NASA's TESS Finds Second Earth-Size World in Planetary System

Newly discovered planet TOI 700 e orbits a dwarf star. Three other known planets, TOI 700 b, c, and d, are also visible. Credit: NASA/JPL-Caltech/Robert Hurt

January 11, 2023

Scientists have discovered a planet the size of Earth named TOI 700 e that is circling within the habitable zone of its star, or the range of distances where liquid water might exist on a planet's surface. This planet was discovered using data from NASA's Transiting Exoplanet Survey Satellite. It is 95% as big as Earth and probably made of rocks.

The TOI 700 b, c, and d planets were the first three planets in this system to be found by astronomers. The habitable zone is where planet d also revolves. But scientists needed an additional year of TESS observations to discover TOI 700 e. 

The study's lead author, Emily Gilbert, a postdoctoral fellow at NASA's Jet Propulsion Laboratory in Southern California, noted that this is one of the few known systems containing several small, livable planets. As a result, the TOI 700 system presents a promising opportunity for further investigation.The system also demonstrates how additional TESS observations help us discover ever-smaller worlds because planet e is around 10% smaller than planet d. At the 241st meeting of the American Astronomical Society in Seattle, Gilbert delivered the findings on behalf of her team.  The Astrophysical Journal Letters approved a paper on the recently discovered planet.

A tiny, cool M dwarf star called TOI 700 can be found in the southern constellation Dorado at a distance of about 100 light-years. Gilbert and others announced the finding of three planets in 2020, including the Earth-sized, habitable-zone planet d, which is on a 37-day orbit. The innermost planet, TOI 700 b, orbits the star every ten days and is nearly 90% the size of Earth. The orbit of TOI 700 c, which is more than 2.5 times larger than Earth, lasts 16 days. The planets are likely tidally locked, meaning they rotate just once per circle so that one side always faces the star, just as the Moon always faces Earth from one side of its orbit.

TESS observes broad areas of the sky, known as sectors, for around 27 days at a time. These prolonged gazes enable the satellite to monitor variations in stellar brightness brought on by an event known as a transit, in which a planet appears to pass in front of its star from our perspective. Starting in 2018, the expedition followed this plan to investigate the southern sky before moving on to the northern sky. It went back to the southern sky in 2020 to make more measurements. The researchers was able to improve the first planet sizes, which are around 10% smaller than earlier estimations, because to the additional year of data.

Planet e is situated in the so-called optimistic habitable zone between planets c and d on TOI 700 e, which may also be tidally locked. The range of distances from a star where liquid surface water may have existed at some point in a planet's history is what scientists refer to as the optimistic habitable zone. To either side of the conservative habitable zone—the region where scientists believe liquid water might last for the majority of the planet's lifetime—lies this region. This area is where TOI 700 d orbits. Planetary scientists can learn more about the past of our own solar system by discovering other systems in this region that have Earth-sized worlds.

It will be interesting to see what additional information James Webb Space Telescope will find once it gets to observe this planetary system.

Source - NASA