NASA announced recently that it had received the last data sets from the New Horizons mission to Pluto.  The data had been collected during the spacecraft’s flyby of the dwarf planet, in July 2015, but had to be stored in the craft’s onboard recorders and gradually transmitted back to Earth over a period of 15 months.

“We have our pot of gold.”  — New Horizons Mission Operations Manager Alice Bowman, Johns Hopkins Applied Physics Laboratory

Now that New Horizons has reached this milestone, it seems an opportune time to display a collection of the most spectacular images of Pluto and its moon Charon that NASA has shared from the historic mission.

Pluto Shows Its Heart

When Pluto was discovered by Clyde Tombaugh, in 1930, no one could have imagined how fascinating the far-away world would turn out to be.  Relying on calculations made by Percival Lowell and W. H. Pickering, Tombaugh used photographic plates and a blink microscope to identify the Solar System’s temporarily recognized “ninth planet.”  (Pluto was demoted to dwarf planet status in 2006.)  Until the 21st century, there was simply no means to produce clear images of such a small body orbiting the Sun at an average distance of about 3.66 billion miles (5.9 billion km).

New Horizons was launched from Cape Canaveral, Florida, in 2006, and took more than eight years to reach its primary destination.  From about 280,000 miles, the spacecraft’s Long Range Reconnaissance Imager captured a beautiful portrait of Pluto (below), revealing for the first time the evocative heart-shaped feature covering a significant portion of the surface.

Image Credit: NASA/JHUAPL/SwRI

A Multifaceted World

The first global, true-color image of Pluto revealed an incredibly diverse topography.    For example, the Sputnik Planum, which comprises the western “lobe” of Pluto’s heart, is a basin about 560 miles across that may have been formed by an asteroid impact.  Brown University scientists believe that it may be an indication of a large, salty ocean sloshing around beneath the surface.

Pluto’s varied surface features rifts and mountains, expansive flat plains and heavily cratered regions.  As it neared its closest approach, New Horizons captured a superb image (below) of a tortoise-shell plain with isolated mountains rising from it.

Image credit: NASA/JHUAPL/SwRI

Hazy Shades of Pluto’s Sky

One of the most interesting surprises from the New Horizon mission was the discovery of an atmosphere surrounding Pluto.  The largest component of the atmosphere is nitrogen, with smaller amounts of methane and carbon monoxide also being present.  Scientists believe that the world actually undergoes changes of weather on a day-to-day basis, much as we experience here on Earth.

As Pluto moves closer to and farther from the Sun in its somewhat eccentric orbit, ices appear to thaw and then re-freeze.  The atmosphere gives the sky a bluish tint, which is quite apparent in the back-lit image (below) of layers of haze rising from the dwarf planet’s surface.  As many as 20 layers of haze are visible, extending more than 100 miles into the surroundings.

Image credit: NASA/JHUAPL/SwRI

Charon Rows into View

In addition to Pluto itself, New Horizon’s imagers focused their lenses on its five known moons:  Charon, Styx, Nix, Kerberos, and Hydra.  Most intriguing is the largest satellite, Charon, which has a diameter about half that of Pluto.  Much has been made of the reddish splotch that covers a large portion of the moon’s north polar region (seen in enhanced color below).  Mission scientists believe that the coloring is caused by Pluto essentially “spray-painting” Charon with methane gas that escapes from the dwarf planet’s atmosphere.

Image credit: NASA/JHUAPL/SwRI

‘Super Canyon’ Gouges a Moon

Another striking feature of Charon is a deep canyon that, from a particular angle, looks like it virtually slices clear through a section of the moon’s surface.  Informally dubbed Argo Chasma, the canyon (below) is thought to be approximately 430 miles long and several miles deep – much longer and deeper than the Grand Canyon in the southwestern United States.

Image credit: NASA/JHUAPL/SwRI

A Thousand Pictures Tell a Story

Last year, the New Horizons team collected thousands of photographs in response to its “#Pluto Time” social media campaign.  All of the pictures were taken in low-light settings on Earth as a way of approximating the sunlight on Pluto at high noon.  NASA then assembled them into mosaics of Pluto and Charon and posted them to the New Horizons Web site.

If you zoom in on the western lobe of the heart-shaped region in the mosaic below, you will see a red-bracketed photo of Clyde Tombaugh – a fitting tribute to the astronomer with a sharp eye who first spotted Pluto.

Image Credit: NASA/JPL

Farther On

Pluto is now just a speck of light in the rear-view mirror of New Horizons.  Who knows when another explorer from Earth will visit that world again?  As the spacecraft proceeds on its journey toward a small object in the Kuiper Belt called 2014 MU69, the 50 gigabytes of golden data it carries on board will be deleted to create room for more.  However, scientists will continue to comb through the stream of information they’ve received, and maybe we will be treated to exciting new findings in the coming months and years.  Or so we can hope.