The TESS satellite, a worthy successor to the Kepler telescope, has just completed its main two-year mission with several significant discoveries to its credit. The instrument is now embarking on an extended mission for two more years, with many additional exoplanets in our address book.

Launched into orbit in April 2018, TESS (short for Transiting Exoplanet Survey Satellite), had the heavy burden of succeeding the Kepler telescope. And for good reason, the latter is at the origin of two thirds of the discoveries of more than 4,200 exoplanets made to date.

And it’s not over. While Kepler has been officially retired since October 2018, the data it collected is still being analyzed. Thus, hundreds of other worlds could potentially be discovered again thanks to it.

Despite the pressure, TESS did more than well. At the end of its main two-year mission, which ended on July 4, the satellite had already discovered 66 planets. Among them is TOI 700 d, comparable in size to Earth, which orbits in the habitable zone of its star 100 light years away. In addition, nearly 2,100 potential candidates have yet to be screened.

Hunting technique

To carry out its mission, TESS uses the transit method, which consists of detecting small and regular drops in stellar luminosity. The latter generally testify to repeated passages of planets between the observer (TESS) and the host star.

During those first two years, the telescope focused on analyzing 200,000 nearby stars. To do this, it relied on four cameras that allowed it to study areas of the sky 24 by 96 degrees for about a month at a time. For reference, your clenched fist held at arm’s length covers about 10 degrees of the sky.

TESS spent the first year of its primary mission surveying sectors in the southern sky, then moved to the northern sky in its second year. So far, it has managed to cover about 75% of the night sky. But its job is not finished.

The satellite has just started its extended mission, which will continue until September 2022. Once again, it must focus on the southern sky for the first 12 months before moving north.

A bonus mission

TESS’s core mission budget was capped at $200 million, to which were added the start-up costs, estimated at an additional $87 million.

This so-called “extended” mission should be considered as a bonus, insofar as it will not be very demanding in terms of funding. For example, the New Horizons probe’s extended mission operations, which began in 2017, cost less than $15 million per year, while its main mission cost more than $780 million.

During these two additional years, TESS will also benefit from some improvements of its instruments. For example, its cameras can now capture a full image every 10 minutes, which is three times faster than during the main mission. In other words, the telescope will be able to scan the sky faster than before, which should maximize the number of discoveries to come.