Extrasolar planet
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An extrasolar planet, alternatively termed an exoplanet, is a planet which orbits a star other than the Sun, and therefore belongs to a planetary system other than the solar system.
Although extrasolar planets were long posited, no planets orbiting main sequence stars were discovered until the 1990s. Since the beginning of the current decade, however, about two dozen are discovered every year. The discovery of extrasolar planets raises the question of whether they might support extraterrestrial life.
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History of detection
Discoveries regarding extrasolar planets were first published in 1989, [1] [2] when variations in the radial velocities of HD 114762 and Alrai (γ Cephei) were explained as being caused by sub-brown dwarf masses, possibly giant planets (11 MJ & 2-3 MJ respectively). Alrai had been the subject of a paper [3] the year before, but the question of a planetary companion as the cause was left open. Subsequent work in 1992 however concluded that the data were not solid enough to declare the presence of a planet, [4] although ten years later improved techniques allowed the planet to finally be confirmed. The case for HD 114762 has yet to be disproven, but as of 2006 it is considered to be a low-mass star in a face-on orbit. In 1991, Andrew Lyne claimed to have discovered a pulsar planet in orbit around PSR 1829-10, using pulsar timing variations. However he retracted it in 1992, when it was pointed out that his team did not properly account for Earth's motion, and with such accounting, the planet disappeared.
The Polish astronomer Aleksander Wolszczan (with Dale Frail) also claimed to have found the first extrasolar planets in 1993, later confirmed, orbiting the pulsar [[PSR 1257+12]]. They are believed to be formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation, or the rocky cores that remain of gas giants that survived the supernova, and spiralled in to their current orbits.
Extrasolar planets around solar-type stars began to be discovered in large numbers during the late 1990s as a result of improved telescope technology, such as CCD and computer-based image processing. Such advances allowed for more accurate measurements of stellar motion, allowing astronomers to detect planets, not visually (the luminosity of a planet is generally too low for such detection), but by measuring gravitational influences upon stars (see astrometrics and radial velocity). Extrasolar planets can also be detected by measuring the variation in a star's apparent luminosity as a planet passes in front of it (see eclipse).
The first definitive extrasolar planet around a main sequence star (51 Pegasi) was announced on October 6, 1995 by Michel Mayor and Didier Queloz of the University of Geneva. Since then scores of planets have been detected, and some claims from the late 1980s substantiated, 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 υ Andromedæ. The majority of the detected planets have highly elliptical orbits. Most of the planets so far discovered are high-mass and most are larger than Jupiter, but on January 25, 2006 astronomers announced a rocky or ice planet of 5 Earth masses. [5]
In July, 2004, it was announced that the Hubble Space Telescope had been used to detect an additional 100 planets, but the presence of these planets could not yet be confirmed. Besides this, many observations point to the existence of millions of comets also in extrasolar systems.
As of 14 April 2006, there were 157 known planetary systems around main sequence stars, containing at least 181 known planets. [6]
Methods of detection
Image:Extrasolar Planets 2004-08-31.png
There are currently six methods of detecting extrasolar planets which are too faint relative to their much brighter host stars to be directly detected by present conventional optical means.
The planned Space Interferometry Mission, Terrestrial Planet Finder and Darwin would all try to examine planets in a more direct fashion.
Pulsar timing
The first method used to discover extra-solar planets was to observe anomalies in the regularity of pulses from a pulsar. This led to the 'discovery' of the first planet with the orbital period of one year. That was later retracted, as it was actually the failure to account for the motion of the Earth through its orbit. However, this method did lead to the discovery of the first planets, and first stellar system outside of our own, by Aleksander Wolszczan. It also led to the discovery of the oldest known planet, by Steinn Sigurdsson's team, around PSR B1620-26's binary stellar core. This planet is the only known planet to orbit two stars. The pulsar timing method involves precise measurements of the signal of a pulsar in order to determine if there are any timing anomalies in the period of the pulses. Subsequent calculations are used to determine what could cause the anomalies. This method is commonly used to detect pulsar companions but is not used to specifically find planets.
Astrometry
Astrometry is the oldest method used in the search for extrasolar planets, used as early as 1943. A number of candidates have been found since but none of them are confirmed and most astronomers have given up on this method for more successful ones. The method involves measuring the proper motion of a star in the search for an influence caused by its planets, but, unfortunately, changes in proper motion are so small that the best current equipment cannot produce reliable enough measurements. This method requires that the planets' orbits be nearly perpendicular to Earth's line of sight, and so planets detected by it could not be confirmed by other methods.
Radial velocity
The radial velocity method measures variations in the speed with which the star moves away from Earth or towards Earth, that is, the component along the line of sight, of the relative velocity of the star with respect to Earth. The radial velocity can be deduced from the displacement in the parent star's spectral lines due to the Doppler effect. Its variations are induced by the planet orbiting the star, because both orbit their mutual barycenter, as explained by solutions to the two-body problem. The velocity of the star around the barycenter is much smaller than that of the planet because the radii of the orbits and hence also the velocities are inversely proportional to the masses. Velocities down to 1 m/s can be detected with modern spectrometers, as e.g. the HARPS (High Accuracy Radial Velocity Planet Searcher) spectrometer at the ESO 3.6 meter telescope in La Silla Observatory, Chile.
This is the first and by far most successful technique used by planet hunters. It is also known as the "Doppler method" or "Wobble method". But it works only for relatively nearby stars out to about 160 light-years away from Earth. It easily finds planets that are close to stars, but struggles to detect those orbiting at great distances. The Doppler method can be used to confirm findings made by using the transit method.
Gravitational microlensing
The gravitational microlensing effect occurs when the gravitational field of a planet and its parent star act to magnify the light of a distant background star. For the effect to work the planet and star must pass almost directly between the observer and the distant star. Since such events are rare, a very large number of distant stars must be continuously monitored in order to detect planets at a reasonable rate. This method is most fruitful for planets between earth and the center of the galaxy, as the galactic center provides a large number of background stars.
Gravitational microlensing has a checkered past. In 1986, Polish astronomer Bohdan Paczyński of Princeton University first proposed using it to look for mysterious dark matter, the unseen material that is thought to dominate the universe. In 1991 he suggested it might be used to find planets. Successes with the gravity lensing method date back to 2002, when a group of Polish astronomers (Andrzej Udalski, Marcin Kubiak and Michał Szymański from Warsaw, and Bohdan Paczyński) during project OGLE (the Optical Gravitational Lensing Experiment) perfected a workable method. During one month they claimed to find objects, many of which could be planets. Since then, four extrasolar planets have been detected using microlensing, and this technique is viewed as one of the most promising methods for finding Earth-mass planets around sun-like stars.
Lensing events are brief, lasting for weeks or days, as the two stars and Earth are all moving relative to each other. More than 1,000 stars have been detected in microlensing relationships over the past ten years. Observations are usually performed using networks of robotic telescopes.
The key advantage of gravitational microlensing is that it allows low mass (i.e. Earth-mass) planets to be detected using available technology. A notable disadvantage is that the lensing cannot be repeated because the chance alignment never occurs again. Also, the detected planets will tend to be several kiloparsecs away, so follow-up observations would not be possible. However, if enough background stars can be observed with enough accuracy then the method can be used to determine how common earth-like planets are in the galaxy.
In addition to the NASA/National Science Foundation-funded OGLE, the Microlensing Observations in Astrophysics (MOA) group is working to perfect this technique.
Even more ambitious, microlensing observations with a world-spanning telscope network as carried out by the PLANET (Probing Lensing Anomalies NETwork)/RoboNet campaign allow nearly-continuous round-the-clock coverage providing the opportunity to pick up and follow signals from planets with masses as low as Earth. This strategy was successful in detecting the first low-mass planet on a wide orbit, designated OGLE-2005-BLG-390Lb. Currently, there is no other technique capable of detecting low-mass and Earth-like planets.
Transit method
Image:Planetary transit.svg A recently developed method detects a planet's shadow when it transits in front of its host star. This "transit method" works only for the small percentage of planets whose orbits happen to be perfectly aligned from astronomers' vantage point, but can be used on very distant stars. It is expected to lead to the first detection of an Earth-size planet orbiting a sun-like star when employed by NASA's forthcoming space-based Kepler observatory.
While the aforementioned methods allow the determination of a planet's mass, this method can be used to measure the radius of a planet. When combined with the radial velocity technique, one can determine the density of the planet, and hence learn something about the physical structure of the planet.
Most of these extrasolar planets found are of relatively high mass, with at least 40 times that of the Earth. However, a few seem to be approximately the size of the Earth. This reflects 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 planetary systems, are still undetected.
The Kepler Space Mission is a space-based telescope set to launch in 2007, although NASA administrator Mike Griffin has indicated that it may be delayed by diversion of money earmarked for the general space telescope program toward a new Hubble maintenance mission. The Kepler is designed specifically to search large numbers of stars for Earth-sized terrestrial planets using the transit method. The French Space Agency, in conjunction with the European Space Agency, plans a similar mission with its Corot space telescope due to launch in 2006. The transit detection method will also be employed but it is expected that Corot will only find rock planets that are several times larger than Earth.
An extrasolar planet may also be suggested by observations showing the Rossiter-McLaughlin effect, a spectrophotometric subtlety of masking the rotating star.
Circumstellar disks
An even newer approach is the study of circumstellar disks. Many solar systems contain a significant amount of space dust that is present due to frequent dust generation activity such as comets, asteroid and planetary collisions. This dust forms as a disc around a star and absorbs regular star light and re-emits it as infrared radiation. These dust clouds can provide invaluable information through studies of their density and distortion, caused either by an orbiting planet "catching" the dust, or distortion due to gravitational influences of orbiting planets.
Unfortunately this method can only be employed by space-based observations because our atmosphere absorbs most infrared radiation, making ground based observation impossible. Our own solar system contains enough dust to make up about 1/10th the mass of our moon. Although its mass is negligible, its surface area is so great that at a distance, its infrared emissions would outshine all our planets by a factor of 100.
The Hubble Space Telescope is capable of these observations using its NICMOS (Near Infrared Camera and Multi-Object Spectrometer) instrument, but was unable to do so due to a cooling unit malfunction that left NICMOS inoperative between 1999 and 2002. Even better images were then taken by its sister instrument, the Spitzer Space Telescope (formerly SIRTF, the Space Infrared Telescope Facility), in 2003. The Spitzer Telescope was designed specifically for use in the infrared range and probes far deeper into the spectrum than the Hubble Space Telescope can.
Direct observation
In March 2005 it was announced that scientists using the Spitzer Space Telescope were able to detect infrared radiation emitted from two extrasolar planets. The two teams, from the Harvard-Smithsonian Center for Astrophysics, led by David Charbonneau and the Goddard Space Flight Center, led by L. D. Deming studied the planets HD 209458b and TrES-1. They were able to measure the temperatures of the planets: 1,060 kelvins (1,450°F) for TrES-1 and about 1,130 kelvins (1,570°F) for HD 209458b.
In early 2005, two groups, both using the European Southern Observatory's Very Large Telescope array in Chile announced direct infrared images of extrasolar planets: GQ Lupi b and 2M1207b. Both planets are believed to be several times the mass of Jupiter and orbit at distances greater than 50 AU from their primary star. As of May 2005, their status as planetary objects (as opposed to being small brown dwarf stars) has not been firmly established.
Naming
A lower case letter is placed after the star name, starting with "b" instead of "a" (which usually stands for the star) for the first planet found in the system (e.g. 51 Pegasi b, with the next planet being for example "51 Pegasi c", then "51 Pegasi d"...
If two or more planets are found at the same time, the closest planet to it's star gets the next letter. If the planet orbits in a binary system (in which the stars are far apart), the planet is named after the one star it orbits (e.g. HD 188753 Ab). If the planet orbits a binary star in a system where the stars are very close to each other, the letters "a" and "b" are skipped (because they represent the two stars) and the planet is called "c" (e.g. PSR B1620-26c)
Before the discovery of 51 Pegasi b in 1995, naming extrasolar planets were different. The first extrasolar planets found around pulsar [[PSR 1257+12]] were named with capital letters: PSR 1257+12 B and PSR 1257+12 C. When a new closer in exoplanet was found around the pulsar, it was named PSR 1257+12 A, not D.
Solar system formation processes
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, τ 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, which is closer to the star than Mercury orbits the sun. HD 114762 has a planet 11 times Jupiter's mass which is less than half an AU from the orbited star. The reason for these relatively extreme planetary orbits is that astrometrics detects the extrasolar planets due to their gravitational influences and partially-ecliptic interference. Current technology only permits the detection of systems where a large planet is close to the orbited star, but the results do not mean that such systems are the norm. The technological bias towards finding such systems is referred to as a selection effect or selection bias.
Observations of young stellar objects (newly forming stars) has highlighted the properties of the dust disks from which planets are though to have formed, and has provided a number of insights into the planet formation process[7].
The frequency of extrasolar planets is one of the parameters in the Drake equation, which attempts to estimate the probability of communications with extraterrestrial intelligence.
Notable extrasolar planets
- In 1992, Wolszczan and Frail published results indicating that pulsar planets existed around [[PSR B1257+12]] in Nature, volume 355, 145-147. Wolszczan had discovered the millisecond pulsar in question in 1990 at the Arecibo radio observatory. These were the first exoplanets ever verified, all the much more rare, that they orbit a pulsar.
- The first verified discovery of an exoplanet (51 Pegasi b) orbiting a main sequence star (51 Pegasi) was announced on October 6, 1995 by Michel Mayor and Didier Queloz in Nature, volume 378, page 355.
- A microlensing event in 1996 of the gravitationally lensed quasar [[Q0957+561]], observed by R. E. Schild in the A lobe of the double imaged quasar, has led to a controversial, and unconfirmable, speculation that a 3 Earth mass planet is possibly in the unknown lensing galaxy, between Earth and the quasar. This would be the most distant planet, if it could be confirmed, and is assumed to reside at redshift 0.39; 2.4 Gpc away (7.8 billion light years or 74 Ym), where the lensing galaxy is. (The double-image quasar itself, (called The Twin Quasar, or Old Faithful) Q0957+561 A/B, resides at redshift z=1.41)
- In 1999, HD 209458b was the first extrasolar planet seen transiting its parent star, conclusively proving that the radial velocity measurements suspected to be planets actually were planets.
- On November 27, 2001, astronomers using the Hubble Space Telescope announced that they had detected the atmosphere of the planet orbiting HD 209458 (known as HD 209458b and provisionally dubbed "Osiris"). Also during that year, a star was located which had the remnants of one or more planets within the stellar atmosphere — apparently the planet was mostly vaporized. It has been suggested that there may be planets that orbit so closely to their suns that most of their mass has been stripped away by the heat, provisionally referred to as Chthonian planets.
- On July 10, 2003, using information obtained from the Hubble Space Telescope, scientists discovered the oldest extrasolar planet yet. Dubbed Methuselah after the biblical figure, the planet is about 5,600 light years from Earth, has a mass twice that of Jupiter, and is estimated to be 13 billion years old. It is located in the globular star cluster M4, in the constellation Scorpius.
- On April 15, 2004, separate teams announced the discoveries of three planets outside our solar system.
- OGLE-2003-BLG-235L (MOA 2003-BLG-53L) which is 17,000 light years away, more than three times farther away than the previous record holder. The background star that was used in the gravitational lensing is 24,000 light-years away. The newly-discovered planet is estimated to be about 1.5 times the mass of Jupiter and presumed to be similarly gaseous. It orbits the star about 3 astronomical units (AU). Jupiter is 5.2 AU from the Sun.
- The same day, a European team of planet hunters based at the Geneva Observatory announced two giant planets using the transit method. Both planets are called "hot Jupiters," close to one Jupiter-mass but orbiting its star so closely that it completes an orbit in less than two earth days.
- In August 2004, a planet orbiting mu Arae with a mass of approximately 14 times that of the Earth [8] was discovered with the ESO HARPS spectrograph. It is the second lightest extrasolar planet orbiting a main sequence star to be discovered to date, and could be the first terrestrial planet around a main sequence star found outside the solar system.
- In August 2004, a planet was discovered using the transit method with the smallest aperture telescope to date, 4 inches. The planet was discovered by the TrES survey, and provisionally named TrES-1, orbits the star GSC 02652-01324. The finding was confirmed by the Keck Observatory, where planetary specifics were uncovered.
- In June 2005 a third planet orbiting the red dwarf star Gliese 876 was announced by E. Rivera et al.. At only 6 to 8 Earth masses, it is the smallest known extrasolar planet orbiting a normal star, and must almost certainly be rocky in composition. It orbits at 0.021 AU with a period of 1.94 days.
- In July 2005 a planet with the largest core ever was announced. The planet, HD149026b orbits the star HD149026, has a core that is estimated to be 70 Earth masses, accounting for 2/3's of the planet's mass.
- On January 25, 2006 the first low-mass planet on a wide orbit was announced. OGLE-2005-BLG-390Lb orbits a red dwarf star around 21,500 light years away, towards the centre of our galaxy. It was discovered using microlensing. Prior to this discovery, planets with low masses (comparable to that of Neptune) had only been discovered on short-period orbits.
- Astronomers have recently [9] [10] detected a planet in a triple star system, a finding that challenges current theories of planetary formation. The planet, a gas giant slightly larger than Jupiter, orbits the main star of the HD 188753 system, in the constellation Cygnus, and is hence known as HD 188753 Ab. The stellar trio (yellow, orange, and red) is about 149 light-years from Earth. The planet, which is at least 14% larger than Jupiter, orbits the main star (HD 188753 A) once every 80 hours or so (3.3 days), at a distance of about 8 Gm, a twentieth of the distance between Earth and the Sun. The other two stars whirl tightly around each other in 156 days, and circle the main star every 25.7 years at a distance from the main star that would put them between Saturn and Uranus in our own Solar System. The latter stars invalidate the leading hot Jupiter formation theory, which holds these planets form at "normal" distances and then migrate inward through some debatable mechanism. This could not have occurred here, since the outer star pair would have disrupted outer planet formation.
See the list of stars with confirmed extrasolar planets for a list of confirmed observations.
Table of extremes
| Extrasolar Planets | ||||
|---|---|---|---|---|
| Title | Planet | Star | Notes | |
| Oldest | PSR B1620-26c | PSR B1620-26 | 12,700 million years old | |
| Youngest | Unknown | |||
| Heaviest | ? | ? | several planets have minimum masses near 11 MJupiter
| |
| Lightest | [[PSR 1257+12#PSR 1257+12 A|PSR 1257+12 A]] | [[PSR 1257+12]] | 0.02 MEarth
| |
| Largest | HD 209458 b | HD 209458 | Has a radius 1.32 RJupiter
| |
| Smallest | Unknown | |||
| Most distant | OGLE-2005-BLG-390Lb | OGLE-2005-BLG-390L | 21,500 ± 3,300 light years
| |
| Least distant | Epsilon Eridani b | Epsilon Eridani | 10.4 light years | |
| Most dense | HD 149026 b | HD 149026 | 1.4 g/cm³ | |
| Least dense | HD 209458 b | HD 209458 | 0.33 g/cm³ | |
| Longest period | 2M1207b | 2M1207 | 2450+ years | |
| Shortest period | OGLE-TR-56b | OGLE-TR-56 | 1.2 days
| |
| Most eccentric orbit | HD 80606 b | HD 80606 | eccentricity of 0.927 | |
| Least eccentric orbit | PSR 1257+12 A | PSR 1257+12 | eccentricity of 0.0 | |
| Most inclined orbit | TrES-1 | GSC 02652-01324 | inclination 88.2° | |
| OGLE-TR-113b | OGLE-TR-113 | |||
| Least inclined orbit | OGLE-TR-56b | OGLE-TR-56 | inclination 81°
| |
| Fastest orbital velocity | Unknown | |||
| Slowest orbital velocity | Unknown | |||
| Largest orbit | 2M1207b | 2M1207 | 55+ AU | |
| Smallest orbit | Gliese 876 d | Gliese 876 | 0.021 AU
| |
| Firsts | ||||
| First planet discovered | [[PSR 1257+12#The planets|PSR 1257+12 B, C]] | [[PSR 1257+12]] | 1992 | first extrasolar planets discovered
first known pulsar planets |
| 51 Pegasi b | 51 Pegasi | 1995 | first known planet orbiting a Sun-like star first planet discovered by radial velocity method | |
| Gliese 876 b | Gliese 876 | 1998 | first known planet orbiting a red dwarf | |
| HD 209458 b | HD 209458 | 1999 | first transiting planet
| |
| Iota Draconis b | Iota Draconis | 2002 | first known planet orbiting a giant star | |
| OGLE-2003-BLG-235Lb | OGLE-2003-BLG-235L | 2004 | first planet found by gravitational lensing method | |
| PSR B1620-26c | PSR B1620-26 | 1993 | first known planet orbiting a white dwarf (confirmed 2003) | |
| 2M1207b | 2M1207 | 2004 | first known planet orbiting a brown dwarf first directly imaged planet | |
| OGLE-2005-BLG-390Lb | OGLE-2005-BLG-390L | 2006 | first cool, possibly rocky/icy planet around main-sequence star | |
| First free-floating planet discovered | S Ori 70 | n/a | 2004 | has mass of 3 MJupiter, needs confirmation
|
| First planet in a multiple star system discovered | 55 Cancri b | 55 Cancri | 1996 | 55 Cnc has distant red dwarf companion
|
| First planet orbiting multiple stars discovered | PSR B1620-26c | PSR B1620-26 | 1993 | orbits pulsar - white dwarf pair |
| First multiple planet system discovered | PSR 1257+12 A, B, C | PSR 1257+12 | 1992 | a pulsar planetary system |
| First planet in star cluster | PSR B1620-26c | PSR B1620-26 | 1993 | located in Globular Cluster M4 |
| Most Earthlike | ||||
| Closest planet to 1 MEarth | [[PSR 1257+12#PSR 1257+12 C|PSR 1257+12 C]] | [[PSR 1257+12]] | 3.9 MEarth | |
| Closest planet to 1 AU orbital | HD 142 b | HD 142 | 0.980 AU | |
| HD 28185 b | HD 28185 | 1.0 AU | ||
| HD 128311 | HD 128311 | 1.02 AU | ||
| Closest planet to 365-day orbit | HD 142 b | HD 142 | 337 | |
| HD 92788 b | HD 92788 | 378 | ||
| Closest in type | OGLE-2005-BLG-390Lb | OGLE-2005-BLG-390L | around main-sequence star, cool, possibly rocky/icy | |
See also
People:
- Aleksander Wolszczan — discovered first extrasolar planets, pulsar planets, 'solar system', pulsar planetary system.
- Steinn Sigurdsson — discovered oldest planet, and first circumbinary planet.
- Michel Mayor — with Queloz, discovered first planet around a main-sequence star.
- Didier Queloz — with Mayor, discovered first planet around a main-sequence star.
- Geoffrey Marcy — discovered more extrasolar planets than anyone else
- R. Paul Butler — co-discoverer with Marcy
Planets and their Stars:
- PSR B1620-26c, the oldest planet, also known as Methuselah, around neutron star PSR B1620-26, and white dwarf binary companion PSR B1620-26b.
- 51 Pegasi B, a hot Jupiter, and the first planet found around a main-sequence star (51 Pegasi).
- [[PSR 1257+12]]'s first extra-solar planets, planetary system, pulsar planets ever found.
Other:
- Appearance of extrasolar planets
- Asteroid belt
- Astrometric binary
- Hypothetical planet
- Interstellar planet
- List of stars with confirmed extrasolar planets
- Planetary habitability
- Planetary system
- Pulsar planets
- Solar twin
- PlanetQuest
External links
Search projects:
- University of California Planet Search Project
- The Geneva Extrasolar Planet Search Programmes
- PlanetQuest distributed computing project
- Resources
- NASA's PlanetQuest
- German Center for Exo-Planet Research Jena/Tautenburg
- Astrophysical Institute & University Observatory Jena (AIU)
- The Extrasolar Planets Encyclopaedia
- Table of known planetary systems
- Extrasolar Planet XML Database
- Andrew Collier Cameron, Extrasolar planets, Physics World (January 2001). (See the online version.)
- Diagram of planet detection methods - PDF
- searchable dynamic database of extrasolar planets and their parent stars
- List of important exoplanets
- Extrasolar Planets - D. Montes, UCM
- News
- 6-8 Earth-Mass Planet Discovered orbiting Gliese 876
- Newfound World Shatters Distance Record from space.com
- Oldest Known World from space.com
- Earth Sized Planets Confirmed from space.com
- Hubble telescope "discovers 100 new planets": BBC news story
- Planet discovery papers
- A planetary microlensing event and A Jovian-mass Planet in Microlensing Event OGLE-2005-BLG-071 , the first extrasolar planet detections using gravitational microlensing.br:Ezplanedenn
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