NASA satellite touts 'surprising find of promising world' 31 light-years away - MLive.com

Shortly after announcing a “hat trick of discoveries,” NASA’s newest planet-hunting satellite is back at it with a “surprising find of a promising world.”

The latest finding from the Transiting Exoplanet Survey Satellite -- commonly known as TESS -- comes in the form of a planet in the habitable zone of star GJ 357.

NASA reports that planet GJ 357 d could be about twice Earth’s size “if made of rock” and in a system 31 light-years away in the constellation Hydra. As for star GJ 357, the space agency reports it is thought to be 40 percent cooler than our sun.

“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,” Diana Kossakowski, co-author of a paper detailing the findings, says in a NASA news release.

“If the planet had 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.”

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The space agency says that back in February it noted the star dimming every 3.9 days “revealing the presence of a transiting exoplanet.” A transiting exoplanet is a planet beyond our solar system that passes across the face of its star.

NASA reports that the transits it observed earlier this year were found to originate from planet GJ 357 b. This planet is said to be 22 percent larger than Earth and is described as a “hot Earth” that orbits 11 times closer to its star than Mercury does to ours.

As for GJ 357 d, the space agency says that without an atmosphere its equilibrium temperature read at minus 64 degrees. This makes officials believe the world is “more glacial than habitable."

The planet is believed to weigh about 6.1 times than that of the Earth, and that it orbits its star every 55.7 days.

NASA also discovered a middle planet -- GJ 357 c --, which is believed to be 3.4 times the size of Earth and that it orbits its star every 9.1 days. TESS officials say they did not pick up any transits from this world “so it never passes across the star from our perspective.”

“In a way, these planets were hiding in measurements made at numerous observatories over many years,” Rafael Luque, doctoral student at Institute of Astrophysics of the Canary Islands, who NASA said led the discovery team, said in the release.

“It took TESS to point us to an interesting star where we could uncover them.”

While TESS is an additional attempt to add more exoplanet candidates to its database, NASA’s Kepler space telescope has observed more than 300,000 stars and found more than 4,000 exoplanet candidates since it launched in 2009.

The space agency says more than a dozen universities, research institutes and observations are active in the TESS mission.

“To confirm the presence of GJ 357 b and discover its neighbors, Luque and his colleagues turned to existing ground-based measurements of the star’s radial velocity, or the speed of its motion along our line of sight,” the space agency writes in the release.

“An orbiting planet produces a gravitational tug on its star, which results in a small reflex motion that astronomers can detect through tiny color changes in the starlight. Astronomers have searched for planets around bright stars using radial velocity data for decades, and they often make these lengthy, precise observations publicly available for use by other astronomers.”

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