A “dwarf planet” discovered at the start of the 19th century has been mystifying scientists for hundreds of years. Now, researchers from Purdue University and NASA’ Jet Propulsion Laboratory believe that it was once a “muddy ocean world.”
Their work on Ceres, the largest asteroid in our solar system, was published this month in the Nature Astronomy journal.
It was New Year’s Day 1801 when Giuseppe Piazzi first discovered Ceres, according to NASA’s JPL. He was the director of the Palermo Observatory in Sicily, Italy, and he had been working on a catalog of star positions.
During this process, Piazzi saw a faint light “colored as Jupiter” that he looked for on subsequent nights. When he saw it again, Ceres’ position had changed slightly. Piazzi wrote to fellow astronomers that he might have identified a comet, but that its qualities indicated it might be something else.
Some scientists of the day believed that Ceres was a “lost” planet they believed excited between Mars and Jupiter. Eventually it was determined to be part of a new class of space object: asteroids. Today, we know there are thousands of asteroids between Mars and Jupiter.
Piazzi was disappointed that Ceres wasn’t considered a planet. Today, Mike Sori – assistant professor in Purdue’s Department of Earth, Atmospheric, and Planetary Sciences and one of the recent study authors – notes that is does look more like a planet than a typical “lumpy” asteroid. Sori also said the 590-mile diameter “dwarf planet” has features like craters, volcanoes and landslides.
Ceres was the first asteroid observed and it is still the largest known asteroid in our solar system. In 2007, the Dawn mission launched. It reached Ceres in 2015 and was able to orbit the asteroid until 2018.
According to a press release on the recent research from Purdue, Ceres has a battered, dimpled surface covered with impact craters. Scientists have argued in the past that these craters indicate the asteroid isn’t icy. However, the new research indicates that it is actually has a “dirty ice crust.”
In space, the presence of ice also suggests the presence of water, or the past presence of water.
“We think that there’s lots of water-ice near Ceres surface, and that it gets gradually less icy as you go deeper and deeper,” said Sori. “People used to think that if Ceres was very icy, the craters would deform quickly over time, like glaciers flowing on Earth, or like gooey flowing honey. However, we’ve shown through our simulations that ice can be much stronger in conditions on Ceres than previously predicted if you mix in just a little bit of solid rock.”
Previously, scientists estimated that Ceres was around 30% ice. Sori’s team believes that its surface is actually closer to 90% ice.
Long ago, Ceres may have been home to an “ocean world” similar to what scientists believe exists on Europa, the fourth largest of Jupiter’s 95 moons. While evidence suggests Europa has a saltwater ocean, Sori and his team believe Ceres’ ocean was muddy. As it froze over time, the “mud” was trapped in the ice as rocky material.
Ian Pamerleau, a PhD student at Purdue, said the team used computer simulations to model craters on Ceres. These simulations allowed them analyze the asteroid’s surface over billions of years.
“Our computer simulations account for a new way that ice can flow with only a little bit of non-ice impurities mixed in, which would allow for a very ice-rich crust to barely flow even over billions of years,” Pamerleau explained. “Therefore, we could get an ice-rich Ceres that still matches the observed lack of crater relaxation.”
Sori said that this new understanding of Ceres is exciting because it could mean that a frozen ocean world is close to Earth. In fact, he said it might be the most accessible icy world in the universe.
“That makes it a great target for future spacecraft missions,” Sori added. “Some of the bright features we see at Ceres’ surface are the remnants of Ceres’ muddy ocean, now mostly or entirely frozen, erupted onto the surface. So we have a place to collect samples from the ocean of an ancient ocean world that is not too difficult to send a spacecraft to.”