TheGemini Planet Imager (GPI) is a high contrast imaging instrument that was built for theGemini South Telescope inChile. The instrument achieves high contrast at small angular separations, allowing for the direct imaging and integral field spectroscopy ofextrasolar planets around nearbystars.[1]: 1 The collaboration involved in planning and building the Gemini Planet imager includes theAmerican 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, TheSpace Telescope Science Institute (STSCI), theUniversity of Montreal,University of California, Berkeley,University of California, Los Angeles (UCLA),University of California, Santa Cruz (UCSC),University of Georgia.[2]
The Gemini Planet Imager is being used at the Gemini South Telescope, located inCerro Pachon,Chile. It saw thefirst light in November 2013, and entered regular operations in November 2014.[2] It is designed to directly detect younggas giants via theirthermal emission. It will operate at near-infraredwavelengths (Y - K bands), where planets will be reasonably bright, but thermal emission from theEarth'satmosphere is not too strong.[3]: 2
The system consists of multiple components, including a high-order adaptive optics system, acoronagraph, a calibration interferometer, and anintegral field spectrograph. The adaptive optics system, being built at LLNL, uses aMEMSdeformable mirror fromBoston Micromachines Corporation to correctwavefront errors induced bymotion of air in the atmosphere and theoptics in thetelescope. 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. APhoton etc.tunable laser 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.[4] The spectrograph, developed by UCLA and Montreal, images and takesspectra of any detected companion to the star, with aspectral 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 0.2-1arcseconds, down to an H band magnitude of 23.[1]: 3
Present daysearches for exoplanets are insensitive to exoplanets located at the distances from their host star comparable to thesemi-major axes of the gas giants in theSolar System, greater than about 5 AU. Surveys using theradial velocity method require observing a star over at least oneperiod of revolution, which is roughly 30 years for a planet at the distance ofSaturn. Existing adaptive optics instruments become ineffective at small angular separations, limiting them to semi-major axes larger than about 30astronomical units. The high contrast of the Gemini Planet Imager at small angular separations will allow it to detect gas giants with semi-major axes of 5–30astronomical units.[1]: 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 abouthow gas giants form. In particular, the spectrograph will allow determination of thetemperature andsurface gravity, which yield information about the atmospheres and thermal evolution of gas giants.[1]: 2
In addition to its main goal of imaging exoplanets, GPI will be capable of studyingprotoplanetary disks,transition disks, anddebris disks around young stars. This may provide clues aboutplanet formation. The technique used to image disks with this instrument is called polarization differential imaging. Another science case is to studySolar System objects at high spatial resolution and highStrehl ratio. Asteroids and their moons, the satellites ofJupiter andSaturn, 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.[citation needed]
The planet51 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 second strongestmethane signature ever detected on an alien planet (after onlyGJ 504b), which should yield additional clues as to how the planet formed.[5]
In 2022, GPI was removed from theGemini South telescope and shipped to theUniversity of Notre Dame in Indiana to undergo a major upgrade of the whole system called GPI 2.0.[6] GPI 2.0 will be installed on theGemini North telescope and is expected to see first light at the end of 2025.
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