The Transiting Exoplanet Survey Satellite (TESS) and the scientists who study its data have had a busy four years.

The mission just passed a critical discovery milestone, crossing 5,000 TESS Objects of Interest, or TOIs, which include exoplanet candidates and other intriguing signals, according to the researchers. To further comprehend what TESS may have observed, astronomers choose objects from these TOIs to analyze in greater detail and with other instruments.

"This time last year, TESS had found just over 2,400 TOIs. Today, TESS has reached more than twice that number," Michelle Kunimoto, a postdoc at the Massachusetts Institute of Technology (MIT), said in a statement. (MIT scientists lead the TESS mission and Kunimoto is leading a project called the Faint Star Search that has contributed many of the recently added TOIs.) "I'm excited to see thousands more in the years to come!"

Since TESS launched in April 2018, 176 TOIs have been confirmed as planets. Planet confirmations are expected to lag behind candidate detections since it requires more observation time to confirm exoplanet candidates after first spotting a TOI.

Despite completing its observations in 2013, TESS' predecessor, the Kepler space telescope, identified more than 2,000 planet candidates that have yet to be confirmed. (There are over 2,700 confirmed planets in the mission's data.)

TESS was launched with a two-year mission in mind, with the first half of the mission focused on the Southern Hemisphere and the second on the Northern Hemisphere. That pattern has continued when the spacecraft's mission was extended in July 2020; the crew plans to continue observations until at least 2025.

"With data from the first year of the extended mission, we have found dozens of additional candidates to TOIs found during the prime mission," Katharine Hesse, TOI manager at MIT, said in the statement. "I am excited to see how many multi-planet systems we can find during the rest of the extended mission and in upcoming years with TESS."