[meteorite-list] Landslides on Ceres Reflect Ice Content

[Ron Baalke]

https://www.jpl.nasa.gov/news/news.php?feature=6820

Landslides on Ceres Reflect Ice Content
Jet Propulsion Laboratory
April 19, 2017

As NASA's Dawn spacecraft continues exploring Ceres, evidence mounts that 
the enigmatic dwarf planet retains a significant amount of water ice. 
A new study in the journal Nature Geoscience adds to this picture, showing 
how ice may have shaped the variety of landslides seen on Ceres today.

"Images from Dawn show that landslides, many of which are similar to those 
seen on Earth, are very common on Ceres, and further the case that Ceres 
has a lot of water ice involved in its structure," said Britney Schmidt, 
who led the study. She is an associate of the Dawn science team and assistant 
professor at Georgia Institute of Technology in Atlanta.

Types of Landslides

Schmidt and colleagues identified three types of landslides. Type I, which 
are relatively round and large, have thick "toes" at their ends. They 
look similar to rock glaciers and icy landslides on Earth. Type I landslides 
are mostly found at high latitudes on Ceres, which is also where the most 
ice is thought to reside just beneath the surface, suggesting they involve 
the most ice of any of the flow features. Three small Type 1 flows are 
found in Oxo Crater, a tiny bright crater in the northern hemisphere that 
hosts an ice deposit at the surface.

Type II features are often thinner and longer than Type I, and are the 
most common type of landslide on Ceres. The landslide deposits appear 
similar to those left behind by avalanches seen on Earth.

Ceres' Type III features may involve a brief melting of some of the ice 
within the soil-like regolith, causing the material to flow like mud before 
refreezing. These landslides are always associated with large impact craters, 
and may have formed when an impact event melts subsurface ice on Ceres. 
These features have similar appearances to ejected material from craters 
in the icy regions of Mars and on Jupiter's moon Ganymede.

"The locations of these different types of features reinforces the idea 
that the shallow subsurface of Ceres is a mixture of ice and rock, and 
that ice is most plentiful near the surface at the poles," Schmidt said.

Scientists were also surprised at just how many landslides have occurred 
on Ceres in general. About 20 to 30 percent of craters greater than 6 
miles (10 kilometers) wide have some type of landslide associated with 
them. Such widespread "ground ice" features, which formed from of a mixture 
of rock and ice, had only been observed before on Earth and Mars.

Implications and Future Observations

Based on the shape and distribution of landslides on Ceres, study authors 
estimate that the ice in the upper few tens of meters of Ceres may range 
from 10 percent to 50 percent by volume.

"These kinds of flows are not seen on bodies such as Vesta, which Dawn 
studied from 2011 to 2012, because the regolith is devoid of water," said 
Carol Raymond, deputy principal investigator for the Dawn mission, based 
at NASA's Jet Propulsion Laboratory, Pasadena, California.

Now in its extended mission phase, Dawn is using its ion engine to swivel 
the plane of its orbit around Ceres to prepare for observations from a 
new orbit and orientation. At the end of April, the spacecraft will be 
directly between the sun and the mysterious Occator Crater. In this geometry, 
Dawn may deliver new insights about the reflective material of Ceres' 
most famous "bright spot," the highly reflective center of Occator that 
has been named Cerealia Facula.

The Dawn mission is managed by JPL for NASA's Science Mission Directorate 
in Washington. Dawn is a project of the directorate's Discovery Program, 
managed by NASA's Marshall Space Flight Center in Huntsville, Alabama. 
UCLA is responsible for overall Dawn mission science. Orbital ATK Inc., 
in Dulles, Virginia, designed and built the spacecraft. The German Aerospace 
Center, Max Planck Institute for Solar System Research, Italian Space 
Agency and Italian National Astrophysical Institute are international 
partners on the mission team. For a complete list of mission participants, 
visit:

https://dawn.jpl.nasa.gov/mission

More information about Dawn is available at the following sites:

https://www.nasa.gov/dawn

https://dawn.jpl.nasa.gov

News Media Contact
Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, CA
818-354-6425
elizabeth.landau at jpl.nasa.gov

2017-114