A dwarf planet between Mars and Jupiter has a salty ocean beneath its surface, making it a contender for alien life

• A NASA spacecraft has discovered that a saltwater ocean lies deep below the surface of Ceres, a dwarf planet in the asteroid belt between Mars and Jupiter.
• New research shows that shiny salt deposits on Ceres' surface were left by water percolating up from underground.
• Ceres may have once held alien life, scientists say, because of its recent geologic activity, the presence of water, minerals containing ingredients for life, and a possible warm period in its past.

A NASA spacecraft just discovered a hidden ocean in our solar system.

The agency's Dawn probe orbited the dwarf planet Ceres, which sits inside the asteroid belt between Mars and Jupiter, for three years before running out of fuel in 2018. At one point, Dawn zipped 22 miles, or 35 kilometers, above the small world's surface. Scientists are still studying the data it gathered, since it offers an up-close look at some bright regions on Ceres that they'd been scratching their heads over for years.

Already, Dawn helped researchers learn that that those shiny spots were covered in a compound called sodium carbonate, which is made up of sodium, carbon, and oxygen. That salty crust most likely came from liquid that evaporated on Ceres' surface.

But where the liquid came from remained a mystery until Monday, when a series of papers finally said that saltwater had percolated up to the dwarf planet's surface from an underground reservoir about 25 miles deep and hundreds of miles wide.

"This elevates Ceres to 'ocean world' status," Carol Raymond, the principal investigator for the Dawn mission, told Reuters.

That places the dwarf planet in the company of Enceladus (an icy moon of Saturn) and Europa (an icy moon of Jupiter) — other worlds with subsurface oceans. Like them, Ceres is now a contender for alien life.

"The material found on Ceres is extremely important in terms of astrobiology," Maria Cristina De Sanctis, a researcher at the Istituto Nazionale di Astrofisica in Rome, told The Guardian. "We know that these minerals are all essential for the emergence of life."

Ceres's ocean could be the relic of a warmer era

The bright regions Dawn studied lie inside Ceres's Occator crater — the salt deposits are named Cerealia Facula and Vinalia Faculae. They're just 2 million years old, and Dawn researchers think the geologic process that made them is ongoing.

But the forces that allow Enceladus and Europa to maintain their oceans aren't the same for Ceres. The other two ocean worlds feel a strong gravitational pull from their planets: As they orbit Saturn and Jupiter, those massive bodies stretch and compress the moons, building friction that heats the moons from the inside.

But in Ceres' case, asteroid impacts may have played a role.

"For the large deposit at Cerealia Facula, the bulk of the salts were supplied from a slushy area just beneath the surface that was melted by the heat of the impact that formed the crater about 20 million years ago," Raymond said in a NASA press release. "The impact heat subsided after a few million years; however, the impact also created large fractures that could reach the deep, long-lived reservoir, allowing brine to continue percolating to the surface."

In other words, asteroid impacts may have briefly kept the dwarf planet warm enough for liquid water to persist below its surface. Scientists think the underground saltwater they discovered via Dawn may be a surviving pocket of a global ocean that froze as Ceres cooled.

In the brief period of time when conditions were warm enough, life may have arisen.

"The probability of finding life on another world keeps going up," NASA Administrator Jim Bridenstine said on Twitter. "Ceres is the latest evidence that our solar system is filled with ancient habitable environments."