TOI 700 is a small, cool M dwarf star located about 100 light-years away in the southern constellation of Dorado. In 2020, Gilbert and others announced the discovery of the Earth-sized, habitable-zone planet d, which is in a 37-day orbit, along with two other worlds.
The innermost planet, TOI 700 b, is about 90% the size of Earth and orbits the star every 10 days. TOI 700 c is more than 2.5 times larger than Earth and completes one orbit every 16 days. The planets are likely tidally locked, meaning they rotate only once per orbit, so that one side always faces the star, just as one side of the Moon always rotates toward Earth.
TESS monitors large swaths of the sky, called sectors, for about 27 days at a time. These long looks allow the satellite to track changes in stellar brightness caused by a planet crossing in front of its star from our perspective, an event called a transit. The mission used this strategy to observe the southern sky beginning in 2018, before moving to the northern sky. In 2020, it returned to the southern sky for additional observations. The additional year of data allowed the team to refine the original sizes of the planets, which are about 10% smaller than initial estimates.
“If the star were a little closer or the planet a little bigger, we could have detected TOI 700 e in the first year of TESS data,” said Ben Hord, a PhD candidate at the University of Maryland, College Park and a researcher. graduate of NASA Goddard Space Flight Center in Greenbelt, Maryland. “But the signal was so weak that we needed an additional year of transit observations to identify it.”
