Exoplanet Hunter Racks up 5,000 “Objects of Interest”

Since 2018 NASA’s Transiting Exoplanet Survey Satellite (TESS) has been taking a broad view of the cosmos. Its primary mission is to find exoplanets, and it has surpassed all expectations. Now in its fourth year, the satellite has identified its 5,000th exoplanet candidate (also known as “TESS object of interest,” or TOI).

That object, TOI-5000, is a multi-planet system with two exoplanet candidates, a pair of hot Jupiters with periods of just 5.5 and 15.3 days, respectively. Such planets almost always orbit alone, so this system may be a rare exception. But before it’s studied, it needs to be vetted.

TESS finds exoplanets by monitoring nearby stars for brief dips in their light. These transits suggest that a planet is passing in front of its host star, but a star’s own periodic dimming or the passage of a binary star companion can produce similar signatures. That’s why, once a TOI is identified, the exoplanet community takes their turn at the data.

There’s too much data for the science team to parse on their own, but, since the observations are made public as soon as possible, interested parties usually only have to wait between a week and a month to see what peculiar blips and dips the stars have in store. This approach has spawned a global effort, with citizen scientists and academics across the world working together to identify TOIs and sift the false positives from the definite planets.

Much of the gain in TOIs has come from Michelle Kunimoto (MIT), who leads TESS’s Quick-Look Pipeline team. She has focused on finding planets around the millions of faint stars that TESS observes every month. Kunimoto wrote an algorithm that simulates the standard methods used to discover transits, partially automating the process. This innovation helped increase the number of TOIs from 2,400 to 5,000 over the last year alone.

“TESS focuses mainly on bright stars,” Kunimoto says. “My group took another look at the fainter stars in the historic data and found lots of candidates. We also used this technique to analyze incoming data and found more TOIs per sector that way than had been seen before.”

Will TESS Find Earth 2.0?

TESS is a NASA Explorer-class mission, built for just $200 million (excluding launch costs). Its primary mission lasted two years, but in 2020 NASA extended it two more; it seems a given that another extension is in the cards.

David Latham, TESS’s Director of Science, says that the exoplanet hunter has also proven popular with astrophysicists, especially in the emerging field of asteroseismology, which studies stars by their vibrations.

“TESS looks at stars to find planets, but the data we get on the stars is interesting, too,” Latham says. “In fact, more studies have been published by astrophysicists using TESS for other projects than we have published identifying planets.”

As of December 2021, 175 of TESS-discovered planets have been confirmed. Now that the James Webb Space Telescope (JWST) has successfully launched and deployed, the team is keen for a closer look at them.

The teams had planned a synergy between JWST and TESS from the beginning. “We got all this basic information on these worlds, so that later, more advanced telescopes like JWST would know where to look,” Latham says. “And it’s very exciting that it has finally launched, because now, hopefully, we will be able to see if these worlds have atmospheres, and what they are made of.”

The JWST has been a long time coming. It has been so highly anticipated by the astronomy community that it might turn out to be more oversubscribed than the Hubble Space Telescope. For this reason, JWST’s handlers aren’t keen to aim it in a particular direction unless they have a very good reason for doing so. TESS’s highly vetted planet catalog leaves nothing to be desired on this front. The main concern will be deciding which world to look at first.

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