[meteorite-list] Bright Spots and Color Differences Revealed on Ceres

Tue Mar 22 18:44:35 EDT 2016

http://www.jpl.nasa.gov/news/news.php?feature=6168

Bright Spots and Color Differences Revealed on Ceres
Jet Propulsion Laboratory
March 22, 2016

Scientists from NASA's Dawn mission unveiled new images from the spacecraft's 
lowest orbit at Ceres, including highly anticipated views of Occator Crater, 
at the 47th annual Lunar and Planetary Science Conference in The Woodlands, 
Texas, on Tuesday.

Occator Crater, measuring 57 miles (92 kilometers) across and 2.5 miles 
(4 kilometers) deep, contains the brightest area on Ceres, the dwarf planet 
that Dawn has explored since early 2015. The latest images, taken from 
240 miles (385 kilometers) above the surface of Ceres, reveal a dome in 
a smooth-walled pit in the bright center of the crater. Numerous linear 
features and fractures crisscross the top and flanks of this dome. Prominent 
fractures also surround the dome and run through smaller, bright regions 
found within the crater.

"Before Dawn began its intensive observations of Ceres last year, Occator 
Crater looked to be one large bright area. Now, with the latest close 
views, we can see complex features that provide new mysteries to investigate," 
said Ralf Jaumann, planetary scientist and Dawn co-investigator at the 
German Aerospace Center (DLR) in Berlin. "The intricate geometry of the 
crater interior suggests geologic activity in the recent past, but we 
will need to complete detailed geologic mapping of the crater in order 
to test hypotheses for its formation."

Color Differences

The team also released an enhanced color map of the surface of Ceres, 
highlighting the diversity of surface materials and their relationships 
to surface morphology. Scientists have been studying the shapes of craters 
and their distribution with great interest. Ceres does not have as many 
large impact basins as scientists expected, but the number of smaller 
craters generally matches their predictions. The blue material highlighted 
in the color map is related to flows, smooth plains and mountains, which 
appear to be very young surface features.

"Although impact processes dominate the surface geology on Ceres, we have 
identified specific color variations on the surface indicating material 
alterations that are due to a complex interaction of the impact process 
and the subsurface composition," Jaumann said. "Additionally, this gives 
evidence for a subsurface layer enriched in ice and volatiles."

Counting Neutrons

Data relevant to the possibility of subsurface ice is also emerging from 
Dawn's Gamma Ray and Neutron Detector (GRaND), which began acquiring its 
primary data set in December. Neutrons and gamma rays produced by cosmic 
ray interactions with surface materials provide a fingerprint of Ceres' 
chemical makeup. The measurements are sensitive to elemental composition 
of the topmost yard (meter) of the regolith.

In Dawn's lowest-altitude orbit, the instrument has detected fewer neutrons 
near the poles of Ceres than at the equator, which indicates increased 
hydrogen concentration at high latitudes. As hydrogen is a principal constituent 
of water, water ice could be present close to the surface in polar regions.

"Our analyses will test a longstanding prediction that water ice can survive 
just beneath Ceres' cold, high-latitude surface for billions of years," 
said Tom Prettyman, the lead for GRaND and Dawn co-investigator at the 
Planetary Science Institute, Tucson, Arizona.

The Mystery of Haulani Crater

But the subsurface does not have the same composition all over Ceres, 
according to data from the visible and infrared mapping spectrometer (VIR), 
a device that looks at how various wavelengths of sunlight are reflected 
by the surface, allowing scientists to identify minerals.

Haulani Crater in particular is an intriguing example of how diverse Ceres 
is in terms of its surface material composition. This irregularly-shaped 
crater, with its striking bright streaks of material, shows a different 
proportion of surface materials than its surroundings when viewed with 
the VIR instrument. While the surface of Ceres is mostly made of a mixture 
of materials containing carbonates and phyllosilicates, their relative 
proportion varies across the surface.

"False-color images of Haulani show that material excavated by an impact 
is different than the general surface composition of Ceres. The diversity 
of materials implies either that there is a mixed layer underneath, or 
that the impact itself changed the properties of the materials," said 
Maria Cristina de Sanctis, the VIR instrument lead scientist, based at 
the National Institute of Astrophysics, Rome.

Water at Oxo

Dawn scientists also reported in an LPSC scientific session that the VIR 
instrument has detected water at Oxo Crater, a young, 6-mile-wide (9-kilometer-wide) 
feature in Ceres' northern hemisphere. This water could be bound up in 
minerals or, alternatively, it could take the form of ice.

Jean-Philippe Combe of the Bear Fight Institute, Winthrop, Washington, 
said that this water-bearing material could have been exposed during a 
landslide or an impact -- perhaps even a combination of the two events.

Oxo is the only place on Ceres where water has been detected at the surface 
so far. Dawn will continue to observe this area.

The Big Picture

Dawn made history last year as the first mission to reach a dwarf planet, 
and the first to orbit two distinct extraterrestrial targets -- both of 
them in the main asteroid belt between Mars and Jupiter. The mission conducted 
extensive observations of Vesta during its 14-month orbit there in 2011-2012.

"We're excited to unveil these beautiful new images, especially Occator, 
which illustrate the complexity of the processes shaping Ceres' surface. 
Now that we can see Ceres' enigmatic bright spots, surface minerals and 
morphology in high resolution, we're busy working to figure out what processes 
shaped this unique dwarf planet. By comparing Ceres with Vesta, we'll 
glean new insights about the early solar system," said Carol Raymond, 
deputy principal investigator for the Dawn mission, based at NASA's Jet 
Propulsion Laboratory, Pasadena, California.

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

Updated on 3/22/16 at 3:20 p.m.

Media Contact

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

2016-081