Extrasolar Planets - Exoplanets
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. 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.
Fomalhaut b is an extrasolar planet orbiting the star Fomalhaut. It is the first exoplanet observed directly in visible light, after researchers spent eight years trying to pinpoint its position. The planet's existence was theoretically predicted. NASA released the photograph, taken by the Hubble Space Telescope's ACS, on November 13, 2008. In the image, the bright outer oval band is the dust ring, while the features inside of this band represent noise from scattered starlight.
The Fomalhaut system is located 25 light-years away from Earth, in the constellation Piscis Austrinus. Fomalhaut b is believed to be the coolest, lowest-mass object ever seen outside our own solar neighbourhood. The existence of the planet was inferred in 2005 due to its influence on the Fomalhaut dust belt; the belt is not centered on the star, and has a sharper inner boundary than would normally be expected. However, the planet was only located in May 2008 after Paul Kalas singled it out of Hubble photographs taken in 2004 and 2006.
Kalas remarked, "Itıs a profound and overwhelming experience to lay eyes on a planet never before seen. I nearly had a heart attack at the end of May when I confirmed that Fomalhaut b orbits its parent star." The planet is estimated to be approximately the same size as Jupiter, with a maximum mass of three Jupiters and a most probable mass of 0.5 to two. It is 115 AU (17 billion km, 11 billion mi, about 20% greater than the aphelion distance of Eris and 3.8 times the semi-major axis of Neptune) from its sun, giving it an orbital period of 872 earth years. Fomalhaut has about 16 times the Sun's luminosity, so Neptune and Fomalhaut b are in regions of similar temperature (due to the inverse square law).
Fomalhaut b is suspected, on the basis of its brightness in visible light and dimness in infrared, to have planetary rings far larger than those of Saturn.
Find Fomalhaut in the Celestial Sea MSNBC - November 14, 2008
In ancient Persia, star announced the arrival of autumn weather
Discovering Fomalhaut b (sounds like "foam-a-lot") NASA - November 14, 2008
First-ever images taken of extrasolar planets MSNBC - November 13, 2008
Major Breakthrough: First Photos of Planets Around Other Stars Live Science - November 13, 2008
Exoplanets finally come into view BBC - November 13, 2008
Two studies show the first direct images of planets outside our Solar System, including a three-planet system.
First Pictures of Alien Planet System Revealed National Geographic - November 14, 2008
'Super-Earths' orbit nearby stars BBC - December 15, 2009
Nearby "Super Earth" May Have Oceans, Thick Atmosphere National Geographic - December 16, 2009
Most Earth-Like Extrasolar Planet Found Right Next Door Wired - December 16, 2009
Discovery of a Retrograde or Highly Tilted Extrasolar Planet PhysOrg - November 18, 2009
32 New Exoplanets Found PhysOrg - October 19, 2009
32 New Planets Found Outside Our Solar System National Geographic - October 19, 2009
First Solid Evidence for a Rocky Exoplanet PhysOrg - September 16, 2009
Strange Dwarf Planet Has Red Spot Live Science - September 15, 2009
Sun-like star's 'oddball' planet BBC - April 29, 2009
Astronomers have discovered a strange Jupiter-sized world circling a star similar to our own Sun.
First Exoplanet With CO2 Heats Up Hunt for Other Earths National Geographic - December 8, 2008
First Picture of Alien Planet Orbiting Sunlike Star? National Geographic - September 16, 2008
Exoplanet circles 'normal star' BBC - September 16, 2008
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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