ATLANTA -- What are believed to be the first planets discovered outside Earth's solar system may be made up of debris left over from a star that was vaporized by a supernova explosion, scientists said Monday.
What may be two new planetary systems -- one features one planet and the other, two -- have been discovered in recent months. In both cases, the planets revolve around the spinning remnants of exploded stars, an ultra-dense type of neutron star known as a pulsar, said astronomer Alexander Wolszczan.
Wolszczan and a team of astronomers discovered the system with two planets. The finding was published in a Jan. 9 issue of the journal Nature and discussed in further detail Monday at the annual meeting of the Amercian Astronomical Society.
At a news conference, Wolszczan said the newly discovered planets have masses greater than that of Earth.
'On principal,' he said, 'they are massive enough to retain an atmosphere.' But, he said, high-energy radiation from the pulsar -- a sort of super solar wind -- would prevent the planets from holding an atmosphere.
Neutron stars are formed in supernova explosions when gravitational collapse crushes atomic particles together with such force that only uncharged neutrons survive in an ultra-dense sphere as small as 10 miles to 12 miles across. A spinning neutron star is called a pulsar.
Wolszczan's pulsar, known as TSR1257+12, and its planetary system are located about 1,300 light years from Earth. A light year is the distance light, traveling at 186,000 miles per second, travels in one year, about 6 trillion miles.
The pulsar, which has a mass of 1.4 times that of the sun, is thus about 7,600,000,000,000,000 miles away.
The two planets orbit the pulsar at about the same distance Mercury is from the sun -- 33.5 to 43.7 million miles. Both are moving in nearly circular orbits, taking 66.6 and 98.2 Earth days to complete each revolution.
Wolszczan and other scientists theorize that the planets were formed when the pulsar 'vaporized' a nearby star. Debris from the stellar wreck may have coalesced and formed the planets.
Wolszczan said the discovery indicates Earth-sized planets orbiting a central body can be formed of gas and dust under 'surprisingly diverse conditions.'
The evidence that a plantery system other than our own may exist was determined by scientists at Cornell University who studied and timed the arrival of radio beams from the pulsar.
Wolszczan, an astronmer at Arecibo Observatory in Puerto Rico, originally spotted the pulsar and its planets in February, 1990. The discovery followed by only a few months a possible finding by British astronomers of a single, planet-sized body orbting another puslar.
Wolszczan told reporters, 'We are not 100 percent certain' that a new planetary system has been discovered. But, 'We are almost certain.'
Dr. Frederic A. Rasio of Cornell said, 'The goal is to devise a test to confirm the existence of the planets.'
Dr. Stanford E. Woosley of the University of California at Santa Cruz predicted at that in the future scientists will find more planetary objects orbiting pulsars in space.