NASA's TESS Discovers 'Super-Earth' and Two Other Exoplanets Just 73 Light Years Away

A "super-Earth" and two other exoplanets have been discovered by NASA's Transiting Exoplanet Survey Satellite (TESS) orbiting a star that's located just 73 light years from our planet.

The three planets are among the smallest and closest exoplanets found to date, according to a team of astronomers led by Maximilian Günther, from MIT's Kavli Institute for Astrophysics and Space Research.

The star system, dubbed TOI-270 by the team, is intriguing for several reasons. For starters, unlike our own solar system, the three planets are not too dissimilar from each other when it comes to size, according to a study describing the findings, published in the journal Nature Astronomy.

The rocky super-Earth is described as such because it has a mass higher than Earth's but significantly lower than that of Uranus and Neptune. Meanwhile, the other two planets are described as "sub-Neptunes" because they are intermediate in size—around half that of the ice giant in our own solar system.

"One of them is just slightly bigger than Earth and likely rocky, the other two are twice the size of Earth and probably of a similar composition as Neptune—rocky cores covered by a very thick gas atmosphere," Günther told Newsweek.

To find two of these intermediate size planets together is significant for astronomers because worlds like this provide the "missing link" when it comes to understanding planetary formation. In fact, no intermediate-sized planets exist in our solar system.

Furthermore, the three planets line up in what's known as a "resonant chain," which means the ratio of their orbits are close to whole numbers.

"For TOI-270, these planets line up like pearls on a string," Günther said in a statement. "That's a very interesting thing, because it lets us study their dynamical behavior. And you can almost expect, if there are more planets, the next one would be somewhere further out, at another integer ratio."

The researchers say that the planet furthest away also lies in the so-called "temperate zone" which mean that the upper portions of its atmosphere may be at just the right temperature to support some forms of life. The surface itself is likely far too hot to support life, due to the extremely thick atmosphere which traps heat.

Finally, TOI-270 is an excellent candidate for further study, according to the astronomers, because of its proximity to Earth—meaning it is bright—and the fact that it is unusually quiet. This steady brightness provides astronomers with a good opportunity to make observations of the surrounding planets.

"There are a lot of little pieces of the puzzle that we can solve with this system," Günther said in the statement. "You can really do all the things you want to do in exoplanet science, with this system."

"TOI-270 is a true Disneyland for exoplanet science, and one of the prime systems TESS was set up to discover," he said. "It is an exceptional laboratory for not one, but many reasons—it really ticks all the boxes."

The star system will now be a target for future observations with the next-generation James Webb Telescope, which will have the power to reveal intricate details about the properties of the planets, as well as search for any additional worlds orbiting the star that may currently be undetected.

Since its launch in July 25, TESS has been searching for planets using the transit method—watching for periodic dips in the brightness of stars caused by an orbiting planet passing in front of them. The mission is focusing on bright stars close to us, less than 300 light-years away.

"For example, we can sometimes observe our Moon, Mercury or Venus passing in front of our Sun—this is a 'transit.' When the orbital alignment is right, we can use the same events on other stars, whenever their exoplanets pass in front of their star," Günther said.

"By now, TESS has discovered 27 confirmed planets—including the three TOI-270 planets—outside our solar system and captured data on other interesting events occurring in the southern sky during its first year of science," he said. "The planets TESS has discovered range from a world 80 percent the size of Earth to those exceeding the size of Jupiter or Saturn. Many of the planets TESS discovers can be studied further to determine key characteristics that could affect their ability to support life, such as atmospheric composition."

Aside from exoplanets, TESS has also made a series of other significant discoveries, including capturing clear images of a newly discovered comet, of supernovae, and of stellar flares.

"On July 18, TESS shifted its gaze to the northern sky to complete the most comprehensive search for planets ever undertaken," Günther said. "By the time TESS completes this second half of its survey, it will have mapped over 85 percent of the sky."

This article was updated to include additional comments from Maximilian Günther.

Illustration of NASA's Transiting Exoplanet Survey Satellite. TESS