The planet-hunting telescope, particularly focusing on exoplanets that pass between Earth and their home star came across the exoplanet, detecting how it was blocking a small percentage of light of its star.
The planets further out from the star are sub-Neptunes, called so because they have rocky cores and gaseous atmospheres, like our solar system's Neptune.
To find two of these intermediate size planets together is significant for astronomers because worlds like this provide the "missing link" when it comes to understanding planetary formation.
The other two, TOI-270 c and TOI-270 d, are icy, gas-dominant sub-Neptunes that are about twice the size of Earth. Insets show information about the planets, including their relative sizes, and how they compare to Earth.
TESS Object of Interest 270 is a faint, cool star more commonly recognized by its catalog name: UCAC4 191-004642.
The sub-Neptune that's farthest from its star appears to be within its habitable zone, meaning the planet is just the right distance away to hold liquid water. The planet is so close to its host star that it only has a 5.36 day-long orbit.More news: Nokia 9.1 PureView with 5G, Better Light Cameras Rumored for Q4, 2019
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'That's a very interesting thing, because it lets us study their dynamical behaviour'. As these are planet candidates they have yet to be confirmed as real, but the authors are confident that based on data from the multi-planet systems, most if not all of the candidates will be actual exoplanets once follow up investigations are complete.
While it takes pictures of the comets, supernovae, and stellar flares it sees along the way, TESS's main objective is to observe star brightness within that small chunk of the sky, looking for telltale periodic dimming that could suggest there's a planet orbiting around it. Researchers hope that TESS will monitor 85 percent of the sky over its two-year mission.
The satellite looks for dips in light that can betray the presence of a planet passing - or "transiting" - in front of its host star.
Illustration of NASA's Transiting Exoplanet Survey Satellite.
Maximilian Günther, a postdoc in MIT's Kavli Institute for Astrophysics and Space Research said, "There are a lot of little pieces of the puzzle that we can solve with this system". "It is an exceptional laboratory for not one, but many reasons - it really ticks all the boxes".
The details of the new planetary system are reported in the Nature Astronomy.
Researchers report finding a new exoplanet orbiting a three-star system.
Then, the following year, it will scour the northern sectors. With Hubble's successor, the James Webb Space Telescope due to be launched in 2021, astronomers are already making a list of targets they'd like it to study.