New Horizons' new view of Pluto shows what could be a polar cap at the 3 o'clock position on the dwarf planet's disk.
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New Horizons' new view of Pluto shows what could be a polar cap at the 3 o'clock position on the dwarf planet's disk.

New Horizons Spots Possible Polar Cap on Pluto

As NASA’s New Horizons spacecraft hurries toward its epic rendezvous with dwarf planet Pluto, the little world is coming into focus a bit more quickly than expected. Today, thanks to some image processing wizardry, new images from New Horizons are already revealing some of the features marking the dwarf planet’s surface, including a possible polar cap.

“We’re actually pulling out details about a month in advance of where we thought we’d be,” said New Horizons project scientist Hal Weaver of the Johns Hopkins Applied Physics Lab. “By the time we get to the closest approach to Pluto, it’s going to blow us all away.”

That’ll happen on July 14, when New Horizons is scheduled to fly within 12,500 kilometers of Pluto.

For now, from about 100 million kilometers away, the still-grainy images are among the best ever taken of the world on the fringe of the easily observable solar system. In them, scientists can spy a patchwork of light and dark blotches blanketing Pluto’s surface. Though not unexpected (Hubble observations made more than a decade ago suggested as much), the wild variations in brightness are clearly visible even in the pixelated blob representing Pluto. It’s not yet clear whether the blotches are the work of geology, topographic features, or compositional differences in the ices painting the dwarf planet’s surface.

“It’s rare to see any planet in the solar system, at this low resolution, displaying such strong surface markings,” said the Southwest Research Institute’s Alan Stern, principal investigator for the New Horizons mission.

As Pluto rotates in the new series of images, one surprising feature stands out: a bright patch, near the planet’s pole, that could be a polar cap. “Pluto, like the planet Uranus, is tipped on its side,” Stern explained, describing how New Horizons is essentially looking down on one of Pluto’s poles. In the images, there’s a persistently bright patch at about the 3 o’clock position. It’s the brightest among all the blotches spotted so far. “That may be evidence for a polar cap,” Stern said. “Which could be very, very exciting. Whether it’s actually a polar cap or not depends upon the data that we’ll be collecting in the future.”

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Charon is so big relative to Pluto that the pair forms a binary planet system. (NASA/JHUAPL/SwRI)

The images also clearly show the small world and its mega-moon Charon whirling around a point in the space between them — a shared center of gravity that, because it’s set outside Pluto, makes the pair more of a binary planet than a regular old planet-moon pair. And while Pluto’s extremely variable surface already stands out, Charon appears to be more uniform in brightness. Pluto’s other known moons (there are four) are still too dim for New Horizons to see, but the spacecraft will be keeping a close eye on them — and searching for still-undiscovered moons — as it approaches the system.

New Horizons has been zooming toward Pluto since 2006, covering more than a million kilometers a day. Now, finally, Pluto is almost within reach. The planned flyby is just 11 weeks away, and at its closest approach, New Horizons will be near enough to see features as small as the ponds in New York City’s Central Park.

For now, “These images that you see in this animation sequence are what I call my ‘meet-Pluto’ moment,” Stern says. “All of it is mysterious to us, but all of it, we’re going to be training our instruments on to try and understand.”