Ceres Joins the Other Potential Oceanic Worlds Discovered so Far

Ceres, the dwarf planet, was once believed to be nothing more than an ancient piece of rock. But just a few years back, NASA‘s spacecraft Dawn unveiled the fact that there’s more to the asteroid belt object than experts were prone to believe.

Now, researchers are starting to discover more about Ceres. The cosmic object is located in the asteroid belt between Mars and Jupiter and is also the largest asteroid in the Solar System, as well as the only dwarf planet closer than Neptune.

And as per new data collected by Dawn and analyzed by experts, Ceres is an ocean world: it has a subsurface body of briny water that could be expanding across the entire dwarf planet. The new finding intensifies the importance of sending another probe to study Ceres in greater detail so we can gauge its potential habitability – and perhaps even search for signs of alien life.

Ancient Brine

It all started back in 2015, even before Dawn arrived for its mission of orbiting Ceres. The spacecraft registered some peculiar and anomalously bright spots known as faculae in the planet‘s Occator crater, which is a 20-million-year-old impact crater

Ceres’ possible ocean. [Credit: NASA/JPL-CalTech/UCLA/MPS/DLR/IDA]
Researchers later determined that these shiny spots were produced by sodium carbonate – a type of salt. Here on Earth, sodium carbonate is found close to hydrothermal vents, deep in the ocean, where heat gets to the water through cracks in the seafloor. Even though they are rather far from the Sun, which makes possible the photosynthesis on which most of our planet’s life depends on, these vents are packed with life, a food chain relying on chemosynthetic bacteria that uses chemical reactions instead of sunlight to produce energy.

However, the source of Ceres’ sodium carbonate remained a topic for debate. Now, as per a series of papers published in Nature journals, it seems like a deep brine layer was there at the time of the impact, which then surfaced, implying that the core of the dwarf planet is hotter than previously considered. Also, it appears like the brine is still there, as several convincing lines of evidence were suggesting this.

Gravity Changes

The data analyzed was gathered in the final phase of Dawn’s expedition. As it ran out of fuel, the probe dropped to an altitude of below 35 kilometers (22 miles), collecting information in remarkable resolution – ten times higher than the first mission, with a particular focus on the Occator crater.

At this outstanding resolution, Dawn was able to record gravity variations in the crater on the scale of the geological units in and around it. These gravity changes, mixed with thermal modeling, imply density variations consistent with a deep reservoir of brine below the surface of the crater.

NASA’s Dawn spacecraft heads toward the dwarf planet Ceres in an artist’s conception. [Credit: NASA/JPL-Caltech]
The reservoir could have been triggered by the heat and fracturing that came as a result of the impact, jetting up and out the produce the salt deposits discovered.

“Moreover,” the researchers wrote, “we find that pre-existing tectonic cracks may provide pathways for deep brines to migrate within the crust, extending the regions affected by impacts and creating compositional heterogeneity.”

Recent Gurgling Within Ceres

second study using the gravity data, along with shape data, discovered that Ceres​’ crust is rather porous, which decreases in depth, likely as the rock combines with salt. Even though the crater is approximately 20 million years old, there’s proof to imply the salts on top of it are a lot younger.

High-resolution images suggest that the ice volcanoes of the dwarf planet could have been active about 2 million years ago, a millennia after the heat from the clash would have dissolved, suggesting a deep source of brine.

This is also supported by a surprise discovery, namely the existence of a rare mineral – hydrohalite. Spectrometry unveiled this hydrated type of sodium chloride at the top of the Cerealia Facula, the brightest place in the Occator crater.

What’s interesting about this is that the mineral requires moisture, and dehydrates rather quickly (within tens of hundreds of years). This indicates that it must have boiled up from inside Ceres sometime recently.

Ceres, the dwarf planet, was once believed to be nothing more than an ancient piece of rock. [Credit: NASA/JPL-CalTech/UCLA/MPS/DLR/IDA]

Other Implications

However, the deposition of various salts on the surface has another ramification – they could have appeared from different sources.

First of all, the heat of impact melted a good part of the ice, which flowed out and changed the terrain inside the crater, depositing salts in the Cerealia and Pasola Faculae. Then, more gradually, brine from a deeper reservoir made its way to the surface, adding to both Cerealia and Pasola, and entirely creating the thinner Vinalia Faculae on the crater floor.

This all adds up to a rather confusing picture. Ceres​ is a lot more peculiar and complex than researchers knew, joining the moons Europa, Ganymede, Callisto, Enceladus, Titan and Mimas, and dwarf planet Pluto, as potential ocean worlds.

However, the way Ceres​ formed and where it comes from are both enigmas. A NASA mission to the dwarf planet was recently selected to be created as a concept study, due for publishing in the 2023 Planetary Science Decadal Survey.

The papers detailing the findings have been published in Nature AstronomyNature Geoscience, and Nature Communications.

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