Any planet is an extremely faint light source compared to its parent star. In addition to the intrinsic difficulty of detecting such a faint light source, the light from the parent star causes a glare that washes it out. For those reasons, only a very few extrasolar planets have been observed directly. This article is about the astronomical term. ... This article is about the astronomical object. ... An extrasolar planet, or exoplanet, is a planet beyond the Solar System. ...

Instead, astronomers have generally had to resort to indirect methods to detect extrasolar planets. At the present time, six different indirect methods have yielded success.

Established detection methods

Astrometry

Main article: Astrometry

In this diagram a planet (smaller object) orbits a star, which itself moves in a small orbit. The system's center of mass is shown with a red plus sign. (In this case, it always lies within the star.)

Astrometry is the oldest search method for extrasolar planets. It consists of precisely measuring a star's position in the sky and observing how that position changes over time. If the star has a planet, then the gravitational influence of the planet will cause the star itself to move in a tiny circular or elliptical orbit. Effectively, star and planet each orbit around their mutual center of mass (barycenter), as explained by solutions to the two-body problem. Since the star is much more massive, its orbit will be much smaller.^[1] Illustration of the use of optical wavelength interferometry to determine precise positions of stars. ... Image File history File links Two bodies with a major difference in mass orbiting around a common barycenter (red cross) with circular orbits. ... Image File history File links Two bodies with a major difference in mass orbiting around a common barycenter (red cross) with circular orbits. ... In physics, the center of mass of a system of particles is a specific point at which, for many purposes, the systems mass behaves as if it was concentrated. ... In classical mechanics, the two-body problem is to determine the motion of two point particles that interact only with each other. ...

During the 1950s and 1960s, claims were made for the discovery of planets around more than ten stars using this method. Astronomers now generally regard those claims as erroneous. Unfortunately, the changes in stellar position are so small that even the best ground-based telescopes cannot produce precise enough measurements. In 2002, however, the Hubble Space Telescope did succeed in using astrometry to characterize a previously discovered planet around the star Gliese 876.^[2] Future space-based observatories such as NASA's Space Interferometry Mission may succeed in uncovering large numbers of new planets via astrometry, but for the time being it remains a minor method of planetary detection. The Hubble Space Telescope (HST; also known colloquially as the Hubble or just Hubble) is a space telescope that was carried into Earth orbit by the Space Shuttle in April 1990. ... Artists concept of Space Interferometry Mission spacecraft The Space Interferometry Mission (SIM), also called SIM PlanetQuest, is a NASA instrument originally expected to be launched in December of 2011; however due to budget cuts it will now launch no sooner than between October 2014 and April 2015. ...

One potential advantage of the astrometric method is that it is most sensitive to planets with large orbits. This makes it complementary to other methods that are most sensitive to planets with small orbits. However, very long observation times will be required — years, and possibly decades, as planets far enough from their star to allow detection via astrometry also take a long time to complete an orbit.

Radial velocity

Main article: Doppler spectroscopy

Like the astrometric method, the radial-velocity method uses the fact that a star with a planet will move in its own small orbit in response to the planet's gravity. The goal now is to measure variations in the speed with which the star moves toward or away from Earth. In other words, the variations are in the radial 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. Diagram showing how a smaller object (such as an extrasolar planet) orbiting a larger object (such as a star) could produce changes in position and velocity of the latter as they orbit their common center of mass (red cross). ... A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ... A source of waves moving to the left. ...

The velocity of the star around the barycenter is much smaller than that of the planet because the radius of its orbit around the center of mass is so small. Velocity variations down to 1 m/s can be detected with modern spectrometers, such as the HARPS (High Accuracy Radial Velocity Planet Searcher) spectrometer at the ESO 3.6 meter telescope in La Silla Observatory, Chile, or the HIRES spectrometer at the Keck telescopes. In physics, the center of mass of a system of particles is a specific point at which, for many purposes, the systems mass behaves as if it was concentrated. ... Spectrometer A spectrometer is an optical instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. ... The High Accuracy Radial velocity Planet Searcher (HARPS) is a high-precision echelle spectrograph installed in 2002 with first light achieved February 2003 on ESOs 3. ... The European Southern Observatory (ESO) is an international astronomical organisation, composed and supported by ten countries from the European Union plus Switzerland and was created in 1962. ... La Silla Observatory is an astronomical observatory in Chile with eighteen telescopes. ... The W. M. Keck Observatory is home to the two largest optical/near-infrared telescopes at the 4,145 meter (13,600 ft) summit of Mauna Kea in Hawaii. ...

This has been by far the most productive technique used by planet hunters. It is also known as Doppler spectroscopy. The method is distance independent, but requires high signal-to-noise ratios to achieve high precision, and so is generally only used for relatively nearby stars out to about 160 light-years from Earth. It easily finds massive planets that are close to stars, but detection of those orbiting at great distances requires many years of observation. Planets with orbits perpendicular to the line of sight from Earth produce smaller wobbles, and are thus more difficult to detect. One of the main disadvantages of the radial-velocity method is that it can only estimate a planet's minimum mass. Usually the true mass will be within 20% of this minimum value, but if the planet's orbit is almost perpendicular to the line of sight, then the true mass will be much higher. Signal-to-noise ratio (often abbreviated SNR or S/N) is an electrical engineering concept defined as the ratio of a signal power to the noise power corrupting the signal. ... The term true mass is synonymous with the term mass, but is used in astronomy to differentiate the measured mass of a planet from the lower limit of mass usually obtained from radial velocity techniques. ...

The radial-velocity method can be used to confirm findings made by using the transit method. When both methods are used in combination, then the planet's true mass can be estimated.

Pulsar timing

Artist's impression of the pulsar PSR 1257+12's planetary system

A pulsar is a neutron star: the small, ultradense remnant of a star that has exploded as a supernova. Pulsars emit radio waves extremely regularly as they rotate. Because the intrinsic rotation of a pulsar is so regular, slight anomalies in the timing of its observed radio pulses can be used to track the pulsar's motion. Like an ordinary star, a pulsar will move in its own small orbit if it has a planet. Calculations based on pulse-timing observations can then reveal the parameters of that orbit. ^[3] Image File history File linksMetadata Download high resolution version (3000x2400, 2719 KB) Summary Licensing File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File linksMetadata Download high resolution version (3000x2400, 2719 KB) Summary Licensing File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... PSR 1257+12 (also catalogued as PSR B1257+12, PSR 1300+1240, or PSR J1300+1240) is a pulsar located 980 light years from Earth. ... It has been suggested that Radio pulsar be merged into this article or section. ... For other uses, see Supernova (disambiguation). ...

This method was not originally designed for the detection of planets, but is so sensitive that it is capable of detecting planets far smaller than any other method can, down to less than a tenth the mass of Earth. It is also capable of detecting mutual gravitational perturbations between the various members of a planetary system, thereby revealing further information about those planets and their orbital parameters.

The main drawback of the pulsar-timing method is that pulsars are relatively rare, so it is unlikely that a large number of planets will be found this way. Also, life as we know it could not survive on planets orbiting pulsars since high-energy radiation there is extremely intense.

In 1992 Aleksander Wolszczan and Dale Frail used this method to discover planets around the pulsar PSR 1257+12.^[4] Their discovery was quickly confirmed; making it the first confirmation of planets outside our Solar System. Aleksander Wolszczan (b. ... Dale Frail is an astronomer. ... PSR 1257+12 (also catalogued as PSR B1257+12, PSR 1300+1240, or PSR J1300+1240) is a pulsar located 980 light years from Earth. ... This article is about the Solar System. ...

Transit method

Transit method of detecting extrasolar planets. The graph below the picture demonstrates the light levels received over time by Earth.

While the above methods provide information about a planet's mass, this method can determine the radius of a planet. If a planet crosses (transits) in front of its parent star's disk, then the observed visual brightness of the star drops a small amount. The amount the star dims depends on the size of the star on the size of the planet. For example, in the case of HD 209458, the star dims 1.7%. Image File history File links Planetary_transit. ... Image File history File links Planetary_transit. ... 2003 Transit of Mercury The term transit or astronomical transit has two meanings in astronomy: A transit is the astronomical event that occurs when one celestial body appears to move across the face of another celestial body, as seen by an observer at some particular vantage point. ... HD 209458 is an 8th magnitude star in the constellation Pegasus. ...

This method has two major disadvantages. First of all, planetary transits are only observable for planets whose orbits happen to be perfectly aligned from astronomers' vantage point. The probability of a planetary orbital plane being directly on the line-of-sight to a star is the ratio of the diameter of the star to the diameter of the orbit. About 10% of planets with small orbits have such alignment, and the fraction decreases for planets with larger orbits. For a planet orbiting a sun-sized star at 1 AU, the probability of a random alignment producing a transit is 0.47% However, by scanning large areas of the sky containing thousands or even hundreds of thousands of stars at once, transit surveys can in principle find extrasolar planets at a rate that could potentially exceed that of the radial-velocity method ^[5], although it would not answer the question of whether any particular star is host to planets. The astronomical unit (AU or au or a. ...

Secondly, the method suffers from a high rate of false detections. A transit detection requires additional confirmation, typically from the radial-velocity method.^[6]

The main advantage of the transit method is that the size of the planet can be determined from the lightcurve. When combined with the radial velocity method (which determines the planet's mass) one can determine the density of the planet, and hence learn something about the planet's physical structure. The nine planets that have been studied by both methods are by far the best-characterized of all known exoplanets.^[7]

The transit method also makes it possible to study the atmosphere of the transiting planet. When the planet transits the star, light from the star passes through the upper atmosphere of the planet. By studying the high-resolution stellar spectrum carefully, one can detect elements present in the planet's atmosphere. A planetary atmosphere (and planet for that matter) could also be detected by measuring the polarisation of the starlight as it passed through or is reflected off the planet's atmosphere. Additionally, the secondary eclipse (when the planet is blocked by its star) allows direct measurement of the planet's radiation. If the star's photometric intensity during the secondary eclipse is subtracted from its intensity before or after, only the signal caused by the planet remains. It is then possible to measure the planet's temperature and even to detect possible signs of cloud formations on it. In March 2005, two groups of scientists carried out measurements using this technique with the Spitzer Space Telescope. 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 TrES-1 and HD 209458b respectively. The measurements revealed the planets' temperatures: 1,060 K (790°C) for TrES-1 and about 1,130 K (860°C) for HD 209458b. ^[8][9] Photometry is a technique of astronomy concerned with measuring the flux, or intensity of an astronomical objects electromagnetic radiation. ... The Spitzer Space Telescope (formerly the Space Infrared Telescope Facility [SIRTF]) is an infrared space observatory, the fourth and final of NASAs Great Observatories. ... The Harvard-Smithsonian Center for Astrophysics (CfA) is located in Cambridge, Massachusetts. ... David Charbonneau is an astronomer at the Harvard-Smithsonian Center for Astrophysics. ... Aerial view of Goddard Space Flight Center. ... The planet, dubbed TrES-1 was discovered by the Trans-Atlantic Exoplanet Survey (TrES). ... HD 209458b is an extrasolar planet that orbits the Sun-like star HD 209458 in the constellation Pegasus, some 150 light years from Earths solar system. ... For other uses, see Kelvin (disambiguation). ... For other uses, see Celsius (disambiguation). ...

A French Space Agency mission, COROT, began in 2006 to search for planetary transits from orbit, where the absence of atmospheric scintillation allows improved accuracy. This mission was designed to be able to detect planets "a few times to several times larger than Earth" and is currently performing "better than expected," with two exoplanet discoveries^[10] (both "hot jupiter" type) as of early 2008. In early 2009, a NASA mission Kepler will be launched to scan a large number of stars in the constellation Cygnus with a measurement precision expected to detect and characterize Earth-sized planets. (see section on Observations from space below). This article is about the space agency. ... For a French painter, see Jean-Baptiste-Camille Corot. ... Scintillation or twinkling are generic terms for rapid variations in apparent brightness or color of a distant luminous object viewed through the atmosphere. ... For other uses, see NASA (disambiguation). ... Johannes Kepler Johannes Kepler (December 27, 1571 – November 15, 1630), a key figure in the scientific revolution, was a German astronomer, mathematician and astrologer. ... Cygnus (Latin for swan) is a northern constellation. ... Any planet is an extremely faint light source compared to its parent star. ...

Gravitational microlensing

Main article: Gravitational microlensing

Gravitational Microlensing

Gravitational microlensing occurs when the gravitational field of a star acts like a lens, magnifying the light of a distant background star. This effect occurs only when the two stars are almost exactly aligned. Lensing events are brief, lasting for weeks or days, as the two stars and Earth are all moving relative to each other. More than a thousand such events have been observed over the past ten years. Gravitational microlensing is an astronomical technique used to detect planets - stellar mass objects in space using the gravitational lens effect. ... Image File history File links Gravitational_micro_rev. ... Image File history File links Gravitational_micro_rev. ...

If the foreground lensing star has a planet, then that planet's own gravitational field can make a detectable contribution to the lensing effect. Since that requires a highly improbable alignment, a very large number of distant stars must be continuously monitored in order to detect planetary microlensing contributions 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.

In 1991, astronomers Shude Mao and Bohdan Paczyński of Princeton University first proposed using gravitational microlensing to look for exoplanets. Successes with the 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) developed a workable technique. During one month they found several possible planets, though limitations in the observations prevented clear confirmation. Since then, four confirmed extrasolar planets have been detected using microlensing. As of 2006 this is the only method capable of detecting planets of Earthlike mass around ordinary main-sequence stars.^[11] Bohdan PaczyÅ„ski (born 8 February 1940) is a Polish astronomer, a leading scientist in theory of the evolution of stars. ... Princeton University is a private coeducational research university located in Princeton, New Jersey. ... For other uses, see Warsaw (disambiguation) and Warszawa (disambiguation). ... The Optical Gravitational Lensing Experiment (OGLE) survey. ... 2006 is a common year starting on Sunday of the Gregorian calendar. ... A Hertzsprung-Russell diagram plots the actual brightness (or absolute magnitude) of a star against its color index (represented as B-V). ...

A notable disadvantage of the method 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 with other methods are usually impossible. However, if enough background stars can be observed with enough accuracy then the method should eventually reveal how common earth-like planets are in the galaxy.

Observations are usually performed using networks of robotic telescopes. In addition to the NASA/National Science Foundation-funded OGLE, the Microlensing Observations in Astrophysics (MOA) group is working to perfect this approach. A robotic telescope is an astronomical telescope and detector system that makes observations without the intervention of a human. ... For other uses, see NASA (disambiguation). ... The logo of the National Science Foundation The National Science Foundation (NSF) is an independent United States government agency that supports fundamental research and education in all the non-medical fields of science and engineering. ... Microlensing Observations in Astrophysics (MOA) is a collaborative project involving researchers from New Zealand and Japan that aims to observe dark matter, extra-solar planets, and stellar atmospheres from the Southern Hemisphere via microlensing. ...

The PLANET (Probing Lensing Anomalies NETwork)/RoboNet project is even more ambitious. It allows nearly continuous round-the-clock coverage by a world-spanning telescope network, providing the opportunity to pick up microlensing contributions 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.^[11] The Probing Lensing Anomalies NETwork (PLANET) collaboration coordinates a network of telescopes to rapidly sample photometric measurements of the magnification of stars in the galactic bulge undergoing gravitational microlensing by intervening foreground stars (or other compact massive objects). ... OGLE-2005-BLG-390Lb is a super-Earth extrasolar planet orbiting the star OGLE-2005-BLG-390L, which is situated 21,500 ± 3,300 light years away from Earth, near the center of the Milky Way galaxy. ...

Circumstellar disks

An artist's conception of two Pluto-sized dwarf planets in a collision around Vega.

Disks of space dust (debris disks) surround many stars. The dust can be detected because it absorbs ordinary starlight and re-emits it as infrared radiation. Even if the dust particles have a total mass well less than that of Earth, they can still have a large enough total surface area that they outshine their parent star in infrared wavelengths.^[12] Image File history File linksMetadata Download high resolution version (3000x2400, 2225 KB) Summary Source: [1] Image Credit: NASA/JPL-Caltech Image produced by: T. Pyle (SSC/Caltech) Licensing File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File linksMetadata Download high resolution version (3000x2400, 2225 KB) Summary Source: [1] Image Credit: NASA/JPL-Caltech Image produced by: T. Pyle (SSC/Caltech) Licensing File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... For other uses, see Pluto (disambiguation). ... For other uses, see Vega (disambiguation). ... Debris disk around star AU Microscopii. ... For other uses, see Infrared (disambiguation). ...

The Hubble Space Telescope is capable of observing dust disks with its NICMOS (Near Infrared Camera and Multi-Object Spectrometer) instrument. Even better images have now been taken by its sister instrument, the Spitzer Space Telescope, which can see far deeper into infrared wavelengths than the Hubble can. Dust disks have now been found around more than 15% of nearby sunlike stars.^[13] The Hubble Space Telescope (HST; also known colloquially as the Hubble or just Hubble) is a space telescope that was carried into Earth orbit by the Space Shuttle in April 1990. ... The Spitzer Space Telescope (formerly the Space Infrared Telescope Facility [SIRTF]) is an infrared space observatory, the fourth and final of NASAs Great Observatories. ... For other uses, see Infrared (disambiguation). ...

The dust is believed to be generated by collisions among comets and asteroids. Radiation pressure from the star will push the dust particles away into interstellar space over a relatively short timescale. Therefore, the detection of dust indicates continual replenishment by new collisions, and provides strong indirect evidence of the presence of small bodies like comets and asteroids that orbit the parent star.^[13] For example, the dust disk around the star tau Ceti indicates that that star has a population of objects analogous to our own Solar System's Kuiper Belt, but at least ten times thicker.^[12] For other uses, see Asteroid (disambiguation). ... Tau Ceti (Ï„ Cet / Ï„ Ceti) is a star commonly mentioned by science fiction authors since it is similar to the Sun in mass and spectral type in addition to being relatively close to us. ... The Kuiper belt, derived from data from the Minor Planet Center. ...

More speculatively, features in dust disks sometimes suggest the presence of full-sized planets. Some disks have a central cavity, meaning that they are really ring-shaped. The central cavity may be caused by a planet "clearing out" the dust inside its orbit. Other disks contain clumps that may be caused by the gravitational influence of a planet. Both these kinds of features are present in the dust disk around epsilon Eridani, hinting at the presence of a planet with an orbital radius of around 40 AU (in addition to the inner planet detected through the radial-velocity method).^[14] Epsilon Eridani (ε Eri / ε Eridani) is a notable main-sequence K2 class star in the constellation of Eridanus. ... The astronomical unit (AU or au or a. ...

Direct imaging

As mentioned previously, planets are extremely faint light sources compared to stars and what little light comes from them tends to be lost in the glare from their parent star. So in general, it is very difficult to detect them directly. In certain cases, however, current telescopes may be capable of directly imaging planets. Projects to equip the current generation of telescopes with new, planet-imaging-capable instruments are underway at the Gemini telescope (GPI), the VLT (SPHERE), and the Subaru telescope (HiCiao). Specifically, this may be possible when the planet is especially large (considerably larger than Jupiter), widely separated from its parent star, and young (so that it is hot and emits intense infrared radiation). The Gemini Observatory is an astronomical observatory consisting of 8-metre telescopes at two different sites. ... The four telescopes of the European Southern Observatory Paranal site. ... Subaru Telescope (In Japanese: すばる望遠鏡) is the 8. ...

In July 2004, a group of astronomers used the European Southern Observatory's Very Large Telescope array in Chile to produce an image of 2M1207b, a companion to the brown dwarf 2M1207. ^[15] In December 2005, the planetary status of the companion was confirmed.^[16] The planet is believed to be several times more massive than Jupiter and to have an orbital radius greater than 40 AU. The European Southern Observatory (ESO) is an international astronomical organisation, composed and supported by ten countries from the European Union plus Switzerland. ... One of the four telescopes that make up the VLT, named Kueyen. ... 2M1207b is an extrasolar planet orbiting the brown dwarf 2M1207, a star in the constellation Hydra approximately 200 light years from Earth. ... This brown dwarf (smaller object) orbits the star Gliese 229, which is located in the constellation Lepus about 19 light years from Earth. ... Atmospheric characteristics Atmospheric pressure 70 kPa Hydrogen ~86% Helium ~14% Methane 0. ...

Three other possible exoplanets have now been directly imaged: GQ Lupi b, AB Pictoris b, and SCR 1845 b.^[17] As of March 2006 none have been confirmed as planets; instead, they might themselves be small brown dwarfs.^[18][19] Infrared image of the star GQ Lupi (A) orbited by a planet (b) at a distance of approximately 20 times the distance between Jupiter and our Sun. ... Brown dwarfs are sub-stellar objects (~13 to 75 Jupiter masses) that never fuse hydrogen into helium in their cores, as do stars on the main sequence. ...

Future detection methods

Observations from space

Several space missions are planned that will employ already proven planet-detection methods. Astronomical measurements done from space can be more sensitive than measurements done from the ground, since the distorting effect of the Earth's atmosphere is removed, and the instruments can view in infrared wavelengths that do not penetrate the atmosphere. Some of these space probes should be capable of detecting planets similar to our own Earth.

The Kepler Mission, a future NASA mission which will be able to detect extrasolar planets

The Terrestrial Planet Finder (note: as of 2007, NASA has cut funding for it, and funding has gone towards the Kepler Mission

The NASA Kepler Mission will use the transit method to scan a hundred thousand stars in the constellation Cygnus for planets. Kepler will be sensitive enough to detect planets even smaller than Earth. By scanning a hundred thousand stars sumultaneously, it will not only be able to detect Earth-sized planets, it will be able to collect statistics on the numbers of such planets around sunlike stars ^[20]. Image source: http://www. ... Image source: http://www. ... The Kepler Mission is a space observatory being developed by NASA that will search for extrasolar planets and will only be the second space-based telescope particularly constructed for that task, the first one being COROT. For this purpose, it will observe the brightness of about 100,000 stars over... For other uses, see NASA (disambiguation). ... Image File history File links Download high resolution version (1900x1425, 138 KB) Terrestrial Planet Finder - Infrared interferometer concept source: http://photojournal. ... Image File history File links Download high resolution version (1900x1425, 138 KB) Terrestrial Planet Finder - Infrared interferometer concept source: http://photojournal. ... Terrestrial Planet Finder - Infrared interferometer concept The Terrestrial Planet Finder (TPF) is a plan by NASA for a telescope system that would be capable of detecting extrasolar terrestrial planets. ... 2007 is a common year starting on Monday of the Gregorian calendar. ... The Kepler Mission is a space observatory being developed by NASA that will search for extrasolar planets and will only be the second space-based telescope particularly constructed for that task, the first one being COROT. For this purpose, it will observe the brightness of about 100,000 stars over... The Kepler Mission is a space observatory being developed by NASA that will search for extrasolar planets and will only be the second space-based telescope particularly constructed for that task, the first one being COROT. For this purpose, it will observe the brightness of about 100,000 stars over...

Kepler should also be able to detect the reflected light from giant planets in close orbits, even though it will not be able to resolve that light into an image. The amount of light reflected from such a planet will vary over time because, like the Moon, it goes through phases from full to new and back again. The variation, although small, will be the signature of a planet. The phase function of the giant planet may be constrained, which will lead to constraints on the actual particle size distribution of its atmospheric particles. This reflected-light method may actually provide the greatest number of planets to be discovered by the Kepler satellite.^[21] This article is about Earths moon. ... Planetary phase is the term used to describe the appearance of the illuminated section of a planet. ...

NASA's Space Interferometry Mission, currently scheduled for launch in 2014, will use astrometry. It may be able to detect Earth-like planets around several nearby stars. The European Space Agency's Darwin probe and NASA's Terrestrial Planet Finder [1] probes will attempt to image planets directly. A recently proposed idea is the New Worlds Mission, which will use an occulter to block a star's light, allowing astronomers to directly observe the dimmer orbiting planets. Artists concept of Space Interferometry Mission spacecraft The Space Interferometry Mission (SIM), also called SIM PlanetQuest, is a NASA instrument originally expected to be launched in December of 2011; however due to budget cuts it will now launch no sooner than between October 2014 and April 2015. ... ESA redirects here. ... Darwin is a proposed European Space Agency (ESA) mission designed to directly detect Earth-like planets orbiting nearby stars, and search for evidence of life on these planets. ... For other uses, see NASA (disambiguation). ... Terrestrial Planet Finder - Infrared interferometer concept The Terrestrial Planet Finder (TPF) is a plan by NASA for a telescope system that would be capable of detecting extrasolar terrestrial planets. ... This article does not cite any references or sources. ... An occulter is any object, natural or man-made, that blocks the light of an object from an observer. ...

(On February 2, 2006 NASA announced an indefinite suspension of work on the Terrestrial Planet Finder due to budget problems.^[22] Then in June 2006, the Appropriations Committee of the U.S. House of Representatives partially restored funding, permitting development work on the project to continue at least through 2007.^[23] COROT was launched on December 27, 2006 and Kepler's launch is scheduled for November 2008.) is the 33rd day of the year in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... December 27 is the 361st day of the year in the Gregorian calendar (362nd in leap years). ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ...

Huge proposed ground telescopes may also be able to directly image extrasolar planets. ESO is considering building the extremely large telescope, with a mirror diameter between 30 and 60 meters. An extremely large telescope (ELT) is a telescope of more than 20m diameter[1]. There are currently ten such telescopes in various stages of design or construction: E-ELT: European Extremely Large Telescope JELT: Japanese ELT Project TMT: Thirty Meter Telescope GSMT: Giant Segmented Mirror Telescope OWL: Overwhelmingly Large Telescope...

Eclipsing binary minima timing

When a double star system is aligned such that the stars pass in front of each other in their orbits, the system is called an "eclipsing binary" star system. The time of minimum light, when the star with the brighter surface area is at least partially obscured by the disc of the other star, is called the primary eclipse, and approximately half an orbit later, the secondary eclipse occurs when the brighter surface area star obscures some portion of the other star. These times of minimum light, or central eclipse, constitute a time stamp on the system, much like the pulses from a pulsar (except that rather than a flash, they are a dip in the brightness). If there is a planet in circum-binary orbit around the binary stars, the stars will be offset around a binary-planet barycenter. As the stars in the binary are displaced by the planet back and forth, the times of the eclipse minima will vary; they will be too late, on time, too early, on time, too late, etc.. The periodicity of this offset may be the most reliable way to detect extrasolar planets around close binary systems.^[24][25][26]. When two stars are so nearly in the same direction as seen from Earth that they appear to be a single star to the naked eye but may be separated by the use of telescopes, they are referred to as a double star. ... This article is about astronomical eclipses. ... It has been suggested that Radio pulsar be merged into this article or section. ... Pluto and Charon are sometimes informally considered to be a double (dwarf) planet. ... In physics, the center of mass of a system of particles is a specific point at which, for many purposes, the systems mass behaves as if it were concentrated. ...

Orbital phase reflected light variations

Short period giant planets in close orbits around their stars will undergo reflected light variations changes because, like the Moon, they will go through phases from full to new and back again. Although the effect is small — the photometric precision required is about the same as to detect an Earth-sized planet in transit across a solar-type star — such Jupiter-sized planets should be detectable by space telescopes such as the Kepler Space Observatory. This method may actually constitute the most planets that will be discovered by that mission because the reflected light variation with orbital phase is largely independent of orbital inclination of the planet's orbit. In addition, the phase function of the giant planet may be constrained which will, in turn, lead to constraints on the actual particle size distribution of the atmospheric particles^[27]. This article is about Earths moon. ... Planetary phase is the term used to describe the appearance of the illuminated section of a planet. ... Conceptual drawing of the Kepler Space Observatory Kepler is a space observatory planned by NASA that will search for extrasolar planets. ...

Polarimetry

Main article: Polarimetry

Light given off by a star is un-polarised, i.e. the direction of oscillation of the light wave is random. However, when the light is reflected off the atmosphere of a planet, the light waves interact with the molecules in the atmosphere and they are polarized.^[28] Polarimetry is the measurement of the polarization of light; a polarimeter is the scientific instrument used to make these measurements. ...

By analyzing the polarization in the combined light of the planet and star (about one part in a million), these measurements can in principle be made with very high sensitivity, as polarimetry is not limited by the stability of the earth's atmosphere.

Astronomical devices used for polarimetry, called polarimeters, are capable of detecting the polarized light and rejecting the unpolarized beams (starlight). Groups such as ZIMPOL/CHEOPS^[29] and PLANETPOL^[30] are currently using polarimeters to search for extra-solar planets, though no planets have yet been detected using this method.

See also

• Astronomy
• Extrasolar Planet
• Extremely Large Telescope
• Kepler Space Observatory
• Star
• Terrestrial Planet Finder
• Solar System

For other uses, see Astronomy (disambiguation). ... An extrasolar planet, or exoplanet, is a planet beyond the Solar System. ... An extremely large telescope (ELT) is a telescope of more than 20m diameter[1]. There are currently ten such telescopes in various stages of design or construction: E-ELT: European Extremely Large Telescope JELT: Japanese ELT Project TMT: Thirty Meter Telescope GSMT: Giant Segmented Mirror Telescope OWL: Overwhelmingly Large Telescope... Conceptual drawing of the Kepler Space Observatory Kepler is a space observatory planned by NASA that will search for extrasolar planets. ... This article is about the astronomical object. ... Terrestrial Planet Finder - Infrared interferometer concept The Terrestrial Planet Finder (TPF) is a plan by NASA for a telescope system that would be capable of detecting extrasolar terrestrial planets. ... This article is about the Solar System. ...

References

Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 253rd day of the year (254th in leap years) in the Gregorian calendar. ... is the 27th day of the year in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 253rd day of the year (254th in leap years) in the Gregorian calendar. ... Aleksander Wolszczan (b. ... Dale Frail is an astronomer. ... is the 9th day of the year in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 120th day of the year (121st in leap years) in the Gregorian calendar. ... is the 120th day of the year (121st in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 253rd day of the year (254th in leap years) in the Gregorian calendar. ... April 7 is the 97th day of the year in the Gregorian calendar (98th in leap years). ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 185th day of the year (186th in leap years) in the Gregorian calendar. ... Year 2003 (MMIII) was a common year starting on Wednesday of the Gregorian calendar. ... is the 263rd day of the year (264th in leap years) in the Gregorian calendar. ... is the 37th day of the year in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 198th day of the year (199th in leap years) in the Gregorian calendar. ... is the 165th day of the year (166th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 255th day of the year (256th in leap years) in the Gregorian calendar. ... Year 2003 (MMIII) was a common year starting on Wednesday of the Gregorian calendar. ... is the 263rd day of the year (264th in leap years) in the Gregorian calendar. ...

External links

• NASA's PlanetQuest