Citizen Scientist Tom Jacobs was responsible for a really cool discovery: a large exoplanet in the data collected by NASA’s Transiting Exoplanet Survey Satellite, TESS.

The planet, TOI-2180 b, has three times the mass of Jupiter but is roughly the same size, suggesting that it is denser than the gas giant in our solar system. It orbits its stars in 261 days, slightly longer than Venus takes to go around the Sun. This might appear short, given that Jupiter takes about 12 years, but many Jupiter-sized worlds discovered beyond the solar system have a year that is just a few days longer. An extreme case orbits its stars in a few hours.

This exciting discovery, reported in The Astronomical Journal and presented at an American Astronomical Society virtual meeting, was possible thanks to Jacobs's dedication. He had previously participated in the Planet Hunter, an initiative of citizen science portal Zooniverse with NASA funding, looking at data collected by the previous exoplanet hunter Kepler. He now collaborates with a group of citizen scientists and two veteran astronomers examining the TESS data by eye using special software. It was in this way that he spotted what turned out to be a planet.

TESS observes the light of stars, registering changes over a long period. If a planet happens to cross the star as the satellite is looking at it, it might dim it slightly. Repeated dips at regular intervals in this light curve indicate a planet.

On February 1, 2020, Jacob spotted such a singular dip and flagged it as a potential interesting find to two professional scientist collaborators: Paul Dalba at the University of California, Riverside, and Diana Dragomir, assistant professor at the University of New Mexico.

“Discovering and publishing TOI-2180 b was a great group effort demonstrating that professional astronomers and seasoned citizen scientists can successfully work together,” Jacobs said in a statement. “It is synergy at its best.”

A planet is only confirmed if two independent methods can prove its presence, so Dalba used the Automated Planet Finder Telescope at Lick Observatory in California to hunt for this confirmation. With 27 hours of observations spread over 500 days, Dalba and his team measured the gravitational pull that the planet has on its star.

“With this new discovery, we are also pushing the limits of the kinds of planets we can extract from TESS observations,” Dragomir said. “TESS was not specifically designed to find such long-orbit exoplanets, but our team, with the help of citizen scientists, are digging out these rare gems nonetheless.”

Automated software has done great strides, but in many data sets, human eyes are still beating computers to the punch – and the work of citizen scientists in going through such a huge amount of data is truly invaluable.