Eliptical Orbit

A CNN article by Associated Press dated October 23, 1996.
New rebel planet found outside solar system
It's roller-coaster orbit stuns scientists

A new planet that breaks all the rules about how and where planets form has been identified in orbit of a twin star about 70 light years from Earth in a constellation commonly known as the Northern Cross. The new planet has a roller-coaster like orbit that swoops down close to its central star and then swings far out into frigid fringes, following a strange egg-shaped orbit that is unlike that of any other known planet. "We don't understand how it could have formed in such an orbit," said William D. Cochran, head of University of Texas team that discovered the planet at the same time that a group from San Francisco State found it independently.

The researchers presented papers on the new planet Wednesday at a national meeting of the American Astronomical Society's planetary division. The new planet is the latest in a series of bodies found in orbit of stars outside the solar system and is part of a quickening effort by astronomers to find distant worlds. Cochran said the planet orbits the smaller of twin stars in the constellation Cygnus, a prominent stellar grouping known as the Northern Cross. The planet's star is called 16 Cygni B and the larger companion star is 16 Cygni A.

"Of all the stars you might see in the sky, Cygni B is the most similar to our sun," said Cochran. It has the same mass and temperature as the sun, but the nearby twin star of Cygni B creates an entirely different type of environment. Every 250,000 years, Cygni A and B pass within 65 billion miles of each other, a grazing passage by stellar standards. Cochran said the stars are so close, that the gravitational tug of Cygni A may have pulled the new planet into its wildly eccentric orbit.

It is unlikely that life exists on the new planet, said Cochran, because it probably is more like the gaseous planets, such as Jupiter or Saturn, than the rocky planets such as Earth or Mars. The wide-swinging orbit of the planet would also cause extreme fluctuations in temperature, he said. During one part of its 804-day-long year, the planet would pass within 67 million miles of its sun. This would be the planet's summer, said Cochran. Then the planet would swing far out, reaching a point 158 million miles from the star. This would be its winter and it would last more than 500 days, the researcher said. Most planets in the solar system have an almost circular orbit, like that of the Earth, and most theories about how planets form are based on them settling into a circular orbit. The eccentric orbit of the new planet adds a new dimension that astronomers will have to consider in theories about planetary formation, Cochran said.

The University of Texas and San Francisco astronomers found the new planet by studying the movement of Cygni B. They discovered that the star tended to change its speed of motion in a way that could only be explained by the presence of an orbiting companion. Cygni A has no such motion, said Cochran, suggesting it has no planet. By some counts, the new planet is the ninth to be found outside the solar system, although some astronomers say there have been up to 11 found. Cochran said the exact number is controversial because not all of the discoveries have been generally accepted as actual planets.

And there were skeptics even of the Cochran discovery. "It is a really nice piece of work" said David Black of the Lunar and Planetary Institute in Houston. "But I really question whether this is a planet or a brown dwarf." A brown dwarf is a failed star, an object that never collected enough mass to start stellar burning. Black said it is possible that most of the recently discovered planets are really brown dwarfs.