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THE earth may not be the only planet capable of supporting life. Two new planets sighted recently can possibly do the same, as they show the ability to hold water and other building blocks of life. The exciting discovery was announced on January 17, 1996 at the winter meeting of the American Astronomical Society at San Antonio, Texas, by Geoffrey Marcy and researcher Paul Butler of the San Francisco State University, USA.

Marcy had earlier confirmed the existence of a planet around the star 51 Pegasi in October last year (DOWN To Earth, Vol 4, No 13), which M discovered by Michel Mayor and Did Queloz of the Geneva Observatory Switzerland.

Astronomers have been searching for planets beyond the earth's solar system for a long time now and have achieved success only recently. The main method of locating these planets are by detecting 'wobbles' in the normal spectrum of light emitted by the stars. The wobble effect is caused due to the gravitational pull of the star the body revolving around it. The an and orbital distances have also been estimated from the shifts in the spectral from the stars. Jupiter produces a 12.5 metre-per-second wobble in the sun's orbit.

Lying within a distance of 35 light years, these two planets are relatively close to earth. The stars around which they revolve are visible to the naked eye and are the 70 Virginis of the Virgo constellation and 47 Ursae Majoris of the Big Dipper or Great Bear constellation. The star, 70 Virginis, is very similar to the sun, but a few hundred degrees cooler and three billion years older.

One of the new worlds, which has a mass nine times that of Jupiter, sweeps around 70 Virginis in an elongated path, taking 116 days to complete one revolution.

Marcy and Butler, who conducted the studies at the University of California, Berkeley, used the standard formulae for sunlight absorption and heat radiation to measure the temperature of this planet. It was found to be about 85'c, which according to Marcy, "is cool enough to permit molecules to exist, ranging from carbon dioxide to complicated organic molecules", such as those which make up living cells. The boiling point of water is 100C; therefore, there is a definite possibility that this planet could have water in the form of rain or oceans, he opines.

The second planet is nearly three times the mass of Jupiter, and takes 1,100 days to go around its star - 47 Ursae Majoris - at an orbital distance twice that of the earth from the sun. With temperatures as low as minus 80'c, it may seem incapable of supporting life forms, but Butler is optimistic and feels that below the atmospheric layers, the temperatures may be high enough to hold water in the liquid form. He says, "There could be a zone where a cauldron of organic molecules cooks with water." Enthusing about the Great Bear system he says, "This system is the closest thing we have seen to anything like our own solar system."

Both the planets are giant balls of gas, with no hard surface, but a thick atmosphere like that of Jupiter. Whether life forms are present on their surface is a question which only biologists can answer. Says Paul Murdin, director of science at the British National Space Centre, UK, "The planets would have extremely heavy gravity, so if there are creatures, they are going to be short and fat, not long and thin like us. They will be more crabs and limpets than sheep it horses and would move scuttling sideways."

Marcy and Butler conjecture that the planets could have moon-like satellites similar to or larger than Mars, orbiting around them. These satellites might also have carth-like gravities and atmospheres which could harbour life.

Whether life is possible or not is a question difficult to answer at this early stage, but whatever else, this discovery has led to "the culmiation of 500 years of intellectual history" which began with Copernicus's conclusion that the earth is not the centre of the universe, says Robert A Brown of the Space Telescope Science Institute in Baltimore, US.

The data collected by Marcy and Butter since 1997 show that these planets follow Keppler's and Newton's laws of orbital motion with an eerie precision. The duo have monitored 120 sun-like stars and analysed data on 60 of them, before coming to the conclusion on these two planets. The recent spurt of planet discoveries lies in the fact that earlier, the technology available was not sensitive enough to detect movement of celestial bodies so small, dim, and at such a distance through space.

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