New Planet Discovered [Picture]

Scientists photograph a planet outside solar system

The first direct photographic evidence of a planet circling another star outside the Earth's solar system has been found by a team headquartered at the University of California, Berkely.

The planet is a bloated gas giant 150% that of Jupiter's size, but having only 63% the mass, astronomer Geoffery Marcy and his collegues revealed last Saturday (13Nov99).

Marcy and his collaborator Paul Butler of the Carnegie Institution of Washington and other astronomers have previously produced a variety of indirect evidence hinting at the existence of at least 28 other planets circling distant stars. But Saturday's finding marks the first time a planet has actually been photographed.

Planets are normally too dim to be seen from Earth, even with the finest telescopes. In this case, however, astronomer Greg Henry of Tennessee State University was able to photograph the gas giant passing in front of the star 'HD 209458', producing an eclipse-like image.

"This is the first independent confirmation of a planet", Marcy said. "And it also gives us the first ever measure of the size of one of these planets."

Although most cosmologists are convinced that planetary systems are common throughout the universe, proving it has been difficult. Although we generally think about planets orbitting suns, a planet and a sun actually orbit a common center of mass. Because the sun is so much bigger than the planet, its orbital motion is much smaller. Nonetheless, researchers have now observed many stars whose motion suggests that they are being orbitted by a large planet.

Researchers have also seen stars surrounded by large discs od dust - the primordial material from which planets are formed. In some cases, they have even observed voids in the dust that they believe have been swept clean by newly forming planets. But until now, they have never been able to see a planet itself.

Marcy and Butler first detected a wobble in HD 209458 on 5Nov99. The star 153 light-years from Earth in the constellation Pegasus, and is about the same age, colour and size as our own sun.

Based on the star's wobble, Marcy and Butler concluded that the planet orbits its star once every 3.523 days. As they routinely do, they notified Henry of their discovery and told him the best chance of observing the planet was 7Nov99. Observing a planet is a hit and miss proposition because it can only be seen if its orbital plane brings it between the star and a telescope on Earth. With previously discovered wobbling stars, that has not happened.

In this case, however, the astronomers were lucky and the planet was captured on film. Henry observed a 1.7 % dip in the brightness of the star as the planet passed in front of it.

"This planetary transit occurred at exactly the time predicted from Marcy's observation, confirming absolutely the presence of a companion," Henry said. "We've essentially seen the shadow of the planet and used it to measure its size."

All of the data and observations "hang together" to indicate the existence of the planet, Marcy said. "This is what we have been waiting for."

The short orbital period indicates that the planet is very close to HD 209458, and that closeness suggests that the planet is very hot and unlikely to have any life on it.

The team hopes to be able to learn more about the planet. Because the planet passes in front of the star, some of the star's light will pass through its atmosphere. Telescopes on Earth thus should be able to learn a great deal about its composition.

-An Article by Thomas H Maugh II, published in Times of India