NASA’s Transiting Exoplanet Survey Satellite (TESS) has found three confirmed exoplanets in its first three months of observations.
The planet hunter’s latest discovery—a small planet outside our Solar System—was announced at this week’s American Astronomical Society meeting in Seattle.
Dubbed HD 21749b, the globe orbits a nearby dwarf star about 53 light years from Earth, in the constellation Reticulum, and appears to have the longest orbital period of the triad.
Compared to TESS’s other two sightings—Pi Mensae b, a “super-Earth” with a 6.3-day orbit, and LHS 3844b, a rocky world that speeds around its star in 11 hours—HD 21749b is downright lazy, taking 36 days to complete one rotation.
The new planet’s surface reaches about 300℉, which, according to the MIT Kavli Institute for Astrophysics and Space Research, is “relatively cool,” considering the proximity to its star, which is almost as bright as our Sun.
“It’s the coolest small planet that we know of around a star this bright,” Diana Dragomir, a postdoc in MIT Kavli Institute who led this latest discovery, said in a statement.
“We know a lot about atmospheres of hot planets, but because it’s very hard to find small planets that orbit farther from their stars, and are therefore cooler, we haven’t been able to learn much about these smaller, cooler planets,” she continued. “But here we were lucky, and caught this one, and can now study it in more detail.”
About three times the size of Earth (and a whopping 23 times as massive), HD 21749b is categorized as a “sub-Neptune.” Unfortunately, it is unlikely the gaseous planet is habitable.
On the bright side, there is evidence of a second, still unconfirmed planet in the same system, this one with a much shorter 7.8-day orbit. If confirmed, it could be the first Earth-sized world discovered by TESS.
During its initial two-year mission, the Transiting Exoplanet Survey Satellite will observe nearly the entire sky, looking for transit—a phenomenon that occurs when a planet passes in front of its star, causing a dip in the star’s brightness.
“We’ve confirmed three planets so far, and there are so many more that are just waiting for telescope and people time to be confirmed,” Dragomir said. “So it’s going really well, and TESS is already helping us to learn about the diversity of these small planets.”
Its sensitive cameras also captured 100 short-lived changes—including six supernova explosions recorded from space before being discovered by ground-based telescopes.
Astronomers are now conducting follow-up observations on more than 280 exoplanet candidates.
