An artist's conception shows NASA's Transiting Exoplanets Survey Satellite, or TESS, with an assortment of exoplanets.
Known to scientists as HD 21749b, it is a mere 53 light-years from Earth in the southern constellation of Reticulum.
Scientists said the system may hold an additional planet that is about the size of Earth that has an orbit of only eight days.
George Ricker, the mission's principal investigator at MIT, predicted that there will be many more discoveries to come as the team is "only halfway through Tess's first year of operations and the data floodgates are just beginning to open".
"It's a very exciting discovery due to how it was found [and] its temperate orbit and because planets of this size seem to be relatively uncommon", Adina Feinstein, a University of Chicago graduate student and lead author of the study, said in the statement.
"This star was already known to host a planet, called Pi Mensae b, which is about 10 times the mass of Jupiter and follows a long and very eccentric orbit", said Chelsea Huang, a Juan Carlos Torres Fellow at the Massachusetts Institute of Technology's (MIT) Kavli Institute for Astrophysics and Space Research (MKI) in Cambridge.
"It's the coolest small planet that we know of around a star this bright", Dragomir said. The recently discovered world is categorized as a "sub-Neptune", about three times larger than Earth but approximately 23 times as massive.
However, it is unlikely that the planet is rocky and therefore habitable; it's more likely made of gas, of a kind that is much more dense than the atmospheres of either Neptune or Uranus.
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There is also evidence that a second planet could exist in this system with a 7.8-day orbit - which could be the first Earth-size planet dicovered by TESS.
Tess monitors sections of the sky and waits for momentary dips in the light of about 200,000 nearby stars, likely to be a sign that a planet has passed in front of that star. Feinstein presented the find January 7 at the American Astronomical Society's winter meeting in Seattle.
HD 21749b completes one orbit of its host star, which is almost as bright as our sun, every 36 Earth days. To put it in context, Michael Fausnaugh, a pipeline scientist on TESS, discussed this in comparison to NASA's now defunct Kepler telescope. Because TESS stares non-stop at one slice of the sky for 27 days, then moves to a neighbouring slice, it captures an unprecedented view of these exploding stars as they brighten and then dim.
NASA's Kepler space telescope is dead.
Tess is 5 feet (1.5 meters) wide and is shorter than most adults.
In addition to observing exoplanets, TESS has spotted many other types of astronomical phenomena, including comets and asteroids, flare stars and mutually eclipsing binary stars, white dwarf stars and supernovae.
By studying objects much brighter than the Kepler targets, it's hoped TESS could uncover new clues on the possibility of life elsewhere in the universe.
An illustration of NASA's Kepler space telescope.
Follow-up observations were made with multiple telescopes to confirm the exoplanet.