The second ExoMars mission will be launched in 2020 to target an ancient location interpreted to have strong potential for past habitability and for preserving physical and chemical biosignatures (as well as abiotic/prebiotic organics). The mission will deliver a lander with instruments for atmospheric and geophysical investigations and a rover tasked with searching for signs of extinct life. The ExoMars rover will be equipped with a drill to collect material from outcrops and at depth down to 2 m. This subsurface sampling capability will provide the best chance yet to gain access to chemical biosignatures. Using the powerful Pasteur payload instruments, the ExoMars science team will conduct a holistic search for traces of life and seek corroborating geological context information. Key Words: Biosignatures—ExoMars—Landing sites—Mars rover—Search for life. Astrobiology 17, 471–510.

Von Kármán crater (diameter = ~186 km), lying in the northwestern South Pole‐Aitken (SPA) basin, was formed in the pre‐Nectarian. The Von Kármán crater floor was subsequently flooded with one or several generations of mare basalts during the Imbrian period. Numerous subsequent impact craters in the surrounding region delivered ejecta to the floor, together forming a rich sample of the SPA basin and farside geologic history. We studied in details the targeted landing region (45.0–46.0°S, 176.4–178.8°E) of the 2018 Chinese lunar mission Chang'E‐4, within the Von Kármán crater. The topography of the landing region is generally flat at a baseline of ~60 m. Secondary craters and ejecta materials have covered most of the mare unit and can be traced back to at least four source craters (Finsen, Von Kármán L, Von Kármán L', and Antoniadi) based on preferential spatial orientations and crosscutting relationships. Extensive sinuous ridges and troughs are identified spatially related to Ba Jie crater (diameter = ~4 km). Reflectance spectral variations due to difference in both composition and physical properties are observed among the ejecta from various‐sized craters on the mare unit. The composition trends were used together with crater scaling relationships and estimates of regolith thickness to reconstruct the subsurface stratigraphy. The results reveal a complex geological history of the landing region and set the framework for the in situ measurements of the CE‐4 mission, which will provide unique insights into the compositions of farside mare basalt, SPA compositional zone including SPA compositional anomaly and Mg‐pyroxene annulus, regolith evolution, and the lunar space environment.

The Rümker region (41–45°N, 49–69°W) is located in northern Oceanus Procellarum of the Moon. Mons Rümker is the most distinctive geological feature in the area. The region is characterized by prolonged lunar volcanism (Late Imbrian Period to Eratosthenian Period), forming multiple geologic units in the area, including very low‐Ti to low‐Ti mare basalts, high‐Ti mare basalts, and volcanic complexes. Each geologic unit has distinct element composition and mineral assemblages. The Rümker region, overlying the Procellarum KREEP Terrain, was selected as the landing region for China's Chang'E‐5 lunar sample return mission. Prelanding analyses of the geologic context and scientific potential are reported in this contribution. We conducted detailed geological mapping using image, spectral, and altimetry data. Fourteen geological units were defined, a geologic map was constructed, and the geologic history was outlined. The western mare units (Im1, Im2, and Im3) are Imbrian‐aged (~3.4–3.5 Ga) representing the major stage of lunar mare eruptive volcanism. The eastern young mare units (Em3 and Em4; <2 Ga) are among the youngest mare basalts on the Moon. They have never been explored in situ or studied in the laboratory. We suggest that samples returned from the eastern mare unit (Em4) could answer many fundamental questions and that this unit should be listed as the top priority landing site for Chang'E‐5 sample return mission.