Exoplanet listing

by **Spooky_Zalost** Wed Dec 29, 2010 8:48 am

ok so here I will be keeping a list of famous exoplanets
For a complete list go to http://www.planetary.org/exoplanets/list.php

Citations from the planetary society

51 Pegasi b
The first exoplanet ever detected orbiting a main-sequence star. Its discovery in 1995 by Michel Mayor and Didier Queloz of the Geneva Observatory launched a tidal wave of exoplanet discoveries that continues to this day. 51 Pegasi b orbits a star 50 lightyears from Earth, and like most of the exoplanets found in the early years it is a "hot Jupiter" – a gas giant orbiting very close to its home star. Its minimum mass is about half that of Jupiter, and it completes each orbit in a mere 4 days. As a result its surface is extremely hot, estimated at around 1000 degrees Celsius (1800 degrees Fahrenheit).

Despite close observations over a decade and a half, astronomers have found no sign of any additional planets orbiting 51 Pegasi. This suggests that hot Jupiters can effectively clean out a planetary system as they migrate from the distant regions in which they were formed to their final orbits close to their home star.

55 Cancri
Orbited by five known exoplanets, possesses the most complete planetary system known today around a star other than the Sun. With at least five planets in orbit, 55 Cancri is home to more known exoplanets than any other star. What is more, the planets' orbital arrangement is broadly reminiscent of our own solar system.

The largest of the planets is a gas giant about four times the mass of Jupiter, orbiting the star at a distance of about 6 astronomical units (AU), compared to Jupiter's 5.2 AU. The four smaller planets orbit within 0.8 astronomical units of the star, reminiscent of the four planets of the inner solar system, all of which orbit within 1.5 AU from the Sun. Even so, however, all the planets around 55 Cancri are gas giants, and even the smallest of them is 14 times the mass of the Earth.

The most intriguing of planets around 55 Cancri is a Saturn-sized gas giant, orbiting at 0.79 AU from its star and completing each revolution in just under 261 days. This places it near 55 Cancri's "habitable zone," the narrow band of space where water can remain in a liquid state. While this is not relevant to a gas giant, it is nevertheless possible that the planet possesses rocky moon, just like Jupiter and Saturn in our solar system. Such a moon, scientists speculate, could potentially have pools of liquid water on its surface. And where there is water, there could also be life.

COROT-Exo-7
This Exoplanet is only twice the mass of the Earth, and is the smallest exoplanet found as of early 2009. It was detected by the European planet-hunting spacecraft COROT, which uses transit photometry to search for terrestrial exoplanets. The planet orbits very close to its star and completes each revolution in a mere 20 hours. As a result, its surface temperature is approximately 1200 degrees Kelvin, enough to turn a rocky surface into molten lava.

Fomalhaut b
This system has the smallest of a handful of planets that have been directly imaged from Earth. Obtaining images of an exoplanet is only possible in exceptional circumstances, not only because planets are small and dim, but also because they are always in the vicinity of much larger and more brilliant stars. Fomalhaut b was found because it orbits a young star surrounded by a dense cloud of gas and dust. Scientists observing the star with the Hubble Space Telescope noticed that the inner edge ends abruptly, suggesting that a planet had cleared away the debris in that region. After closely observing a series of images taken at different times, they found a dot that moved around the star – a planet. According to estimates Fomalhaut b is three times the mass of Jupiter and orbits its star at a distance of 17 billion kilometers, equivalent to ten times the distance of Saturn from the Sun. At such a distance it takes the planet more than 800 years to complete each orbit. Because of its unusual brilliance, scientists believe that it is surrounded by a thick set of bright rings, many times larger and more dense than Saturn's.

Gliese 581c
This is one of the most Earth-like planet discovered to date. It is the third of four planets orbiting the red dwarf Gliese 581, 20.5 light years away, completing each orbit in a mere 13 days. Significantly, it is one of the smallest known exoplanets, measuring only 1.5 times the Earth's diameter and only 5 times its mass, and it is almost certainly a rocky world like our own. Even more suggestively it orbits close to the band around its star known as the "habitable zone," the only region where conditions are mild enough that water can exist in liquid form. Move closer to the star and all water will turn to vapor; move further away and water will turn to ice. But near the habitable zone water can remain liquid and life as we know it could potentially exist.

A small rocky planet with a mild climate where water can flow? Sounds a lot like our own world, and brings us one step closer to the discovery we are waiting for: another Earth, orbiting a distant Sun.

Gliese 581d
This is the outermost of the four known planets orbiting the red dwarf Gliese 581, 20.5 light years from earth. When first detected in 2007, Gliese was thought to have an orbital period of 82 days, placing it in an orbit just outside its star's "habitable zone" (HZ), where liquid water is stable. But additional observations over the next two years determined that the planet's true period is 67 days, which places it squarely at the heart of the HZ. With a minimum mass 7 times greater than the Earth, Gliese 581d is probably too massive to be a rocky planet like the Earth, and is more likely an icy world similar to Neptune. If this is the case, the planet might be completely covered by a deep ocean, making it the first serious candidate for a "water world."

Gliese 581e
This is the lowest mass exoplanet discovered to date. Detected in 2009, it is the innermost of the four planets orbiting the red dwarf Gliese 581. With a minimum mass of only 1.9 "Earths" Gliese 581d is almost certainly a small rocky world like our own. But with an orbital period of just over 3 days, the planet is far too close to its star -- and therefore much too hot -- to sustain liquid water or life as we know it. The planet was discovered through the radial velocity technique, using HARPS spectrograph at the European Southern Observatory's 3.6 telescope at La Silla, Chile. It's discovery suggested that the radial velocity method, responsible for detecting the vast majority of known exoplanets. may prove sensitive enough to detect Earth-mass worlds orbiting in their star's habitable zone.

HD 80606b
in some respects this is a normal exoplanet: It is a gas giant slightly smaller than Jupiter, but much denser, with a mass more than 4 times greater than our giant neighbor. In other respects, however, HD 80606b is an oddity. For starters, it orbits a star that is part of a binary system, in which two stars constantly revolve around each other. For another, it has the second most elongated orbit of any known exoplanet, with an eccentricity of 0.93. To put it differently, the planet comes as close as 0.03 AU to its star at one end of its orbit, and as far as 0.84 AU at the other. As a result the temperature on its surface swings wildly from relatively mild to scalding hot.

On top of it all HD 80606b is that rare bird – a transiting planet that passes both in front of its star and behind it when observed from Earth. This means that the planet's orbit around its star is almost precisely "edge-on" when viewed from Earth. This fortunate situation has made it possible astronomers to learn the planet's diameter and mass with a high degree of certainty. In the future, it could also make it possible to analyze the composition of its atmosphere.

HD 189733b
This exoplanet is a gas giant, 13% more massive than Jupiter orbiting a Sun-like star 62 lightyears away. Unlike Jupiter, however, it orbits its star at an average distance of only about 5,000,000 kilometers (3,000,000 miles), or 30times closer than the Earth is to the Sun. As a result the temperature on the planet is a scalding 900 degrees Celsius (1600 degrees Fahrenheit), and supersonic winds blow through the atmosphere. One can hardly imagine a more hostile environment for life as we know it.

The special thing about HD 189733b is that it is very bright and was detected in 2005 by two different methods: first by radial velocity, then by transit photometry. Thanks to this scientists have been able to learn more about HD 189733b than about almost any other known exoplanet.

First scientists were able to determine HD 189733b's mass, size, and density with a high degree of accuracy. They then used the Hubble and the Spitzer space telescopes to carefully measure the degree to which the planet absorbs light during transit at different wavelengths. >From this they created an "absorption spectrum" for the planet's atmosphere. This in turn, provides a strong indication of the different gasses that are present in the planet's atmosphere.

Observations so far have revealed a complex atmosphere containing a range of organic and inorganic molecules. There is water vapor, carbon dioxide, and methane. There are also hints of potassium, sodium, ammonia, and carbon monoxide, and likely condensates of iron, silicates, and aluminum oxide. Nothing like this rich detail is available for any other world outside the solar system.

HD 209458b
This Exoplanet is a "hot Jupiter" orbiting a Sun-like star 150 lightyears away, completing each revolution in a mere three and a half days. Like HD 189733b, HD 209458b is a transiting planet, meaning that it passes directly between its star and an observer on Earth. Thanks to this unique feature and the fact that both planet orbit very bright stars, the two planets are among the most studied and best understood exoplanets. In fact, HD 209458b, originally discovered using the radial velocity technique, was the first planet known to transit.

In March 2005 HD 209458b became one of the first two exoplanets to have its light isolated. Distinguishing a planet's light from that of its star is an extrememly difficult feat of observation, since the dim planet, which shines only in reflected light, is swallowed up the brilliance of its parent star. To accomplish this, scientists took advantage of the planet's "secondary transit," the time when it completely disappears behind the star. Using the Spitzer space telescope, they measured the star's normal infrared radiation and compared it with the measurement during a secondary transit. The difference between the two was the infrared light from the planet itself, indicating that its temperature is a searing 1100 degrees Kelvin.

By observing the planet's primary transit and measuring the light absorption at different points of the spectrum, scientists have put together a complex picture of the atmosphere of HD 209458b. It contains hydrogen, oxygen, and carbon, all of which appear to be leaking off the top of the atmosphere and enveloping the planet in a football-shaped cloud. In 2007 scientists announced they had detected water vapor in the atmosphere, making HD 209458b the first exoplanet in which water has been found.

HR 8799 is home to the first planetary system ever detected by direct imaging. Its three known planets, designated HR 8799b, c, and d, are all gas giants estimated at 7 to 10 times the mass of Jupiter. The overall architecture of the system is reminiscent of our own solar system, since the giant planets are located at great distances from their star, leaving plenty of room for smaller planets closer in. But the scale of HR 8799's system is much larger than the Sun's: Its three planets orbit at distances of approximately 25, 40, and 70 AU from their star, and their orbital periods are estimated at 100, 190, and 460 years respectively. By comparison, Jupiter orbits at only 5 AU form the Sun, Saturn at 9.5 AU, and Uranus at 19 AU. But HR 8799 weighs in at one and a half times the mass of the Sun and is five times more brilliant. As a result the radiation absorbed by its giant planets is comparable to that of Saturn and Uranus.

HR 8799
This is a young star, approximately 60 million years old, and is surrounded by a thick disk of gas and dust. In 2007 and 2008 astronomers took images of the star with the Gemini and Keck telescopes in Hawaii. They focused on the region inside the inner edge of the disk, where they assumed the debris had been cleared by the gravitational action of orbiting planets. By observing in the infrared range they hoped to take advantage of the heat radiation left over from the formation of the planets, which on an astronomical scale was very recent. By November 2008 they found what they were looking for: three tiny specks moving in orbit around HR 8799. It was a planetary system.

VB 10b
This is the first exoplanet discovered through astrometry -- the precise measurement of a star's location in the sky as it moves to the tug of an orbiting planet. Astrometry is the oldest method used in the search for exoplanets, and claims of planets discovered by astrometry go back to the 1940's. None of the claims, however, survived scientific scrutiny. VB 10 b, whose discovery was announced in May 2009, is therefore the first confirmed exoplanet discovered by this method.

The discovery is significant for other reasons as well. VB 10, the planet's home star, is a red dwarf, the most common type of star in the galaxy. In fact 70% of the stars in the galaxy are of this type. Located 20 light-years from Earth with a mass one twelfth that of the Sun, VB 10 is a particularly small red dwarf and was long the smallest known star. The fact that such a star is home a planet bodes well for the prevalence of planets in the galaxy. VB 10 b is a gas giant 6.4 times the mass of Jupiter and orbiting closer to its star than Mercury is to the Sun. Despite this proximity VB 10 b is a "cold" Jupiter, since its star is so small that it heats it no more than the Sun heats Jupiter. Accordingly VB 10 might be home to a solar system similar to our own, but on a miniature scale. It is possible that small rocky planets like Earth are present inside the orbit of VB 10 b.