| 1. |
- Cartwright, Richard J., et al.
(författare)
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Revealing Callisto's Carbon-rich Surface and CO2 Atmosphere with JWST
- 2024
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Ingår i: The Planetary Science Journal. - : American Astronomical Society. - 2632-3338. ; 5:3
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Tidskriftsartikel (refereegranskat)abstract
- We analyzed spectral cubes of Callisto’s leading and trailing hemispheres, collected with the NIRSpec Integrated Field Unit (G395H) on the James Webb Space Telescope. These spatially resolved data show strong 4.25 μm absorption bands resulting from solid-state 12CO2, with the strongest spectral features at low latitudes near the center of its trailing hemisphere, consistent with radiolytic production spurred by magnetospheric plasma interacting with native H2O mixed with carbonaceous compounds. We detected CO2 rovibrational emission lines between 4.2 and 4.3 μm over both hemispheres, confirming the global presence of CO2 gas in Callisto’s tenuous atmosphere. These results represent the first detection of CO2 gas over Callisto’s trailing side. The distribution of CO2 gas is offset from the subsolar region on either hemisphere, suggesting that sputtering, radiolysis, and geologic processes help sustain Callisto’s atmosphere. We detected a 4.38 μm absorption band that likely results from solid-state 13CO2. A prominent 4.57 μm absorption band that might result from CN-bearing organics is present and significantly stronger on Callisto’s leading hemisphere, unlike 12CO2, suggesting these two spectral features are spatially antiassociated. The distribution of the 4.57 μm band is more consistent with a native origin and/or accumulation of dust from Jupiter’s irregular satellites. Other, more subtle absorption features could result from CH-bearing organics, CO, carbonyl sulfide, and Na-bearing minerals. These results highlight the need for preparatory laboratory work and improved surface-atmosphere interaction models to better understand carbon chemistry on the icy Galilean moons before the arrival of NASA’s Europa Clipper and ESA’s JUICE spacecraft.
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| 2. |
- Davidsson, Björn J. R., et al.
(författare)
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Thermal inertia and surface roughness of Comet 9P/Tempel 1
- 2013
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Ingår i: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 224:1, s. 154-171
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Tidskriftsartikel (refereegranskat)abstract
- Re-calibrated near-infrared spectroscopy of the resolved nucleus of Comet 9P/Tempel 1 acquired by the Deep Impact spacecraft has been analyzed by utilizing the post-Stardust-NExT nucleus shape model and spin pole solution, as well as a novel thermophysical model that explicitly accounts for small-scale surface roughness and thermal inertia. We find that the thermal inertia varies measurably across the surface, and that thermal emission from certain regions only can be reproduced satisfactory if surface roughness is accounted for. Particularly, a scarped/pitted terrain that experienced morning sunrise during the flyby is measurably rough (Hapke mean slope angle similar to 45 degrees) and has a thermal inertia of at most 50J m(-2) K-1 s(-1/2), but probably much lower. However, thick layered terrain and thin layered terrain experiencing local noon during the flyby have a substantially larger thermal inertia, reaching 150J m(-2) K-1 s(-1/2) if the surface is as rough as the scarped/pitted terrain, but 200J m(-2) K-1 s(-1/2) if the terrain is considered locally flat. Furthermore, the reddening of the nucleus near-infrared 1.5-2.2 gm spectrum varies between morphological units, being reddest for thick layered terrain (median value 3.4% k angstrom(-1)) and most neutral for the smooth terrain known to contain surface water ice (median value 3.1% k angstrom(-1)). Thus, Comet 9P/Tempel 1 is heterogeneous in terms of both thermophysical and optical properties, due to formation conditions and/or post-formation processing.
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| 3. |
- Jones, Geraint H., et al.
(författare)
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The Comet Interceptor Mission
- 2024
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Ingår i: Space Science Reviews. - : Springer Nature. - 0038-6308 .- 1572-9672. ; 220:1
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Tidskriftsartikel (refereegranskat)abstract
- Here we describe the novel, multi-point Comet Interceptor mission. It is dedicated to the exploration of a little-processed long-period comet, possibly entering the inner Solar System for the first time, or to encounter an interstellar object originating at another star. The objectives of the mission are to address the following questions: What are the surface composition, shape, morphology, and structure of the target object? What is the composition of the gas and dust in the coma, its connection to the nucleus, and the nature of its interaction with the solar wind? The mission was proposed to the European Space Agency in 2018, and formally adopted by the agency in June 2022, for launch in 2029 together with the Ariel mission. Comet Interceptor will take advantage of the opportunity presented by ESA’s F-Class call for fast, flexible, low-cost missions to which it was proposed. The call required a launch to a halo orbit around the Sun-Earth L2 point. The mission can take advantage of this placement to wait for the discovery of a suitable comet reachable with its minimum Δ V capability of 600 ms − 1 . Comet Interceptor will be unique in encountering and studying, at a nominal closest approach distance of 1000 km, a comet that represents a near-pristine sample of material from the formation of the Solar System. It will also add a capability that no previous cometary mission has had, which is to deploy two sub-probes – B1, provided by the Japanese space agency, JAXA, and B2 – that will follow different trajectories through the coma. While the main probe passes at a nominal 1000 km distance, probes B1 and B2 will follow different chords through the coma at distances of 850 km and 400 km, respectively. The result will be unique, simultaneous, spatially resolved information of the 3-dimensional properties of the target comet and its interaction with the space environment. We present the mission’s science background leading to these objectives, as well as an overview of the scientific instruments, mission design, and schedule.
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