NASA’s Dawn mission recently spotted mysterious bright spots in the center of Occator Crater on the dwarf planet Ceres. According to a new study published in the journal Geophysical Research Letters, these bright spots are salts extruded from a large cryomagma reservoir in the crust that melted during the asteroid impact that formed Occator Crater.
The bright spots near the center of Occator crater are shown in enhanced color in this view from NASA’s Dawn robotic spacecraft. Lower resolution color data have been overlaid onto a higher resolution view of the crater. The view was produced by combining the highest resolution images of Occator obtained in February 2016 with color images obtained in September 2015. The three images used to produce the color were taken using spectral filters centered at 438, 550 and 965 nanometers. Dawn’s close-up view reveals 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. Image credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA / PSI / LPI.
At 585 miles (941 km) across, Ceres is the largest planetary body in the asteroid belt between Mars and Jupiter.
Forged billions of years ago from rock and ice and far enough from the influence of other planets, planetary scientists had thought that Ceres’ days of active geology had come to close.
But NASA’s Dawn mission changed that view when the orbiter sent back pictures of bright spots at the bottom of impact craters. The spots turned out to be the remnants of cryomagma.
The location of the spots at or near the center of crater basins suggests that the heat and energy generated by asteroid impacts could jumpstart geology on Ceres, creating reservoirs of cryomagma that were then brought to the surface by conduits such as fractures.
In the new study, Dr. Marc Hesse from the University of Texas at Austin and Dr. Julie Castillo-Rogez of NASA’s Jet Propulsion Laboratory looked specifically at the deposits on the floor of the 90-mile (145 km) wide Occator Crater, which was formed about 20 million years ago.
However, the deposits here are as young as 4 million years old, indicating a relatively recent formation geologically speaking with respect to the crater itself.
Earlier research found that the conditions on Ceres wouldn’t allow for the cryomagma generated by the Occator impact to exist for more than about 400,000 years.
The age discrepancy between salt deposits and impact timing raises a question: how could a reservoir of melt stay in a liquid state for millions of years after impact on an otherwise geologically stagnant world?
Dr. Hesse and Dr. Castillo-Rogez were able to significantly extend the life of the cryomagma by including more up-to-date details on Ceres’ crustal chemistry and physics.
“It’s difficult to maintain liquid so close to the surface. But our new model includes materials inside the crust that tend to act as insulators consistent with the results from the Dawn observations,” Dr. Castillo-Rogez said.
The team’s calculations indicate that the cryomagma of Occator Crater could last up to 10 million years.
“Now that we’re accounting for all these negative feedbacks on cooling — the fact that you release latent heat, the fact that as you warm up the crust it becomes less conductive — you can begin to argue that if the ages are just off by a few million years you might get it,” Dr. Hesse said.
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M.A. Hesse & J.C. Castillo-Rogez. Thermal Evolution of the Impact-Induced Cryomagma Chamber Beneath Occator Crater on Ceres. Geophysical Research Letters, published online December 5, 2018; doi: 10.1029/2018GL080327
