Extrasolar Planets
An extrasolar planet is a planet which orbits a star other than the Sun, i.e. which belongs to a planetary system other than our solar system.
Extrasolar planets were discovered during the 1990s as a result of improved telescope technology, such as CCD and computer-based image processing along with the Hubble Space Telescope. Such advances allowed for more accurate measurements of stellar motion, allowing astronomers to detect planets, not visually (the luminosity of a planet being too low for such detection), but by measuring gravitational influences upon stars (see astrometrics). In addition, extrasolar planets can be detected by measuring the variance in a star's apparent luminosity, as a planet passes in front of it. Besides the detection of at least 80 planets (mostly gas giants), many observations point to the existence of millions of comets also in extrasolar systems.
The Polish astronomer Aleksander Wolszczan claimed to have found the first extrasolar planets in 1993, orbiting the pulsar PSR 1257+12. Subsequent investigation has determined that these objects are not "true" planets in that they are technically "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 "true" extrasolar 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's Lick and Keck Observatories. The first system to have more than one planet detected was Upsilon Andromedae. The majority of the detected planets have highly elliptical orbits.
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.
Most of the planets found are of relatively high mass (at least 40 times that of the Earth); however, a couple seem to be approximately the size of 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.
One question raised by the detection of extrasolar planets is why so many of the detected planets are gas giants which, in comparison to Earth's solar system, are unexpectedly close to the orbited star. For example, Tau Boötis has a planet 4.1 times Jupiter's mass, which is less than a quarter of an astronomical unit (AU) from the orbited star; HD 114762 has a planet 11 times Jupiter's mass, which is less than half an AU from the orbited star.
One possible answer to these unexpected planetary orbits is that since astrometrics detects the extrasolar planets due to their gravitational influences and partially-ecliptic interference, perhaps current technology only permits the detection of systems where a large planet is close to the orbited star, rather than such systems being the norm.
Three "Super-Earths" Found Orbiting Sun-Like Star National Geographic - June 17, 2008
New Mini-Planet Found; "Shot in the Arm" for ET Search National Geographic - June 3, 2008
Mysterious "Super Earth" Is Smallest Known Exoplanet? National Geographic - April 12, 2008
Methane Detected on Distant Planet for First Time National Geographic - March 19, 2008
Methane found on distant world BBC - March 19, 2008
The 10 most intriguing extrasolar planets MSNBC - September 18, 2007
Largest Planet
The largest planet ever discovered is also one of the strangest
and theoretically should not even exist, scientists say.
Largest-known planet befuddles scientists MSNBC - August 7, 2007
Largest Known Planet Found, Has Density of Cork National Geographic - August 8, 2007
Team finds largest exoplanet yet BBC - August 7, 2007
Largest Known Exoplanet Discovered Space.com - August 7, 2007
28 New Exoplanets Discovered Space.com - May 29, 2007
Astronomer finds that hottest measured extrasolar planet is 3700 degrees PhysOrg - May 9, 2007
Distant Planets Could Have Plants of "Alien" Colors National Geographic - April 12, 2007
First Sign of Water on Planet Outside Our System National Geographic - April 11, 2007
Future Space Telescopes Could Detect Earth Twin Science Daily - April 12, 2007
Triple Sunset: Planet Discovered in 3-Star System Space.com - July 13, 2005
Smallest extrasolar planet found BBC - June 13, 2005
'Tail wagging dog' seen in star-exoplanet system Spaceflight Now - May 17, 2005
Eccentric Worlds: Strange Orbits Puzzle Astronomers Space.com May 10, 2005
Of the more than 130 planets found around distant stars,
a large number have highly elliptical orbits, crazy oblong
shapes that have surprised theorists who try to explain the
configurations with near collisions or perturbing disks of gas.
First extrasolar planet seen BBC - March 2005
First Light from Extrasolar Planets Astrobiology Magazine - March 2005
Glow of alien extrasolar planets glimpsed at last New Scientist - March 2005
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