NASA scientists have identified a second Earth-sized exoplanet existing in the habitable zone of its parent star, a small red dwarf named TOI 700.
“Exoplanet” refers to any planet residing outside of our solar system.
NASA discovered this world — dubbed TOI 700 e — using data collected from its Transit Exoplanet Survey Satellite (TESS), which, according to Paul Hertz, a senior advisor to the Associate Administrator of the Science Mission Directorate, “was designed and launched specifically to find Earth-sized planets orbiting nearby stars.”
TESS monitors large portions of the sky for 27 days at a time. This extended look allows the satellite to track changes in stellar brightness caused by transits. Transits occur when a planet or celestial object crosses in front of a star from the perspective of Earth.
Scientists used TESS to observe the southern sky starting in 2018 before turning to the northern sky to complete a two-year survey. The telescope turned its gaze to the southern sky for additional observations in 2020. They used the extra year of data to reassess planet sizes, which were determined to be about 10% smaller than the original measurements.
“If the star was a little closer or the planet a little bigger, we might have been able to spot TOI 700 e in the first year of TESS data,” said Ben Hord, a graduate researcher at NASA’s Goddard Space Flight Center. “But the signal was so faint that we needed the additional year of transit observations to identify it.”
A total of three exoplanets — TOI 700 b, c, and d — had already been identified in this system, with only planet d orbiting the star in the habitable zone.
For a planet to be in the habitable zone of a star, it must be at a distance that allows for the planet to sustain liquid water.
TOI 700 e is actually about 10% smaller than planet d and approximately 95% the size of Earth.
Scientists say that it is most likely a rocky planet that is tidally locked, just like Earth is around the Moon. It takes 28 days to complete an orbit around its star, whereas Earth takes 365 days to orbit the Sun.
“This is one of only a few systems with multiple, small, habitable-zone planets that we know of,” said Emily Gilbert, a postdoctoral fellow at NASA’s Jet Propulsion Laboratory in Southern California, according to NASA.
“That makes the TOI 700 system an exciting prospect for additional follow-up,” she continued.
This system is about 100 light-years away in the constellation Dorado, named in Spanish for its resemblance to the dolphinfish.
So far, NASA has confirmed the existence of over 5,000 exoplanets.