Reexamination of the large smooth patch on comet 9P/Tempel 1 as observed by the Deep Impact and Stardust missions

Tempel 1 (T1) is the only comet that has been visited by a spacecraft twice: first by Deep Impact mission in 2005 [1], and later by the Stardust-NExT mission [2] in 2011. As a result, we can study not only the physical properties of its surface but also its evolution over a full orbital period (5.6 yr.).

The images acquired by both spacecrafts cover ~70% of the surface and reveal a morphologically diverse body made up of rough, pitted terrain and, in two observed cases, regions of smooth terrain that appear distinct from their surroundings. These km-scale smooth patches are thus far unique to T1. In this work we examine a smooth patch located at the south pole of T1, surrounded by rough terrain and embedded in a cliff, which has previously been suggested to be the results of flows depositing materials on the surface [3], and that shows a clear evolution caused by sublimation of ice.

We present an exhaustive list of registered variations comparing both sets of images, as well as multispectral measurements of this smooth feature and its surroundings. In addition, we use an updated stereophotoclinometry-based shape model [4] which provides ~20x improvement in resolution (ground sample distance up to 8 m), to characterize the thickness and extent of this region, as well as to get the gravitational potential of the surface. The results presented here will serve to constrain and encourage discussion about the origin and significance of this feature.

References: [1] M. F. A’Hearn et. al. (2005) Space Sci. Rev. 117, 1–21. [2] J. Veverka et al. (2013) Icaurs 424-435. [3] P. Thomas et al. (2013) Icarus 453-466. [4] C. M. Ernst et al. (2019) 50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132)