Citizen Astronomers Help Confirm New Temperate Jupiter

NASA’s Transiting Exoplanet Survey Satellite (TESS) has made yet another exciting discovery—but it never works alone. Thanks to a recent study showcasing the efforts of professional astronomers and citizen scientists around the globe, including observers from the SETI Institute & Unistellar Network, the newly confirmed planet TOI-4465 b has found its place in our understanding of the universe.

TOI-4465 b is a gas giant located about 400 light-years away, orbiting a Sun-like star, albeit one slightly older than our own, as indicated by its lower metallicity (i.e., its lower content of elements heavier than hydrogen and helium). This newfound world has nearly six times the mass of Jupiter but is only about 25% larger in size, making it unusually dense. Yet what’s even more fascinating is how this planet was confirmed.

A graphic of Unistellar observers’ data that captured the transit of TOI-4465b. Credit: John Pickering, citizen astronomer and co-author on the study.

This planet’s story began when astronomers from the Giant Outer Transiting Exoplanet Mass (GOT’EM) survey spotted a single event resembling an exoplanet transit in the TESS light curves of the host star—a measurement of the star’s brightness over time. Their first clue was a dip in the star’s light curve lasting nearly 12 hours. Based on that lone TESS transit, astronomers inferred the planet likely had an orbital period longer than about 13 days, since TESS observes any given patch of sky for only 27 days at a time.

However, additional data were needed to prove the planet’s existence. From observatories around the world, astronomers collected radial velocity measurements, which detect a star’s wobble over time as other bodies (like planets) exert gravitational tugs on it. This data confirmed that a planet-sized object was indeed influencing the star and allowed astronomers to estimate the planet’s orbital period.

Although there was some uncertainty in the exact timing, astronomers predicted that the next transit would occur between August 9 and August 12, 2022. Under the auspices of the NASA-sponsored program Unistellar Network Investigating TESS Exoplanets (UNITE), the SETI & Unistellar Network launched an ambitious campaign to observe during this entire window. Citizen astronomers from the United States, Japan, New Zealand, Italy, Germany, France, the Netherlands, the United Kingdom, Austria, and Switzerland teamed up to capture the transit. Over the three-day window, 24 Unistellar observers — including three SETI Institute astronomers — gathered 46 datasets, totaling nearly 230 hours of observations. The global reach of the SETI Institute & Unistellar Network made near-continuous monitoring possible; as the Sun rose in one part of the world, another region picked up the observation.

Other citizen science groups contributed as well, including the TESS Follow-up Observing Program Sub Group 1 (TFOP SG1) and the TESS Single Transit Planet Candidate (TSTPC) Working Group, making this a truly communal endeavor. Thanks to everyone’s combined efforts, astronomers were able to finally confirm the existence of TOI-4465b.

“The discovery and confirmation of TOI-4465 b not only expands our knowledge of planets in distant star systems but also shows how passionate astronomy enthusiasts can play a direct role in frontier scientific research,” said Dr. Zara Essack, Postdoctoral Fellow at the University of New Mexico and lead author of the study. “It’s a powerful example of citizen science, teamwork, and the importance of global collaboration in astronomy.”

This isn’t the first planet confirmed with help from the SETI & Unistellar Network, which is particularly well-suited for such discoveries.

“Now, people equipped with a digital smart telescope can observe and confirm exoplanets from their backyard, helping NASA map nearby planetary systems discovered by the TESS mission,” said Dr. Franck Marchis, Senior Astronomer at the SETI Institute and Chief Scientific Officer at Unistellar. “The likelihood of TESS observing another transit of a planet like TOI-4465 b, which happens only every 102 days, is low. So the SETI & Unistellar network is essential for these discoveries.”

TOI-4465 b represents an important piece of the planetary puzzle, helping bridge the gap between hot Jupiters that orbit close to their stars and our own Solar System’s cold gas giants. This new world is a “temperate” Jupiter: it shares some orbital properties with warm Jupiters, but its modest orbital eccentricity keeps its temperature relatively mild. TOI-4465 b is the most massive long-period giant known to transit a sub-solar metallicity star and has the largest radius of any known planet with an orbital period exceeding 100 days. As a result, it provides a unique test case for studying gas giants and helps fill gaps in our planetary knowledge.

“It’s really astounding what science can achieve when we work together,” said Dr. Lauren Sgro, Postdoctoral Fellow at the SETI Institute and co-author of the study. “I’m excited to see how future observations of this planet inform our understanding of gas giant formation, and knowing that citizen scientists are part of this process is truly inspiring.”

TOI-4465 b is also well-suited for follow-up studies of its atmosphere with instruments such as the James Webb Space Telescope, so this is only the beginning of its story. Perhaps the next chapter belongs to another new planet, waiting to be explored by professional and citizen astronomers alike.