“Still a Puzzle” –Organics-Rich Region on Ceres Found to Be Native to the Dwarf Planet (VIDEO)

 

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Since NASA's Dawn mission fits went into orbit around Ceres,  evidence has been found for organic material on the  dwarf planet, the largest body in the main asteroid belt between Mars and Jupiter. Scientists using the spacecraft's visible and infrared mapping spectrometer (VIR) detected the material in and around a northern-hemisphere crater called Ernutet. Organic molecules are interesting to scientists because they are necessary, though not sufficient, components of life on Earth.


"This is the first clear detection of organic molecules from orbit on a main belt body," said Maria Cristina De Sanctis, lead author of the study, based at the National Institute of Astrophysics, Rome. The discovery is reported in the journal Science.

The organics discovery adds to Ceres' attributes associated with ingredients and conditions for life in the distant past. Previous studies have found hydrated minerals, carbonates, water ice, and ammoniated clays that must have been altered by water. Salts and sodium carbonate, such as those found in the bright areas of Occator Crater, are also thought to have been carried to the surface by liquid.

“This discovery adds to our understanding of the possible origins of water and organics on Earth,” said Julie Castillo-Rogez, Dawn project scientist based at NASA's Jet Propulsion Laboratory in Pasadena, California.

The VIR instrument was able to detect and map the locations of this material because of its special signature in near-infrared light.

 

 

The organic materials on Ceres are mainly located in an area covering approximately 400 square miles (about 1,000 square kilometers). The signature of organics is very clear on the floor of Ernutet Crater, on its southern rim and in an area just outside the crater to the southwest. Another large area with well-defined signatures is found across the northwest part of the crater rim and ejecta. There are other smaller organic-rich areas several miles (kilometers) west and east of the crater. Organics also were found in a very small area in Inamahari Crater, about 250 miles (400 kilometers) away from Ernutet.

In enhanced visible color images from Dawn's framing camera, the organic material is associated with areas that appear redder with respect to the rest of Ceres. The distinct nature of these regions stands out even in low-resolution image data from the visible and infrared mapping spectrometer.

"We're still working on understanding the geological context for these materials," said study co-author Carle Pieters, professor of geological sciences at Brown University, Providence, Rhode Island.

 

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This enhanced color composite image above from Dawn's visible and infrared mapping spectrometer shows the area around Ernutet Crater on Ceres. The instrument detected the evidence of organic materials in this area, as reported in a 2017 study in the journal Science. In this view, areas that appear pink with respect to the background appear to be rich in organics, and green areas are where organic material appears to be less abundant.Light with a wavelength of 2000 nanometers is shown in blue, 3400 nanometers is shown in green and 1700 nanometers is shown in red. (NASA/JPL-Caltech/UCLA/ASI/INAF)

When NASA's Dawn spacecraft started orbiting Ceres mission scientists expected to find a heavily cratered body generally resembling the protoplanet Vesta, Dawn's previous port of call. Instead, as the spacecraft drew near to Ceres, a somewhat different picture began to emerge: Something has happened to remove its biggest impact basins, suggesting that suggest that Ceres has experienced significant geological evolution, possibly erasing the large basins, as well as organic rich regions that have important astrobiological implications.

Since then, the Dawn spacecraft has detected localized organic-rich material that Southwest Research Institute(SwRI) scientists have studying to explore different scenarios for its origin. After considering the viability of comet or asteroid delivery, the preponderance of evidence suggests the organics are most likely native to Ceres.

"The discovery of a locally high concentration of organics close to the Ernutet crater poses an interesting conundrum," said Dr. Simone Marchi, a principal scientist at SwRI, who is discussing his team findings today at a press conference at the American Astronomical Society's 49th Division for Planetary Sciences Meeting in Provo, Utah. "Was the organic material delivered to Ceres after its formation? Or was it synthesized and/or concentrated in a specific location on Ceres via internal processes? Both scenarios have shortfalls, so we may be missing a critical piece of the puzzle."

Ceres is believed to have originated about 4.5 billion years ago at the dawn of our solar system. Studying its organics can help explain the origin, evolution, and distribution of organic species across the solar system. The very location of Ceres at the boundary between the inner and outer solar system and its intriguing composition characterized by clays, sodium- and ammonium-carbonates, suggest a very complex chemical evolution. The role of organics in this evolution is not fully understood, but has important astrobiological implications.

 

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SwRI scientists are studying the geology associated with the organic-rich areas on Ceres. Dawn spacecraft data show a region around the Ernutet crater where organic concentrations have been discovered (background image). The color coding shows the surface concentration of organics, as inferred from the visible and near infrared spectrometer. The inset shows a higher resolution enhanced color image of the Ernutet crater acquired by Dawn's framing camera. Regions in red indicate higher concentration of organics.

"Earlier research that focused on the geology of the organic-rich region on Ceres were inconclusive about their origin," Marchi said. "Recently, we more fully investigated the viability of organics arriving via an asteroid or comet impact."

Scientists explored a range of impact parameters, such as impactor sizes and velocities, using iSALE shock physics code simulations. These models indicated that comet-like projectiles with relatively high impact velocities would lose almost all of their organics due to shock compression.

Impacting asteroids, with lower incident velocities, can retain between 20 and 30 percent of their pre-impact organic material during delivery, especially for small impactors at oblique impact angles. However, the localized spatial distribution of organics on Ceres seems difficult to reconcile with delivery from small main belt asteroids.

"These findings indicate that the organics are likely to be native to Ceres," Marchi said.

The Daily Galaxy via  NASA/Dawn Mission Organics  and NASA/Astrobiology.com

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