Gemini Observatory Instrumental in Exoplanet Harvest
Gemini Observatory plays a key role in the latest harvest of over 100 confirmed exoplanets from NASA’s K2 mission, the repurposed Kepler spacecraft. Three instruments on the Gemini North telescope delivered precise images verifying many of the candidate stars as planetary system hosts. Researchers note that these systems could contain a considerable number of rocky, potentially earthlike exoplanets.
The Gemini North telescope on Hawaii’s Maunakea helped verify many of the over 100 new worlds announced in the initial crop of discoveries from the NASA K2 mission, according to Ian Crossfield of the University of Arizona. Crossfield led the international team of scientists who announced the findings, which are published online in The Astrophysical Journal Supplement Series. A preprint of the paper is available here.
“Gemini North was instrumental because it delivered extremely high-resolution images of over 70 of the almost 200 potential planetary systems that K2 uncovered,” says Crossfield. ”In total we used three instruments, or cameras, on Gemini to complete our studies – so you could say that Gemini was instrumental in that way too!”
Once K2’s data are analyzed to identify potential exoplanet candidates, many of the world’s most powerful telescopes, like Gemini, are set into motion. This is so astronomers can rule out other explanations that can produce the signature of a planet orbiting a star. “This is where the discovery happens,” says astronomer Christopher Davis of the US National Science Foundation, which funds over 70% of Gemini. “Once other possibilities are eliminated, like nearby background stars, the team can say with extreme certainty that we have a new exoplanet system.”
One of the instruments used at Gemini is a visiting instrument called the Differential Speckle Survey Instrument (DSSI) which is led by Steve Howell of NASA’s Ames Research Center. “These observations are a critical part of the exoplanet validation process,” says Howell. “It’s essentially the only way to validate small, earth-sized planets orbiting around other stars.” Howell’s DSSI instrument uses many extremely short (typically about 60 millisecond) exposures of a star to capture fine detail by combining the images and subtracting momentary distortions caused by the Earth’s atmosphere. With this technique astronomers can see details at, or very near, the theoretical limit of the 8-meter Gemini mirror which is like being able to resolve two automobile headlights at a distance of about 2000 miles.
In its initial mission, Kepler surveyed just one patch of sky in the northern hemisphere, measuring the frequency with which planets whose size and temperature are similar to Earth occur around stars like our Sun. But when the satellite lost its ability to precisely stare at its original target area in 2013, a brilliant fix created a second life for the telescope that is proving remarkably fruitful.
The new K2 mission provides fields of view within the ecliptic which presents greater opportunities for Earth-based observatories in both the northern and southern hemispheres. Additionally, the new mission opened up the observations to the entire scientific community, not just specific targets picked by science team members. K2 now looks at new types of populations, including a larger fraction of cooler, smaller, red dwarf-type stars, which are much more common in our Milky Way than Sun-like stars. The space observatory discovers new planets by measuring the subtle dip in a star’s brightness caused by a planet passing in front of its star.
The Gemini followup observations were made as part of what is called a Large and Long program intended to provide access to Gemini for studies requiring more observing time, or extended periods of observations to yield high-impact results. In addition to observations with DSSI, Gemini’s Near-InfraRed Imager (NIRI) with the Altair adaptive optics system, and the Gemini Near-InfraRed Spectrograph (GNIRS) were used to make the verification observations.
In addition to Gemini, follow-up ground-based observations were made by W. M. Keck Observatory also on Maunakea in Hawai‘i, the Automated Planet Finder of the University of California Observatories, and the Large Binocular Telescope operated by the University of Arizona.