NASA has announced that TESS (Transiting Exoplanet Survey Satellite) has discovered a third “small” planet outside our solar system. The announcement was made by scientists this week, and the new planet is called HD 21749b. The planet orbits a bright dwarf star that is about 53 light-years away in the constellation Reticulum.
HD 21749b has the longest orbit of the three planets that TESS has discovered so far making a trip around its host star once every 36 days. That is fast by Earth standards, but the other two planets include Pi Mensae b with a 6.3-day orbit and LHS 3844b that orbits its star at a blistering pace of once every 11 hours. These three planets were all discovered in the first three months of TESS observations.
Scientists estimate that the surface of HD 21749b is around 300 degrees Fahrenheit. As hot as that is, it’s cool considering the proximity to the host star, which is said to be almost as bright as the sun. Project member Diana Dragomir says that this is the coolest small planet known around a star this bright.
Calling the planet small is a bit misleading, the team says that HD 21749b is about three times the size of Earth placing it into the sub-Neptune category. Despite being only three times as large as the Earth, the planet is said to be 23 times as massive.
Scientists don’t think that the planet is rocky, they believe that it is most likely made of gas of the sort that is much denser than the atmosphere of Neptune or Uranus, it’s not believed to be habitable. Currently, the team is investigating a second planet in the system with a shorter 7.8-day orbit.