The Gemini Planet Imager (GPI) is a high contrast imaging instrument that was built for the

Gemini South Telescope The Gemini Observatory is an astronomical observatory consisting of two 8.1-metre (26.6 ft) telescopes, Gemini North and Gemini South, which are located at two separate sites in Hawaii and Chile, respectively. The twin Gemini telescopes prov ...

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...

. The instrument achieves high contrast at small angular separations, allowing for the direct imaging and integral field spectroscopy of

extrasolar planet 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, init ...

s around nearby

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

s. The collaboration involved in planning and building the Gemini Planet imager includes the

American Museum of Natural History The American Museum of Natural History (abbreviated as AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. In Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 26 inter ...

(AMNH), Dunlap Institute,

Gemini Observatory The Gemini Observatory is an astronomical observatory consisting of two 8.1-metre (26.6 ft) telescopes, Gemini North and Gemini South, which are located at two separate sites in Hawaii and Chile, respectively. The twin Gemini telescopes prov ...

Herzberg Institute of Astrophysics The NRC Herzberg Astronomy and Astrophysics Research Centre (NRC Herzberg, HAA) is the leading Canadian centre for astronomy and astrophysics. It is based in Victoria, British Columbia. The current Director-General, as of 2021, is Luc Simard. ...

(HIA),

Jet Propulsion Laboratory The Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center in the City of La Cañada Flintridge, California, United States. Founded in the 1930s by Caltech researchers, JPL is owned by NASA an ...

, Lawrence Livermore National Lab (LLNL),

Lowell Observatory Lowell Observatory is an astronomical observatory in Flagstaff, Arizona, United States. Lowell Observatory was established in 1894, placing it among the oldest observatories in the United States, and was designated a National Historic Landmark ...

SETI Institute The SETI Institute is a not-for-profit research organization incorporated in 1984 whose mission is to explore, understand, and explain the origin and nature of life in the universe, and to use this knowledge to inspire and guide present and futu ...

, The

Space Telescope Science Institute The Space Telescope Science Institute (STScI) is the science operations center for the Hubble Space Telescope (HST), science operations and mission operations center for the James Webb Space Telescope (JWST), and science operations center for th ...

(STSCI), the

University of Montreal A university () is an institution of higher (or tertiary) education and research which awards academic degrees in several academic disciplines. Universities typically offer both undergraduate and postgraduate programs. In the United States, the ...

University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public land-grant research university in Berkeley, California. Established in 1868 as the University of California, it is the state's first land-grant u ...

University of California, Los Angeles The University of California, Los Angeles (UCLA) is a public land-grant research university in Los Angeles, California. UCLA's academic roots were established in 1881 as a teachers college then known as the southern branch of the California St ...

(UCLA),

University of California, Santa Cruz The University of California, Santa Cruz (UC Santa Cruz or UCSC) is a public university, public Land-grant university, land-grant research university in Santa Cruz, California. It is one of the ten campuses in the University of California syste ...

(UCSC),

University of Georgia , mottoeng = "To teach, to serve, and to inquire into the nature of things.""To serve" was later added to the motto without changing the seal; the Latin motto directly translates as "To teach and to inquire into the nature of things." , establ ...

Specifications

The Gemini Planet Imager is being used at the Gemini South Telescope, located in Cerro Pachon,

. It saw the first light in November 2013, and entered regular operations in November 2014. It is designed to directly detect young

gas giant A gas giant is a giant planet composed mainly of hydrogen and helium. Gas giants are also called failed stars because they contain the same basic elements as a star. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" ...

s via their

thermal emission Thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. Thermal radiation is generated when heat from the movement of charges in the material (electrons and protons in common forms of matter) is ...

. It will operate at near-

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...

s (Y - K bands), where planets will be reasonably bright, but thermal emission from the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...

is not too strong. The system consists of multiple components, including a high-order adaptive optics system, a

coronagraph A coronagraph is a telescopic attachment designed to block out the direct light from a star so that nearby objects – which otherwise would be hidden in the star's bright glare – can be resolved. Most coronagraphs are intended to view ...

, a calibration interferometer, and an

integral field spectrograph Integral Field Spectrographs (IFS) combine spectrographic and imaging capabilities in the optical or infrared wavelength domains -from 0.32 μm to 24 μm- to get from a single exposure spatially resolved spectra in a bi-dimensional region. Develop ...

. The adaptive optics system, being built at LLNL, uses a

MEMS Microelectromechanical systems (MEMS), also written as micro-electro-mechanical systems (or microelectronic and microelectromechanical systems) and the related micromechatronics and microsystems constitute the technology of microscopic devices, ...

deformable mirror Deformable mirrors (DM) are mirrors whose surface can be deformed, in order to achieve wavefront control and correction of optical aberrations. Deformable mirrors are used in combination with wavefront sensors and real-time control systems in ada ...

from

Boston Micromachines Corporation Boston Micromachines Corporation is a US company operating out of Cambridge, Massachusetts. Boston Micromachines manufactures and develops instruments based on MEMS technology to perform open and closed-loop adaptive optics. The technology is app ...

to correct

wavefront In physics, the wavefront of a time-varying ''wave field'' is the set (locus) of all points having the same ''phase''. The term is generally meaningful only for fields that, at each point, vary sinusoidally in time with a single temporal freque ...

errors induced by motion of air in the atmosphere and the

optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviole ...

in the

telescope A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to observe ...

. The coronagraph, being built at AMNH, blocks out the light from the star being observed, which is necessary in order to see a much dimmer companion. Before sending the GPI at Gemini South it was essential to test the coronagraph by reproducing the exact experimental conditions in which it was going to be used. A Photon etc.

tunable laser A tunable laser is a laser whose wavelength of operation can be altered in a controlled manner. While all laser gain media allow small shifts in output wavelength, only a few types of lasers allow continuous tuning over a significant wavelength ran ...

source was used for this and helped determine that, at its most efficient wavelength, the imager could detect a planet only slightly more massive than Jupiter around a 100-million-year-old Sun-like star. The spectrograph, developed by UCLA and Montreal, images and takes spectra of any detected companion to the star, with a spectral resolving power of 34 - 83, depending on wavelength. The expected instrument performance will allow for detection of companions one ten millionth as bright as their hosts at angular separations of roughly 0.2-1

arcsecond A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...

s, down to an H band magnitude of 23.Macintosh ''et al.'' (2006), p. 3.

Scientific goals

Present day searches for exoplanets are insensitive to exoplanets located at the distances from their host star comparable to the semi-major axes of the gas giants in the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...

, greater than about 5 AU. Surveys using the

radial velocity method Doppler spectroscopy (also known as the radial-velocity method, or colloquially, the wobble method) is an indirect method for finding extrasolar planets and brown dwarfs from radial-velocity measurements via observation of Doppler shifts in t ...

require observing a star over at least one

period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

of revolution, which is roughly 30 years for a planet at the distance of

Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...

. Existing adaptive optics instruments become ineffective at small angular separations, limiting them to semi-major axes larger than about 30

astronomical unit The astronomical unit (symbol: au, or or AU) is a unit of length, roughly the distance from Earth to the Sun and approximately equal to or 8.3 light-minutes. The actual distance from Earth to the Sun varies by about 3% as Earth orbits t ...

s. The high contrast of the Gemini Planet Imager at small angular separations will allow it to detect gas giants with semi-major axes of 5–30

s.Macintosh ''et al.'' (2006), p. 2. The Gemini Planet Imager will be most effective at detecting young gas giants, one million to one billion years old. The reason for this is that young planets retain heat from their formation, and only gradually cool. While a planet is still hot, it remains bright, and is thus more easily detected. This limits GPI to younger targets, but means that it will yield information about how gas giants form. In particular, the spectrograph will allow determination of the

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

and

surface gravity The surface gravity, ''g'', of an astronomical object is the gravitational acceleration experienced at its surface at the equator, including the effects of rotation. The surface gravity may be thought of as the acceleration due to gravity experien ...

, which yield information about the atmospheres and thermal evolution of gas giants. In addition to its main goal of imaging exoplanets, GPI will be capable of studying

protoplanetary disks A protoplanetary disk is a rotating circumstellar disc of dense gas and dust surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star. The protoplanetary disk may also be considered an accretion disk for the star itself, be ...

, transition disks, and

debris disks Debris (, ) is rubble, wreckage, ruins, litter and discarded garbage/refuse/trash, scattered remains of something destroyed, or, as in geology, large rock fragments left by a melting glacier, etc. Depending on context, ''debris'' can refer to ...

around young stars. This may provide clues about

planet formation The nebular hypothesis is the most widely accepted model in the field of cosmogony to explain the formation and evolution of the Solar System (as well as other planetary systems). It suggests the Solar System is formed from gas and dust orbitin ...

. The technique used to image disks with this instrument is called polarization differential imaging. Another science case is to study

objects at high spatial resolution and high

Strehl ratio The Strehl ratio is a measure of the quality of optical image formation, originally proposed by Karl Strehl, after whom the term is named. Used variously in situations where optical resolution is compromised due to lens aberrations or due to imag ...

. Asteroids and their moons, the satellites of

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...

and

, and the planets Uranus and Neptune are all good targets for GPI. The final ancillary science case is to study the mass loss from evolved stars via their outflow.

Achievements

The planet 51 Eridani b is the first exoplanet discovered by the Gemini Planet Imager. It is a million times fainter than its parent star and shows the strongest

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...

signature ever detected on an alien planet, which should yield additional clues as to how the planet formed.

Gallery

File:Hy4796aGPI.png, GPI Image of star HR4796a showing the debris disk as seen through polarization measurements.

References

Bibliography

* * {{Exoplanet Telescope instruments Exoplanet search projects