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Extra-solar planets

Extra Solar Planets


The image above was created by John Whatmough, Extrasolar Visions.

One Hundred and One Planets

The study of extra solar planets will be one of the most important areas of research in astronomy in this century. It is one of those subjects in astronomy that captures the attention of the public and professional astronomers alike. Is is often said that scientific questions that can be easily understood by schoolchildren are normally the most important. The existence of extrasolar planets, their habitability, the possible presence of life, and the existence of intelligent life are definitely among such questions.

The first planets outside the solar system were found in 1992 around the millisecond pulsar PSR B1257+12 by Alex Wolszczan at the Arecibo Observatory.

Apart from the fact that I work at the Arecibo Observatory, my own involvement in extra solar planet research was so far quite short. In 2003, myself and my collaborators searched for planets around 16 of the 22 millisecond pulsars in 47 Tuc. One of these pulsars, PSR J0024-7204H, might have a planet orbiting it, but it is still too soon to say for sure. In 1994, I worked with Jean Schneider, from the Observatoire de Paris at Meudon. We were searching for planets orbiting the binary star CM Draconis, from Observatoire de Haute-Provence, in southeastern France. That was the place where, in 1995, Michel Mayor and Didier Queloz, from the Geneva Observatory, discovered the first planet around a main-sequence star, (51 Pegasi b) using the radial velocity perturbations method. Soon after this discovery, Geoffrey Marcy and Paul Butler, then working at the San Francisco State University's planet search confirmed this discovery. These two groups have been the most prolific planet discoverers so far.

The photometric technique we tried in 1994 for CM Draconis has been used recently to detect the passage of the planet orbiting HD 209458b in front of its parent star. This proved beyond doubt that at least some of the planets detected by the radial velocity method are real, and apart from providing a clear value for the mass of the planet, it also provides a good estimate of the size of the planet, allowing a calculation of its density. The future of this technique is very promising: in January 2003, the first planet found using this technique was announced: OGLE-TR-56. This planet has an orbital period of about 1.2 days. By August 2004, a total of six transiting planets were already known, one of them was even found with a 10-cm telescope! Three space missions based on this principle (MOST, COROT and Kepler) have already been launched or approved, and have the last one at least has the potential to find Earth-sized planets.

The year 2004 has also seen the discovery of the first Neptune-mass planet, which is likely to be giant rock ball with about twice Earth's diamater. If confirmed, this is the first rocky planet around a main-sequence star! More than 120 planets are now known (see the Extra -solar Planets Catalog).

Future Planet Searches

Large space-based searches for extra solar planets are among the most fascinating projects for the 21st century. Some projects already in the drawing board have the potential to discover many thousands (or even millions) of new planets. The bulk of such space missions measures stellar positions very accurately (astrometry), building on the huge success of ESA'sHipparcos mission. SIM (NASA) is one of such missions. Designed to measure the positions of a few tens of thousands of stars to an accuracy of just a few microarcseconds, it can detect Earth-Mass planets from astrometry alone. It will also be used, among many other things, to test general relativity. GAIA is a complementary ESA project, which has the ambitious goal of measuring positions, velocities, distances and proper motions of more than 1 billion stars. The latter mission might discover hundreds of thousands of Jupiter-sized planets. Perhaps even more exciting, in 2008 NASA will launch the Kepler Mission. This will be able to find, for the first time, terrestrial-sized planets orbiting distant stars!

An excellent survey of these can be seen in The Extra solar Planets Encyclopaedia. From this web site, you can obtain updated information on these new missions, on all extra solar planets and obtain a large and updated bibliography, tutorials on detection methods and links to other sites on planet searching. This page is maintained by the aforementioned Jean Schneider.