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Physical Chemistry

New Horizons Up-Close Photos Reveal Geological Details About Pluto

Planetary Science: Photos taken by spacecraft show that the planet and its moon Charon are geologically active

by Elizabeth K. Wilson
July 16, 2015 | APPEARED IN VOLUME 93, ISSUE 29

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Credit: NASA/JHU/APL/Southwest Research Institute
During the Pluto flyby, the New Horizons spacecraft sent back images of water ice mountains on the dwarf planet’s surface.
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Credit: NASA/JHU/APL/Southwest Research Institute
During the Pluto flyby, the New Horizons spacecraft sent back images of water ice mountains on the dwarf planet’s surface.

The NASA spacecraft New Horizons performed a historic, close-up flyby of the dwarf planet Pluto on July 14, after a 3 billion-mile journey that took nearly 10 years.

[+]Enlarge
Credit: NASA/JHU/APL/Southwest Research Institute
The New Horizons spacecraft sent back an image of Pluto in unprecedented detail, just before its close flyby.
09329-notw2-PLORRIcxd.jpg
Credit: NASA/JHU/APL/Southwest Research Institute
The New Horizons spacecraft sent back an image of Pluto in unprecedented detail, just before its close flyby.
[+]Enlarge
Credit: NASA/JHU/APL/Southwest Research Institute
New Horizons shows Pluto’s large moon Charon’s cliffs, troughs, and a large dark spot.
09329-notw2-charon.jpg
Credit: NASA/JHU/APL/Southwest Research Institute
New Horizons shows Pluto’s large moon Charon’s cliffs, troughs, and a large dark spot.

Telescopes, including NASA’s Hubble Space Telescope, have never been able to observe Pluto as much more than a smudgy ball. Now, pictures snapped as the craft flew 7,750 miles above the planet’s surface are providing incredible details of Pluto, indicating that it and its large moon Charon are geologically active.

Instead of being pockmarked by impact craters, large surface areas on Pluto and Charon appear remarkably smooth, having been coated by some as-yet-unknown process.

The discovery is significant because it implies that these two distant icy bodies have a heat source driving geological activity. In all other cases of smooth-surfaced icy bodies, such as Neptune’s moon Triton, heat is produced by tidal forces caused by the gravity of a nearby giant planet. In the case of tiny Pluto, there can be no tidal heating.

“This is going to send a lot of geophysicists back to drawing boards,” Alan Stern, the mission’s principal investigator, said at a briefing July 15.

Pluto also features 11,000-foot-high mountain ranges made of water ice. Scientists have known that Pluto’s surface is covered in methane and nitrogen ice. However, “you can’t make mountains out of that stuff,” said deputy team leader John Spencer. “It doesn’t have the strength.”

Water ice, on the other hand, does. But how these mountains formed is a mystery.

The Pluto mission, led by Johns Hopkins University Applied Physics Laboratory and NASA, also marks the completion of humankind’s robotic tour of the solar system: Spacecraft have finally visited every planet.

New Horizons is speeding away from Pluto, but over the next 16 months it will send back the data it took during the flyby. The team plans to continue releasing data and images over the coming weeks. “I don’t think any one of us could have imagined that it was this good of a toy store,” Stern said of the mission.

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