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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.
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.