New insights into Pluto’s geology, composition, and haze presented at conference
Members of the New Horizons team discussed new details about Pluto’s complex geological processes, varied composition, and layered hazes at the fall meeting of the American Geophysical Union in San Francisco.
The latest data sent back by NASA’s New Horizons spacecraft shows geological evidence for glacial activity, both past and present. Remarkably, networks of eroded valleys on Pluto’s surface, described by some scientists as “hanging valleys”, are similar to those at Yellowstone National Park on Earth.
Sputnik Planum, a 620-mile (1,000- km)-wide basin on the left side of the heart-shaped feature known as Tombaugh Regio, holds a deep layer of solid nitrogen along with other volatile ices.
By creating new, numerical models depicting the process of thermal convection within these ice layers, scientists are uncovering an explanation for this region’s polygonal features.
The current theory is that the nitrogen in Sputnik Planum evaporates, then condenses back on higher terrain, resulting in ices flowing back toward the basin.
According to these models, nitrogen ice flow continues to transform Pluto’s surface. The models also suggest that ice on Sputnik Planum could be several miles thick.
“Pluto has greatly exceeded our expectations in diversity of landforms and processes – processes that continue to the present,” explained Alan Howard of the University of Virginia at Charlottesville, who is working with New Horizons’ Geology, Geophysics, and Imaging (GGI) team.
Pluto’s haze, which stretches hundreds of miles above its surface, is also proving to be far more complex than anticipated.
Using data and images returned by the spacecraft over the last five months, scientists are trying to identify the haze’s origin as well as explain why it forms layers and how it varies spatially around the small planet.
“Like almost everything on Pluto, the haze is much more complicated than we thought,” emphasized New Horizons co-investigator Andy Cheng of the Johns Hopkins University Applied Physics Lab in Laurel, Maryland.
“But with the excellent New Horizons data currently in hand, we soon expect to have a much better understanding,” he noted.
One of the latest images sent back by the probe highlights the variety of terrains on Pluto’s encounter side in high resolution. Clearly visible are the cratered plains on the encounter hemisphere’s western side, which give way to many conspicuous faults.
The photo also shows the dark region unofficially known as Cthulhu Regio, skims over the mountainous Wright Mons, which scientists believe might be cryovolcanic, and ends at the terminator, which separates the planet’s day and night sides.
Also visible are overlapping areas of Sputnik Planum’s smooth, bright terrain, and the dark border of Cthulhu Regio.
The close-up images were taken by the Long Range Reconnaissance Imager (LORRI) along with the LEISA spectrometer, which together captured the “zigzag” pattern. They show details as small as 500 yards (500 meters), and viewers can zoom in on any region by clicking on that part of the image.
“We’re much less than halfway through transmitting data about the Pluto system to Earth, but a wide variety of new scientific results are already emerging,” emphasized Principal Investigator Alan Stern of the Southwest Research Institute in Boulder, Colorado.
The New Horizons team also discussed infrared spectral images of Charon taken by LEISA, noting these show evidence of low-level ammonia absorption across much of the large moon’s surface. Charon’s Organa Crater has an unusually high concentration of ammonia.
Initially, high ammonia concentrations were seen only in a few locations. Scientists have not yet determined whether the ammonia originates inside Charon or from an external source or the process by which it is distributed across the moon’s surface.
Another topic of discussion was the interaction of Pluto and its moons with the solar wind, the plasma stream coming from the Sun at 900,000 miles (1.4 million km) per hour.
During the July flyby, the Chandra X-ray Observatory, currently in orbit around the Earth, observed Pluto, looking for X-ray emissions to assist the mission team in determining the escape rate of Pluto’s atmosphere.
Neutral atoms in Pluto’s escaping atmosphere can exchange electrons with positively charged oxygen, nitrogen, and carbon atoms in the solar wind.
One of the latest images (shown left) sent back by the spacecraft is a panchromatic view of Pluto’s small moon Nix, taken by the Multispectral Visible Imaging Camera (MVIC).
Taken on the day of the flyby from a distance of 14,000 miles (23,000 km), the image shows an illuminated surface 12 miles (19 kilometers) by 29 miles (47 kilometers). Enough detail is visible to provide clues about the geological history of Pluto’s third largest moon.
In a December 18 blog post, GGI scientist Dr. Orkan Umurhan discusses his participation in the team’s efforts to understand the complex flow and convection processes being seen on Pluto’s surface. Interested readers can view his writing here.
The last raw LORRI images for 2015 (available here) were published on Friday, December 18. Posting of new images will resume on Friday, January 8, 2016.
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.