The first habitable zone, Earth-sized planet, discovered with a spacecraft for detecting exoplanets

TESS, the Transiting Exoplanet Survey Satellite, was launched in 2018 with the aim of discovering small planets around the Sun’s closest neighbors, stars bright enough to allow follow-up characterization of their planets’ masses and atmospheres. TESS has so far discovered seventeen small planets around eleven nearby stars that are M dwarfs, stars smaller than the Sun (less than about 60% of the Sun’s mass) and colder (surface temperatures below about 3900 Kelvin). In a series of three articles that appeared together this month, astronomers report that one of these planets, TOI-700d, is the size of Earth and is also in the habitable zone of its star; they also discuss its possible climate.

Center for Astrophysics astronomers Joseph Rodriguez, Laura Kreidberg, Karen Collins, Samuel Quinn, Dave Latham, Ryan Cloutier, Jennifer Winters, Jason Eastman and David Charbonneau were part of the teams that studied TOI-700d, one of three small planets in orbit. around a dwarf M. star (its mass is 0.415 solar masses) located one hundred and two light years from Earth. Analysis of the TESS data found that the provisional dimensions of the planets are approximately the size of the Earth, 1.04, 2.65 and 1.14 Earth radii, respectively, and their orbital periods of 9.98, 16.05 respectively. and 37.42 days. In our solar system, Mercury orbits the Sun in about 88 days; it is so close to the Sun that its temperature can exceed 400 degrees Celsius. But because this dwarf star M is relatively cold the orbit of its third planet, although much closer to the star than Mercury is to the Sun, places it in the habitable zone, the region within which temperatures allow surface water (if any) to remain liquid when there is also an atmosphere. This makes this Earth-sized TOI-700d planet particularly interesting as a potential host for life.

The TESS detections were exciting but uncertain: the signals were weak and there remained a small chance that the TOI-700d detection was spurious. Due to the potential importance of finding a nearby Earth-sized planet in a habitable zone, TESS scientists turned to the Spitzer Space Observatory’s IRAC camera for confirmation. Before being shut down by NASA in February 2020, the IRAC camera was by far the most sensitive near-infrared camera in space. The TESS team observed TOI-700 with IRAC in October 2019 and January 2020, acquiring clear detections of the planets with about twice the signal-to-noise ratio of TESS, enough to give a 61% improvement in orbit. of the planet and significantly refine our knowledge of its other characteristics by refining the radius as above and finding the mass to be 2.1 earth masses. The results, especially when compared to the properties of other planets, suggest that this planet may be rocky and may be “martially locked” with one side of the planet always facing the star.

If there were liquid water on the surface of the TOI-700d, astronomers argue, there would also be water-carrying clouds in the atmosphere, and the team uses models of the climate system to estimate their possible properties and what more sensitive measurements they could find. They conclude, however, that pending space missions, including the JWST, will likely lack the sensitivity to detect atmospheric characteristics by a factor of ten or more. However, their detailed climate studies will help astronomers narrow down the types of telescopes and instruments that will be needed to investigate this exciting new neighbor.