Astronomers Find Atmosphere on Planet Outside Solar System

Using the Hubble Space Telescope, astronomers have noticed atmospheric evidence of a nearby planet orbiting a star just outside the solar system. Located only 150 light-years from Earth, it is a large gas planet (HD 209458 b) circling a star named HD 209458.

Researchers from the National Center for Atmospheric Research made the discovery while observing HD 209458 b when it would pass between the Earth and the star. During four passes, which are called transits, they used the Telescope Imaging Spectrograph instrument on board the Hubble to search for any signs of an atmosphere surrounding the planet. What they found in the images were traces of atomic sodium that must have come from the planet's atmosphere.

"This opens up an exciting new phase of extra-solar planet exploration," says David Charbonneau, one of the leading researchers on the project. "[Now] we can begin to compare and contrast the atmospheres of planets around other stars."

The planet's existence was detected in 1999 and the scientists have always suspected it had an atmosphere; they were looking to prove their theory. The planet is very similar to Jupiter but is only about 70 percent of Jupiter's mass. Scientists were able to estimate its size by measuring the fraction of light blocked as it passed its star. What is known about the planet is that is only seven million kilometers from its star with a three-and-one-half-day orbit.

Further studies are going to be necessary to determine the exact makeup of the planet's atmosphere, but researchers suspect that the planet has a very extensive gas atmosphere. Scientists at the Harvard-Smithsonian Center for Astrophysics and Space Telescope Science Institute are going to be taking a closer look at the planet, using the star's individual spectrum to filter the planet's atmosphere and pick up traces of other chemicals.

When the Hubble was launched above the Earth, extra-solar observation was not in its original mission plans. But, with the discovery of extra-solar planets within the last few years, this was the first attempt by scientists to use the Hubble and its instruments to explore those planets. The scientists are very pleased with the results and the telescope's ability to probe beyond the solar system.

In the future, astronomers will be able to detect the atmosphere of exoplanets without relying on convenient transits. Within the next ten years, there will be two new orbiting observatories -- NASA's Terrestrial Planet Finder and ESA's Darwin -- which will utilize advanced technology giving researchers more data than the Hubble is presently capable of providing.

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