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Spectrograph Analyzes Light From Extrasolar Planets

Press Release From: Princeton University
Posted: Monday, November 21, 2016

A team of scientists and engineers led by Princeton researchers recently reported the successful operation of a new instrument for the Subaru Telescope in Hawaii that will allow astronomers to make direct observations of planets orbiting nearby stars.

The instrument, dubbed CHARIS, was designed and built by a team led by N. Jeremy Kasdin, a professor of mechanical and aerospace engineering. It allows astronomers to isolate light reflecting from planets larger than Jupiter and then analyze the light to determine details about the planets' size, age and atmospheric constituents. The recent observation is known in the astronomical community as a "first light," a first field test of the instrument on the telescope that demonstrates it is operating successfully.

"We couldn't have been more pleased by the results," said Kasdin. "CHARIS exceeded all of our expectations. I can't praise our team enough for their extremely hard work and dedication that made CHARIS a success. It is on track to be available for science observations starting in February 2017."

CHARIS, an acronym for the Coronagraphic High Angular Resolution Imaging Spectrograph, is part of a major effort in astronomy to find and analyze planets orbiting distant stars, known as exoplanets. Since the first discovery of an exoplanet in 1995, researchers have discovered over 1,000 such planets, a large majority coming from NASA's Kepler space observatory. Nearly all of those discoveries relied on using minute changes in stellar light to identify the presence of planets; as a result, those observations cannot tell scientists much about the planets themselves.

More recent projects have demonstrated the ability to capture light reflected from a planet and separate it from the light shining directly from its parent star. Those efforts allow scientists to examine the light and determine the chemical makeup of the planet's atmosphere in the same way that chemists use the spectrum of light (the wavelength or colors of light) to analyze the composition of material in a lab. The CHARIS project is part of that effort. Currently, CHARIS is the only spectrograph dedicated to exoplanet research on an 8-meter class telescope in the Northern Hemisphere.

"CHARIS is a key addition to the growing exoplanet imaging and characterization capabilities at Subaru Telescope," said Olivier Guyon, the leader of the adaptive optics program at Subaru and a faculty member at the University of Arizona. "With CHARIS spectra we can now do a lot more than simply detect planets: we can measure their temperatures and atmosphere compositions."

The CHARIS project is part of a long-term collaboration among Princeton, the University of Tokyo and the National Astronomical Observatory of Japan, which operates the Subaru Telescope at Mauna Kea, Hawaii. The CHARIS instrument was designed and built at Princeton under the direction of Tyler Groff, a former doctoral student and associate research scholar working with Kasdin, who now works for NASA's Goddard Space Flight Center.

"By analyzing the spectrum of a planet, we can really understand a lot about the planet," Groff said. "You can see specific features that can allow you to understand the mass, the temperature, the age of the planet."

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