http://www.jpl.nasa.gov/news/news.php?feature=6611

Ceres' Geological Activity, Ice Revealed in New Research
Jet Propulsion Laboratory
September 1, 2016

A lonely 3-mile-high (5-kilometer-high) mountain on Ceres is likely volcanic 
in origin, and the dwarf planet may have a weak, temporary atmosphere. 
These are just two of many new insights about Ceres from NASA's Dawn mission 
published this week in six papers in the journal Science.

"Dawn has revealed that Ceres is a diverse world that clearly had geological 
activity in its recent past," said Chris Russell, principal investigator 
of the Dawn mission, based at the University of California, Los Angeles.

A Temporary Atmosphere

A surprising finding emerged in the paper led by Russell: Dawn may have 
detected a weak, temporary atmosphere. Dawn's gamma ray and neutron (GRaND) 
detector observed evidence that Ceres had accelerated electrons from the 
solar wind to very high energies over a period of about six days. In theory, 
the interaction between the solar wind's energetic particles and atmospheric 
molecules could explain the GRaND observations.

A temporary atmosphere would be consistent with the water vapor the Herschel 
Space Observatory detected at Ceres in 2012-2013. The electrons that GRaND 
detected could have been produced by the solar wind hitting the water 
molecules that Herschel observed, but scientists are also looking into 
alternative explanations.

"We're very excited to follow up on this and the other discoveries about 
this fascinating world," Russell said.

Ahuna Mons as a Cryovolcano

Ahuna Mons is a volcanic dome unlike any seen elsewhere in the solar system, 
according to a new analysis led by Ottaviano Ruesch of NASA's Goddard 
Space Flight Center, Greenbelt, Maryland, and the Universities Space Research 
Association. Ruesch and colleagues studied formation models of volcanic 
domes, 3-D terrain maps and images from Dawn, as well as analogous geological 
features elsewhere in our solar system. This led to the conclusion that 
the lonely mountain is likely volcanic in nature. Specifically, it would 
be a cryovolcano -- a volcano that erupts a liquid made of volatiles such 
as water, instead of silicates. "This is the only known example of a 
cryovolcano 
that potentially formed from a salty mud mix, and that formed in the 
geologically 
recent past," Ruesch said.

For more details on this study, see:
http://www.nasa.gov/feature/goddard/2016/ceres-cryo-volcano

Ceres: Between a Rocky and Icy Place

While Ahuna Mons may have erupted liquid water in the past, Dawn has detected 
water in the present, as described in a study led by Jean-Philippe Combe 
of the Bear Fight Institute, Winthrop, Washington. Combe and colleagues 
used Dawn's visible and infrared mapping spectrometer (VIR) to detect 
probable water ice at Oxo Crater, a small, bright, sloped depression at 
mid-latitudes on Ceres.

Exposed water-ice is rare on Ceres, but the low density of Ceres, the 
impact-generated flows and the very existence of Ahuna Mons suggest that 
Ceres' crust does contain a significant component of water-ice. This is 
consistent with a study of Ceres' diverse geological features led by Harald 
Hiesinger of the Westfälische Wilhelms-Universität, Münster, Germany. 
The diversity of geological features on Ceres is further explored in a 
study led by Debra Buczkowski of the Johns Hopkins Applied Physics Laboratory, 
Laurel, Maryland.

Impact craters are clearly the most abundant geological feature on Ceres, 
and their different shapes help tell the intricate story of Ceres' past. 
Craters that are roughly polygonal -- that is, shapes bounded by straight 
lines -- hint that Ceres' crust is heavily fractured. In addition, several 
Cerean craters have patterns of visible fractures on their floors.

Some, like tiny Oxo, have terraces, while others, such as the large Urvara 
Crater (106 miles, 170 kilometers wide), have central peaks. There are 
craters with flow-like features, and craters that imprint on other craters, 
as well as chains of small craters. Bright areas are peppered across Ceres, 
with the most reflective ones in Occator Crater. Some crater shapes could 
indicate water-ice in the subsurface.

The dwarf planet's various crater forms are consistent with an outer shell 
for Ceres that is not purely ice or rock, but rather a mixture of both 
-- a conclusion reflected in other analyses. Scientists also calculated 
the ratio of various craters' depths to diameters, and found that some 
amount of crater relaxation must have occurred. Additionally, there are 
more craters in the northern hemisphere of Ceres than the south, where 
the large Urvara and Yalode craters are the dominant features.

"The uneven distribution of craters indicates that the crust is not uniform, 
and that Ceres has gone through a complex geological evolution," Hiesinger 
said.

Distribution of Surface Materials

What are the rocky materials in Ceres' crust? A study led by Eleonora 
Ammannito of the University of California, Los Angeles, finds that clay-forming 
minerals called phyllosilicates are all over Ceres. These phyllosilicates 
are rich in magnesium and also have some ammonium embedded in their crystalline 
structure. Their distribution throughout the dwarf planet's crust indicates 
Ceres' surface material has been altered by a global process involving 
water.

Although Ceres' phyllosilicates are uniform in their composition, there 
are marked differences in how abundant these materials are on the surface. 
For example, phyllosilicates are especially prevalent in the region around 
the smooth, "pancake"-like crater Kerwan (174 miles, 280 kilometers in 
diameter), and less so at Yalode Crater (162 miles, 260 kilometers in 
diameter), which has areas of both smooth and rugged terrain around it. 
Since Kerwan and Yalode are similar in size, this may mean that the composition 
of the material into which they impacted may be different. Craters Dantu 
and Haulani both formed recently in geologic time, but also seem to differ 
in composition.

"In comparing craters such as Dantu and Haulani, we find that their different 
material mixtures could extend beneath the surface for miles, or even 
tens of miles in the case of the larger Dantu," Ammannito said.

Looking Higher

Now in its extended mission, the Dawn spacecraft has delivered a wealth 
of images and other data from its current perch at 240 miles (385 kilometers) 
above Ceres' surface, which is closer to the dwarf planet than the 
International 
Space Station is to Earth. The spacecraft will be increasing its altitude 
at Ceres on Sept. 2, as scientists consider questions that can be examined 
from higher up.

Dawn's 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:

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

More information about Dawn is available at the following sites:

http://dawn.jpl.nasa.gov

http://www.nasa.gov/dawn

News Media Contact
Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6425
elizabeth.lan...@jpl.nasa.gov

2016-229

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