Surface changes on comet 67P/Churyumov-Gerasimenko suggest a more active past

Abstract

The Rosetta spacecraft spent ~2 years orbiting comet 67P/Churyumov-Gerasimenko, most of it at distances that allowed surface characterization and monitoring at submeter scales. From December 2014 to June 2016, numerous localized changes were observed, which we attribute to cometary-specific weathering, erosion, and transient events driven by exposure to sunlight and other processes. While the localized changes suggest compositional or physical heterogeneity, their scale has not resulted in substantial alterations to the comet's landscape. This suggests that most of the major landforms were created early in the comet's current orbital configuration. They may even date from earlier if the comet had a larger volatile inventory, particularly of CO or CO ices, or contained amorphous ice, which could have triggered activity at greater distances from the Sun.

Surface evolution of the Anhur region on comet 67P/Churyumov-Gerasimenko from high-resolution OSIRIS images

“…See the online movie (Area1.gif), which shows the morphological changes between these two epochs. estimate the depth or height of surface landmarks in the imageresolved studies of bodies throughout the solar system (Arthur 1974;Chappelow & Sharpton 2002;El-Maarry et al, 2017;Hasselmann et al, 2019). The shadow length L sha is measured using the generalized distance connecting the top of a structure to the tip of its shadow, but regarding the projected Sun direction (azimuth angle) with respect to the image frame.…”

“…A number of localized morphological changes were reported for several regions of 67P (see El-Maarry et al 2015a and for a definition of the regions on 67P). The reports suggested compositional and/or physical heterogeneity (El-Maarry et al, 2017). A region with extensive changes is Imhotep, for which exhumation of structures (boulders and roundish features) by the removal of ∼ 4 m dust coating (Auger et al 2016, El-Maarry et al, 2017 and the appearance of two roundish structures with a diameter of ∼ 240 m and 140 m and a height of 5±2 m in the large smooth central area were reported.…”

“…A region with extensive changes is Imhotep, for which exhumation of structures (boulders and roundish features) by the removal of ∼ 4 m dust coating (Auger et al 2016, El-Maarry et al, 2017 and the appearance of two roundish structures with a diameter of ∼ 240 m and 140 m and a height of 5±2 m in the large smooth central area were reported. The transport of unconsolidated materials removes the dust coating; this is also observed on Anubis and Hapi (El-Maarry et al, 2017), the latter also showing aeolian-like ripples . The two roundish features observed in Imhotep had a high expansion rate, higher than 18 cm hour −1 , that was not produced by the simple sublimation process.…”

“…In the Khonsu region, surface changes were also observed, including the 140 m displacement of a 30 m wide boulder (El-Maarry et al, 2017), the appearance of a new 50 meter-sized boulder (Hasselmann et al, 2019), several ice-enriched patches, one of which survived for several months (Deshapriya et al, 2016), and the sublimation of some thick dust layers (Hasselmann et al, 2019). However, even though numerous localized changes were reported, they did not substantially change the cometary landscape, which was very probably shaped much earlier in its history (El-Maarry et al, 2017). This paper aims at investigating Anhur, a region in the southern hemisphere.…”

Supercooled and glassy water: Metastable liquid(s), amorphous solid(s), and a no-man’s land

“…However, water is not restricted to Earth. It is found on the planets of our solar system and their moons and on asteroids and comets (1), possibly in its glass (i.e., amorphous ice) form (2). Water as an amorphous solid is also abundant in the interstellar medium (3), where it may play a fundamental role in the formation of complex organic molecules such as amino acids and sugars (4).…”