Organics on Ceres are likely native

Distribution of organic materials is inconsistent with delivery by comets or asteroids.
By Laurel Kornfeld | Oct 19, 2017
Organic materials found on dwarf planet Ceres by NASA's Dawn spacecraft are likely native to the small world, according to research by scientists at the Southwest Research Institute (SwRI) in San Antonio, Texas.

The researchers specifically focused on a localized region of organic-rich material near Ernutet Crater, a 32-mile- (52-km-) wide opening on Ceres' northern hemisphere.

Two origins are theorized for these organic materials or carbon-based compounds. They could have been brought to Ceres by impacting asteroids or comets after the dwarf planet formed 4.5 billion years ago, or they could have been synthesized through an internal process on the dwarf planet.

Located at the boundary of the solar system's rocky planets and gas giants, Ceres is composed of clays and both sodium- and ammonium-carbonates, all of which indicate the small planet underwent complex chemical evolution.

"Earlier research that focused on the geology of the organic-rich region on Ceres were inconclusive about their origin," explained Simone Marchi, an SwRI principal investigator who presented the findings Wednesday at a press conference held at the American Astronomical Society's 49th Division for Planetary Sciences Meeting in Provo, Utah.

"Recently, we more fully investigated the viability of organics arriving via an asteroid or comet impact."

Through computer simulations, scientists considered a range of variables, including the sizes and velocities of impacting objects.

The simulations indicated comet-like objects that hit Ceres at very high velocities would have had their organic materials destroyed by a mechanism known as shock compression, in which total pressure is lost.

Impacting asteroids, which would have lower velocities, would hold onto between 20 and 30 percent of their organic materials, depending on the angle at which they hit.

However, the localized distribution of organic materials on Ceres is not consistent with what would be seen if those organics had been delivered by small asteroids from the belt between Mars and Jupiter.

While researchers admit they still do not have all the pieces of the puzzle when it comes to Ceres' organics, "These findings indicate that the organics are likely to be native to Ceres," Marchi said.

Ceres is geologically differentiated, with a rocky core and icy mantle, and may harbor a subsurface ocean that could possibly be home to microbial life.

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