An examination of the Deep Impact collision site on Comet Tempel 1 via Stardust-NExT: Placing further constraints on cometary surface properties

In this work, we describe a detailed study of the Deep Impact (DI) collision site on Comet 9P Tempel 1 as imaged by the Stardust-NExT spacecraft in February of 2011. This investigation reveals a tentatively identified, barely resolvable, shallow impact crater located at the previously identified impact site, 49 ± 12 m in diameter; surrounded by an area of slightly brightened material marking a potential ejecta blanket 85–120 m in diameter. Assuming that this crater identification is correct, we use this diameter to place further constraints on the surface material struck by the DI impactor to yield crater scaling-law constants of μ = 0.45 ± 0.05 (exponential constant), K1 = 0.15 ± 0.05 (linear proportionality constant), and Y ¯ = 1 – 10 kPa (effective target strength) utilizing the expressions and nomenclature of Holsapple (Holsapple, K.A. [1993]. Annu. Rev. Earth Planet. Sci. 21, 333–373). These material constants are roughly analogous to the material properties of a lightly-packed, ‘dry’ mountain snow. Additional modeling yields refined values for the total ejected mass produced by the DI event of 1.2 × 106 kg (5.4 × 105–2.6 × 106 kg), with 60% ± 20% of that mass ejected at greater than the comet’s escape velocity of 1.4 m/s, and producing a relatively thin ejecta blanket with a thickness at the final crater rim of 2.7 mm (0.5–13 mm). These values are consistent with our previous analysis of the Deep Impact event’s ejecta behavior as seen from the DI flyby spacecraft, as well as the observations conducted by other Earth-orbiting and Earth-based telescopes.