Although the global ocean below the planet’s surface may be frozen over time, its remnants can still exist beneath a large impact crater on the Ceres. The presence of salt can preserve liquid in the form of brine, despite its cold temperature.
This new study is based on observations made in Dawn’s orbit of Ceres between 2015 and 2018, which has nearly crossed it made of dwarf planets just 22 miles above the surface by the end of the mission.
During that time, Dawn focused on the 57-mile-wide Occator Crater, a 22-million-year-old feature that appeared to showcase bright spots. These eye-catching features were found to be sodium carbonate, or a compound that includes oxygen, carbon, and sodium.
But it̵7;s not clear how those bright spots were in the crater.
Data from the end of Dawn’s mission show a large, flaccid reservoir of salt water, or salty liquid, underneath the crater. It’s 25 miles deep and extends out for hundreds of miles.
When the crater-generating collision occurred with Ceres, it may have allowed the reservoir to deposit visible bright salts in the crater by cracking the planet’s crust. When the faults reach salt reservoirs, the salt water can reach the surface of the crater layer. As the water evaporated, a bright, salty crust remained.
And the brine may still be rising to the surface today – this suggests the activity on the Ceres was not caused by melting but could have happened when the planet collided.
In fact, Dawn data also points to the presence of hydrated chloride salts in the center of the largest bright area in the crater center, known as Cerealia Facula. This hydrohalite compound is common in sea ice on Earth, but this is the first time hydrohalite has been found outside of our planet.
The salts seem to lose water fairly quickly on the surface, at least, astronomically. This water loss happened hundreds of years.
But measurements taken by Dawn showed that the water was still there. This suggests that salt water could still rise to the surface of the crater and salty liquid could still exist inside the Ceres.
“For the large mine in Cerealia Facula, most of the salt provided from a muddy area just below the surface has been melted by the crater formation impact of about 20 million,” said Carol Raymond, principal of Dawn. last year. investigator at NASA’s Jet Propulsion Laboratory in California, in a statement.
“The impact heat decreases after a few million years; however, the impact also creates large cracks that can reach deep, long-lasting aquifers, allowing salt water to continue seeping into the surface.”
There are also mounds and hills visible in craters that can be created when water currents freeze in place, indicating geological activity on the Ceres. These conical hills are similar to pingo on Earth, or small ice mountains found in the polar regions. Although features like these have also been found on Mars, this is the first time they have been detected on a dwarf planet.
An unusual dwarf planet
Structures like pingo and water pushed up through cracks in craters suggest that Ceres actually underwent freezing, or ice volcanoes, which started about 9 million years ago. This may be in progress.
This type of cryovolcanic activity has been seen on icy moons in the outer solar system, with beams of matter ejected 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 been shown to be rich in water and certainly active.
As a survivor of the earliest days of the solar system when it formed 4.5 billion years ago, Ceres is more like an “embryonic planet”; it basically started to take shape, but it never ended.
Jupiter, the largest planet in our solar system, and its gravity could inhibit Ceres’ growth. So about 4 billion years ago, Ceres found her home in the asteroid belt along with all the other things left over from the formation of the solar system.
The idea that liquid water can be conserved on dwarf planets and asteroids is a compelling idea to scientists.
Unlike other icy oceanic worlds in our solar system, such as Saturn’s moon Enceladus and Jupiter’s moon Europa, asteroids and dwarf planets don’t get hot inside. Enceladus and Europa benefit from the internal warming that occurs when they gravitationally interact with the large planets they orbit.
The Dawn mission ended in 2018 when the spacecraft ran out of fuel and could no longer communicate with NASA. It is placed into long-term orbit around the Ceres to prevent impact, protecting organic materials and liquids under its surface.
Marc Rayman, Dawn’s mission director at JPL, said: “Dawn has accomplished more than we had hoped for at the beginning of her extraordinary extraterrestrial expedition.” “These exciting new discoveries after the end of its long and efficient mission are a great tribute to this remarkable interplanetary explorer.”