Pluto’s heart may be cold as ice

Pluto’s heart may be cold as ice
In this image of Pluto taken by NASA's New Horizons spacecraft, different colors represent different compositions of surface ices, revealing a surprisingly active body.

Sputnik Planitia is a 1,000-kilometer wide basin within the iconic heart-shaped region observed on Pluto’s surface.

It could be in its present location because accumulation of ice made the dwarf planet roll over, creating cracks and tensions in the crust that point towards the presence of a subsurface ocean.

Published in the Nov. 17 issue of Nature, these are the conclusions of research by James Keane, a doctoral student at the University of Arizona’s Lunar and Planetary Laboratory, and his adviser, assistant professor Isamu Matsuyama.

They propose evidence of frozen nitrogen pileup throwing the entire planet off kilter, much like a spinning top with a wad of gum stuck to it, in a process called true polar wander.

“There are two ways to change the spin of a planet,” Keane said.

“The first–and the one we’re all most familiar with–is a change in the planet is a change in the planet’s obliquity, where the spin axis of the planet is reorienting with respect to the rest of the solar system.”

“The second way is through true polar wander, where the spin axis remains fixed with respect to the rest of the solar system, but the planet reorients beneath it.”

Planets like to spin in such a way that minimizes energy. In short, this means that planets like to reorient to place any extra mass closer to the equator, and any mass deficits closer to the pole.

For example, if a giant volcano were to grow on Los Angeles, the earth would reorient itself to place L.A. on the equator.

To understand polar wander on Pluto, one first has to realize that unlike Earth, whose spin axis is only slightly tilted so that the regions around the equator receive the most sunlight, Pluto is like a spinning top lying on its side.

Therefore, the planet’s poles get the most sunlight. Depending on the season, it’s either one or the other, while Pluto’s equatorial regions are extremely cold, all the time.

Because Pluto is almost 40 times farther from the sun than we are, it takes the little ball of rock and ice 248 Earth years to complete one of its own years.

At Pluto’s lower latitudes near the equator, temperatures are almost as cold as minus 400 degrees Fahrenheit, cold enough to turn nitrogen into a frozen solid.

Over the course of a Pluto year, nitrogen and other exotic gases condense on the permanently shadowed regions.

Eventually, as Pluto goes around the sun, those frozen gases heat up, become gaseous again and re-condense on the other side of the planet, resulting in seasonal “snowfall” on Sputnik Planitia.

In a sense, Pluto is a (dwarf) planet whose shape and position in space are controlled by its weather.

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Citation: Keane JT, et al. (2016). Reorientation and faulting of Pluto due to volatile loading within Sputnik Planitia. Nature, published online. DOI:10.1038/nature20120.
Figure legend: This image is credited to NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.