Astronomers use new technology developed with help from UC Irvine professor to look for habitable planets

The Habitable Planet Finder, right, is carried by forklift to the McDonald Observatory in the Davis Mountains of Texas. The Hobby-Eberly Telescope is at left. The HPF began routine scientific operations in February.
(Courtesy of Gudmundur Stefansson)

Planets capable of supporting life are in a star system not so far, far away, and astronomers will be able to study them closely with the Habitable Planet Finder, developed with help from a UC Irvine professor.

The Habitable Planet Finder is a spectrograph that UCI assistant professor Paul Robertson said is like a digital camera that uses infrared light to amplify the light of small, cool stars called M-dwarfs that otherwise could not be seen.

“We’ve learned from experiments like the Kepler space telescope that the galaxy is just full of planets,” Robertson said. “You can look out at night, pick your favorite star and, rest assured, it will be orbited by a planet.

“There’s one population of stars that still hasn’t been studied in this way. These stars just aren’t bright enough for visible [light] wavelength. By moving into the infrared, we can pursue this last group of star and planet system.”

The Habitable Planet Finder, housed in the basement of the Hobby-Eberly Telescope in Texas, measures the movement of stars due to the gravity of their planets. It works in tandem with the telescope and a laser frequency comb, the latter developed by the National Institute of Standards and Technology to calibrate the HPF to look for planets in “habitable zones,” where surface water could occur.

“We are hoping to find not only more exoplanets but more Earth-like exoplanets,” said Jack Lubin, a first-year graduate student working with Robertson. “That is to say, more planets that are roughly the same mass as Earth that are orbiting their host star at just the right distance so the planet could exist in a liquid state.”

“This has also been called the ‘Goldilocks Zone,’” Lubin said — not so far away that water might freeze and not so close that it would boil.

Robertson and his graduate team are studying a collection of M-dwarfs near the Sun — about 25 light years away — but plan to also observe planets discovered by the Kepler telescope, which was retired in late October, and the Transiting Exoplanet Survey Satellite, which was launched in April.

With the HPF, astronomers can survey stars for new planets as well as observe planets already revealed by Kepler and TESS.

Scientists install fiber optic cable for the Habitable Planet Finder to connect to the Hobby-Eberly Telescope in Texas.
(Courtesy of Gudmundur Stefansson)

“When Kepler or TESS finds a planet, we can use a spectrometer like HPF to get the mass,” Robertson said. “Then we have both the radius and mass and we can estimate the planet’s density. This gives a lot of information about the planet, such as its likely composition and the size of its atmosphere.”

Formal development of the instrument began in September 2011.

In July 2013, Robertson joined a team at Penn State University, where he was a researcher, seeing it as an opportunity to continue the work he began as a graduate student.

“I was using a visible-light spectrometer to study some of these nearby, very cool stars. I was never able to push the limits of that the way I wanted to,” said Robertson, who has been at UCI since January 2018. “So this opportunity sort of came up where there was this team at Penn State developing this instrument. I didn’t have a lot of experience, but they were like, ‘Look, if you’re really compelled by the science and want to use the instrument, you can learn on the job.’”

The instrument was completed and in operation by November last year and began routine scientific operations in February.

“HPF opens a major new window by allowing astronomers to search for Earth-like planets around the most common stars in the galaxy,” said professor James Bullock, chairman of UCI’s physics and astronomy department. “It will be exciting to see what Professor Robertson and his team discover with this amazing tool they’ve helped to build.”

The long-term goal, Robertson said, is to find bio-signatures — gases in a planet’s atmosphere, such as oxygen or methane, that could only be produced by living things.