July 28, 2015 | David F. Coppedge

Ski Pluto: Glaciers Are Flowing

Planetary scientists are dumbfounded by more evidence of youth at Pluto, both on the surface and in the atmosphere.

Last Friday’s news conference contained more detailed images of Pluto. Alan Stern first shared a global portrait with twice the resolution of the previous image, then a false-color processed image that brings more information out of the data.

False-color image of Pluto from New Horizons, July 24, 2015

False-color image of Pluto from New Horizons, July 24, 2015

The lightest part of the left (west) lobe of the “heart”-shaped light region, named tentatively Tombaugh Regio, appears to be a source of ices that spread over adjacent regions by wind or sublimation, eliminating craters that would otherwise indicate an old surface, although some infilled craters are evident. Space.com posted clips of the press conference.

Michael Summers relished the new atmospheric image that stunned the science team, showing haze high in the atmosphere backlit by the sun, reaching 100 miles above the surface—five times higher than predicted. The atmosphere shows structure. Stern said that the pressure at the base of the atmosphere is lower than predicted. Summers explained that complex hydrocarbons, like ethylene and acetylene, are produced by solar radiation of methane, producing the red hue of tholins on the surface. He did not explain how much of the material should accumulate over 4.5 billion years, nor how the atmosphere could be replenished to the level we observe today.

Sputnick Planum showing glacial activity, New Horizons July 24, 2015

Sputnick Planum showing glacial activity, New Horizons July 24, 2015

William McKinnon showed a high-res image of the northern edge of Tombaugh Regio where movement of nitrogen glaciers is evident. Eric Hand at Science Magazine summarizes the physics of Plutonian glaciology. Though water ice would be hard as rock,

At Pluto temperatures, ices of nitrogen, methane and carbon monoxide are soft and malleable enough to flow. “We interpret them to be just like glacial flows on Earth,” says McKinnon, who says the flows occurred as recently as within the past few tens of millions of years—a blink of an eye, geologically speaking.

Where do the ices come from? Any explanation needs to take into account that present activity must speak to the history of the dwarf planet, too.

The flow images are “breathtaking,” says Alexander Hayes, a planetary scientist at Cornell University. “We’re seeing activity on the surface. That means it’s powered by something.” Debate has centered on two mechanisms: bottom-up, in which icy materials would burble up through Pluto’s crust and out onto its surface, driven by residual heat in the dwarf planet’s interior; and top-down, in which frosts from Pluto’s atmosphere eventually accumulate into thick glaciers. Hayes favors the bottom-up mechanism, because he finds it difficult to envision frosts accumulating into the hundreds-of-meters-thick layers needed for them to flow like glaciers. “My gut reaction upon first seeing is that that might be tough to do,” he says.

But McKinnon says there are other places around the fringe of Tombaugh Regio where ice appears to be flowing into the heart. It could be that, as Pluto’s extreme seasons push reservoirs of ice around the globe, it just ends up in Tombaugh Regio. The heart might be Pluto’s wellspring; it might also be Pluto’s bathtub.

Nature adds, “But nitrogen ice could [flow], if it is roughly a kilometre thick and heated by radioactive decay leaking from Pluto’s interior.” But why should any radioactive heat remain on a small world after billions of years? And can the same material move around the globe, year after Pluto year?

The team is speculating that Pluto’s atmosphere may be in stages of collapse as the body moves away from the sun after its 1989 perihelion. Perhaps the atmosphere resurrects each orbital lap of 248 earth-years. Even so, during its assumed lifetime of 4.5 billion years, Pluto should have made over 18 million orbits by now.

None of the articles so far are asking where Pluto got its methane. If it were not replenished, it would quickly be depleted (in geologic terms) by solar radiation forming tholins on the surface.  This has been a long-standing problem on Saturn’s moon Titan (see 4/16/13, 6/21/14).

Other features appear young. As for the southern mountains that are comparable in height to the Rockies, McKinnon commented, “This is really a young unit” (National Geographic). And regarding Sputnik Planum—that crater-free, polygonal, smooth, Texas-sized area deep in the heart of Tombaugh Regio—he said, “So, we actually have evidence for recent geological activity” (BBC News).

His definition of “recent” was “no more than a few tens of millions of years“. “And what we know about nitrogen ice and what we can estimate about the heat-flow coming from the interior of Pluto – there’s no reason why this stuff cannot be going on today.

National Geographic posted a flyover video produced out of the images. More image data is expected in September after maneuvers and downloads of non-imaging data. While the team members are clearly delighted with New Horizon’s success, it is evident they did not expect to see such youthful features. Reporters (e.g., Space.com) often refer to “big surprises” in the data. Astrobiology Magazine spoke of “recent geologic activity, something scientists hoped to find but didn’t expect.National Geographic‘s reporter says, “It’s surprising to see that amount of activityon such a small world in a part of the solar system where failed planetary building blocks revolve in perpetual dusk.”

This is too much fun. We get the thrill of discovery, and the amusement of watching moyboys dumbfloundering by the evidence.

Deep in the Heart of Tombaugh

The glaciers flow, how we don’t know,

Deep in the heart of Tombaugh;

There ain’t no heat, but sure is neat,

Deep in the heart of Tombaugh.

It looks so young, our theory’s dung,

Deep in the heart of Tombaugh;

Crev.info guys see our surprise,

Deep in the heart of Tombaugh.


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