New Celestial Bodies Found

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For the first time in history, astronomers have found planets outside our solar system that are smaller than Saturn, a team of scientists announced on March 29.

In previous observations, UC Berkeley professor Geoff Marcy, in conjunction with other scientists, has found 30 extrasolar planets - all between one and eight times the size of Jupiter, which is approximately three times more massive than Saturn and 100 times the mass of Earth. Marcy, who has found more than 20 planets to date, was also a member of the team that made the latest discovery.

Marcy has compared the discovery of different-sized planets to finding different sizes of rocks on the beach. At first, astronomers were only able to detect "large boulders," but now, using more advanced telescopes, they are able to detect "rocks." Soon, they hope to detect planets approximately the mass of Earth, which would be the equivalent of finding "pebbles."

"We guess, but we do not know, that our galaxy harbors more small planets than large ones," Marcy said. "In our solar system, we have many small planets and only one Jupiter. We imagine that for every Jupiter, there are dozens of the small planets. We expect to find more and more of the small, low-mass planets, compared to the big gas giants like Jupiter."

There are two classes of planets - gas giants and planets made up of rocks. Mercury, Venus, Earth, Mars and Pluto are all rock planets. Scientists have yet to detect any extrasolar rock planets because these are not massive enough to be found using currently available techniques.

The researchers found two planets; one is at least 80 percent of the size of Saturn, located 109 light years away and orbits the star HD46375. In addition, they found a planet at least 70 percent of the mass of Saturn located 117 light years away and orbiting the star 79 Ceti, in the constellation Cetus.

The two planets are both located close to their stars and have relatively small orbits, which helped scientists to detect the bodies quickly. Because of the size of their orbit, the two planets complete one circle around their stars in 3.02 days and 75 days, respectively.

The scientists found the planets by searching for "star wobbles." Stars normally move slightly, and this movement can be detected by studying the redshift, which occurs when light travels long distances.

As the lightwaves travel, the wavelengths grow longer, providing a sort of map that can be used to determine the distance between a star and Earth.

When planets orbit a star, they exert a gravitational pull on the star that causes it to move in a circle. Over time, scientists can watch the pattern of a star's movement and then determine whether or not a planet is exerting a gravitational force on the star.

Because of the existence of brown dwarfs- stillborn stars that can be approximately the mass of Jupiter- scientists were not previously sure that the objects that they were detecting were actually planets.

The existence of the smaller planets, which are not massive enough to be brown dwarfs, confirms the presence of extrasolar planets.

Although previous studies conducted using the UC- operated Lick Observatory could only detect planets at least the size of Jupiter, the new study used W.H. Keck Observatory - located on top of a volcano in Hawaii - which is 10 times bigger.

Because of the increased power of the Keck telescope, the research team has been able to increase the precision of their planet detection and has been able to find increasingly less massive planets.

In order to further the search for extrasolar planets, NASA has announced plans to build a "space-borne" telescope, dubbed the Terrestrial Planet Finder, that will be able to detect not only light from stars but also from planets reflecting light.

Scientists hope the new system, slated to be completed within the next 15 years, will permit researchers to discover many more small planets.

"The exciting prospect is that NASA is going to build a space-borne telescope called an inferometer," Marcy said. "This space-borne telescope will be able to block out the light from the stars and let the light from the planets shine through. The idea is to see the light reflected off planets."

The discovery of the small planets was made by Marcy, Paul Butler of the Carnegie Institution of Washington, and Steve Vogt of UC Santa Cruz.

The discovery of the smaller planets is part of a long-term study funded by NASA and the National Science Foundation that investigates wobbles found in 1,100 stars located within a 300-light-year radius of Earth.


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