What's inside Ceres? New findings from gravity data

What’s inside Ceres? New findings from gravity data
This artist's concept shows a diagram of how the inside of Ceres could be structured, based on data about the dwarf planet's gravity field from NASA's Dawn mission. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

In the tens of thousands of photos returned by NASA's Dawn spacecraft, the interior of Ceres isn't visible. But scientists have powerful data to study Ceres' inner structure: Dawn's own motion.

Since gravity dominates Dawn's orbit at Ceres, scientists can measure variations in Ceres' gravity by tracking subtle changes in the motion of the spacecraft. Using data from Dawn, scientists have mapped the variations in Ceres' gravity for the first time in a new study in the journal Nature, which provides clues to the dwarf planet's internal structure.

"The new data suggest that Ceres has a weak interior, and that water and other light materials partially separated from rock during a heating phase early in its history," said Ryan Park, the study's lead author and the supervisor of the dynamics group at NASA's Jet Propulsion Laboratory, Pasadena, California.

Ceres' is measured by monitoring radio signals sent to Dawn, and then received back on Earth, by NASA's Deep Space Network. This network is a collection of large antennas at three locations around the globe that communicate with interplanetary spacecraft. Using these signals, scientists can measure the spacecraft's speed to a precision of 0.004 inches (0.1 millimeters) per second, and then calculate the details of the gravity field.

Ceres has a special property called "hydrostatic equilibrium," which was confirmed in this study. This means that Ceres' interior is weak enough that its shape is governed by how it rotates. Scientists reached this conclusion by comparing Ceres' gravity field to its shape. Ceres' hydrostatic equilibrium is one reason why astronomers classified the body as a in 2006.

The data indicate that Ceres is "differentiated," which means that it has compositionally distinct layers at different depths, with the densest layer at the core. Scientists also have found that, as they suspected, Ceres is much less dense than Earth, the moon, giant asteroid Vesta (Dawn's previous target) and other rocky bodies in our solar system. Additionally, Ceres has long been suspected to contain low-density materials such as water ice, which the study shows separated from the rocky material and rose to the outer layer along with other light materials.

"We have found that the divisions between different layers are less pronounced inside Ceres than the moon and other planets in our solar system," Park said. "Earth, with its metallic core, semi-fluid mantle and outer crust, has a more clearly defined structure than Ceres," Park said.

Scientists also found that high-elevation areas on Ceres displace mass in the interior. This is analogous to how a boat floats on water: the amount of displaced water depends on the mass of the boat. Similarly, scientists conclude that Ceres' weak mantle can be pushed aside by the mass of mountains and other high topography in the outermost layer as though the high-elevation areas "float" on the material below. This phenomenon has been observed on other planets, including Earth, but this study is the first to confirm it at Ceres.

The internal density structure, based on the new gravity data, teaches about what internal processes could have occurred during the early history of Ceres. By combining this new information with previous data from Dawn about Ceres' surface composition, they can reconstruct that history: Water must have been mobile in the ancient subsurface, but the interior did not heat up to the temperatures at which silicates melt and a forms.

"We know from previous Dawn studies that there must have been interactions between water and rock inside Ceres," said Carol Raymond, a co-author and Dawn's deputy principal investigator based at JPL. "That, combined with the new density structure, tells us that Ceres experienced a complex thermal history."


Explore further

Dawn completes primary mission

More information: R. S. Park et al. A partially differentiated interior for (1) Ceres deduced from its gravity field and shape, Nature (2016). DOI: 10.1038/nature18955
Journal information: Nature

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Citation: What's inside Ceres? New findings from gravity data (2016, August 4) retrieved 26 August 2019 from https://phys.org/news/2016-08-ceres-gravity.html
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Aug 04, 2016
I am glad the Ceres' spots are no longer in the news. What a sham! What happened to the mystery?

Aug 05, 2016
I am glad the Ceres' spots are no longer in the news. What a sham! What happened to the mystery?


I assume you are referring to the "bright spots"? [ http://www.nasa.g...on-ceres ] Those are tied to this discovery, since it is now believed to be salts left after hydrothermal vents, water activity which is not unsurprising if Ceres innards hosts melt water. (In other versions of these news, they claim ongoing heating from radioactivity.)

What is the "sham" you talk about? The spots hasn't gone anywhere, and their "mystery" (really?) seems to be predicted by recent finds.

Aug 09, 2016
I am sorry, I am tired of misrepresented news and sometimes I let my frustration overwhelm my comments. I am tired of hearing "flossing isn't good for you," "being overweight is healthy," "there are mice on Mars," and (the kicker) "The U.S. is heading into a recession!" These are just a few of the quotes on the internet and in the news every day that make absolutely no sense. This is why I question the legitimacy of every headline and blog post. Sometimes it gets the best of me and I think 90% of all news is fake or fictional. These Ceres spots might be salt or water, but I was tired of hearing about the mystery over and over with no results. Add that to the other misinformation published daily and you may understand.

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