An astronomer from the University of California Riverside (UCR) and a group of citizen scientists have discovered a planet gas giant hidden from view by stargazing systems.
The planet, TOI-2180 b, has the same diameter as Jupiter, but it is almost three times as massive. Researchers also believe that it contains 105 times the mass of Earth in elements heavier than helium and hydrogen. Nothing like it exists in our solar system.
Details of the finding were published in the Astronomical Journal and presented at the American Astronomical Society’s virtual press event.
“TOI-2180 b is an exciting planet”UCR astronomer Paul Dalba, who helped confirm the existence of the planet, said in a statement. “It achieves the trifecta of 1) having an orbit of several hundred days; 2) being relatively close to Earth (379 light years is considered close for an exoplanet); and 3) being able to see him transit in front of his star. It is very rare for astronomers to discover a planet that ticks all three boxes.”
Dalba also explained that the planet is special because it takes 261 days to complete one trip around its star, a relatively long time compared to many known gas giants outside our solar system. Its relative proximity to Earth and the brightness of the star it orbits also make it likely that astronomers can learn more about it.
To locate exoplanets, which orbit stars other than our sun, the TESS satellite of the NASA observe a part of the sky for a month and then continue. It’s looking for dips in brightness that occur when a planet crosses in front of a star.
“The general rule of thumb is that we need to see three ‘dips’ or transits before we believe we have found a planet,” Dalba said. A single transit event could be caused by an unstable telescope or a star disguised as a planet. For these reasons, TESS does not focus on these unique traffic events. However, a small group of citizen scientists is.
Reviewing the TESS data, Tom Jacobs, a member of the group and a former US naval officer, saw the light from star TOI-2180 dim just once. His group alerted Dalba, who specializes in studying planets that take a long time to orbit their stars.
Using the Lick Observatory’s Automated Planet Finder Telescope, Dalba and colleagues observed the planet’s gravitational pull on the star, which allowed them to calculate TOI-2180’s mass and estimate a range of possibilities for its orbit.
Hoping to observe a second transit event, Dalba organized a campaign using 14 different telescopes on three continents in the Northern Hemisphere. Over the course of 11 days in August 2021, the effort resulted in 20,000 images of the star TOI-2180, although none of them confidently detected the planet.
However, the campaign led the group to estimate that TESS will see the planet transit its star again in February, when they are planning a follow-up study.
The planet-hunting citizen group takes publicly available data from NASA satellites like TESS and looks for unique transit events. While professional astronomers use algorithms to scan vast amounts of data automatically, the Visual Survey Group uses a program they created to inspect telescope data with the naked eye.
“The effort they put in is really important and impressive, because it’s hard to write code that can reliably identify unique traffic events,” Dalba said.