"It's a very exciting discovery due to how it was found, its temperate orbit and because planets of this size seem to be relatively uncommon", said Adina Feinstein, a University of Chicago graduate student in astrophysics and lead author of a paper describing the new planet that was accepted for publication by The Astronomical Journal. Its discovery was announced by scientists at the annual American Astronomical Society meeting in Seattle.
"It's the coolest small planet that we know of around a star this bright", Dr Dragomir said. As hot as that is, it's cool considering the proximity to the host star, which is said to be nearly as bright as the sun.
According to NASA, the planet, named HD 21749b, is about three times Earth's size and 23 times its mass. But the gas that makes it up it is probably more dense than that of Uranus or Neptune. "The planet likely has a density of water or a thick atmosphere".
Currently, the team is investigating a second planet in the system with a shorter 7.8-day orbit. Like NASA's recently deceased Kepler space telescope, which is responsible for about 70 percent of all known exoplanet discoveries to date, TESS uses the "transit method". Compared to the Sun, the larger of the two stars in the binary system is around half as massive, while the smaller is only about one-third as massive.
The stellar system has two dim, cool M-type stars about 5.1 billion miles apart, which is about six times the distance between Saturn and the sun. It's probably a "lava world", Huang said, given how close some of the planet's rocky surface is to its star.
Less than a year after NASA's TESS spacecraft was launched, the scientists behind the mission have unveiled their third confirmed planet, a weird alien world that's between Earth and Neptune in size. If confirmed, it could be the smallest TESS planet to date.More news: Trump said to want China trade deal to boost stock market
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During this initial survey, TESS also witnessed six supernova explosions that it recorded before ground-based telescopes ever saw them.
"Some of the most interesting science occurs in the early days of a supernova, which has been very hard to observe before TESS", said Michael Fausnaugh, a TESS researcher at MKI. Indeed, HD 21749b is very far-flung for TESS; two other smallish worlds found by the mission have orbital periods of 11 hours and 6.3 days, respectively.
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.
TESS is in the process of scanning the entire southern sky, after which it will turn and canvass the northern sky. The planet orbits a binary star system consisting of two stars that are smaller than our own Sun. If the light "dips", momentarily decreasing in brightness, it suggests that a planet may be orbiting the star.
"This is only the ninth system discovered containing six or more planets", he said.
If you think scientists aren't the most imaginative bunch when it comes to naming things, then think again because boffins over in the States think they may have discovered a 'super Earth'.