[meteorite-list] Lowdown on Ceres: Images From Dawn's Closest Orbit

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.php?feature=4802

Lowdown on Ceres: Images From Dawn's Closest Orbit
Jet Propulsion Laboratory
December 22, 2015

[Image]
This image of Ceres was taken in Dawn's low-altitude mapping orbit around 
a crater chain called Gerber Catena. A 3-D view is also available. 
Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

NASA's Dawn spacecraft, cruising in its lowest and final orbit at dwarf 
planet Ceres, has delivered the first images from its best-ever viewpoint. 
The new images showcase details of the cratered and fractured surface. 
3-D versions of two of these views are also available.

Dawn took these images of the southern hemisphere of Ceres on Dec. 10, 
at an approximate altitude of 240 miles (385 kilometers), which is its 
lowest-ever orbital altitude. Dawn will remain at this altitude for the 
rest of its mission, and indefinitely afterward. The resolution of the 
new images is about 120 feet (35 meters) per pixel.

Among the striking views is a chain of craters called Gerber Catena, located 
just west of the large crater Urvara. Troughs are common on larger planetary 
bodies, caused by contraction, impact stresses and the loading of the 
crust by large mountains -- Olympus Mons on Mars is one example. The fracturing 
found all across Ceres' surface indicates that similar processes may have 
occurred there, despite its smaller size (the average diameter of Ceres 
is 584 miles, or 940 kilometers). Many of the troughs and grooves on Ceres 
were likely formed as a result of impacts, but some appear to be tectonic, 
reflecting internal stresses that broke the crust.

"Why they are so prominent is not yet understood, but they are probably 
related to the complex crustal structure of Ceres," said Paul Schenk, 
a Dawn science team member at the Lunar and Planetary Institute, Houston.

The images were taken as part of a test of Dawn's backup framing camera. 
The primary framing camera, which is essentially identical, began its 
imaging campaign at this lowest orbit on Dec. 16. Both cameras are healthy.

Dawn's other instruments also began their intense period of observations 
this month. The visible and infrared mapping spectrometer will help identify 
minerals by looking at how various wavelengths of light are reflected 
by the surface of Ceres. The gamma ray and neutron detector is also active. 
By measuring the energies and numbers of gamma rays and neutrons, two 
components of nuclear radiation, it will help scientists determine the 
abundances of some elements on Ceres.

Earlier in December, Dawn science team members revealed that the bright 
material found in such notable craters as Occator is consistent with salt 
-- and proposed that a type of magnesium sulfate called hexahydrite may 
be present. A different group of Dawn scientists found that Ceres also 
contains ammoniated clays. Because ammonia is abundant in the outer solar 
system, this finding suggests that Ceres could have formed in the vicinity 
of Neptune and migrated inward, or formed in place with material that 
migrated in from the outer solar system.

"As we take the highest-resolution data ever from Ceres, we will continue 
to examine our hypotheses and uncover even more surprises about this mysterious 
world," said Chris Russell, principal investigator of the Dawn mission, 
based at the University of California, Los Angeles.

Dawn is the first mission to visit a dwarf planet, and the first mission 
outside the Earth-moon system to orbit two distinct solar system targets. 
It orbited protoplanet Vesta for 14 months in 2011 and 2012, and arrived 
at Ceres on March 6, 2015.

Dawn's mission is managed by the Jet Propulsion Laboratory 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


Media Contact

Elizabeth Landau / Preston Dyches
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6425 / 354-7013
Elizabeth.Landau at jpl.nasa.gov / preston.dyches at jpl.nasa.gov 

2015-384