Young crater discovered on Charon; Pluto crescent image released
A crater on the Pluto-facing side of the distant natural satellite Charon is profoundly different from other, older craters on the large moon’s surface – its ammonia-rich composition showing it to be unusually young.
NASA’s New Horizons spacecraft has sent back its highest infrared composition scans of Charon. While studying them, New Horizons mission scientists found that the crater, unofficially named Organa, and surrounding ejected material, known as ejecta, absorbs infrared at wavelengths of 2.2 microns, confirming a composition of frozen ammonia.
In contrast, a nearby crater unofficially named Skywalker is composed primarily of water ice, much like most of the craters on Charon’s surface. Both Organa and Skywalker are about three miles (five km) in diameter. The craters resemble one another in that both are surrounded by thin rays of ejecta, but their appearances are slightly different – Organa’s ejecta has a dark central region.
A map created from data taken by the Ralph/LEISA instrument shows ammonia-rich material extending beyond the crater’s central dark area.
“Why are these two similar-looking and similar-sized craters, so near to each other, so compositionally distinct?” questioned New Horizons Composition team lead Will Grundy of the Lowell Observatory in Flagstaff, Arizona, the site where Pluto was first discovered in 1930.
“We have various ideas when it comes to the ammonia in Organa. The crater could be younger, or perhaps the impact that created it hit a pocket of ammonia-rich subsurface ice. Alternatively, maybe Organa’s impactor delivered its own ammonia,” Grundy speculated.
Bill McKinnon, deputy lead of the mission’s Geology, Geophysics, and Imaging (GGI) team, noted that ammonia, which acts as an anti-freeze, could indicate Charon’s surface has been formed by cryovolcanism.
If the ammonia is coming from Charon’s interior, it could be erupting onto the surface within cold, ammonia-water magmas, he explained.
A composite image of Charon showing both Organa and Skywalker was created from Ralph/LEISA data taken when New Horizons was within 50,000 miles (81,000 km) of the large moon on July 14. The spatial resolution is three miles (five km) per pixel.
Panchromatic images taken by the Long Range Reconnaissance Imager (LORRI) were used to create the background in the composite image. The ammonia-absorption area is highlighted in green while the region within the yellow box is 174 miles (280 km) across.
The New Horizons team also released a new image showing Pluto’s crescent taken 15 minutes after closest approach as the spacecraft looked back at Pluto in the direction of the Sun. Additional processing by the science team since the September release of the stunning Pluto backlit image enabled the team to create entire, detailed images of the small backlit planet.
Taken at a wide angle by New Horizons’ Multispectral Visible Imaging Camera (MVIC) from a distance of 11,000 miles (18,000 km), with a resolution of 0.4 miles (700 meters), the image shows more than a dozen layers of Pluto’s surrounding haze.Silhouettes of Pluto’s jagged terrain are visible on the night (left) side while the smooth Sputnik Planum can be seen on the sunlit (right) side, along with the 11,000-foot (3,500-meter) high water ice mountains to the plain’s left. The Hillary Montes range can be seen outlined against the sky while the Norgay Montes range is visible in the image’s foreground. Glaciers that break up more rugged terrain can be seen to the east of (below) Sputnik Planum. Along the top of Pluto’s disk, viewers can see the shadow cast by the planet on its atmospheric hazes. Horizontal streaks in the background beyond Pluto are actually stars smeared by the cameras as they focused on Pluto.
Meanwhile, the spacecraft successfully carried out its third maneuver toward its next target – Kuiper Belt Object 2014 MU69 – on October 28. The primordial KBO is located one billion miles beyond Pluto. New Horizons will make its closest approach to the tiny object on January 1, 2019. The spacecraft’s third of four targeting maneuvers, conducted via its hydrazine-fueled thrusters, was the largest move it has ever undertaken, and lasted approximately 30 minutes.
Through NASA’s Deep Space Network, mission controllers received data eight hours after the 1:15 p.m. EDT maneuver confirming its success.
A final maneuver is scheduled for November 4 – though additional ones may be done in the future as more is learned about the orbit of 2014 MU69 and its location.
New Horizons’ science team, which plans to submit a formal proposal to NASA for an extended mission in 2016, hopes to fly even closer to this KBO than the 7,750-mile (12,500-km) closest approach to Pluto.
Traveling at more than 32,000 miles per hour, New Horizons is now 79 million miles (127 million km) past Pluto, 3.17 billion miles (5.1 billion km) from Earth, and 900 million miles (1.45 billion km) from 2014 MU69, with all its systems and instruments remaining healthy.
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.