Super-precise satellites help find 'hide and seek' exoplanets

An international team of researchers has identified a number of elusive exoplanets by developing a new technique that might find many more to come.
John Loeffler
An exoplanet
An exoplanet

ESO/M. Kornmesser 

Exoplanet research is one of the most exciting new fields in astronomy thanks to powerful new telescopes and innovative discovery techniques to help identify planets orbiting stars other than our sun, but it isn’t always easy. Now, however, an international team of researchers has devised a way to identify more elusive exoplanets that have previously thwarted confirmation.

Exoplanet hunters using NASA’s TESS satellite have been able to identify thousands of exoplanets by looking at a star and measuring its luminosity. If the luminosity dips, it might be because an exoplanet in orbit around the star passed between us and the star, blocking some of its light. 

However, one transit event, as this dimming is called, isn’t enough to confirm it is actually an exoplanet. Multiple follow-up observations are needed to determine if the amount of dimming detected during a possible transit occurs at regular intervals, which would be the case if the dimming is caused by an exoplanet orbiting the star.

“NASA’s TESS satellite excels at detecting the transits of exoplanets, even for the most challenging small planets. However, it changes its field of view every 27 days in order to scan rapidly most of the sky, which prevents it from finding planets on longer orbital periods,” Dr. Hugh Osborn of the University of Bern said in a statement.

To solve this problem, Osborn, along with three other researchers turned to the joint European Space Agency (ESA) and Swiss satellite CHEOPS for help. TESS had already identified transits of a number of exoplanets like TOI 5678b and HIP 9618c, but given their longer orbital periods, TESS was unable to observe possible follow-up transits for confirmation. 

“This is where CHEOPS comes into play: Focusing on a single-star at a time, CHEOPS is a follow-up mission which is perfect to continue observing these stars to find the missing bits of information,” said team member Dr. Solène Ulmer-Moll of the Universities of Bern and Geneva.

To narrow down the most likely windows for follow-up transits, Osborn developed software that took what was known about the exoplanet candidates and produced a number of possible transit windows, which then allowed the team to secure precious time with the CHEOPS satellite.

“We then play a sort of ‘hide and seek’ game with the planets, using the CHEOPS satellite,” Osborn said. “We point CHEOPS towards a target at a given time, and depending if we observe a transit or not, we can eliminate some of the possibilities and try again at another time until there is a unique solution for the orbital period.”

It took a few attempts to confirm transits for TOI 5678b and HIP 9618c, but the team was able to find orbital periods of 48 days and 52.5 days for the two planets, respectively. The findings were published in a series of papers in the journals Monthly Notices of the Royal Astronomical Society and Astronomy & Astrophysics.