The National Aeronautics and Space Administration (Nasa) which launched Transiting Exoplanet Survey Satellite (Tess) for searching exoplanets in April, 2018 has discovered a third small planet outside our solar system.
Previous 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.
There might be yet another planet that's a bit smaller than Earth and orbits even closer to the star HD 21749, making a complete round every eight days. If confirmed, it could be the first Earth-sized world discovered by TESS.
"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", the lead author of a paper on the discovery, Adina Feinstein said in a NASA news release. 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. "If confirmed, it will be the smallest planet we have found to date", study co-author Chelsea Huang, a colleague of Dragomir's at the MIT Kavli Institute, said today during a briefing at the American Astronomical Society's winter meeting in Seattle. The recently discovered world is categorized as a "sub-Neptune", about three times larger than Earth but approximately 23 times as massive.
"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.
"We think this planet wouldn't be as gaseous as Neptune or Uranus, which are mostly hydrogen and really puffy". The last of these three has astroboffins excited because while it's too hot for life at 150°C (300°F), it could either be a water planet or be home to what Hubble Fellow Diana Dragomir called a "substantial atmosphere".
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It is the third confirmed exoplanet sighted by TESS, with the first being Pi Mensae c, roughly twice Earth's size and visible to the unaided eye in constellation Mensa. If the light "dips", momentarily decreasing in brightness, it suggests that a planet may be orbiting the star. 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.
The discovery is unique for a number of reasons - not least of which is that it was made by amateur astronomers - but the biggest surprise for scientists was its size.
Launched in April 2018 for a two-year mission, Tess will survey almost the entire sky by monitoring and piecing together overlapping slices of the night sky. The exoplanet lies in the stellar system K2-288, which has two dim, cool stars. 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.
These findings are from just the first few sectors TESS has observed in the Southern Hemispheres, beginning in July.
TESS is considered to be a "bridge to the future", finding exoplanet candidates to study in more detail. Using ground-based telescopes, astronomers are now conducting follow-up observations on more than 280 TESS exoplanet candidates.
These exoplanets will be studied so that NASA can determine the best targets for future missions, like the James Webb Space Telescope.