A newly discovered exoplanet is really making astronomers prove their mettle. Planet GJ 367b is smaller than Earth, denser than iron and hot enough to melt, researchers report in the Dec. 3 Science.
“We think the surface of this exoplanet could be molten,” says astronomer Kristine Wei Fun Lam of the Institute of Planetary Research at the German Aerospace Center in Berlin.
Signals of the planet were first spotted in data from NASA’s TESS telescope in 2019. The small world swung around its host star every 7.7 hours.
Using data from TESS and the ground-based HARPS spectrograph at the European Southern Observatory in Chile, Lam and her colleagues measured the planet’s radius and mass. GJ 367b clocked in at about 0.72 times Earth’s radius and 0.55 times its mass. That makes it the first ultrashort-period planet — a class of worlds with years shorter than one Earth day and with mysterious origins — known to be smaller and lighter than Earth.
Using those measurements, the team then calculated the planet’s density: about 8.1 grams per cubic centimeter, or slightly denser than iron. A computer analysis of the planet’s interior structure suggests that 86 percent of it could comprise an iron core, with only a sliver of rock left on top.
Mercury has a similarly large core, Lam notes (SN: 4/22/19). Scientists think that’s a result of a giant impact with another planet that stripped away most of its outer layers. GJ 367b could have formed after a similar collision. It could also have once been a gaseous planet whose atmosphere was blasted off by radiation from its star (SN: 7/1/20).
Whatever its origins, GJ 367b is so close to its star that it’s almost certainly covered in melted metallic lava now. “At 1400° Celsius, I don’t think it would be very nice to stand on it,” Lam says.While a flurry of missions crowded around Mars this year, some lesser-explored parts of the solar system are about to get fresh eyes.
Three countries visited the Red Planet in 2021, sending orbiters, landers, rovers and even a helicopter. The United Arab Emirates successfully put its first interplanetary spacecraft, called Hope, into orbit in February, to study Mars’ climate. China’s Zhurong rover has been trundling around the planet’s surface since May, studying the local geology and searching for underground water ice (SN Online: 5/19/21). And NASA’s Perseverance rover, which landed in February, has been collaborating with a helicopter called Ingenuity to explore an ancient lake bed and collect rocks for a future delivery mission to Earth (SN Online: 2/17/21; SN Online: 4/30/21).But while all eyes were on Mars, other missions are embarking on journeys to study even more far-flung places. After years of delays and billions of dollars over budget, the James Webb Space Telescope is finally set to launch, no earlier than December 25, to probe the universe’s earliest galaxies, among other things (SN: 10/9/21 & 10/23/21, p. 26).
Meanwhile, spacecraft are heading off to visit 11 asteroids in the solar system in search of clues to the origins of the planets, and water and life on Earth, as well as ways to keep our planet safe from errant space rocks.
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