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New Pluto maps released; Pluto’s interaction with the solar wind found to be unique

Pluto: A Global Perspective

NASA’s New Horizons mission science team has produced this updated panchromatic (black-and-white) global map of Pluto. (Click to enlarge) Image Credit: NASA/JHU-APL/SwRI

With about half of New Horizons’ flyby data now returned, the mission team has released a new, updated global map of Pluto and a new elevation map depicting the “sunken” terrain of Sputnik Planum.

At the same time, data collected by the spacecraft’s Solar Wind Around Pluto (SWAP) instrument indicates Pluto’s interaction with the solar wind – the continuous stream of charged particles emitted by the Sun – is unique and more like that of the larger planets than that of a comet.

The global panchromatic map, titled “Pluto: A Global Perspective“, is in black-and-white and composed of all resolved images of Pluto’s surface taken between July 7 and 14 of the encounter hemisphere.

Elevation Map of Pluto’s Sunken ‘Heart’

This shaded relief view of the region surrounding the left side of Pluto’s heart-shaped feature – informally named Sputnik Planum – shows that the vast expanse of the icy surface is on average 2 miles (3 kilometers) lower than the surrounding terrain. Angular blocks of water ice along the western edge of Sputnik Planum can be seen ‘floating’ in the bright deposits of softer, denser solid nitrogen. (Click to enlarge) Credits: NASA/JHU-APL/SwRI

It includes images returned as late as April 25 of this year. As more data is sent back, mission scientists will add more photos to the map.

Pixel resolution ranges from 770 feet (235 meters) on the encounter side, visible at the image’s center, to 18 miles (30 km) on the far, Charon-facing side – seen on the map’s left and right edges.

Because the far side was imaged from a greater distance, photos of its areas contain less detail than those on the encounter side.

Members of the New Horizons team are currently working on improved color maps of the planet.

The new elevation close-up of Sputnik Planum, the left side of Pluto’s iconic ‘heart’ feature, is a topographic map made from digital analysis of data collected by the spacecraft on July 14, 2015, the day of the flyby.

Digital terrain maps can be lit from any direction to highlight different features.

In this image (shown right), north is up – though the map is artificially lit from the south. The elevation difference between the lowest and highest features in the map is approximately four miles (six km).

This close-up shows Sputnik Planum’s icy surface to be sunken, sitting approximately two miles (three km) below the terrain that surrounds it.

On Sputnik Planum’s western edge, angular blocks of ice appear to be floating on top of soft, bright areas of nitrogen ice.

Digital stereo-image mapping tools make it possible to show individual features obtained at different times and enable scientists to obtain accurate measurements of individual features’ heights.

Meanwhile, a new study published on May 4 in the Journal of Geophysical Research – Space Physics, a publication of the American Geophysical Union, notes that the way Pluto interacts with the solar wind is unique in the Solar System.

The solar wind is composed of plasma being emitted by the Sun, traveling at the supersonic speed of 100 million miles (160 million km) per hour.

Scientists had thought Pluto would interact with the solar wind much like a comet does. Unlike planets, which abruptly divert the solar wind when it hits them, comets gently slow the solar wind over large regions while approaching them.

However, SWAP found Pluto’s interaction with the solar wind to be more like those of Mars and Venus, though it still has some comet-like features.

“This is a type of interaction we’ve never seen before anywhere in our solar system. The results are astonishing,” noted the study’s lead author David J. McComas, professor of astrophysical sciences at Princeton University, vice president of the Princeton Plasma Physics Laboratory, and leader of New Horizons’ SWAP team.

Pluto in natural color

Four images from New Horizons’ Long Range Reconnaissance Imager (LORRI) were combined with color data from the Ralph instrument to create this global view of Pluto. The images, taken when the spacecraft was 280,000 miles (450,000 kilometers) away from Pluto, show features as small as 1.4 miles (2.2 kilometers). (Click to enlarge) Image & Caption Credits: NASA/JHUAPL/SwRI

Because Pluto is so far from the Sun – 30 to 49 AU (4.4–7.4 billion km) – and because it is so small, scientists also thought its gravity is too weak to hold onto the heavy ions in its tenuous atmosphere. Instead, New Horizons data shows Pluto’s atmosphere is not escaping. According to McComas, “Pluto’s gravity clearly is enough to keep material relatively confined.” 

Using SWAP, scientists succeeded in separating the main gas that is escaping from Pluto’s atmosphere – heavy methane ions – from the light hydrogen ions coming from the Sun.

Southwest Research Institute (SwRI) astrophysicist Heather Elliott, who co-authored the paper, stated, “Comparing the solar-wind/Pluto interaction to the solar wind interaction for other planets and bodies is interesting because the physical conditions are different for each, and the dominant physical processes depend on those conditions.”

The SWAP data could even help scientists understand the magnetized plasma likely to be found around other stars, McComas emphasized.

Pluto's solar wind interaction

Schematic diagram of Pluto’s interaction with the solar wind as inferred from SWAP observations along the trajectory of the New Horizons flyby. New Horizons crossed the Sun-Pluto line from the dawn/southern portion of the tail (dashed portion of trajectory) into the dusk/northern (solid portion of the trajectory in the cutaway) at ∼44 Pluto radii down-tail. Portions of the trajectory inside the heavy ion tail behind Pluto are indicated in red and light ion sheath that surrounds the tail are in blue. The bow shock observed near Pluto has dissipated into just a bow wave by the distance back that New Horizons exited through it. Image & Caption Credit: American Geophysical Union.

SWAP’s data from Pluto includes several other significant findings. Much like Earth, Pluto has a long ion tail that has “considerable structure”, is filled with heavy ions from its atmosphere, and extends at minimum about 100 Pluto radii (73,800 miles or 118,700 km).

Pluto does not block the solar wind until it comes relatively close – within several Pluto radii (1,844 miles or 3,000 km).

The “Plutopause” or boundary between Pluto’s heavy ion tail and the sheath of the solar wind is very thin, but it still disrupts the solar wind’s flow.

“These results speak to the power of exploration,” said mission Principal Investigator Alan Stern. “Once again, we’ve gone to a new kind of place and found ourselves discovering entirely new kinds of expression in nature.”

Many people were surprised by Pluto’s complex geology and atmosphere. This paper shows that there is even more that is surprising in the dwarf planet’s vicinity, including its atmosphere/solar-wind interaction.

In the latest of a series of blogs by mission scientists, Henry Throop, a New Horizons team member and planetary scientist at the Planetary Science Institute in Mumbai, India, discusses how scientists planned for the single-day Pluto encounter.

Titled “Planning for Pluto with GeoViz“, his blog post discusses the software tool, called GeoViz, that Throop developed for the encounter.

Short for Geometry Visualizer, Geo Viz shows the sky and planets from the viewpoint of the spacecraft. The software is still being used by the New Horizons team now to analyze the spacecraft’s observations.


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.

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