First Picture of Planetary System Beyond the Sun
Scientists Have Finally Imaged More than One Planet around a Star
Nov 13, 2008
140 light-years away from our solar system lies another planetary system of objects orbiting their own sun. The newly discovered planets are gas giants, orbiting a star that is about one-and-a-half times larger than our sun. The three planets seen by astronomers are 10, 10 and 7 times the mass of Jupiter, with the smaller planet farther from its parent star, just as our less massive gas giants (Uranus and Neptune) lie farther from the sun than do Jupiter and Saturn.
The Star HR 8799 and Its Planets
The newly discovered system is a bit like our own solar system but super-sized. The star that is the center of this system is called HR 8799. Its dusty disk is one of the most massive within 300 light-years of Earth. HR 8799 is a bright and blue A-type star that is younger than our sun and about five times more luminous. The star (but not its planets) can be seen by the unaided eye from a dark site or better yet with a pair of binoculars or a small telescope. Use the finder chart below to find HR 8799 in the constellation Pegasus.
The planets formed about 60 million years ago and are still young enough that they are glowing with the heat of their contractions. They orbit at distances of 24, 37, and 67 AU from their parent star. 1 AU equals the distance between Earth and the sun, or 93 million miles. In comparison, Neptune orbits at 30 AU from the sun. Another similarity to our solar system is the large disk of dusty debris seen just beyond the planets, which is similar to the Kuiper belt of comets beyond Neptune. Studies have shown that all three planets possess complex atmospheres with dusty clouds partially trapping and re-radiating the escaping heat.
The Significance of the Newly Seen Stellar System
This discovery marks the first time scientists have seen planets orbiting a normal star. Astrophysicist Bruce Macintosh from the Lawrence Livermore National Laboratory, who is working on the project, explains more: "Every extrasolar planet detected so far has been a wobble on a graph. These are the first pictures of an entire system. We've been trying to image planets for eight years with no luck and now we have pictures of three planets at once."
Adaptive optics on the Gemini and Keck telescopes led to the discovery. Adaptive optics allows astronomers to limit the blurring effects of our atmosphere and see distant objects in unprecedented detail. "Seeing these planets directly - separating their light from the star - lets us study them as individuals and use spectroscopy to study their properties, like temperature or composition," says Macintosh.
Even more exciting may be the parts of this system that we can't see. "One of the things that distinguishes this system from most of the extrasolar planets that are already known is that HR 8799 has its giant planets in the outer parts - like our solar system does - and so has 'room' for smaller terrestrial planets - far beyond our current ability to see - in the inner parts," says Macintosh.
HR 8799 is one of 80 similar young, dusty stars being observed in the nearby galaxy. The discovery of this planetary system so early on in the research gives scientists hope that these types of stellar families are common in the universe.
Sources: Lawrence Livermore National Laboratory and Gemini Observatory
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