Extrasolar Planet — An extrasolar planet is a planet orbiting around a star other than the Sun. Extrasolar planets were first discovered in the 1990s as a result of improved telescope technology, CCD and computer-based image processing which allowed far more accurate measurements of stellar motions.
The first extrasolar planets were reported by the astronomer Aleksander Wolszczan in 1993, orbiting the pulsar PSR 1257+12. Subsequent investigation has determined that they are only planets in the technical sense of “sub-brown dwarf masses orbiting an object that is or once was a star”; it is believed that they are unusual remnants of the supernova that produced the pulsar, and did not form as conventional planets do.
The first “real” extra-solar planet was announced on October 6, 1995 by Michael Mayor and Didier Queloz; the primary star was 51 Pegasi. Since then dozens of planets have been detected, many by a team led by Geoffrey Marcy at the University of California, Berkeley.
There are two main methods of detecting extrasolar planets, which are too faint to be detected by present conventional optical means. The first involves measuring the displacement in the parent star’s spectral lines due to the Doppler effect induced by the planet orbiting the star and moving it through mutual gravitation.
The second involves catching the planet as it passes in front of the star’s tiny disk which will cause the light of the star to “dip” in a distinctive way, and do so periodically as the planet completes multiple orbits. The second method is theoretically more sensitive, but is newer and has scored fewer successes.
It also depends on the plane of the planet’s orbit being aligned with the line of sight between the star and the Earth. As a result, any number of stars with planets that are not so aligned will be missed.
All planets found as of 2003 are of very high mass (at least 40 times the Earth). This reflects the current telescope technology, which is not able to detect smaller planets. The mass distribution should not be taken as a reference for a general estimate, since it is likely that many more planets with smaller mass, even in nearby solar systems, are still undetected.
On November 27, 2001, astronomers using the Hubble space telescope announced that they had detected the atmosphere of the planet orbiting HD 209458, from its absorption of light when passing in front of its star.
In 2002 a group of Polish astronomers (Prof. Andrzej Udalski, Prof. Marcin Kubiak, Dr Michal Szymanski from Warsaw and Polish-American prof. Bogdan Paczynski from Princeton) during project OGLE (The Optical Gravitational Lensing Experiment) worked out a method of easily finding extrasolar planets, based on a photometrical method. During one month they claimed to find 46 objects, many of which could be planets.
The Kepler Space Mission will be launched in the next few years. It is a space-based telescope designed specifically to search large numbers of stars for earth-sized terrestrial planets.
The frequency of extrasolar planets is one of the parameters in the Drake equation, which attempts to estimate the probability of communications with extraterrestrial intelligence.
Image Caption: Glowing a dark magenta, the newly discovered exoplanet GJ 504b — illustrated here with an artist’s depiction — weighs in with about four times Jupiter’s mass, making it the lowest-mass planet ever directly imaged around a star like the sun. Credit: NASA’s Goddard Space Flight Center/S. Wiessinger