|
Exoplanetology
This page describes exoplanet orbital and physical parameters. Orbital parameters Most known extrasolar planet candidates have been discovered using indirect methods and therefore only some of their physical and orbital parameters can be determined. For example, out of the six independent parameters that define an orbit, the radial-velocity method can determine four: semi-major axis, eccentricity, longitude of periastron, and time of periastron. Two parameters remain unknown: inclination and longitude of the ascending node. Distance from star and orbital period There are exoplanets that are much closer to their parent star than any planet in the Solar System is to the Sun, and there are also exoplanets that are much further from their star. Mercury, the closest planet to the Sun at 0.4 astronomical units (AU), takes 88 days for an orbit, but the smallest known orbits of exoplanets have orbital periods of only a few hours, see Ultra-short period planet. The Kepler-11 sy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Exoplanet
An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, initially detected in 1988, was confirmed in 2003. There are many methods of detecting exoplanets. Transit photometry and Doppler spectroscopy have found the most, but these methods suffer from a clear observational bias favoring the detection of planets near the star; thus, 85% of the exoplanets detected are inside the tidal locking zone. In several cases, multiple planets have been observed around a star. About 1 in 5 Sun-like starsFor the purpose of this 1 in 5 statistic, "Sun-like" means G-type star. Data for Sun-like stars was not available so this statistic is an extrapolation from data about K-type stars. have an "Earth-sized"For the purpose of this 1 in 5 statistic, Earth-sized means 1–2 Earth radii. planet in the habitable zone. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ultra-short Period Planet
An ultra-short period (USP) planet is a type of exoplanet with orbital period less than one day. At this short distance, tidal interactions lead to relatively rapid orbital and spin evolution. Therefore when there is a USP planet around a mature main-sequence star it is most likely that the planet has a circular orbit and is tidally locked. There are not many USP planets with sizes exceeding 2 Earth radii. About one out of 200 Sun-like stars ( G dwarfs) has an ultra-short-period planet. There is a strong dependence of the occurrence rate on the mass of the host star. The occurrence rate falls from (1.1 ± 0.4)% for M dwarfs to (0.15 ± 0.05)% for F dwarfs. Mostly the USP planets seem consistent with an Earth-like composition of 70% rock and 30% iron, but K2-229b has a higher density suggesting a more massive iron core. WASP-47e and 55 Cnc e have a lower density and are compatible with pure rock, or a rocky-iron body surrounded by a layer of water (or other volatiles). A di ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transit Method
Any planet is an extremely faint light source compared to its parent star. For example, a star like the Sun is about a billion times as bright as the reflected light from any of the planets orbiting it. 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, very few of the exoplanets reported have been observed directly, with even fewer being resolved from their host star. Instead, astronomers have generally had to resort to indirect methods to detect extrasolar planets. As of 2016, several different indirect methods have yielded success. Established detection methods The following methods have at least once proved successful for discovering a new planet or detecting an already discovered planet: Radial velocity A star with a planet will move in its own small orbit in response to the planet's gravity. This leads to variations in the speed with which the star mov ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Methods Of Detecting Extrasolar Planets
Any planet is an extremely faint light source compared to its parent star. For example, a star like the Sun is about a billion times as bright as the reflected light from any of the planets orbiting it. 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, very few of the exoplanets reported have been observed directly, with even fewer being resolved from their host star. Instead, astronomers have generally had to resort to indirect methods to detect extrasolar planets. As of 2016, several different indirect methods have yielded success. Established detection methods The following methods have at least once proved successful for discovering a new planet or detecting an already discovered planet: Radial velocity A star with a planet will move in its own small orbit in response to the planet's gravity. This leads to variations in the speed with which the star move ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Exoplanet Period-Mass Scatter
An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, initially detected in 1988, was confirmed in 2003. There are many methods of detecting exoplanets. Transit photometry and Doppler spectroscopy have found the most, but these methods suffer from a clear observational bias favoring the detection of planets near the star; thus, 85% of the exoplanets detected are inside the tidal locking zone. In several cases, multiple planets have been observed around a star. About 1 in 5 Sun-like starsFor the purpose of this 1 in 5 statistic, "Sun-like" means G-type star. Data for Sun-like stars was not available so this statistic is an extrapolation from data about K-type stars. have an "Earth-sized"For the purpose of this 1 in 5 statistic, Earth-sized means 1–2 Earth radii. planet in the habitable zone.F ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Direct Imaging
Any planet is an extremely faint light source compared to its parent star. For example, a star like the Sun is about a billion times as bright as the reflected light from any of the planets orbiting it. 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, very few of the exoplanets reported have been observed directly, with even fewer being resolved from their host star. Instead, astronomers have generally had to resort to indirect methods to detect extrasolar planets. As of 2016, several different indirect methods have yielded success. Established detection methods The following methods have at least once proved successful for discovering a new planet or detecting an already discovered planet: Radial velocity A star with a planet will move in its own small orbit in response to the planet's gravity. This leads to variations in the speed with which the star move ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photoevaporation
Photoevaporation denotes the process where energetic radiation ionises gas and causes it to disperse away from the ionising source. This typically refers to an astrophysical context where ultraviolet electromagnetic radiation, radiation from hot stars acts on clouds of material such as molecular clouds, protoplanetary disks, or planetary atmospheres. Molecular clouds One of the most obvious manifestations of astrophysical photoevaporation is seen in the eroding structures of molecular clouds as luminous stars are born within. Evaporating Gaseous Globules (EGGs) Evaporating Gaseous Globules or EGGs were first discovered in the Eagle Nebula. These small cometary globules are being photoevaporated by the stars in the nearby cluster. EGGs are places of ongoing star-formation. Planetary atmospheres A planet can be stripped of its atmosphere (or parts of the atmosphere) due to high energy photons and other electromagnetic radiation. If a photon interacts with an atmospheric molecule ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rogue Planet
A rogue planet (also termed a free-floating planet (FFP), interstellar, nomad, orphan, starless, unbound or wandering planet) is an interstellar object of planetary-mass, therefore smaller than fusors (stars and brown dwarfs) and without a host planetary system. Such objects have been ejected from the planetary system in which they formed or have never been gravitationally bound to any star or brown dwarf. The Milky Way alone may have billions to trillions of rogue planets, a range the upcoming Nancy Grace Roman Space Telescope will likely be able to narrow down. Some planetary-mass objects may have formed in a similar way to stars, and the International Astronomical Union has proposed that such objects be called sub-brown dwarfs. A possible example is Cha 110913−773444, which may have been ejected and become a rogue planet, or formed on its own to become a sub-brown dwarf. Astronomers have used the Herschel Space Observatory and the Very Large Telescope to observe a very ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Exoplanet Host Stars
Planet-hosting stars are stars which host planets, therefore forming planetary systems. This article describes the correlations between stars' characteristics and the characteristics of the planets that orbit them, and other connections between stars and their planets. Proportion of stars with planets Most stars have planets but exactly what proportion of stars have planets is uncertain because not all planets can yet be detected. That said it has been calculated that there is at least one planet on average per star. One in five Sun-like stars are expected to have an "Earth-sized" planet in the habitable zone. The radial-velocity method and the transit method (which between them are responsible for the vast majority of detections) are most sensitive to large planets in small orbits. Thus many known exoplanets are "hot Jupiters": planets of Jovian mass or larger in very small orbits with periods of only a few days. A 2005 survey of radial-velocity-detected planets found that about ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gemini Planet Imager
The Gemini Planet Imager (GPI) is a high contrast imaging instrument that was built for the Gemini South Telescope in Chile. The instrument achieves high contrast at small angular separations, allowing for the direct imaging and integral field spectroscopy of extrasolar planets around nearby stars. The collaboration involved in planning and building the Gemini Planet imager includes the American Museum of Natural History (AMNH), Dunlap Institute, Gemini Observatory, Herzberg Institute of Astrophysics (HIA), Jet Propulsion Laboratory, Lawrence Livermore National Lab (LLNL), Lowell Observatory, SETI Institute, The Space Telescope Science Institute (STSCI), the University of Montreal, University of California, Berkeley, University of California, Los Angeles (UCLA), University of California, Santa Cruz (UCSC), University of Georgia. Specifications The Gemini Planet Imager is being used at the Gemini South Telescope, located in Cerro Pachon, Chile. It saw the first light in Novem ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Binary Star
A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in which case they are called ''visual binaries''. Many visual binaries have long orbital periods of several centuries or millennia and therefore have orbits which are uncertain or poorly known. They may also be detected by indirect techniques, such as spectroscopy (''spectroscopic binaries'') or astrometry (''astrometric binaries''). If a binary star happens to orbit in a plane along our line of sight, its components will eclipse and transit each other; these pairs are called ''eclipsing binaries'', or, together with other binaries that change brightness as they orbit, ''photometric binaries''. If components in binary star systems are close enough they can gravitationally distort their mutual outer stellar atmospheres. In some cases, thes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
VLT-SPHERE
Spectro-Polarimetric High-contrast Exoplanet REsearch (VLT-SPHERE) is an adaptive optics system and coronagraphic facility at the Very Large Telescope (VLT). It provides direct imaging as well as spectroscopic and polarimetric characterization of exoplanet systems. The instrument operates in the visible and near infrared, achieving, albeit over a limited field of view, superior image quality and contrast for bright targets. Results from SPHERE complement those from other planet finder projects which include HARPS, CoRoT, and the Kepler Mission. The instrument was installed on Unit Telescope "Melipal" (UT3) and achieved first light in June, 2014. At the time of installation, it was the latest of a series of second generation VLT-instruments such as X-shooter, KMOS and MUSE. Science goals Direct imaging of exoplanets is extremely challenging: # The brightness contrast between the planet and its host star typically ranges from 10−6 for hot young giant planets emitting sign ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
