Scientists in awe of ‘vigorous, diverse’ Pluto
Details of research mission to Pluto published in journal
In July, NASA’s New Horizons successfully completed a historic flyby of Pluto, beaming back jaw-dropping images of the dwarf planet in the process. But the spacecraft has much more to offer than pretty pictures. On Thursday, the New Horizons team published its first scientific results in the journal Science.
Researchers were astonished by the data downlinked to Earth.
“It’s a vigorous and diverse world that is active today,” said William McKinnon, a professor of earth and planetary sciences at Washington University in St. Louis and deputy lead for the New Horizons Geology, Geophysics and Imaging team. Nitro-bergs Pluto has a giant plain, full of volatile ices — nitrogen ice, mostly, but also methane and carbon monoxide ice — known as the Sputnik Planum. Part of the plain, stamped with a cellular pattern, seems to be flowing, churning nitrogen glaciers. The plain is ringed by clumpy hills and mountains, a rugged landscape of water ice, and these may even be floating in the frozen nitrogen sea — an extraterrestrial dreamscape that awed researchers. “It’s a phenomenon we’ve never seen in the solar system,” McKinnon said. Charon Scientists would have been happy to see a few interesting features on Pluto’s big moon, Charon: some craters or fault lines that would help reveal its history. Instead, they got a violent smorgasbord. The moon is blistered with canyons, craters and landslides, and “the whole thing is basically split open,” McKinnon said — an entire half of the moon looks to have been resurfaced, with smoother, younger features. What prompted Charon’s unexpected upheaval? One possibility is “cryovulcanism,” icy lavas that split the surface as a vast internal ocean froze. Hazy days As New Horizons flew into Pluto’s shadow, it turned backward and captured the dwarf planet backlit by the sun. The blue halo we see is light scattering off haze particles in Pluto’s atmosphere, and its colour and brightness offer clues about the particles’ size and composition, says Michael Summers, a planetary scientist at George Mason University and deputy lead on New Horizons’ atmospheres team. Blue suggests the haze is made of very small particles. One theory is that the particles are forming very high up in the atmosphere and, as they fall, undergoing a series of reactions, becoming carbon-rich. “It’s like a very thin mist that keeps falling onto the surface,” Summers said. This material building up over time may account for Pluto’s reddish-brownish hue and its tar-coloured patches. Atmospheric shrinkage Results from REX, a radio instrument, have hinted that Pluto’s atmospheric pressure is unexpectedly dropping. The icy dwarf planet has a much more elliptical orbit around the sun than Earth: perhaps the spacecraft arrived as the atmosphere began to freeze. “We may have gotten to Pluto just as it is beginning to catastrophically condense onto the surface. We’re not sure of that, but that’s what appears to be happening,” Summers said. Snakeskin terrain To the east of the Sputnik Planum is a region of strangely patterned, undulating “snakeskin” terrain: linear ridges with what look like blades of ice. “We’re still talking about how we think they might be made. It’s certainly one of the more striking images we got back from the spacecraft,” McKinnon said. The snakeskin area, known as the Tartarus Dorsa, is actually not discussed in the Science paper, because pictures of it beamed back after the manuscript had been submitted: new information is still coming in thick and fast from New Horizons. What’s next The spacecraft will stop returning data temporarily while it turns on its thrusters and scoots further out in the Kuiper Belt, the icy region beyond our planetary system, where New Horizons will observe a new object. “We should expect to see this kind of activity . . . on other dwarf planets in the Kuiper Belt. The fun doesn’t stop when you get far away from your parent star,” McKinnon said.
Downlinking all the data will take many more months after that, and exciting results are still streaming in, the team says. The very highest-resolution photos are beginning to arrive now. “Just stay tuned,” Summers said.