A new study supports the theory that Pluto may have an underground ocean.

It has long been suspected the dwarf planet has a deep sea beneath its frozen surface. Observations and studies from a flight past Pluto in 2015 by NASA's New Horizons and published in this week's journal Nature focus on a 600-mile basin known as Sputnik Planitia in the left lobe of Pluto's heart-shaped region.

Evidence suggests tidal forces with jumbo moon Charon may have prompted Pluto to roll over on its axis eons ago. The weight of an ocean beneath the surface of Pluto could have been the cause.

Sputnik Planitia is aligned with Pluto's tidal axis, so much so that it's unlikely to be a coincidence, according to the researchers. More likely, the nitrogen ice-coated basin has extra mass — below the surface — to cause Pluto to reorient itself and have Sputnik Planitia on the opposite side of the dwarf planet as Charon.

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The smooth expanse of the informally named Sputnik Planum (right) is flanked to the west (left) by rugged mountains up to 11,000 feet high.

(NASA/JHUAPL/SwRI)

At a Glance

A recent study supports the case that a sea lies beneath Pluto's surface.Tidal forces with a jumbo moon may have caused the dwarf planet to roll over on its axis eons ago.The underground sea is suspected to be water with some sort of "antifreeze."

"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," lead author Francis Nimmo of the University of California, Santa Cruz, said in a statement.

Nimmo suspects the ocean is primarily water with some ammonia or other "antifreeze" thrown in. Slow refreezing of this ocean would conceivably crack the planet's shell — a scenario consistent with photos taken by New Horizons.

Subsurface oceans may also be on other similarly sized worlds orbiting in the Kuiper Belt, a so-called twilight zone on the fringes of our solar system, according to Nimmo.

"They may be equally interesting, not just frozen snowballs," he noted.

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New Horizons is managed from Johns Hopkins University.

Close to the sun, meanwhile, Mercury has a big new valley. Scientists attribute surface buckling, caused by global contraction.

The valley is more than 600 miles long, 250 miles wide and 2 miles deep.

A research team led by Thomas Watters, a senior scientist at the Smithsonian Institution's National Air and Space Museum, discovered the valley from images taken by NASA's Messenger spacecraft. The spacecraft orbited Mercury for four years before crashing deliberately into the innermost planet last year.

Earth has experienced this type of buckling, involving both oceanic and continental plates, Watters said.

"But this may be the first evidence" of it on Mercury, he noted.

This Great Valley, as it's known, was revealed Wednesday. The study was published in Geophysical Research Letters, a journal of the American Geophysical Union.

MORE ON WEATHER.COM: New Horizons Findings

New Horizons scientists made this false-color image of Pluto using a technique called principal component analysis to highlight the many subtle color differences between Pluto's distinct regions. The image data were collected by the spacecraft’s Ralph/MVIC color camera on July 14 at 11:11 AM UTC, from a range of 22,000 miles (35,000 kilometers). (Credits:NASA/JHUAPL/SwRI)