NASA's TESS Spots a 2nd Earth-Size Planet that may Retain Liquid Water

Astronomers 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 (TESS). The planet likely consists of rocks and is 95% the size of Earth, as per NASA's report.

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.

However, it took researchers another year of TESS observations to find TOI 700 e.

"This is one of only a few systems with multiple, small, habitable-zone planets that we know of," Emily Gilbert, leader of the study and a postdoctoral fellow at NASA's Jet Propulsion Laboratory, said in a statement.

Dwarf Star

NASA said that the tiny, cool M dwarf star TOI 700 can be found in the southern constellation Dorado at a distance of about 100 light-years.

Gilbert and others reported the finding of three planets in 2020, including the Earth-sized, habitable-zone planet d, which is in a 37-day orbit.

TOI 700 b, the innermost planet, 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.

NASA noted that these planets are likely to be tidally locked, suggesting that they rotate just once per circle so that one side always faces the star.

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.

This approach allowed the mission to observe the southern sky beginning in 2018 before moving on to the northern sky. It returned to the southern sky in 2020 to conduct additional observations.

The team's initial estimates of the sizes of the planets were improved by around 10% thanks to the additional year of data.

Optimistic Habitable Zone

Planet e is situated between planets c and d in the so-called optimistic habitable zone since TOI 700 spends 28 days orbiting its star.

The optimistic habitable zone, according to scientists, is the range of distances from a star where liquid surface water might have existed on a planet.

The conservative habitable zone, the region where scientists believe liquid water might last for the majority of the planet's lifespan, includes this region as well as both sides of it. TOI 700 d orbits in this region.

NASA explains that planetary scientists can learn more about the past of our solar system by locating other systems in this region that have Earth-sized planets.

According to Gilbert, further research into the TOI 700 system using both ground- and space-based observatories is ongoing and could provide new information about this unusual system.