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What do you do when the exoplanet transit you鈥檙e observing falls out of sight halfway through? Unistellar citizen astronomer Bruno Guillet solved the quandary by reaching across the Atlantic Ocean. He and fellow Unistellar citizen astronomer Justus Randolph recently made a transatlantic observation of exoplanet candidate TOI 2031.01, gathering enough data for Unistellar and SETI Institute scientists to verify it as a positive detection.

Unistellar citizen astronomer Bruno Guillet (France)

The two citizen astronomers were following up on one of the SETI Institute/Unistellar Exoplanet Team鈥檚 targets for that month. Exoplanet candidate TOI 2031.01 was identified by NASA鈥檚 Transiting Exoplanet Survey Satellite (TESS) in 2020. The orbiting telescope identified TOI 2031.01 as a potential planet outside our solar system. (TOI is an acronym for TESS Object of Interest.) Guillet, in France, and Randolph, in the U.S., planned to watch TOI 2031.01 as it passed in front of its star, an听. But there was a problem: It would be below the horizon for half of their observing time. So, the two hatched a plan.

鈥淏runo had the brilliant idea to split up the data collection among multiple observers so that the data from several partial observations would cover the whole duration of the transit,鈥� Randolph says.

Unistellar citizen astronomer Justus Randolph (USA)

In mid-November of 2020, Guillet, in France, took the first shift, watching TOI 2031.01 until around 3:45 a.m. his time. He then passed the torch to Randolph, who finished the observation from the U.S.

鈥淚 am very happy to share this first successful transcontinental joint detection with Justus,鈥� Guillet says.

The result was one seamless light curve, stitched together from two separate continents. And their teamwork paid off: together, they made a positive detection of TOI 2031.01, with a little data processing help by Arin Avsar, Unistellar Exoplanet Data Analyst and UC Berkeley student as well as Tom Esposito, Unistellar Space Science Principal and researcher at the SETI Institute and UC Berkeley.

Esposito noted, 鈥淲ith so many eVscope observers around the world now, we鈥檙e excited to do more science like this. We can learn so much more from people cooperating, and I think Bruno and Justus showed that.鈥�

Transit light curves like this one are used to visualize an exoplanet transit from collected data. This light curve shows the transit of TOI 2031.01 as it passed in front of its star, which caused the flux (brightness) of its host star to dim and then return to normal. Timing the transit tells us that the planet orbits close to its star (circling once every 5.7 days) and, as a result, is very hot (over 1000 掳C). The depth of the dip tells us about the planet鈥檚 size; about 1/10th the diameter of its star, or a little larger than Jupiter.

鈥淲orking together, we were all able to accomplish what we wouldn鈥檛 have been able to accomplish alone,鈥� Randolph says.

Guillet says there鈥檚 more to come, too. He and Randolph have made more split observations, and are eagerly awaiting the results of their efforts.

鈥淚 think this is just the beginning of this type of transcontinental observation,鈥� he says.

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