Ceres Prank Lands Bart Simpson In Detention For Eternity

Do you see Bart Simpson's face on these surface features on Ceres? Researchers studying the surface of the dwarf planet for evidence of the presence of ice do. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA, taken by Dawn Framing Camera

Human-kind has a long history of looking up at the stars and seeing figures and faces. In fact, there’s a word for recognizing faces in natural objects: pareidolia. But this must be the first time someone has recognized Bart Simpson’s face on an object in space.

Researchers studying landslides on the dwarf planet Ceres noticed a pattern that resembles the cartoon character. The researchers, from the Georgia Institute of Technology, are studying massive landslides that occur on the surface of the icy dwarf. Their findings are reinforcing the idea that Ceres has significant quantities of frozen water.

Dwarf planet Ceres is the largest object in the asteroid belt between Mars and Jupiter. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA, taken by Dawn Framing Camera
Dwarf planet Ceres is the largest object in the asteroid belt between Mars and Jupiter. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA, taken by Dawn Framing Camera

In a new paper in the journal Nature Geoscience, the team of scientists, led by Georgia Tech Assistant Professor and Dawn Science Team Associate Britney Schmidt, examined the surface of Ceres looking for morphologies that resemble landslides here on Earth.

Research shows us that Ceres probably has a subsurface shell that is rich with water-ice. That shell is covered by a layer of silicates. Close examination of the type, and distribution, of landslides at different latitudes adds more evidence to the sub-surface ice theory.

Ceres is pretty big. At 945 km in diameter, it’s the largest object in the asteroid belt between Mars and Jupiter. It’s big enough to be rounded by its own gravity, and it actually comprises about one third of the mass of the entire asteroid belt.

Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA, taken by Dawn Framing Camera
Type 1 landslides on Ceres are large and occur at higher latitudes. Image: Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA, taken by Dawn Framing Camera

The team used observations from the Dawn Framing Camera to identify three types of landslides on Ceres’ surface:

  • Type 1 are large, rounded features similar to glacier features in the Earth’s Arctic region. These are found mostly at high latitudes on Ceres, which is where most of the ice probably is.
  • Type 2 are the most common. They are thinner and longer than Type 1, and look like terrestrial avalanche deposits. They’re found mostly at mid-latitudes on Ceres. The researchers behind the study thought one of them looked like Bart Simpson’s face.
  • Type 3 occur mostly at low latitudes near Ceres’ equator. These are always found coming from large impact craters, and probably formed when impacts melted the sub-surface ice.
Type 3 landslides on Ceres occur at low latitudes at large craters, and form when ice is melted by impacts. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA, taken by Dawn Framing Camera
Type 3 landslides on Ceres occur at low latitudes at large craters, and form when ice is melted by impacts. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA, taken by Dawn Framing Camera

The authors of the study say that finding larger landslides further away from the equator is significant, because that’s where most of the ice is.

“Landslides cover more area in the poles than at the equator, but most surface processes generally don’t care about latitude,” said Schmidt, a faculty member in the School of Earth and Atmospheric Sciences. “That’s one reason why we think it’s ice affecting the flow processes. There’s no other good way to explain why the poles have huge, thick landslides; mid-latitudes have a mixture of sheeted and thick landslides; and low latitudes have just a few.”  

Key to understanding these results is the fact that these types of processes have only been observed before on Earth and Mars. Earth, obviously, has water and ice in great abundance, and Mars has large quantities of sub-surface ice as well. “It’s just kind of fun that we see features on this small planet that remind us of those on the big planets, like Earth and Mars,” Schmidt said. “It seems more and more that Ceres is our innermost icy world.”

“These landslides offer us the opportunity to understand what’s happening in the upper few kilometers of Ceres,” said Georgia Tech Ph.D. student Heather Chilton, a co-author on the paper. “That’s a sweet spot between information about the upper meter or so provided by the GRaND (Gamma Ray and Neutron Detector) and VIR (Visible and Infrared Spectrometer) instrument data, and the tens of kilometers-deep structure elucidated by crater studies.”

It’s not just the presence of these landslides, but the frequency of them, that upholds the icy-mantle idea on Ceres. The study showed that 20% to 30% of craters on Ceres larger than 10 km have some type of landslide. The researchers say that upper layers of Ceres’ could be up to 50% ice by volume.

Massive Ice Avalanches on Iapetus

We’ve seen avalanches on Mars, but now scientists have found avalanches taking place on an unlikely place in our solar system: Saturn’s walnut-shaped, two-toned moon Iapetus. And these aren’t just run-of-the-mill avalanches: they are huge inundations of debris. These events are specifically known as long-runout landslides — debris flows that have traveled unusually long distances. Just how these avalanches are occurring is somewhat of a mystery, according to Bill McKinnon from Washington University in St. Louis.

“This is really about the mystery of long-runout landslides, and no one really knows for sure what causes them,” said McKinnon, speaking at the Lunar and Planetary Science Conference this week.

These avalanches or landslides certainly have their Earthly counterparts and, as noted, similar events are found on Mars, where they are especially associated with the steep canyon walls of the Valles Marineris system. However, the large mass movements on Iapetus in the form of long-runout landslides are less common.

McKinnon said the amount of material that has been moved in all the avalanches on Iapetus that he and his team have found exceeds all the material moved in known Martian landslides (in published data), even though Mars is much bigger than Iapaetus.

“The mechanics of long-runout landslides are poorly understood, and mechanisms proposed for friction reduction are so numerous I can’t fit them all on one Powerpoint slide,” McKinnon said during his talk. Possible explanations include water (such as released groundwater), wet or saturated soil, ice, trapped or compressed air, acoustic fluidization, and more.

On Iapetus there is obviously no water or atmosphere to create conducive conditions for avalanches. But McKinnon and his team have identified over two dozen avalanche events as seen in images from the Cassini spacecraft.

Many of the landslides are seen from crater and basin walls and steep scarps. McKinnon and his team have found two types of avalanches: ‘blocky’ with rough-looking debris and smoother lobate landslides. They also see evidence that over time, multiple avalanches have likely occurred in the same location, so Iapetus must have a long history of mass wasting and landslides.

So, what allows for the huge avalanches on Iapetus? McKinnon said ice provides the best answer to that question. The low density of Iapetus indicates that it is mostly composed of ice, with only about 20% of rocky materials.

“There seems to be a necessity for a fluidization or liquid mechanism,” McKinnon said. “If ice is warmed just enough it will become slippery,” reducing the friction and cohesiveness of the crater or basin wall.

What they are seeing, especially in the lobate landslides, is consistent with ‘rheological’ flow similar to molten lava or fluid mudslides.

So, ice rubble within the rocky faces of crater and basin walls are heated just enough – either by flash heating or friction — that the surfaces become slippery. “The energetics are favorable for this mechanism on Iapetus,” McKinnon said.

Iapetus has a very slow rotation, longer than 79 days, and such a slow rotation means that the daily temperature cycle is very long — so long that the dark material can absorb heat from the Sun and warm up. Of course the dark part of Iapetus absorbs more heat than the bright icy material; therefore, McKinnon said, this is all fairly enigmatic.

Plus, saying that it “warms up” on Iapetus is a bit of an overstatement. Temperatures on the dark region’s surface are estimated to reach 130 K (-143 °C; -226 °F) at the equator and temperatures in the brighter area only reach about 100 K (-173 °C; -280 °F).

Whatever the mechanisms, the long-runout landslides on Iapetus are fairly unique when it comes to icy planetary bodies. McKinnon referenced that just two mass movements of modest scale have been detected on Callisto, and there is limited evidence of similar events on Phoebe.

These ice avalanches certainly deserve more investigation on a moon which McKinnon described as having “singularly spectacular topography,” and additional research and a more detailed paper are forthcoming.

Read the LPSC abstract: Massive Ice Avalanches on Iapetus, and the Mechanism of Friction Reduction in Long-Runout Landslides