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Images of Pluto’s dark side produced using reflected sunlight from Charon

This is a fuzzy view of Pluto's dark, non-encounter side, as imaged by New Horizons. Reflected sunlight from Charon reveals some surface features. Credit: NOIRLAB/SwRI/JHUAPL/NASA

This is a fuzzy view of Pluto’s dark, non-encounter side, as imaged by New Horizons. Reflected sunlight from Charon reveals some surface features. Credit: NOIRLAB/SwRI/JHUAPL/NASA

A team of scientists produced images of Pluto’s dark side using reflected sunlight from its large moon Charon in images taken by the New Horizons spacecraft to tease out features on that side in low resolution.

Because New Horizons was a flyby mission, it could image just one side of Pluto — known as the encounter side — in high resolution. Much blurrier, low-resolution photos captured some of the planet’s far side. Some areas, such as the south polar region, were left in complete darkness.

Now, a science team led by Tod Lauer of the National Optical Infrared Astronomy Research Laboratory (NOIRLab), conducted the difficult process of identifying features on Pluto’s far side illuminated by reflected sunlight from Charon using new imagery techniques.

Pluto and Charon are separated by just 12,200 miles (19,640 kilometers), as compared with the Earth and Moon, which are separated by approximately 238,855 miles (384,400 kilometers).

To produce an image with at least partially identifiable features, the researchers had to account for the glare of the Sun, Pluto’s hazy atmosphere and a general blurring caused by the spacecraft’s speed in traversing the system.

Their efforts revealed Pluto’s south polar region to have a low level of brightness or albedo. This is surprising because other regions of Pluto are very bright due to the presence of nitrogen ice deposits. The low albedo means this region, which is now experiencing winter and in perpetual darkness, does not have many nitrogen ice deposits, a surprising development given that ice condenses and falls back to the surface as snow during the colder seasons.

One possibility is that Pluto experiences thermal inertia, a phenomenon in which an object resists temperature changes that bring its temperature in line with — that of its environment. Pluto’s south pole is just coming out of its warmer summer season, and the slow temperature change could also be related to organic material on its southern hemisphere’s surface.

Lauer’s team did find one region with a high albedo, probably a crater with ice deposits like those seen on Pluto’s encounter side.

Identification of these features, which until now have been difficult to see, will help scientists better understand Pluto’s seasonal cycles and the atmospheric changes that characterize these cycles.

A paper on the findings has been published in The Planetary Science Journal.


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.

Reader Comments

I consider the New Horizons mission to be the equivalent of a modern-day miracle. The precision required to get there and the stunning results are a historical achievement. My hat is off to everyone who took part in getting us to Pluto, Arrokoth, and beyond.

Wow! The New Horizons spacecraft and its ongoing discoveries never ceases to amaze. Pluto is without question a planet. I remember when Neil deGrasse Tyson said there were six moons in our solar system larger than Pluto (really there are 7, but whatev) as a reason to deny Pluto’s planethood. Well, Mr. Tyson, Ganimede and Titan are both larger than Mercury.

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