The Large Smooth Patch on Comet 9P/Tempel 1: Remnant of a Recent Past Event

TL;DR

This study reassesses the large smooth patch on comet 9P/Tempel 1 using data from space missions, simulations, and shape models, suggesting it formed 600-1200 years ago possibly due to external dynamical events.

Contribution

It provides a comprehensive analysis combining observational data and simulations to propose a formation mechanism for the smooth patch, linking it to orbital changes caused by Jupiter.

Findings

The smooth patch is about 25 meters thick with a lobate U-shape.

Spectral analysis indicates an endogenous origin.

A single event likely formed the patch and related features 600-1200 years ago.

Abstract

We present a comprehensive reassessment of the region containing the large smooth patch on comet 9P/Tempel 1, leveraging data from the Deep Impact and Stardust-NExT missions, an updated stereophotoclinometry-based shape model, and numerical simulations. The study seeks to understand the nature, the triggering mechanism, and the chronology of this distinctive feature. Morphological and spectral analysis reveals that the smooth patch has a thickness of approximately 25 meters, a notable lobate U-shape, and a spectral composition indistinguishable from the surrounding terrain, which favors an endogenous origin. Gravitational flow simulations demonstrate that a single event could have formed the large smooth patch, the secondary smooth units observed on other faces of the comet, and the topographic terrace features adjacent to the northern smooth unit. We estimate this event occurred between 600 and 1,200 years ago, a temporal window that notably coincides with a period of abrupt orbital changes caused by multiple close encounters with Jupiter. We propose that these encounters may have played a role in triggering a mass flow. Although with the underlying mechanism still unresolved, these results shed new light on the geology of cometary nuclei and on the role of external dynamical processes in shaping their surfaces.