First-ever images taken of extrasolar planets

By Jeanna Bryner

updated 3:42 p.m. ET Nov. 13, 2008

Astronomers have taken what they say are the first-ever direct images of planets outside of our solar system, including a visible-light snapshot of a single-planet system and an infrared picture of a multiple-planet system.

Earthlike worlds might also exist in the three-planet system, but if so they are too dim to photograph. The other newfound planet orbits a star called Fomalhaut, which is visible without the aid of a telescope. It is the 18th-brightest star in the sky.

The massive worlds, each much heftier than Jupiter (at least for the three-planet system), could change how astronomers define the term "planet," one planet-hunter said.

Breakthrough technology
Until now, scientists have inferred the presence of planets mainly by detecting an unseen world's gravitational tug on its host star or waiting for the planet to transit in front of its star and then detecting a dip in the star's light. While these methods have helped to identify more than 300 extrasolar planets to date, astronomers have struggled to actually directly image and see such inferred planets.

The four photographed exoplanets are discussed in two research papers published online Thursday by the journal Science.

"Every extrasolar planet detected so far has been a wobble on a graph. These are the first pictures of an entire system," said Bruce Macintosh, an astrophysicist from Lawrence Livermore National Laboratory in California, and part of the team that photographed the multi-planet system in infrared light. "We've been trying to image planets for eight years with no luck and now we have pictures of three planets at once."

Astronomers have claimed previously to have directly imaged a planet, with at least two such objects, though not everybody agreed the objects were planets. Instead, they may be dim, failed stars known as brown dwarfs.

Multiplanet snapshots
Macintosh, lead researcher Christian Marois of the NRC Herzberg Institute of Astrophysics in Canada, and colleagues used the Gemini North telescope and W.M. Keck Observatory on Hawaii's Mauna Kea to obtain infrared images. Infrared radiation represents heat and, along with everything from radio waves to visible light and X-rays, is part of the electromagnetic spectrum.

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The trio of worlds orbits a star named HR 8799, which is about 130 light-years away in the constellation Pegasus and about 1.5 times as massive as the sun. The planets are located at distances from their star of 24, 38 and 68 astronomical units (AU). (An astronomical unit equals the average Earth-sun distance of 93 million miles, or about 150 million kilometers.) Other planet-finding techniques work out to only about 5 AU from a star.

The planet closest to the star weighs in at 10 times the mass of Jupiter, followed by another 10 Jupiter-mass planet and then, farther out, a world seven times the heft of Jupiter.

By astronomical standards, the planets are fresh out of the oven, forming about 60 million years ago. That means the orbs are still glowing from heat leftover from their formation. Earth, by comparison, is about 4.5 billion years old.

The most distant planet orbits just inside a disk of dusty debris, similar to that produced by the icy objects of the solar system's Kuiper belt, which lies just beyond the orbit of Neptune.

Gemini Observatory This Gemini Telescope image shows two of the three planets in the extrasolar "first family," labeled b and c. The central star has been blotted out to remove its glare.

The setup of this planetary system, along with its dusty belt, suggests it is a scaled-up version of our solar system, Macintosh said. That means other planets closer in to the host star could be waiting for discovery.

"I think there's a very high probability that there are more planets in the system that we can't detect yet," Macintosh said. "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."

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