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. Read more ...
Star system has record eight exoplanets BBC - December 14, 2017
Nasa has found a distant star circled by eight planets, equal to the complement in our own Solar System. It's the largest number of worlds ever discovered in a planetary system outside our own. The star known as Kepler-90, is just a bit hotter and larger than the Sun; astronomers already knew of seven planets around it. The newly discovered world is small enough to be rocky, according to scientists. "This makes Kepler-90 the first star to host as many planets as our own Solar System," said Christopher Shallue, a software engineer at Google, which contributed to the discovery. Engineers from Google used a type of artificial intelligence called machine learning to find planets that were missed by previous searches.
Extremely massive exoplanet discovered in the Milky Way's bulge PhysOrg - November 6, 2017
As a result of NASA's Spitzer Space Telescope observations of a microlensing event, astronomers have found an extremely massive alien world circling a star located in the Milky Way's bulge. The newly discovered planet, designated OGLE-2016-BLG-1190Lb, is the first Spitzer microlensing exoworld residing in the galactic bulge.
Exoplanet shines with glowing water atmosphere Scientific American - January 23, 2017
Credit: Engine House VFX, At-Bristol Science Centre, University of Exeter
Scientists have found compelling evidence for a stratosphere on an enormous planet outside our solar system. The planet's stratosphere -- a layer of atmosphere where temperature increases with higher altitudes -- is hot enough to boil iron.
' Signs of Alien Air Herald a New Era of Exoplanet Discoveries Scientific American - January 23, 2017
For astronomers seeking Earth twins around other stars, the exoplanet GJ 1132 b probably isn't an identical sibling - but it may be the closest cousin yet found. It weighs in at just over one Earth mass, but circles its star in a warm orbit that could make it more like Venus than our own world. Moreover, its diameter is nearly 50 percent larger than that of Earth, suggesting it possesses a thick atmosphere. Now, after taking the closest-ever look at GJ 1132 b, a European collaboration has confirmed the presence of its atmosphere and found hints it might contain water and methane.
Earth-like planet just 39 light years away has a thick atmosphere Daily Mail - January 23, 2017
A rocky, oven-hot Earth-sized spotted orbiting a small nearby star just over a year ago is one of the best chances we have of finding alien life outside our solar system. The planet, named GJ1132b, is around 1.2 times the size of Earth and appears to be predominantly composed of rock and iron. Now scientists have taken the closest look yet at GJ1132b, confirming the presence of its thick atmosphere and finding hints the planet could be rich in water.
Newborn giant planet grazes its star Science Daily - June 21, 2016
For the past 20 years, exoplanets known as 'hot Jupiters' have puzzled astronomers. These giant planets orbit 100 times closer to their host stars than Jupiter does to the Sun, which increases their surface temperatures. But how and when in their history did they migrate so close to their star? Now, an international team of astronomers has announced the discovery of a very young hot Jupiter orbiting in the immediate vicinity of a star that is barely two million years old -- the stellar equivalent of a week-old infant. This first-ever evidence that hot Jupiters can appear at such an early stage represents a major step forward in our understanding of how planetary systems form and evolve.
The Five Most Earth-Like Exoplanets (So Far) Epoch Times - November 19, 2015
Many of the claims about the habitability of exoplanets are greatly exaggerated. Here are the five top candidates for an Earth-twin, based on their ESI values.
1. Kepler 438b
2. Gliese 667Cc
3. Kepler 442b
4. Kepler 62e & 62f
5. Kepler 452b
Bizarre Comet-like Alien Planet Is First of Its Kind Live Science - June 25, 2015
A Neptune-size planet appears to be masquerading as a comet, with a gargantuan stream of gas flowing behind it like a comet's tail. The bizarre find is the first of its kind ever discovered by astronomers. The strange, comet-like planet, known as GJ 436b, is orbiting a red dwarf star and is about 22 times as massive as Earth. Astronomers detected the giant gas cloud around the planet using NASA's Hubble Space Telescope and Chandra X-ray Observatory.
Earth-size Kepler-186f NASA - April 18, 2014
Planet Kepler-186f is the first known Earth-size planet to lie within the habitable zone of a star beyond the Sun. Discovered using data from the prolific planet-hunting Kepler spacecraft, the distant world orbits its parent star, a cool, dim, M dwarf star about half the size and mass of the Sun, some 500 light-years away in the constellation Cygnus. M dwarfs are common, making up about 70 percent of the stars in our Milky Way galaxy. To be within the habitable zone, where surface temperatures allowing liquid water are possible, Kepler-186f orbits close, within 53 million kilometers (about the Mercury-Sun distance) of the M dwarf star, once every 130 days. Four other planets are known in the distant system. All four are only a little larger than Earth and in much closer orbits, also illustrated in the tantalizing artist's vision. While the size and orbit of Kepler-186f are known, its mass and composition are not, and can't be determined by Kepler's transit technique. Still, models suggest that it could be rocky and have an atmosphere, making it potentially the most Earth-like exoplanet discovered so far ...
First potentially habitable Earth-sized planet confirmed by Gemini and Keck observatories Science Daily - April 18, 2014
The first Earth-sized exoplanet orbiting within the habitable zone of another star has been confirmed by observations with both the W. M. Keck Observatory and the Gemini Observatory. The initial discovery, made by NASA's Kepler Space Telescope, is one of a handful of smaller planets found by Kepler and verified using large ground-based telescopes. It also confirms that Earth-sized planets do exist in the habitable zone of other stars.
NASA - March 3, 2014
Is Earth the only known world that can support life? In an effort to find life-habitable worlds outside our Solar System, stars similar to our Sun are being monitored for slight light decreases that indicate eclipsing planets. Many previously-unknown planets are being found, including over 700 worlds recently uncovered by NASA's Kepler satellite. Depicted above in artist's illustrations are twelve extrasolar planets that orbit in the habitable zones of their parent stars. These exoplanets have the right temperature for water to be a liquid on their surfaces, and so water-based life on Earth might be able to survive on them. Although technology cannot yet detect resident life, finding habitable exoplanets is a step that helps humanity to better understand its place in the cosmos.
Kepler telescope bags huge haul of planets BBC - February 27, 2014
The science team sifting data from the US space agency's (Nasa) Kepler telescope says it has identified 715 new planets beyond our Solar System. This is a huge new haul. In the nearly two decades since the first so-called exoplanet was discovered, researchers had claimed the detection of just over 1,000 new worlds. Kepler's latest bounty are all in multi-planet systems; they orbit only 305 stars. The vast majority, 95%, are smaller than our Neptune, which is four times the radius of the Earth. Four of the new planets are less than 2.5 times the radius of Earth, and they orbit their host suns in the "habitable zone" - the region around a star where water can keep a liquid state.
Researchers use Hubble Telescope to reveal cloudy weather on alien world PhysOrg - December 31, 2013
Weather forecasters on exoplanet GJ 1214b would have an easy job. Today's forecast: cloudy. Tomorrow: overcast. Extended outlook: more clouds. A team of scientists led by researchers in the Department of Astronomy and Astrophysics at the University of Chicago report they have definitively characterized the atmosphere of a super-Earth class planet orbiting another star for the first time.
Distant 'waterworld' is confirmed BBC - February 20, 2012
GJ 1214b is one of the most interesting exoplanets yet detected. Astronomers have confirmed the existence of a new class of planet: a waterworld with a thick, steamy atmosphere. Exoplanet GJ 1214b is a so-called "Super Earth" - bigger than our planet, but smaller than gas giants such as Jupiter. Observations using the Hubble telescope now seem to confirm that a large fraction of its mass is water. The planet's high temperatures suggest exotic materials might exist there. The planet was discovered in 2009 by ground-based telescopes. It is about 2.7 times the Earth's diameter, but weighs almost seven times as much. It orbits its red-dwarf star at a distance of just two million km, meaning temperatures on GJ 1214b probably reach above 200C.
Re-thinking an alien world PhysOrg - January 16, 2012
Forty light years from Earth, a rocky world named "55 Cancri e" circles perilously close to a stellar inferno. Completing one orbit in only 18 hours, the alien planet is 26 times closer to its parent star than Mercury is to the Sun. If Earth were in the same position, the soil beneath our feet would heat up to about 3200 F. Researchers have long thought that 55 Cancri e must be a wasteland of parched rock.
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