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1.
  • Li, Jian-Yang, et al. (författare)
  • Ejecta from the DART-produced active asteroid Dimorphos
  • 2023
  • Ingår i: Nature. - : Springer Nature. - 0028-0836 .- 1476-4687. ; 616, s. 452-456
  • Tidskriftsartikel (refereegranskat)abstract
    • Some active asteroids have been proposed to be formed as a result of impact events1. Because active asteroids are generally discovered by chance only after their tails have fully formed, the process of how impact ejecta evolve into a tail has, to our knowledge, not been directly observed. The Double Asteroid Redirection Test (DART) mission of NASA2, in addition to having successfully changed the orbital period of Dimorphos3, demonstrated the activation process of an asteroid resulting from an impact under precisely known conditions. Here we report the observations of the DART impact ejecta with the Hubble Space Telescope from impact time T + 15 min to T + 18.5 days at spatial resolutions of around 2.1 km per pixel. Our observations reveal the complex evolution of the ejecta, which are first dominated by the gravitational interaction between the Didymos binary system and the ejected dust and subsequently by solar radiation pressure. The lowest-speed ejecta dispersed through a sustained tail that had a consistent morphology with previously observed asteroid tails thought to be produced by an impact4,5. The evolution of the ejecta after the controlled impact experiment of DART thus provides a framework for understanding the fundamental mechanisms that act on asteroids disrupted by a natural impact1,6.
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2.
  • Davidsson, Björn J. R., et al. (författare)
  • Thermal inertia and surface roughness of Comet 9P/Tempel 1
  • 2013
  • Ingår i: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 224:1, s. 154-171
  • 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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