[meteorite-list] Bright Spots and Color Differences Revealed on Ceres
From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 22 Mar 2016 15:44:35 -0700 (PDT)
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."
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."
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,
More information about Dawn is available at the following sites:
Updated on 3/22/16 at 3:20 p.m.
Jet Propulsion Laboratory, Pasadena, CA
elizabeth.landau at jpl.nasa.gov
Received on Tue 22 Mar 2016 06:44:35 PM PDT