New analysis adds to support for a subsurface ocean on Pluto

Related Articles

Related Articles

A liquid ocean lying deep beneath Pluto’s frozen surface is the best explanation for features revealed by NASA’s New Horizons spacecraft, according to a new analysis. The idea that Pluto has a subsurface ocean is not new, but the study provides the most detailed investigation yet of its likely role in the evolution of key features such as the vast, low-lying plain known as Sputnik Planitia (formerly Sputnik Planum).

Sputnik Planitia, which forms one side of the famous heart-shaped feature seen in the first New Horizons images, is suspiciously well aligned with Pluto’s tidal axis. The likelihood that this is just a coincidence is only 5 percent, so the alignment suggests that extra mass in that location interacted with tidal forces between Pluto and its moon Charon to reorient Pluto, putting Sputnik Planitia directly opposite the side facing Charon. But a deep basin seems unlikely to provide the extra mass needed to cause that kind of reorientation.

“It’s a big, elliptical hole in the ground, so the extra weight must be hiding somewhere beneath the surface. And an ocean is a natural way to get that,” said Francis Nimmo, professor of Earth and planetary sciences at UC Santa Cruz and first author of a paper on the new findings published November 16 in Nature. Another paper in the same issue, led by James Keane at the University of Arizona, also argues for reorientation and points to fractures on Pluto as evidence that this happened.

 

Like other large basins in the solar system, Sputnik Planitia was most likely created by the impact of a giant meteorite, which would have blasted away a huge amount of Pluto’s icy crust. With a subsurface ocean, the response to this would be an upwelling of water pushing up against the thinned and weakened crust of ice. At equilibrium, because water is denser than ice, that would still leave a fairly deep basin with a thin crust of ice over the upwelled mass of water.

“At that point, there is no extra mass at Sputnik Planitia,” Nimmo explained. “What happens then is the ice shell gets cold and strong, and the basin fills with nitrogen ice. That nitrogen represents the excess mass.”

Nimmo and his colleages also considered whether the extra mass could be provided by just a deep crater filled with nitrogen ice, with no upwelling of a subsurface ocean. But their calculations showed that this would require an implausibly deep layer of nitrogen, more than 25 miles (40 kilometers) thick. They found that a nitrogen layer about 4 miles (7 km) thick above a subsurface ocean provides enough mass to create a “positive gravity anomaly” consistent with the observations.

“We tried to think of other ways to get a positive gravity anomaly, and none of them look as likely as a subsurface ocean,” Nimmo said.

Coauthor Douglas Hamilton of the University of Maryland came up with the reorientation hypothesis, and Nimmo developed the subsurface ocean scenario. The scenario is analogous to what occurred on the moon, where positive gravity anomalies have been accurately measured for several large impact basins. Instead of a subsurface ocean, however, the dense mantle material beneath the moon’s crust pushed up against the thinned crust of the impact basins. Lava flows then flooded the basins, adding the extra mass. On icy Pluto, the basin filled with frozen nitrogen.

“There’s plenty of nitrogen in Pluto’s atmosphere, and either it preferentially freezes out in this low basin, or it freezes out in the high areas surrounding the basin and flows down as glaciers,” Nimmo said. The images from New Horizons do show what appear to be nitrogen glaciers flowing out of mountainous terrain around Sputnik Planitia.

As for the subsurface ocean, Nimmo said he suspects it is mostly water with some kind of antifreeze in it, probably ammonia. The slow refreezing of the ocean would put stress on the icy shell, causing fractures consistent with features seen in the New Horizons images.

There are other large objects in the Kuiper belt that are similar to Pluto in size and density, and Nimmo said they probably also have subsurface oceans. “When we look at these other objects, they may be equally interesting, not just frozen snowballs,” he said.

UNIVERSITY OF CALIFORNIA – SANTA CRUZ

Download the HeritageDaily mobile application on iOS and Android

More on this topic

LATEST NEWS

Camulodunum – The First Capital of Britannia

Camulodunum was a Roman city and the first capital of the Roman province of Britannia, in what is now the present-day city of Colchester in Essex, England.

African Crocodiles Lived in Spain Six Million Years Ago

Millions of years ago, several species of crocodiles of different genera and characteristics inhabited Europe and sometimes even coexisted.

Bat-Winged Dinosaurs That Could Glide

Despite having bat-like wings, two small dinosaurs, Yi and Ambopteryx, struggled to fly, only managing to glide clumsily between the trees where they lived, according to a new study led by an international team of researchers, including McGill University Professor Hans Larsson.

Ancient Maya Built Sophisticated Water Filters

Ancient Maya in the once-bustling city of Tikal built sophisticated water filters using natural materials they imported from miles away, according to the University of Cincinnati.

New Clues Revealed About Clovis People

There is much debate surrounding the age of the Clovis - a prehistoric culture named for stone tools found near Clovis, New Mexico in the early 1930s - who once occupied North America during the end of the last Ice Age.

Cognitive Elements of Language Have Existed for 40 Million Years

Humans are not the only beings that can identify rules in complex language-like constructions - monkeys and great apes can do so, too, a study at the University of Zurich has shown.

Bronze Age Herders Were Less Mobile Than Previously Thought

Bronze Age pastoralists in what is now southern Russia apparently covered shorter distances than previously thought.

Legio IX Hispana – The Lost Roman Legion

One of the most debated mysteries from the Roman period involves the disappearance of the Legio IX Hispana, a legion of the Imperial Roman Army that supposedly vanished sometime after AD 120.

Popular stories

Legio IX Hispana – The Lost Roman Legion

One of the most debated mysteries from the Roman period involves the disappearance of the Legio IX Hispana, a legion of the Imperial Roman Army that supposedly vanished sometime after AD 120.

The Secret Hellfire Club and the Hellfire Caves

The Hellfire Club was an exclusive membership-based organisation for high-society rakes, that was first founded in London in 1718, by Philip, Duke of Wharton, and several of society's elites.

Port Royal – The Sodom of the New World

Port Royal, originally named Cagway was an English harbour town and base of operations for buccaneers and privateers (pirates) until the great earthquake of 1692.

Matthew Hopkins – The Real Witch-Hunter

Matthew Hopkins was an infamous witch-hunter during the 17th century, who published “The Discovery of Witches” in 1647, and whose witch-hunting methods were applied during the notorious Salem Witch Trials in colonial Massachusetts.