Latest New Horizons data reveals frozen plains, wagging tail

Preliminary data from the New Horizons spacecraft has revealed that the dwarf planet Pluto has an atmosphere that extends as much as 1,000 miles (1,600 kilometers) above its surface, a frozen plains in the middle of its “heart”, and a cold, dense “tail” of escaping atmospheric ions.

Those were among the revelations presented by NASA officials and scientists from the mission team during a press conference held by the US space agency today. The findings come even though just one to two percent of its data has been transmitted back to Earth thus far, according to Dr. Jim Green, director of Planetary Science at NASA Headquarters in Washington.

Dr. Green added that New Horizons, which is currently more than two million miles away from the Pluto system and heading towards the Kuiper Belt, is expected to have beamed back between five and six percent of the data it has collected by the end of next week. Already, however, it has sent back color images of both the dwarf planet and its largest moon, Charon.

In addition, principal investigator Dr. Alan Stern, New Horizons of SwRI, also showed off what he called the first well-resolved images of Pluto’s tiny satellite, Nix. This images has twice as many pixels as the best Earth-based images of the planet itself prior to the New Horizons.

Pluto has an extended, nitrogen-rich atmosphere

One of the main discoveries announced during Friday’s press event was the fact that Pluto had a nitrogen-rich atmosphere that extended as much as 1,000 (1,600 kilometers) above the surface of the planet. This marked this first observation of the dwarf planet’s atmospheres at altitudes above 170 miles.

According to NASA, the instrument gathered the information during a period in which the sun, Pluto, and the spacecraft were carefully aligned, starting approximately one hour after the closet approach back on Tuesday morning. During this event, which is called a solar occultation, New Horizons passed through Pluto’s shadow while the sun backlit the dwarf planet’s atmosphere.

Randy Gladstone, New Horizons co-investigator at the SwRI facility in San Antonio, explained that the atmospheres team had to wait until the spacecraft travelled past Pluto in order to obtain its best data set. He and his colleagues also said that the atmosphere was very symmetric on both sides of the planet, and while it would take another one to two months to receive more data, its sluggish nature eliminates some proposed atmospheric models.

SWAP instrument spots a ‘plasma tail’ of nitrogen ions

The spacecraft also detected a region of cold, dense ionized gas tens of thousands of miles past the dwarf planet that was created as a result of its atmosphere being stripped away by the solar wind and lost to space. The nitrogen in the atmosphere was escaping due to weaker gravity and energized by solar wind as it streamed out.

The Solar Wind Around Pluto (SWAP) instrument detected a cavity in the solar wind (or the outflow of electrically charged particles from the Sun), approximately an hour and a half after New Horizons’ closest approach. This cavity was detected between 48,000 and 68,000 miles (77,000 to 109,000 km) downstream of the dwarf planet and was populated with nitrogen ions that formed a “plasma tail” of unknown length and structure.

While Venus and Mars have similar plasma tails, in Pluto’s case, the nitrogen molecules in its atmosphere are ionized by solar UV rays, caught up in the solar wind, and carried beyond the dwarf planet to form the phenomenon detected by New Horizons. Just before the spacecraft’s closest approach, these ions were detected far upstream of Pluto by the probe’s Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) instrument.

Co-investigator Fran Bagenal from the University of Colorado, Boulder, who heads up the New Horizons Particles and Plasma team, said that while they won’t be able to accurately quantify the escaping atmosphere until more data comes back in August, estimates indicate that as much as 500 tons of atmosphere is escaping per hour.

“This is just a first tantalizing look at Pluto’s plasma environment,” Bagenal said in a statement, adding that once additional PEPSSI data comes back, it can be combined with the measurements of the Alice and Rex instruments “to pin down the rate at which Pluto is losing its atmosphere… [and] answer outstanding questions about the evolution of Pluto’s atmosphere and surface and determine to what extent Pluto’s solar wind interaction is like that of Mars.”

Unusual terrain features spotted in ‘Sputnik Planum’ region

Last but not least, the NASA team released a new close-up image of Pluto’s surface that shows a vast, craterless plain that appears to be less than 100 million years old and may even be currently in the process of being shaped by geologic processes. This region is located north of Pluto’s icy mountains in the dwarf planet’s heart feature that was named “Tombaugh Regio” in honor of Clyde Tombaugh, the man who originally discovered Pluto back in 1930.

Jeff Moore, leader of the New Horizons Geology, Geophysics and Imaging Team (GGI) at NASA’s Ames Research Center in Moffett Field, joked during the press conference that he liked to call this terrain the “not easy to explain terrain” terrain. The area is comprised of large, very young, craterless plains that Moore said “exceeds all pre-flyby expectations.”

This new icy plains region has been named “Sputnik Planum” (Sputnik Plain) after the Earth’s first artificial satellite, and it has areas that resemble frozen terrestrial mud cracks. It consists of a broken surface of irregularly shaped portions approximately 12 miles (20 km) across bordered by what appears to be shallow toughs, some of which contain mysterious dark material and some of which are traced by groups of hills appearing to rise above the surrounding terrain.

Other parts of Sputnik Planum appear to have been formed by fields of small pits through the process of sublimation, in which ice transforms directly from solid to gas, similar to the way that dry ice behaves on Earth. Moore said his team has two working theories as to how these segments were formed: they may have been formed by the contraction of surface materials, or by convection, similar to how wax rises to the top of a lava lamp. On Pluto, this would occur within a surface layer of frozen carbon monoxide, methane, and nitrogen.

This so-called “heart of the heart” image was taken by New Horizons when it was 48,000 miles (77,000 km) from Pluto, and shows features as small as one-half mile (1 kilometer) across. Mission scientists said that they expect to find out more about these unusual terrains as the spacecraft transmits higher-resolution and stereo images over the next year.

“This is just a first tantalizing look at Pluto’s plasma environment,” said Bagenal. Green added that while the “decade-long journey to Pluto is over… the science payoff is only beginning,” and Stern said that even though the team had “only scratched the surface of our Pluto exploration… it already seems clear to me that in the initial reconnaissance of the solar system, the best was saved for last.”

(Image credit: NASA)

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