While this ocean of the globe beneath the planet’s surface is likely to freeze over time, its remnants may still be present under a high-impact crater in Ceres. The presence of salts may have preserved the fluid as brine, despite the cold temperatures.
This new research is based on observations made during the Ceres Dawn orbit between 2015 and 2018, including close passes made by the dwarf planet just 22 miles above the surface towards the end of the mission.
During that time, Dawn was focused on the 57-kilometer-wide crater, a 22-million-year-old feature that appeared to display bright spots. These attractive properties were discovered to be sodium carbonate, or a compound comprising oxygen, carbon, and sodium.
But it was not clear how those bright spots appeared in the crater.
Data from the end of the Dawn mission revealed a wide, dilute reservoir of brine, or salt, under the crater. 25 is 25 miles deep and stretches for hundreds of miles.
When the impact that created the crater hit Ceres, it may have allowed the reservoir to deposit bright visible salts into the crater breaking up the planet’s crust. As the fractures reached the saline reservoirs, brine could reach the surface of the crater floor. As the water evaporated, a bright, salty crust remained behind.
And brine may still rise to the surface today – suggesting that activity in Ceres is not due to the melting that may have occurred when the planet was affected.
In fact, Dawn data also showed the presence of hydrated chloride salts in the center of the largest bright area in the center of the crater, called Cerealia Facula. This hydrohalite ingredient is common on sea ice on Earth, but it is the first time hydrohalite has been found outside our planet.
Salts appear to dehydrate fairly quickly on the surface, at least, astronomically. This dehydration occurs over hundreds of years.
But measurements taken by Dawn showed that water was still present. This suggests that brine may still grow on the crater surface and that saline fluid may still exist inside Ceres.
“For the large deposit at Cerealia Facula, most of the salts were supplied from a wet area just below the surface that had melted from the impact heat that formed the crater about 20 million years ago,” said Carol Raymond, director of Dawn Investigator at NASA’s Jet Propulsion Laboratory in California, in a statement.
“The heat of impact was reduced after several million years; however, the impact also created large fractures that could reach the deep, long-life reservoir, allowing brine to continue to penetrate the surface.”
There are also visible hills and hills in the crater likely created when water flows rise in place, suggesting geological activity in Ceres. These conical hills are similar to pingos on Earth, or small mountains made of ice found in the polar regions. Although features like this have also been found on Mars, it is the first time they have been seen on a dwarf planet.
An unusual dwarf planet
Structures like pingo and water pushed through crater fractures revealed that Ceres actually experienced crystallolcanic activity, or ice volcanoes, beginning about 9 million years ago. The process is likely to continue.
This type of cryovolcanic activity has been proven on icy moons in the outer solar system, with amounts of material being poured into space. But it was never expected to occur on dwarf planets or asteroids in the asteroid belt, which are thought to be waterless and inactive.
Ceres changes that theory because it has proven to be rich and definitely active.
A survivor of the earliest days of the solar system as it formed 4.5 billion years ago, Ceres was more of an “embryonic planet”; basically, it started to form, but it never ended.
Jupiter, the largest planet in our solar system, and the force of its gravity are likely to stun Ceres growth. Thus, about 4 billion years ago, Ceres found its home in the asteroid belt along with all the other parts left over from the formation of the solar system.
The idea that liquid water could remain stored on dwarf and asteroid planets is an intriguing one for scientists.
Unlike other icy ocean worlds in our solar system, such as Saturn’s moon Enceladus and Jupiter’s moon Europa, asteroids and dwarf planets do not experience internal heat. Enceladus and Europa benefit from the internal warming that occurs when they interact gravitationally with the massive planets they surround.
The Dawn mission ended in 2018, when the side ship sank from fuel and could no longer communicate with NASA. It was placed in long-term orbit around Ceres that would prevent impact, protecting its organic materials and fluid beneath the surface.
“Dawn achieved far more than we expected when it began its extraordinary extraterrestrial expedition,” Marc Rayman, director of Dawn’s mission at JPL, said in a statement. “These interesting new discoveries from the end of his long and productive mission are a wonderful tribute to this remarkable interplanetary explorer.”