The world's most advanced instrument for directly imaging and analyzing planets around other stars has been built in part by a team of astronomers at the Space Telescope Science Institute (STScI) in Baltimore, Md.
Called the Gemini Planet Imager (GPI), the instrument will photograph faint planets next to bright stars, probe their atmospheres, and study dusty disks from planet formation encircling young stars. Mounted on the Gemini South 8-meter telescope on Cerro Pachon, Chile, GPI detects infrared radiation from young, hot, Jupiter-like planets in wide orbits around other stars.
"Besides being part of the team behind the GPI, our group has been leading efforts to image exoplanets and disks with the Hubble Space Telescope, and we're also working to advance these techniques for future exoplanet-imaging space missions that will someday characterize terrestrial planets around nearby stars," said Marshall Perrin.
The STScI astronomers have been involved with GPI through more than a decade of development, construction, and testing. "Finally seeing the actual images with GPI after all this work is really fantastic," said Anand Sivaramakrishnan, who with Russ Makidon called attention to the idea of this kind of specialized instrument in 2001 and performed early feasibility studies. "The images look exactly like our predictions." Sivaramakrishnan and Makidon, with Remi Soummer, contributed to the conceptual design and proposal that led to GPI's selection as a new facility instrument for Gemini. Soummer invented the type of starlight-blocking coronagraph used in GPI, and Sivaramakrishnan and Soummer developed and tested the coronagraph optics used in GPI, then working at the American Museum of Natural History in New York.
Sivaramakrishnan co-invented an optical device that improves GPI's measurement of faint companion positions relative to their parent stars. Laurent Pueyo, formerly at NASA's Jet Propulsion Laboratory in Pasadena, Calif., was part of the team that developed GPI's interferometric calibration unit and wavefront sensor. Perrin was part of the team that designed and built the integral field spectrograph science camera for GPI and co-invented a new kind of imaging polarimeter that became part of the instrument. Christine Chen provided expertise in circumstellar disks and contributed to developing science plans with GPI. The GPI team at STScI also includes several postdocs and graduate students from Johns Hopkins University in Baltimore, Md.
GPI's first observations targeted previously known planetary systems including a system of planets orbiting HR 8799, a planet orbiting the star Beta Pictoris, and a faint ring of dust orbiting the newborn star HR 4796. Even though testing is not yet complete, GPI's performance already dramatically surpasses prior systems. In 2014, the GPI team will begin a large-scale survey to look at 600 young stars to see what giant planets orbit them.
GPI will also be available to the whole Gemini community for other projects, ranging from studies of planet-forming disks to outflows of dust from massive, dying stars. Perrin leads the team that has developed the data pipeline for GPI, and will be supporting the broader Gemini users in the instrument's calibration and data analysis. Gemini Observatory and STScI are sister organizations, both part of AURA, the Association of Universities for Research in Astronomy. This collaboration on GPI is just the latest example of the two organizations partnering to provide world-leading research tools to the broader astronomical community.
The STScI astronomers are also actively working on preparing for the James Webb Space Telescope, which will have several starlight-blocking coronagraphs on board. "Many of the planets that will be discovered with GPI will later be superb targets for the Webb telescope, which will excel at characterizing these worlds at longer infrared wavelengths, complementing GPI's studies in the near infrared," said Soummer. "Our experience operating this type of complex instrument and observing planets both with Hubble and GPI will help us ensure that the Webb coronagraphs operate as well as possible to extend our knowledge of these planets even further." While GPI, even with its advanced adaptive optics system, will only be able to detect Jupiter-sized worlds through the Earth's atmosphere, a future large space telescope beyond Webb using many of the same techniques as GPI could eventually be able to image and study Earth-sized planets around nearby stars.
STScI astronomers Soummer, Perrin, and Pueyo have been contributing to that effort, building on the coronagraph and data processing technologies developed for GPI. "Extracting a spectrum of an Earth twin with a future NASA mission is a challenge 1,000 times more difficult than what we can achieve now with GPI," said Pueyo, who has developed new techniques to measure planets' spectra from the GPI data, "but there is a roadmap leading to that goal." In a related development, the STScI team is also developing a laboratory optics testbed to test GPI-like, very high contrast imaging on segmented telescopes similar to the James Webb Space Telescope.
"With GPI in operations on the ground, and with Hubble, the Kepler space telescope, and soon the Transiting Exoplanet Survey Satellite (TESS) and Webb, we will be seeing an explosion in the discovery rate and science of exoplanets. More importantly, the technology GPI has successfully deployed on Gemini South, is laying the foundation for future space telescopes that will be capable of detecting life on other planets," said STScI Director Matt Mountain.
Space Telescope Science Institute, Baltimore, Md.
Space Telescope Science Institute, Baltimore, Md.