NASA’s New Horizons mission was a top science story last year and elevated Pluto into the pop culture zeitgeist with the first high-resolution images of a frozen world with active geology and eccentric spinning moons.
“We’re only getting started learning about Pluto’s geology and atmosphere as we seek to improve our understanding of this fascinating planet,” said Dr. Alan Stern, the principal investigator of New Horizons and an associate vice president at Southwest Research Institute (SwRI).
In a year of major space discoveries — including potential liquid water on Mars — the closest Pluto flyby stood out as the historic space exploration achievement of this decade. After traveling over nine years and 3 billion miles, the spacecraft buzzed past Pluto on July 14, 2015, flying within 7,750 miles of its icy surface.
The successful exploration of Pluto by New Horizons earned over 20 awards in 2015 and 2016, including the National Space Society Pioneer Award for Science and Engineering, the American Astronautical Society (AAS) Neil Armstrong Space Flight Achievement Award, the Air and Space Medal of the National Air and Space Museum, the Goddard Trophy of the National Space Club, and the John L. “Jack” Swigert Jr. Award for Space Exploration of the Space Foundation.
Among many results, the New Horizons science team has already discovered two potential cryovolcanoes on Pluto, measured the pressure of Pluto’s atmosphere, and shown evidence of large ice flows that may be shaping the planet’s geology. Over the next several months, the New Horizons team will continue to study the composition and structure of Pluto’s atmosphere as well as the geology, morphology, and temperature of its surface and its five satellites.
Led by SwRI, the mission team includes the Johns Hopkins University Applied Physics Laboratory, NASA’s Goddard Space Flight Center, University of Colorado, Stanford University, and Ball Aerospace & Technologies Corp.
The piano-sized spacecraft has collected over 50 gigabits of Pluto system data with the seven instruments aboard New Horizons. The scientific payload includes the Ralph infrared multi-spectral imager, the Alice ultraviolet spectrograph, the Solar Wind Around Pluto (SWAP) detector, the Long-Range Reconnais-sance Imager, twin Radio Science Experiments, the Pluto Energetic Particle Spectrometer Science Investigation, and the Student Dust Counter.
The Alice instrument, developed and built at SwRI, measured how quickly molecules escape Pluto’s atmosphere. Measurements by the SwRI-built SWAP instrument revealed that the region where the planet’s escaping atmosphere and the solar wind interact is much smaller than expected. Imagers aboard New Horizons found distinct global haze layers stretching high over Pluto’s surface that the atmosphere team, led by SwRI’s Dr. Randy Gladstone, are still trying to understand.
“This is a world-class team effort from so many talented SwRI scientists and partner organizations,” said Dr. Jim Burch, vice president of SwRI’s Space Science and Engineering Division. The mission was also named 2015’s top science story at Discover Magazine, Discovery.com, Science News, and Astrobiology, and it earned recognition from Scientific American and Nature. It was also a banner year for Stern, who led the New Horizons mission from its inception as a proposal 15 years ago. TIME magazine recently named Stern to its 2016 list of the 100 most influential people — for the second time since 2007. Stern also earned the AAS Carl Sagan Memorial Award, the American Ingenuity Award by Smithsonian magazine, and he was named an Honorary Fellow of the Royal Astronomical Society. He also took first place in Space News Leaders Making a Difference for 2015.
Located more than 3 billion miles from the Sun, Pluto has captivated the interest of scientists and school children since astronomer Clyde Tombaugh discovered it in 1930. Widely considered a binary planet, Pluto and its Texas-sized moon Charon are locked in orbit together around one another. Four smaller moons orbit the binary.
MOONS & GEOLOGY
Pluto’s moons have provided some of the most intriguing findings to date. New Horizons revealed that Charon also has experienced extensive resurfacing and extensional tectonics (stretching of the crust) and has somehow acquired a dark, red stain at its north pole. The flyby also showed that the smallest moons — Styx, Nix, Kerberos, and Hydra — actually behave like spinning tops.
Earth’s moon and most moons in our solar system do not spin in this way. Instead, they are locked in synchronous rotations, i.e., with one face always toward the parent body. Hydra, the farthest moon from Pluto, was observed rotating 89 times every time it circled Pluto. Those spin rates may actually vary with a force exerted by Charon. Nix and Hydra also have surface reflectivities that are higher than Charon’s.
In addition to its already known nitrogen and methane ices, Pluto’s surface was discovered to also have widespread water ice. Scientists observed flowing glaciers of solid nitrogen ice with large “floating hills” or “icebergs” of water ice in the informally named “Sputnik Planum” area. New Horizons geologists have presented 3-D maps indicating that two large mountains on Pluto could be cryovolcanoes, or ice volcanoes that may emit water ice, nitrogen, ammonia, or methane.
The scientists are trying to determine the ages of different surface areas on Pluto through the density of impact craters. SwRI researchers have mapped more than 1,000 craters. The estimated surface ages range from 10 million to 4 billion years, meaning that Pluto has been active throughout its over 4 billion year history — a surprise that has delighted scientists.
The New Horizons team hopes to extend the mission deeper into the Kuiper Belt, an area of icy objects at the far reaches of the solar system. Pending approval from NASA, the spacecraft would travel nearly 1 billion miles beyond Pluto to fly by a small (~19 miles wide) Kuiper Belt Object (KBO) known as 2014 MU69 on New Year’s Day in 2019.
“As we continue analyzing data from Pluto and its moons, and then explore the distant Kuiper Belt Object, we can glean a better understanding of how Pluto and other small planets formed in our solar system,” Stern added. “We really know very little about KBOs. They are going to help us connect the dots to understand how planets form. And the great thing about the Kuiper Belt is that it’s colder than anywhere else in our planetary system, so it’s a wonderful environment to preserve chemical and geological information about the origin of the solar system. Going to the Kuiper Belt is like an archaeological dig into the history of the solar system,” Stern said.