NASA's Transiting Exoplanet Survey Satellite (TESS), a mission designed to comb the heavens for exoplanets, has discovered its first potentially habitable world outside of our own solar system - and an international team of astronomers has characterized the super-Earth, about 31 light-years away.

In a new paper in the Astrophysical Journal Letters, a team led by Lisa Kaltenegger, associate professor of astronomy and director of Cornell's Carl Sagan Institute, models the conditions under which the planet - discovered in early 2019 - could sustain life.

"This is exciting, as this is humanity's first nearby super-Earth that could harbor life - uncovered with help from TESS, our small, mighty mission with a huge reach." said Kaltenegger.

As this super-Earth exoplanet is more massive than our own blue planet, Kaltenegger said this discovery will provide insight into Earth's heavyweight planetary cousins. "With a thick atmosphere, the planet GJ 357 d could maintain liquid water on its surface like Earth and we could pick out signs of life with upcoming telescopes soon to be online," she said.

Astronomers from the Institute of Astrophysics of the Canary Islands and the University of La Laguna, both of Spain, announced the discovery of the system July 31 in the journal Astronomy and Astrophysics. They showed that the distant solar system - with a diminutive M-type dwarf sun, about one-third the size of our own Sun - harbors three planets, with one of those in that system's habitable zone: GJ 357 d.

Last February, the TESS satellite observed that the dwarf sun GJ 357 dimmed very slightly every 3.9 days, evidence of a transiting planet moving across the star's face. That planet was GJ 357 b, a so-called "hot Earth" about 22 percent larger than Earth, according to the NASA Goddard Space Flight Center, which guides TESS.

Follow up observations from the ground led to the discovery of two more exoplanetary siblings: GJ 357 c and GJ 357 d. The international team of scientists collected Earth-based telescopic data going back two decades - to reveal the newly found exoplanets' tiny gravitational tugs on its host star, according to NASA.

Exoplanet GJ 357 c sizzles at 260 degrees Fahrenheit, and has at least 3.4 times Earth's mass. However, the system's outermost known sibling planet - GJ 357 d, a super-Earth - could provide conditions just like on Earth and orbits the dwarf star every 55.7 days at a distance about 20 percent of Earth's distance from the Sun. It is not yet known if this planet transits its sun.

Kaltenegger, doctoral candidate Jack Madden and undergraduate student Zifan Lin simulated light fingerprints, climates and remotely detectable spectra for the planet, which could range from a rocky composition to a water world.

Madden explained that investigating new discoveries provides an opportunity to test theories and models. "We built the first models of what this new world could be like," he said. "Just knowing that liquid water can exist on the surface of this planet motivates scientists to find ways of detecting signs of life."

Research Report: "The Habitability of GJ 357d: Possible Climates and Observability"

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