A key to potentially finding habitable planets rests in Nieuwland Hall of Science at the University of Notre Dame, after an extended journey.
Packed in six crates — one of which was only a half-inch smaller than the width of a wide-body freight plane door — the Gemini Planet Imager (GPI) arrived at Notre Dame after a trip from its location several hours north of Santiago, Chile. It passed through Atlanta, then Chicago and finally Elkhart, Indiana, before being loaded onto a semitruck bound for South Bend, Indiana.
It’s fair to say that Jeffrey Chilcote, assistant professor in the Department of Physics and Astronomy, who is heading up a project to revamp and upgrade the equipment, was anxious about the instrument’s trip — but he was also excited to get started, because it has been 14 years since GPI was commissioned and seven years since it was installed.
“GPI was designed and built with a bunch of (educated) guesses in mind,” he said. “Now, we can reconfigure it and get absolutely cutting-edge science.”
After Chilcote and collaborators complete the upgrades — at which time the instrument will be known as GPI 2.0, in late 2023 or early 2024 — the instrument will be installed at Gemini North in Mauna Kea, Hawaii, the twin observatory to the one in Chile.
The instrument was built by a consortium of U.S. and Canadian institutions with Chilcote and Quinn Konopacky, associate professor of physics at University of California, San Diego, as well as astrophysicists at Stanford University, Cornell University and Herzberg Astronomy and Astrophysics in Victoria, British Columbia, Canada. GPI had been mounted to the telescope at the Gemini South Observatory in Chile since 2013, where it aided in the search for Jupiter-like planets until it was removed in August 2020. The instrument was slated to arrive in South Bend in 2020, but the global coronavirus pandemic delayed plans.
In 2017, Chilcote and others approached the broader astronomy community to ask what types of upgrades should be completed. “We asked, ‘What do you need, at a minimum, to go to the next step in your science, now that you’ve learned what directions might be interesting to pursue further?’” he said.
The first iteration of GPI allowed astronomers to observe large, warm planets through their infrared light, as well as faint disks of dust from comets and asteroid belts in faraway solar systems. The upgrade will allow astronomers to see lower-mass planets that orbit more closely to their stars.
“We were limited to something called ninth-magnitude stars, so with these upgrades we’re going to be looking at what are called 14th-magnitude stars, which are about 100 times fainter,” Chilcote said. The brightest stars in the sky are considered first magnitude, while the dimmest to the unaided eye are sixth.
The logistics for removing GPI from the Gemini in Chile were tricky enough, but by the time it arrived in Indiana, the day had to have an almost zero chance of precipitation. Although the telescope is open to the air when assembled, its parts cannot tolerate rain (or snow; originally GPI was scheduled to arrive during winter months).
Chilcote and others cleared out parts of Nieuwland’s machine shop, and they had to purchase a specific type of crane that fits inside the rooms on the ground floor but was still capable of holding the two-and-one-half-ton instrument. On a bright sunny day in June, a team transferred the crates from the truck to Nieuwland. The smallest crates fit through the door, but the largest one was never expected to fit while still in the crate. Chilcote and others opened the crate and, using heavy equipment, turned GPI on its side to get it through the door.
He found himself holding his breath. A lot. Thankfully, the transfer went smoothly.
Researchers have discovered more than 5,000 extrasolar planets, Chilcote said, but most were detected using the transit method. With that method, scientists must detect slight variations in the brightness of a star, caused when a planet crosses in front of it. Others have been detected using the so-called “wobble” method, or radial velocity method, where scientists detect shifts in the star’s spectrum using Doppler. But GPI finds planets by directly imaging them, based on the glare from the star. GPI allows astronomers to measure a planet’s size, temperature and even composition through spectroscopy.
By the time the GPI Exoplanet Survey Team completed its goal in 2019 to characterize exoplanets, more than 500 nearby stars had been reviewed. The instrument discovered seven new debris disks as well as 51 Eridani b, a Jupiter-like planet in the constellation Eridanus that takes 32 Earth years to complete the orbit of its star. The instrument also discovered brown dwarf/gas giant exoplanet HR 2562 B in 2016, currently known as the most massive exoplanet discovered.
The project is funded by the National Science Foundation Major Research Instrumentation Program and the Heising-Simons Foundation. In addition to Notre Dame, the University of California, San Diego, the Herzberg Astronomy and Astrophysics, Cornell, the Gemini program, the Space Telescope Science Institute and the University of California, Santa Cruz also contributed to the construction of and research for the instrument.
Contact: Jessica Sieff, 574-631-3933, jsieff@nd.edu