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New observations from NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA) show that Ceres does not appear to have the carbon-rich surface composition that space- and ground-based telescopes previously indicated. The results were published in the Astronomical Journal on Jan. 16, 2017.
Cross section of Ceres showing the surface layers that are the subject of this study plus a watery mantle and a rocky-metallic core. The column of material at and just below Ceres’ surface (box) – the top layer contains anhydrous (dry) pyroxene dust accumulated from space mixed in with native hydrous (wet) dust, carbonates, and water ice. Image credit: Pierre Vernazza, LAM-CNRS / AMU.
SOFIA detected the presence of substantial amounts of material on Ceres’ surface that appear to be fragments of other asteroids containing mostly rocky silicates.
These observations are contrary to the currently accepted surface composition classification of the dwarf planet as a carbon-rich body, suggesting that it is cloaked by material that partially disguises its real makeup.
“This study resolves a long-time question about whether asteroid surface material accurately reflects the intrinsic composition of the asteroid. Our results show that by extending observations to the mid-infrared, the asteroid’s underlying composition remains identifiable despite contamination by as much as 20 percent of material from elsewhere,” said Dr. Pierre Vernazza, a researcher at the Laboratoire d’Astrophysique de Marseille, France, and lead author on the study.
Planetary researchers have classified Ceres, as well as 75% of all asteroids, in composition class ‘C’ based on their similar colors.
The mid-infrared spectra from SOFIA show that Ceres differs substantially from neighboring C-type asteroids, challenging the conventional understanding of the relationship between Ceres and smaller asteroids.
“SOFIA is the only observatory that can make this kind of observations. These and future mid-infrared observations are key to understanding the true nature and history of the asteroids,” said study co-author Dr. Franck Marchis, a planetary researcher at the Carl Sagan Center of the SETI Institute.
Ceres and asteroids are not the only context where material transported from elsewhere has affected the surfaces of solar system bodies. Dramatic examples include Saturn’s moon Iapetus and the red material seen by New Horizons on Pluto’s moon Charon.
Planetary scientists also hypothesize that material from comets and asteroids provided a final veneer to the then-forming Earth that included substantial amounts of water plus the organic substances of the biosphere.
“Models of Ceres based on data collected by NASA’s Dawn spacecraft plus ground-based telescopes indicated substantial amounts of water- and carbon-bearing minerals such as clays and carbonates,” Dr. Vernazza said.
“Only the mid-infrared observations made using SOFIA were able to show that both silicate and carbonate materials are present on the surface of Ceres.”
To identify where the pyroxene on the surface of Ceres came from, the team turned to interplanetary dust particles (IDPs) that form meteors when they are seen streaking through Earth’s atmosphere.
The researchers had previously shown that IDPs blasted into space by asteroid collisions are an important source of material accumulated on the surfaces of other asteroids.
The implication is that a coating of IDPs has caused Ceres to take on the coloration of some of its dry and rocky neighbors.
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P. Vernazza et al. 2017. Different Origins or Different Evolutions? Decoding the Spectral Diversity among C-type asteroids. AJ 153, 72; doi: 10.3847/1538-3881/153/2/72
This article is based on a press-release from NASA.
