The discovery of the planets was announced by scientists at the annual American Astronomical Society meeting in Seattle, The Guardian reported.
Since the start of the programme in July, the MIT-led Transiting Exoplanet Survey Satellite (TESS) project has discovered Pi Mensae c, a “super-Earth” which travels around its star every six days, and LHS 3844b, a rocky world with an orbit of only 11 hours. The Super-Earth is the second planet discovered in the Pi Mensae system; Pi Mensae b, discovered in 2001, is over ten times more massive than Jupiter.
The latest discovery – HD 21749b, has the longest orbital period of the three 'new' exoplanets, at 36 days. It orbits a bright dwarf star only about 53 light years away in the Reticulum constellation and is thought to have a surface temperature of about 149 Celsius, a relatively cool temperature, considering its proximity to its star.
“It’s the coolest planet we know of around a star this bright. It’s very hard to find small planets that orbit farther from their stars, and are therefore cooler. But here we were lucky, and can now study this one in more detail,” said Diana Dragomir, a Hubble fellow at MIT’s Kavli Institute for Astrophysics and Space Research and the head of the discovery team.
The new planet is 23 times bigger than our own Earth, meaning it highly likely to be gaseous rather than rocky, and it is thought to have an atmosphere more dense than Neptune or Uranus.
“I’m very interested to know whether [it] has an Earth-like density to match its Earth-like radius – this will contribute to our understanding whether Earth-sized planets have diverse compositions or are all roughly similar to Earth”, said Johanna Teske, a co-author of the report.
TESS monitors sections of the sky and waits for momentary flickers in the light of about 200,000 nearby stars – a sign that a planet has passed in front of that star. It is also recording short-lived events such as images of six supernovae in distant galaxies that were later seen by ground-based telescopes.
George Ricker, the mission’s principal investigator at MIT, predicted that there will be many more discoveries to come, as the team is “only halfway through TESS’s first year of operations and the data floodgates are just beginning to open”.