System with two small worlds in habitable zone at 100 light years

In this illustration, the recently discovered Earth-sized planet TOI 700 e orbits in the habitable zone of its star. Its Earth-sized brother, TOI 700 d, can be seen in the distance. -NASA/JPL-CALTECH/ROBERT HURT.

Observations with NASA’s TESS satellite have revealed a second small world — 95% the size of Earth and probably rocky — in the habitable zone of a star 100 light-years away.

TOI 700 e is located at a distance where there could be liquid water on the surface of a planet. It is the same case of TOI 700 d, to which are added two other planets outside the habitable zone. “This is one of the few systems with multiple small planets in the habitable zone that we know of,” said Emily Gilbert, a postdoctoral researcher at NASA’s Jet Propulsion Laboratory who led the work. This makes the TOI 700 system an interesting additional follow-up possibility.” Planet e is about 10% smaller than planet d, so the system also shows how additional TESS observations help us find worlds every time. More smalls.”

After a year of searching, Gilbert presented the result on behalf of his team at the 241st meeting of the American Astronomical Society in Seattle. The Astrophysical Journal Letters accepted a paper on the newly discovered planet. 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 and habitable 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 2.5 times larger than Earth and completes one orbit every 16 days. The planets are likely tidally locked, meaning that they rotate only once per orbit, so that one side always faces the star, just as one side of the Moon always faces Earth. . TESS observes large swaths of the sky, called sectors, for about 27 days at a time. These long gazes 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 returning 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 10% smaller than initial estimates.

“If the star were a little closer or the planet was a little bigger, we could have detected TOI 700 e in the first year of TESS data,” explains Ben Hord, a PhD candidate at the University of Maryland in College Park and a researcher at the NASA Goddard Space Flight Center in Greenbelt, Maryland. “But the signal was so weak that we needed the extra year of transit observations to identify it.” TOI 700 e, which could also be tidally locked, takes 28 days to orbit its star, putting planet e between planets c and d in the so-called optimistic habitable zone. Scientists define the optimistic habitable zone as the range of distances to a star in which liquid water could exist on the surface at some point in a planet’s history. This zone straddles the conservative habitable zone, the range in which the researchers hypothesized liquid water could exist for most of the planet’s lifetime. TOI 700 d orbits in this region.