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Revealed by New Horizons, Pluto's 'heart' named for planet's discoverer



New Horizons' first detailed image of the heart-shaped 'Tombaugh Regio' near Pluto's equator revealed a range of mountains rising as high as 11,000 feet above the icy body. (NASA/JHU APL/SwRI)
July 16, 2015

– As NASA's New Horizons spacecraft flew by and beyond Pluto on Tuesday (July 14), it carried with the ashes of the American astronomer who discovered the dwarf planet in 1930.

Now, the mission's science team has further memorialized Clyde Tombaugh by giving Pluto's prominent heart-shaped feature his name.

"I love the heart and the fact that it is now named after my dad. He was part of my heart, and this means a great deal to me," Annette Tombaugh-Sitze told collectSPACE.

Pluto's "heart," a bright area that spans about 1,000 miles (1,600 km) across near the planet's equator, is now called "Tombaugh Regio" ("regio" is Latin for region).

"A couple of weeks ago, we just started naturally saying, 'That's so prominent, we have to name it — we should call it Tombaugh,'" recalled Alan Stern, New Horizons' principal investigator.


New Horizons' photo of Pluto showing the heart-shaped area now informally named 'Tombaugh Regio'. (NASA/JHUAPL/SWRI)

The name is informal for now, a nickname assigned by the mission's team members to help them refer to the planet's features while working with the images and data the New Horizons probe captured during its historic flyby of Pluto.

But unlike perhaps some of the other names that the team has assigned to the dwarf planet's dark surface details — names inspired by the underworld such as Cthulhu, Krun, Ala and Balrog — Tombaugh Regio is intended to become official. They plan to submit the name to the International Astronomical Union, the governing body that oversees the naming of celestial objects and their surface features, for approval as its official designation.

"I can guarantee you we will submit the Tombaugh feature and I don't think there's going to be any controversy about it," Stern told collectSPACE.

Tombaugh topography

New Horizons sent to Earth its first up-close photos of the Tombaugh Regio on Wednesday (July 15), confirming that Pluto is like no other world in the solar system.

Zooming into the heart-shaped area, the spacecraft's first-released photo from its closest approach to Pluto revealed a mountain range with peaks jutting up as high as 11,000 feet (3,500 m) above the surface of the icy body.


Mountains on Pluto. Click to watch in a pop-up window. (NASA)

"We know the surface is covered in a lot of nitrogen ice, methane ice and carbon dioxide ice – [but] you can't make mountains out of that stuff," John Spencer, deputy lead of New Horizons' geology science team, said during a press briefing at the Johns Hopkins University Applied Physics Laboratory in Maryland. "So what we're seeing here is the bedrock — or the bed-ice — of Pluto."

"Water ice is strong enough at Pluto temperatures to hold up big mountains and that's what we think we are seeing," he said.

The mountains though, are just the 'tip of the iceberg' with regards to what the photos reveal about the distant dwarf planet.

"The most stunning thing about this – well, there is many stunning things – but the most striking geologically is that we've not yet found a single impact crater on this image," Spencer stated. "This means this is a very young surface because Pluto has been bombarded by other objects in the Kuiper Belt and bound to have had craters happen."

"Just eyeballing it, we think it has to be probably less than 100 million years old, which is just a small fraction of the 4.5 billion year age of the solar system. It might be active right now," he said.


New Horizons' team members view the first images returned by the spacecraft after its historic Pluto flyby. (NASA/Bill Ingalls)

Scientists had theorized prior to the New Horizons mission that Pluto was similar in nature to Triton, the largest moon around Neptune. Triton also does not have many impact craters due to ongoing geological activity. But that activity was attributed to forces being imparted by Neptune.

"But that can't happen on Pluto," stated Spencer. "There's no giant body that can be deforming Pluto on an ongoing regular basis to heat the interior. Charon [Pluto's largest moon] is just too small to do that. So this is telling us you don't need tidal heating to power ongoing recent geological activity on icy worlds."

"That's a really important discovery that we just made," he said.

Lunar first looks

The New Horizons spacecraft, which arrived at Pluto after a nine and a half year journey from Earth, also imaged the dwarf planet's moons.


Remarkable details of Pluto's largest moon Charon are revealed in this image from New Horizons taken late on July 13, 2015 from a distance of 289,000 miles. (NASA/JHUAPL/SWRI)

"Charon just blew our socks off," said Cathy Olkin, deputy project scientist for the New Horizons mission. "We have just been thrilled [with the new image]. The team has just been abuzz, 'Look at this! Look at that! Oh my god, that's amazing!'"

The new view of Charon revealed a varied terrain. As with Pluto, the scientists were surprised by the lack of craters. A swath of cliffs and troughs stretching approximately 600 miles (1,000 km) across suggest widespread fracturing of the crust, likely the result of internal geological processes.

The image also showed a canyon estimated to be 4 to 6 miles deep (7 to 9 km), and in Charon's north polar region, dark surface markings with a diffuse boundary, suggesting a thin deposit or stain on the surface.

"There's so much interesting science in this image," Olkin said. "As we have been saying, Pluto did not disappoint, I can add that Charon did not disappoint either."


With a resolution of 2 miles per pixel, this New Horizons image of Hydra shows the tiny potato-shaped moon measures about 27 by 20 miles. (NASA/JHUAPL/SWRI)

New Horizons' first highly-pixelated image of Hydra, one of Pluto's four small moons, is the first to reveal its apparent irregular shape and size, estimated to be around 27 by 20 miles (43 by 33 kilometers).

The image also indicated Hydra reflects about 45 percent of the sunlight reaching it, making it surprisingly bright.

"Hydra's surface is probably composed primarily of water ice," said Hal Weaver, New Horizons' project scientist. "It is the only way to get it that bright, and that's cool."


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