NASA Exoplanet Hunter Finds 'Hot Earth'
For the first time, NASA's Transiting Exoplanet Survey Satellite (TESS) has discovered a distant planet within the zone of potential habitability. The planet is part of a trio orbiting a star known as GJ 357. Known as "GJ 357 d," NASA calls it "especially intriguing."
"This is exciting, as this is TESS's first discovery of a nearby super-Earth that could harbor life—TESS is a small, mighty mission with a huge reach," says Lisa Kaltenegger, associate professor of astronomy, director of Cornell's Carl Sagan Institute, and a member of the TESS science team, in a press statement.
Astronomers confirming a candidate planet found by @NASA_TESS made an exciting discovery when they looked at ground-based observations of its host star — there were two more planets hiding in the data! Meet the planets of the GJ 357 system: https://t.co/fQaGyGLQhI pic.twitter.com/dXtHXt5aOR
— NASA Universe (@NASAUniverse) July 31, 2019
GJ 357 d is around 22 percent larger than Earth, NASA estimates. If the planet was rocky, it would have a mass 6.1 times greater than Earth. It orbits the star every 55.7 days at a range far closer than our own planet's experience, only 20 percent of Earth’s distance from the Sun. So what gives a large planet so close to its star potential habitability?
The size of the GJ 357 star, for one thing. As an an M-type dwarf sun, it's a pipsqueak compared to Earth's sun, around one-third the sun’s mass and size and about 40 percent cooler than our star. That's still plenty hot, but also allows for a sizable habitable zone.
“GJ 357 d is located within the outer edge of its star’s habitable zone, where it receives about the same amount of stellar energy from its star as Mars does from the sun,” says coauthor Diana Kossakowski, of the Max Planck Institute for Astronomy in Heidelberg, Germany, in a press statement. “If the planet has a dense atmosphere, which will take future studies to determine, it could trap enough heat to warm the planet and allow liquid water on its surface.”
There are many unknowns regarding GJ 357 d, including the planet’s exact size and composition, for starters. The planet was discovered with others in the GJ 357 solar system through what are known as "transits," when the planet's orbit places it in between the Earth and its own star, creating a shadow. Telescopes like TESS collect images known as "postage stamps" that capture light from individual stars every two minutes, and wider images every 30 minutes.
These planets are approximately 31 light-years away from Earth. To confirm their existence, NASA looked to existing ground-based measurements of the GJ 357's radial velocity, or the star's speed of motion along our line of sight. Every body in the sky, from Earth's moon to distant planets, exudes its own gravity. The planets orbiting GJ 357 have their own pull on the small star, small reflex motions that scientists can track through tiny alterations in starlight.
Launched in 2018, TESS is NASA's latest satellite to help feed the recent exoplanet boom. Since 1992, scientists have discovered over 4,000 exoplanets, the majority within the last decade. This isn't even the first Earth-like planet that TESS has found.
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