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Exoplanets: Seeing is believing

Scientists have produced the first-ever image of multiple planets orbiting a star other than our own Sun. And, in related news, another research team has directly detected a planet orbiting the star Fomalhaut (pronounced "foh-ma-low"), which is one of the brightest in the sky and just 25 light years from Earth.

Planets are difficult to spot against the bright glare of the stars they orbit, so researchers usually detect them indirectly, looking instead for signs of the planets' gravitational influence on a star. Now, however, using sophisticated optical techniques, a research team has imaged three planets directly using the Keck and Gemini telescopes.

The star, HR 8799, is a "main sequence star," in the prime of its life, fueled by nuclear reactions within its core, and it occurs 128 light years from Earth. The planets traveling around it have masses between five and 13 times that of Jupiter, with the smallest planet closest to its sun and the largest the farthest away. This size relationship, which is generally similar to that of the outer planets in our own solar system, supports a scenario in which the planets formed as through the accretion of particles in a disk of gas and dust whirling around the star.

The system resembles a scaled-up version of the outer portion of our solar system, according to the authors, who estimate that if HR 8799 had been as faint as the Sun, its planets would be at distances similar to those of Saturn, Uranus and Neptune.

These findings are being published online by the journal Science, at the Science Express Web site, on 13 November, 2008.

In another study also appearing that day at Science Express, a second research team used the Hubble Space Telescope to image a planet they call Fomalhaut b, orbiting its star, within a large dust belt. The researchers estimate that the planet's mass is no greater than several times that of Jupiter. If their findings are confirmed, this object will be the coolest and lowest-mass body imaged outside of the solar system.