The Gruithuisen region in northern Oceanus Procellarum on the Moon contains three distinctive domes interpreted as nonmare volcanic features of Imbrian age. A 4 d extravehicular activity (EVA), four-astronaut sortie mission to explore these enigmatic features and the surrounding terrain provides the opportunity to address key outstanding lunar science questions. The landing site is on the mare south of Gruithuisen 3 (36.22°N, 40.60°W). From this site, diverse geologic terrains and features are accessible, including highlands, dome material, mare basalts, multiple craters, small rilles, and a negative topographic feature of unknown origin. Preliminary mission planning is based on Clementine multispectral data, Lunar Prospector geochemical estimates, and high-resolution (0.5 m/pixel) stereo images from the Lunar Reconnaissance Orbiter Narrow Angle Camera. Science objectives for the mission include: (1) determining the nature of the domes, (2) identifying and measuring the distribution of any potassium, rare earth elements, and phosphorus (KREEP)- and thorium-rich materials, (3) collecting samples for age dating of key units to investigate the evolution of the region, and (4) deploying a passive seismic grid as part of a global lunar network. Satisfying the science objectives requires 7 h, ~20 km round-trip EVAs, and significant time driving on slopes up to ~15°.

In response to the need to develop science-conducive architectures for future human exploration of particularly interesting targets on lunar and planetary surfaces, we have developed scenarios for a geological expedition to Marius Hills within current constraints of week-long sortie missions. This area has a dense nest of volcano-tectonic features representing the range of mare volcanic structures, which is one of the reasons why it is so compelling. Two distinct episodes of flood basaltic volcanism are represented, along with volcanic shields, domes, cones, rilles, wrinkle ridges, floor fractures, and a magnetic swirl anomaly. We found two potential landing sites (constrained to 10 km radius) in the southwestern portion of Marius Hills that would allow access to examples of most of the features of interest. We describe the geological context, resulting investigations, daily traverses, and survey/sample sites along those routes, in detail, as well as the required tools, instruments, and surface activities. The resulting science requirements, for a minimum of two rovers plus a few hundred kilograms of science payload, along with implications for a science-conducive architecture, are considered.

The volcanic processes that formed Vallis Schröteri are not well understood. Vallis Schröteri, located on the Aristarchus Plateau, is the largest rille on the Moon, and it displays three key morphologic components: the Cobra Head, the 155-km-long primary rille, and the 240-km-long inner rille. Observations of terrestrial eruptions are applied here to help explain the morphologic relationships observed for Vallis Schröteri. The Cobra Head, a 10-km-wide source vent surrounded by a 35-km-diameter and 900-m-high low shield, might have been constructed from flows, spatter, and pyroclastic deposits erupted during lava fountain events, similar to the early stages of the vent at Pu‘u ‘Ō‘ō in Hawaii and the final morphology of Bandera crater, a cinder cone in New Mexico. The vent fed an initial sheet flow controlled by pre-eruption topography. A channel formed within this sheet flow was the foundation for the primary rille, which deepened through construction and thermomechanical erosion by lava. The inner rille is confined to the flat floor of the primary rille and is characterized by tight gooseneck meanders. This rille crosscuts the distal scarp of the primary rille and extends toward Oceanus Procellarum. This enigmatic relationship can be explained through backup, overflow, and diversion of the lava into a new rille that eroded into the margin of the primary rille. Similar backup, overflow, and redirection of the lava flow were observed during the 1984 Mauna Loa eruption in Hawaii. Analysis of the final morphology of lunar rilles provides key information about lunar volcanic processes and insight into the local stratigraphy.