Why scientists are saying the new planet's surface is relatively cool is because its star is nearly as bright as our very own Sun, the team from the Massachusetts Institute of Technology in Boston said. This causes a regular dip in the measured brightness of the star that signals a planet's presence. It's very hard to find small planets that orbit farther from their stars, and are therefore cooler.
"We learned from Kepler that there are more planets than stars in our sky, and now TESS will open our eyes to the variety of planets around some of the closest stars", Paul Hertz, the director of NASA's astrophysics division, said in March 2018.
The new planet is twice the size of Earth.
"We think this planet wouldn't be as gaseous as Neptune or Uranus, which are mostly hydrogen and really puffy", Dragomir says.
"The planet likely has a density of water, or a thick atmosphere", she added. All three planets were discovered in the first three months of TESS observations.
Last year, Feinstein was part of a team which observed two transits - the dimming of a star when a planet passes its surface.
TESS's other discoveries include a super-hot world, LHS 3844 b, that whirls around its star-a red dwarf only 15% the size of the Sun-every 11 hours.
The newly described planet whizzes around its star on a stretched-out orbit once every 36 days, says Xu Chelsea Huang, a TESS scientist at the Massachusetts Institute of Technology (MIT) in Cambridge. HD 21749b lies about 53 light-years from Earth and orbits a star about the the size of the sun. It's so close to its sun that some of its rocky surface could be molten lava during daytime.
They also used data from the Planet Finder Spectrograph, an instrument installed on the Magellan Telescope in Chile, to further validate their findings and constrain the planet's mass and orbit.
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By NASA [Public domain], via Wikimedia CommonsNASA's planet hunting satellite, known as TESS, has unveiled a distant new world which consists of dense materials and gases.
Astronomers also received data of dozens of short-lived events in space and managed to capture images of six supernovae. The telescope has been in orbit 10 years, although was designed for three years.
But the "reboot" of the Kepler mission in 2014 that led to the K2 mission allowed for multiple observation campaigns that brought in even more data.
TESS does this work by carving the sky up into overlapping sectors, studying each one for 27 days at a time.
In its first year of operation, it will map the 13 sectors that make up the southern sky. Such planets are relatively easier to study and can be analysed using different telescopes.
An illustration of NASA's Kepler space telescope.
Pi Mensae c is roughly twice Earth's size and can be seen in the Mensa constellation with the naked eye.
While impressive, it does not appear the planet has the attributes required to support life as a habitable world.
Even though the Kepler spacecraft ceased operations months ago, after almost a decade in service, its legacy continues: Today, researchers announced that they have found a planet roughly twice as big as Earth, located within what could be its parent star's habitable zone. 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.