the heat radiation left over from the formation of the planets, which on an astronomical scale was very recent. By November 2008 they found what they were looking for: three tiny specks moving in orbit around HR 8799. It was a planetary system.
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