Charon: a beautiful world with a violent past
This week, newly released data from NASA’s New Horizons spacecraft has put Pluto’s largest moon, Charon, in the spotlight – revealing it to be a colorful and beautiful world that had experienced a violent past.
The findings surprised scientists, who expected to find a largely dead, cratered moon in the distant outer Solar System but instead found themselves viewing a world more active than Earth’s moon.
Charon is 754 miles (1,214 km) across, half the diameter of Pluto, making it the largest moon in the Solar System relative to its parent planet. Rather than orbit Pluto, it and Pluto orbit a center of gravity between them, known as a barycenter. Both worlds are tidally locked to one another and always present the same face to their companion.
Many scientists consider Pluto-Charon a binary dwarf planet system rather than a dwarf planet and moon.
The latest high-resolution images sent back by New Horizons, taken on July 14, show a landscape with diverse terrains, including mountains, valleys, canyons, landslides, and color variations.
Most prominent is a giant canyon more than 1,000 miles across, stretching over the entire visible face of Charon, possibly extending even over its far side. Four times as long and twice as deep as Earth’s Grand Canyon, it indicates the large moon at one time endured major geologic upheaval.
“It looks like the entire crust of Charon has been split open,” said mission Geology, Geophysics, and Imaging (GGI) deputy lead John Spencer of Boulder, Colorado’s Southwest Research Institute.
Spencer compared Charon’s system of canyons to the large Valles Marineris system on Mars.
North of the moon’s equator lies a belt of fractures and more canyons.
To the south of the large canyon, in a region informally named Vulcan Planum, are plains with very few craters, made up of smooth terrain and signs of recent geological resurfacing, such as grooves and ridges.
Mission scientists are uncertain as to the cause of this smooth terrain. One possibility is cryovolcanism, triggered by the freezing of what was once a subsurface liquid ocean.
The pressure generated by underground water freezing to ice could have generated surface cracks, through which water-based lava was ejected onto the surface.
“The team is discussing the possibility that an internal water ocean could have frozen long ago, and the resulting volume change could have led to Charon cracking open, allowing water-based lavas to reach the surface at that time,” explained mission team member Paul Schenk of Houston’s Lunar and Planetary Institute.
In terms of color, Charon’s most striking feature is its reddish north polar cap, informally named Mordor Macula. It has a diameter of 754 miles (1,214 km); the new images sent back by New Horizons show features as small as 1.8 miles (2.9 km).
These latest images were taken by New Horizons’ Long Range Reconnaissance Imager (LORRI) and its Ralph/Multispectral Imaging Camera from a distance of 7,750 miles (12,500 km).
Mission team members used the images to create a video simulating a flyover of Charon.
“We thought the possibility of seeing such interesting features on this satellite of a world at the far edge of the Solar System was low, but I couldn’t be more delighted with what we see,” said GGI affiliate Ross Beyer of the SETI Institute and the NASA Ames Research Center.
Better images with higher resolution and more composition data are still awaiting download from the spacecraft.
Project scientist Hal Weaver of the Johns Hopkins University Applied Physics Lab in Laurel, Maryland, is eagerly looking forward to seeing them.
“I predict Charon’s story will become even more amazing,” he said.
Video Courtesy of NASA
Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.