Friday, December 5, 2008

UGA Astronomer Part of Team That Takes First Direct Photographs of Planets Outside Our Own Solar System

Pegasus, the mythical winged horse, left more to human history than the fanciful idea of equine flight. The name wound up on a constellation that’s been known by that name for more than two thousand years.

Now, Pegasus is unexpectedly figuring in a scientific breakthrough, and an astronomer at the University of Georgia is at the center of the discovery.

Inseok Song is part of a team that in mid-November reported the first direct photographs of planets outside our own Solar System. The three planets imaged by the team orbit a star called HR 8799 in the constellation of Pegasus. The discovery, one team member says, makes it “only a matter of time before we get a dot that’s blue and Earthlike.”

“Unfortunately, that’s not true of these three planets, which are gaseous and not remotely habitable,” said Song. “But it’s not unreasonable to think that there are Earthlike planets orbiting HR 8799 hidden in the glow of the star and waiting to be discovered.”

The research was reported in the online edition of the journal Science and involves researchers from the United States, Canada and England.

The scientists made the images using the Gemini and Keck telescopes on the Mauna Kea mountaintop in Hawaii. While the new so-called “exoplanets” are too faint and too close to the central star to see with the human eye, with telescopes or binoculars one can spot the greenish star in Pegasus.

The discovery drew international attention and was reported on the same day as a similar finding of one exoplanet at another star, reported by a NASA team using the Hubble Space Telescope.

HR 8799 has long interested astronomers because it is a sun that is roughly the size of our own, though 1.5 times larger. At 130 light years (trillions of miles) from Earth, it is a relatively close star, but the planets imaged by the team including Song have from seven to 10 times the mass of Jupiter. HR 8799 is also a young star, “only” around 60 million years old.

“Before this, the only way we could determine possible exoplanets was by measuring a wobble they created in their host star or seeing if they dim the star’s light as they pass before it,” said Song, as assistant professor in the department of physics and astronomy in UGA’s Franklin College of Arts and Sciences. “What we did was obtain the first actual photographs of a planetary system—three planets, not just one—circling a star outside our Solar System.”

The vastness of space is difficult to comprehend when talking about taking photographs of these kinds of stars. Our Solar System is in the Milky Way galaxy, which has between 200 and 400 billion stars, for example. But scientists estimate there could be as many as 100 billion galaxies in the observable Universe, and in each galaxy there might be anywhere between 10 million and a trillion stars. And many of these stars could host solar systems not unlike our own.

In the past 13 years, astronomers have discovered nearly 300 planets outside our Solar System, but their existence has been shown only by inference rather than directly.

“At some point, as we improve the imaging techniques, it may well be possible to capture an image of an Earth-like, rocky planet, but we’re not there yet,” said Song. “We believe that rocky planets lie within the gas giants toward a system’s sun, so we do know where to look at least.”

One of Song’s contributions was the idea that the scientists should look for young planets that still maintain the glow from their creation. All planets slowly grow dim over billions of years after they are formed, so younger exoplanets will glow more brightly than older ones and thus be easier to see.

“Finding young planets required finding young stars,” said Song.

He and his colleagues, using publicly available stellar surveys of space, quickly identified some 3,000 young candidate stars very near to the Earth, and after studying the light spectra from them, discovered several hundred “young” and “nearby” stars, and persistent work at the Hawaii observatories led them to HR 8799.

While information discovered at observatories can be accessed at remote locations, Song made numerous trips there over a period of several years and even lived in Hawaii for three years while working at the Gemini Observatory.

“While this is, we believe, a great accomplishment, our abilities are going to get better,” said Song. “I think it’s entirely possible that we may find that blue dot out there in space in 20 years or so. And when we do, it will be amazing.”

The work is supported principally by grants from NASA.

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