The discovery, discussed at the 233rd meeting of the American Astronomical Society (AAS) and in pre-print at arXiv, is just one of several now coming thick and fast for TESS.
It is three times bigger than Earth, which classes it as a Sub-Neptune exoplanet, but it is surprisingly 23 times its mass.
Two other planet's spotted by TESS have been labelled LHS 3884b and Pi Mensae c. Since Kepler has shut its operations, NASA is hoping that a new space telescope - Transiting Exoplanet Survey Satellite (TESS), will take charge of the proceedings.
Since it started surveying the sky in July, the MIT-led Transiting Exoplanet Survey Satellite project has identified Pi Mensae b, a "super-Earth" that travels around its star every six days, and LHS 3844b, a rocky world with an orbit of only 11 hours.
Pi Mensae c is about twice the size of Earth and orbits the star Pi Mensae, 60 light-years away in the Mensa constellation. These stars are about 5.1 billion miles apart, and the dimmer one is one-third as massive as the sun. Because TESS is programmed to look at a portion of the sky for only 27 days, any planets with a longer orbit are hard to identify.
Past year at the American Astronomical Society meeting, it was announced that citizen scientists helped discover five planets between the size of Earth and Neptune around star K2-138, the first multiplanet system found through crowdsourcing. This is relatively cool considering its proximity to its star. If confirmed, it could be the smallest TESS planet to date.
TESS is surveying an area in the sky that is 400 times larger than what Kepler observed, including 200,000 of the brightest nearby stars.
TESS's four cameras, designed and built by MKI and MIT's Lincoln Laboratory in Lexington, Massachusetts, spend almost a month monitoring each observing sector, a single swath of the sky measuring 24 by 96 degrees. "We're only halfway through TESS's first year of operations, and the data floodgates are just beginning to open", he said. It is the longest-period transiting planet within 100 light-years of the solar system, and it has the coolest surface temperature of a transiting exoplanet around a star brighter than 10th magnitude, or about 25 times fainter than the limit of unaided human vision.
Those researchers had also detected a signal, but they couldn't conclusively attribute it to a planet, Dragomir said. Those planets could be the best candidates for supporting life outside our solar system. It lies within its host star's habitable zone, which means the planet may have liquid water on its surface.
Feinstein and Makennah Bristow, an undergraduate student at the University of North Carolina Asheville, worked as interns at NASA's Goddard Space Flight Center, searching the data for transits. That telescope, launching in 2021, would be able to characterize the details and atmospheres of exoplanets in ways scientists have not been able to do.