NASA's planet hunting probe TESS has discovered a third exoplanet outside our Solar System.
Dubbed HD 21749b, it is described as a "sub-Neptune" exoplanet but is about three times the size of the Earth.
According to Scientists, HD 21749b orbits a dwarf star which lies 53 light-years away in the Reticulum constellation. HD 21749b is more likely to be made of gas rather than being a rocky planet. It is also thought to have an atmosphere denser than the atmospheres of Neptune or Uranus.
"We think this planet wouldn't be as gaseous as Neptune or Uranus, which are mostly hydrogen and really puffy," said Diana Dragomir, a post-doctoral student at the Kavli Institute for Astrophysics and Space Research at the Massachusetts Institute of Technology. Diana Dragomir is also the lead researcher of the study.
"The planet likely has a density of water, or a thick atmosphere," she added.
The orbital period of HD 21749 appears to be the longest of all three exoplanets spotted by TESS so far. HD 21749 completes one revolution around its host star in 36 days. In comparison, exoplanet Pi Mensae b completes one circle around its star in 6.3 days, while another exoplanet, labelled LHS 3844b, has an orbital period of just 11 hours.
The surface temperature of HD 21749 is estimated to be around 149 degrees Celsius. "It's the coolest small planet that we know of around a star this bright," Dragomir said.
The team also found evidence of another planet in the same system. However, its presence is yet to be finally confirmed. It is estimated to have an orbital period of 7.8 days, and could be the first Earth-sized exoplanet discovered by TESS outside our Solar System.
TESS satellite was launched in April 2018 and has been working as the successor to NASA's planet-hunting spacecraft Kepler, which ran out of fuel in October.
Before ending its scientific mission, Kepler helped astronomers discover thousands of exoplanets outside the Solar System. Kepler searched one specific patch of sky at all times to discover as many exoplanets as possible.
In comparison, TESS monitors the sky, sector by sector, and tries to spot momentary dips in the light of nearby stars. TESS is looking for exoplanets sitting close to Earth. Such planets are relatively easier to study and can be analysed using different telescopes.
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