A University of California Riverside (UCR) astronomer and a group of eagle-eyed citizen scientists have discovered a giant gas planet hidden from view by typical stargazing tools.
The planet, TOI-2180 b, has the same diameter as Jupiter, but is nearly three times more massive. Researchers also believe it contains 105 times the mass of Earth in elements heavier than helium and hydrogen. It is unlike anything else in the solar system.
Details of the finding have been published in the Astronomical Journal and presented at the American Astronomical Society virtual press event on Jan. 13.
“TOI-2180 b is such an exciting planet to have found,” said UCR astronomer Paul Dalba, who helped confirm the planet’s existence. “It hits the trifecta of 1) having a several-hundred-day orbit; 2) being relatively close to Earth (379 lightyears is considered close for an exoplanet); and 3) us being able to see it transit in front of its star. Astronomers rarely find a planet that ticks all three of these boxes. “
Dalba also explained that the planet is special because it takes 261 days to complete a journey around its star, a relatively long time compared to many known gas giants outside our solar system. Because it is so close to Earth, and because it orbits a bright star, it makes it possible for astronomers to study it.
In order to locate exoplanets, which orbit stars other than our sun, NASA’s TESS satellite looks at one part of the sky for a month, then moves on. It’s looking for brightness dips that occur when a planet crosses over a star.
” The rule of thumb is to see three transits or ‘dips’ before we can believe that we have found a planet. One transit event could be caused either by a telescope that has a jitter or a star that is masquerading itself as a planet. These single transit events are not the focus of TESS. A small number of citizen scientists are.
Looking over TESS data, Tom Jacobs, a group member and former U.S. naval officer, saw light dim from the TOI-2180 star, 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 his colleagues observed the planet’s gravitational tug on the star, which allowed them to calculate the mass of TOI-2180 b and estimate a range of possibilities for its orbit.
Hoping to observe a second transit event, Dalba organized a campaign using 14 different telescopes across three continents in the northern hemisphere. Over the course of 11 days in August 2021, the effort resulted in 20,000 images of the TOI-2180 star, though none of them detected the planet with confidence.
The campaign led the group to conclude that TESS would see the planet transit its star in February. They are planning a follow-up study. The National Science Foundation’s Astronomy and Astrophysics Postdoctoral Fellowship Program provides funding for Dalba’s research.
The citizen planet hunters’ team uses publicly available data from NASA satellites such as TESS to search for single transit events. The algorithms used by professional astronomers to scan large amounts of data are not applicable to the Visual Survey Group. Instead, they use a program to examine telescope data by hand.
“The effort they put in is really important and impressive, because it’s hard to write code that can i