Tom Jacobs of Bellevue, Washington, loves treasure hunts. Since 2010, the former US naval officer has participated in online volunteer projects that allow anyone who is interested – “citizen scientists” – to look through NASA telescope data for signs of exoplanets, planets beyond our solar system.
Now, Jacobs has helped discover a giant gaseous planet about 379 light-years from Earth, orbiting a star with the same mass as the Sun.
The Jupiter-size planet is special for astronomers because its 261-day year is long compared to many known gas giants outside our solar system. The result also suggests the planet is just a bit farther from its star than Venus is from the Sun.
The finding was published in the Astronomical Journal and presented at an American Astronomical Society virtual press event on January 13.
Uncovering this planet and pinning down its size and mass required a large collaboration between professional astronomers and citizen scientists like Jacobs. To track the planet, they engaged in “a global uniting effort, because we all need to go after it together to keep eyes on this particular planet”, said Paul Dalba, astronomer at the University of California, Riverside, and lead author of the study.
“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. “It is synergy at its best.”
How the discovery happened
The signature for the newly discovered planet was hiding in data from NASA’s Transiting Exoplanet Survey Satellite, or TESS. Using TESS data, scientists look for changes in brightness of nearby stars, which could indicate the presence of orbiting planets.
Jacobs is part of a group of citizen scientists who look at plots of TESS data, showing the change in a star’s brightness over time, in search of new planets.
While professional astronomers use algorithms to scan tens of thousands of data points from stars automatically, these citizen scientists use a program called LcTools, created by Alan R. Schmitt, to inspect telescope data by eye.
That’s why Jacobs’ group, which includes several citizen scientists and two veteran astronomers, calls themselves the Visual Survey Group. Many of them met while working on Planet Hunters, a NASA-funded citizen science project through Zooniverse that focused on data from NASA’s Kepler spacecraft.
On February 1, 2020, Jacobs happened to notice a plot showing starlight from TOI-2180 dim by less than half a percent and then return to its previous brightness level over a 24-hour period, which may be explained by an orbiting planet that is said to “transit” as it passes in front of the star from our point of view.
By measuring the amount of light that dims as the planet passes, scientists can estimate how big the planet is and, in combination with other measurements, its density. But a transit can only be seen if a star and its planet line up with telescopes looking for them.
A graph showing starlight over time is called a “light curve”. The Visual Survey Group alerted two professional scientist collaborators – Paul Dalba at the University of California, Riverside, and Diana Dragomir, assistant professor at the University of New Mexico, that this light curve was potentially interesting.
“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.”
Computer algorithms used by professional astronomers are designed to search for planets by identifying multiple transit events from a single star.
That’s why citizen scientists’ visual inspection is so useful when there is only one transit available. Since this is the only instance of the TOI-2180 b star dimming in this dataset, it is called a “single transit event”.
Main image: This illustration depicts a Jupiter-like exoplanet called TOI-2180 b. It was discovered in data from NASA’s Transiting Exoplanet Survey Satellite. Credits: NASA/JPL-Caltech/R. Hurt.
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