The first Earth-sized planet in a habitable zone discovered by an...

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

The Center for Astrophysics’ astronomers Joseph Rodriguez, Laura Kreidberg, Karen Collins, Samuel Quinn, Dave Latham, Ryan Cloutier, Jennifer Winters, Jason Eastman, and David Charbonneau were among the teams that studied TOI-700d, one of three small planets orbiting an M-dwarf star (its mass is 0.415 solar masses) is located one hundred and two light years from Earth. The TESS data analysis revealed that the preliminary sizes of the planets are roughly Earth-sized, 1.04, 2.65 and 1.14 earth radii, and their orbital times 9.98, 16.05 and 37.42 days, respectively. In our solar system, Mercury orbits the sun in about 88 days; It’s so close to the sun that its temperature can reach over 400 degrees Celsius. But because this M dwarf star is comparatively cool, it places the orbit of its third planet, even though it is much closer to the star than Mercury is to the Sun, in the habitable zone – the region where temperatures allow surface water (if any) staying fluid when there is also an atmosphere. This makes this earth-sized planet TOI-700d particularly interesting as a potential host for life.

The TESS detections were exciting but uncertain: the signals were weak and there was a small possibility that the TOI-700d detection was wrong. Because of the potential importance of finding a nearby Earth-sized planet in a habitable zone, TESS scientists turned to the IRAC camera at the Spitzer Space Observatory for confirmation. Before the IRAC camera was shut down by NASA in February 2020, it 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 and received unambiguous detections of the planets with about twice the signal-to-noise ratio of TESS, which is enough to improve the planet’s orbit by 61% and increase it significantly improve refine our knowledge of its other properties, refine the radius as above and find that the mass is 2.1 earth masses. The results, especially when compared to the properties of other planets, suggest that this planet may be rocky and likely to be “tide-locked” with one side of the planet always facing the star.

If there were liquid water on the surface of the TOI-700d, the astronomers believe there would also be aquatic clouds in the atmosphere, and the team is using climate system models to estimate the possible properties and potentially more sensitive measurements. However, they conclude that upcoming space missions, including JWST, are likely not sensitive enough to detect atmospheric features by a factor of ten or more. Their detailed climate studies will nonetheless help astronomers narrow down the types of telescopes and instruments needed to study this exciting new neighbor.

The rediscovery of the “lost” world is a step on the way to habitable planets

Provided by the Harvard-Smithsonian Center for Astrophysics