Gemini Planet Imager
Encyclopedia
The Gemini Planet Imager (GPI) is a high contrast imaging instrument being built for the Gemini South Telescope
in Chile. The instrument will achieve high contrast at small angular separations, allowing for the direct imaging and integral field spectroscopy of extrasolar planet
s around nearby star
s. The collaboration involved in planning and building the Gemini Planet imager includes Lawrence Livermore National Lab (LLNL), the American Museum of Natural History
(AMNH), the Herzberg Institute of Astrophysics
, the Jet Propulsion Laboratory
, the University of California, Berkeley
, the University of California, Los Angeles
, the University of California, Santa Cruz
, the University of Montreal.
, Chile
. It is expected to see first light in mid 2012, and be available for community use after commissioning in early 2013. It is designed to directly detect young gas giant
s via their thermal emission. It will operate at near-infrared
wavelength
s (Y - K bands), where planets will be reasonably bright, but thermal emission from the Earth
's atmosphere
will not be too bright.
The system consist of multiple components, including a high-order adaptive optics system, a coronagraph
, a calibration interferometer, and an integral field spectrograph
. The adaptive optics system, being built at LLNL, uses a MEMS deformable mirror
from Boston Micromachines Corporation
to correct wavefront
errors induced by motion of air in the atmosphere
and the optics
in the telescope
. 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. The spectrograph, developed by UCLA and Montreal, images and takes spectra
of any detected companion to the star, with a spectral resolution
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 arcseconds, down to an H band magnitude of 23.
s 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
, greater than about 5 AU. Surveys using the radial velocity method require observing a star over at least one period
of revolution, which is roughly 30 years for a planet at the distance of Saturn
. Existing adaptive optics instruments become ineffective at small angular separations, limiting them to semi-major axes larger than about 30 astronomical unit
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 astronomical unit
s.
The Gemini Planet Imager will be most effective at detecting young gas giants, 1 Myr to 1 Gyr in age. 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
and surface gravity
, which yield information about the atmospheres and thermal evolution of gas giants.
Gemini Observatory
The Gemini Observatory is an astronomical observatory consisting of two telescopes at sites in Hawai‘i and Chile. Together, the twin Gemini telescopes provide almost complete coverage of both the northern and southern skies...
in Chile. The instrument will achieve high contrast at small angular separations, allowing for the direct imaging and integral field spectroscopy of extrasolar planet
Extrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
s around nearby star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s. The collaboration involved in planning and building the Gemini Planet imager includes Lawrence Livermore National Lab (LLNL), the American Museum of Natural History
American Museum of Natural History
The American Museum of Natural History , located on the Upper West Side of Manhattan in New York City, United States, is one of the largest and most celebrated museums in the world...
(AMNH), the Herzberg Institute of Astrophysics
Herzberg Institute of Astrophysics
The NRC Herzberg Institute of Astrophysics is the leading Canadian centre for astronomy and astrophysics.Named for the Nobel laureate Gerhard Herzberg, it was formed in 1975 as part of the National Research Council of Canada in Ottawa, Ontario...
, the Jet Propulsion Laboratory
Jet Propulsion Laboratory
Jet Propulsion Laboratory is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. The facility is headquartered in the city of Pasadena on the border of La Cañada Flintridge and Pasadena...
, the University of California, Berkeley
University of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...
, the University of California, Los Angeles
University of California, Los Angeles
The University of California, Los Angeles is a public research university located in the Westwood neighborhood of Los Angeles, California, USA. It was founded in 1919 as the "Southern Branch" of the University of California and is the second oldest of the ten campuses...
, the University of California, Santa Cruz
University of California, Santa Cruz
The University of California, Santa Cruz, also known as UC Santa Cruz or UCSC, is a public, collegiate university; one of ten campuses in the University of California...
, the University of Montreal.
Specifications
The Gemini Planet Imager will be used at the Gemini South Telescope, located in Cerro PachonCerro Pachón
Cerro Pachón is a mountain located close to Chilean city of Vicuña and 10 km southeast of the Cerro Tololo Inter-American Observatory, at an altitude of 2,715 m over the sea level in the foothills of the Andes. The location is exceedingly dry, making it suitable for infrared observations....
, Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
. It is expected to see first light in mid 2012, and be available for community use after commissioning in early 2013. It is designed to directly detect young gas giant
Gas giant
A gas giant is a large planet that is not primarily composed of rock or other solid matter. There are four gas giants in the Solar System: Jupiter, Saturn, Uranus, and Neptune...
s via their thermal emission. It will operate at near-infrared
Infrared astronomy
Infrared astronomy is the branch of astronomy and astrophysics that studies astronomical objects visible in infrared radiation. The wavelength of infrared light ranges from 0.75 to 300 micrometers...
wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
s (Y - K bands), where planets will be reasonably bright, but thermal emission from the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
's atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
will not be too bright.
The system consist of multiple components, including a high-order adaptive optics system, a coronagraph
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...
, a calibration interferometer, and an integral field spectrograph
Integral field spectrograph
An integral field spectrograph or a spectrograph equipped with an integral field unit is an optical instrument combining spectrographic and imaging capabilities, used to obtain spatially resolved spectra in astronomy and other fields of research such as bio-medical science and earth observation...
. The adaptive optics system, being built at LLNL, uses a MEMS deformable mirror
Deformable mirror
Deformable mirror represents the most convenient tool for wavefront control and correction of optical aberrations. Deformable mirrors are used in combination with wavefront sensors and real-time control systems in adaptive optics...
from Boston Micromachines Corporation
Boston Micromachines Corporation
Boston Micromachines Corporation is a US company operating out of Cambridge, Massachusetts. Boston Micromachines manufactures and develops MEMS deformable mirrors to perform open- and closed- loop adaptive optics. The technology is applied in Beam Shaping, Astronomy, Vision Science, and general...
to correct wavefront
Wavefront
In physics, a wavefront is the locus of points having the same phase. Since infrared, optical, x-ray and gamma-ray frequencies are so high, the temporal component of electromagnetic waves is usually ignored at these wavelengths, and it is only the phase of the spatial oscillation that is described...
errors induced by motion of air in the atmosphere
Astronomical seeing
Astronomical seeing refers to the blurring and twinkling of astronomical objects such as stars caused by turbulent mixing in the Earth's atmosphere varying the optical refractive index...
and the optics
Optics
Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
in the telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
. 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. The spectrograph, developed by UCLA and Montreal, images and takes spectra
Spectrum
A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...
of any detected companion to the star, with a spectral resolution
Spectral resolution
The spectral resolution of a spectrograph, or, more generally, of a frequency spectrum, is a measure of its ability to resolve features in the electromagnetic spectrum...
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 arcseconds, down to an H band magnitude of 23.
Expected impact
Present day searches for exoplanetMethods of detecting extrasolar planets
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...
s are insensitive to exoplanets located at the distances from their host star comparable to the semi-major axes
Semi-major axis
The major axis of an ellipse is its longest diameter, a line that runs through the centre and both foci, its ends being at the widest points of the shape...
of the gas giants in the Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
, greater than about 5 AU. Surveys using the radial velocity method require observing a star over at least one period
Orbital period
The orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...
of revolution, which is roughly 30 years for a planet at the distance of Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
. Existing adaptive optics instruments become ineffective at small angular separations, limiting them to semi-major axes larger than about 30 astronomical unit
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
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 astronomical unit
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
s.
The Gemini Planet Imager will be most effective at detecting young gas giants, 1 Myr to 1 Gyr in age. 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
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
and surface gravity
Surface gravity
The surface gravity, g, of an astronomical or other object is the gravitational acceleration experienced at its surface. The surface gravity may be thought of as the acceleration due to gravity experienced by a hypothetical test particle which is very close to the object's surface and which, in...
, which yield information about the atmospheres and thermal evolution of gas giants.