Artist’s impression of planetary light

Astronomers have announced that for the first time, they've detected the light of two planets hundreds of light years away.  The scientists say the development paves the way for the discovery of earth-like planets outside our solar system.

Since 1995, astronomers have been able to detect planets beyond our solar system through indirect means, such as the wobble that the planets' gravity exerts on nearby stars.

Scientists detected some 130 extrasolar planets this way.  But now, with the development of more powerful telescopes, scientists are able to see the planets directly.

This week, two of those planets showed themselves to two independent teams of astronomers using instruments aboard the Spitzer Space Telescope, funded by the U.S. space agency NASA.   Using two different instruments aboard the infrared telescope, the scientists picked up the light of the two planets on the edge of the galaxy.  One of the planets is 140 light years from Earth and the other one is 500 light years. 

David Charbonneau of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts headed one of the teams.  Dr. Charbonneau says the planets have been difficult to see in visible light because they are outshown by their stars, which are 10,000 times brighter.  He says viewing the solar systems through the red tones of the infrared spectrum reduces the glare.

"If we put on our infrared goggles with the Spitzer Space Telescope, then suddenly the planet brightens up, and the contrast ratio, the difference in light between the star and planet is much, much more favorable, and we are to isolate that light from the planet directly and study it," he said.

The planets can be seen during their solar orbits.  When passing across the front of the sun, each planet causes its sun it to dim slightly. The solar system also dims when the planets disappear behind the back of the stars. By observing this secondary phase, or eclipse, through the infrared spectrum, astronomers are able to tease out the faint planetary light against the brightness of the stars.

Mr. Charbonneau believes the discoveries will be the first of many direct planetary sightings outside our solar system.

"Spitzer has allowed us to directly detect the light from planets orbiting other stars, not once, but twice,” he added.  “Two separate planets, you know, you have two separate teams.  And they even used two different instruments on the Spitzer telescope.  And both the detections are very robust, they're very secure.  So, the excitement is that Spitzer should be able to do this many more times in the next few years."

The planets are what astronomers call "hot Jupiters," that is they are large, fluffy gas planets like the planet Jupiter in our solar system.  Because the extrasolar planets are twenty times closer to their suns than earth is to its star, scientists estimate the temperature on the planets is probably around 850 degrees Celsius.

Now that they're able to see distant planets beyond our solar system, astronomers hope to learn about the temperatures, atmospheres and orbits of many planets hundreds of light years away. In addition to gaseous planets, scientists look forward to discovering rocky planets like earth and the possibility of life forms.

"I think these discoveries today have taken us a major step along that way,” said Astronomer Alan Boss, who is with the Carnegie Institution of Washington.  “These truly are epochal discoveries, and we're well along the way toward establishing astrobiology as a new discipline."

The astronomers published their discoveries of the two extrasolar planets in the journals Nature and The Astrophysical Journal.