Abstract
Abstract Comet C/2013 US10 (Catalina) was a dynamically new Oort cloud comet whose apparition presented a favorable geometry for observations near close-Earth approach (≃0.93 au) at heliocentric distances ≲2 au when insolation and sublimation of volatiles drive maximum activity. Here we present mid-infrared 6.0 ≲ λ(μm) ≲ 40 spectrophotometric observations at two temporal epochs from NASA’s Stratospheric Observatory for Infrared Astronomy and the NASA Infrared Telescope Facility that yield an inventory of the refractory materials and their physical characteristics through thermal modeling analysis. The grain composition is dominated by dark dust grains (modeled as amorphous carbon) with a silicate-to-carbon ratio ≲0.9, little crystalline stoichiometry (no distinct 11.2 μm feature attributed to Mg-rich crystalline olivine), and the submicron grain-size distribution peaking at ≃0.6 μm. The 10 μm silicate feature was weak, ≈12.8% ± 0.1% above the local continuum, and the bolometric grain albedo was low (≲14%). Comet C/2013 US10 (Catalina) is a carbon-rich object. This material, which is well represented by the optical constants of amorphous carbon, is similar to the material that darkens and reddens the surface of comet 67P/Churyumov–Gerasimenko. We argue this material is endemic to the nuclei of comets, synthesizing results from the study of Stardust samples, interplanetary dust particle investigations, and micrometeoritic analyses. The atomic carbon-to-silicate ratio of comet C/2013 US10 (Catalina) and other comets joins a growing body of evidence suggesting the existence of a C/Si gradient in the primitive solar system, providing new insight into planetesimal formation and the distribution of isotopic and compositional gradients extant today.
Highlights
Traces of primordial materials, and their leastprocessed products, are to be found in the outermost regions of the solar system in the form of ices of volatile materials (H2O, Crystalline olivine (CO), CO2, and other more rare species), and more refractory dust grains
The grain composition is dominated by dark dust grains with a silicate-to-carbon ratio
In this paper we report our post-perihelion (TP = 2015 Nov 15.721 UT) spectrophotometric observations of comet C/2013 US10 (Catalina), a dynamically new Oort Cloud comet with 1/aorg = 5.3 × 10−6 AU−1 (Williams 2019) and discuss important new interpretations that the coma grain composition of comets from remote sensing observations can bring to understanding disk processing in the primitive solar system
Summary
Their leastprocessed products, are to be found in the outermost regions of the solar system in the form of ices of volatile materials (H2O, CO, CO2, and other more rare species), and more refractory dust grains. Information on the nature of these grains comes from a variety of sources, including remote sensing through telescopic observations (ground-based, airborne, and spacebased), rendezvous/encounter experiments (i.e., Giotto, Rosetta/Philae, Deep Impact ), collection of interplanetary dust particles (IDPs) in the Earth’s stratosphere, and a sample return mission (Stardust ). All these activities have made important contributions to our understanding of these grains.
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