Rima Seuss, rough around the edges

With peppered flanks, Rima Suess wanders over 150 km through Oceanus Procellarum. The rocks that rest on the walls of this sinuous rille are perhaps remnants of much larger boulders that have eroded down to meter sized rocks due to relentless micro and macro meteorite bombardment, "gardening" 3 centimeters into lunar dust every 2 million years or so. The pyroclastic flow that carved through the terrain was remarkably fast, considering the long scar left behind has lasted perhaps 3 billion years. From the extraordinary low altitude of only 23 km (see below), the 400 meter field of view above is cropped from LROC NAC observation M168516400R  [NASA/GSFC/Arizona State University].

Raquel Nuno
LROC News System

Rima Suess (7.81°N, 312.41°E), located in Oceanus Procellarum, is a long, meandering narrow depression called a sinuous rille.

Sinuous rilles, most commonly found in mare surfaces, are thought to have been carved by fast rivers of lava, which thermally and mechanically eroded the channels we see today.

About 3.1 billion years ago the Moon was much more volcanically active, pouring vast amounts of lava onto the surface. The large dark mare regions of the Moon were formed by massive eruptions of iron-rich basaltic lava during this time.

Very close-up on Rima Suess, the LROC NAC observation from which this and the LROC Featured Image were processed was from among one of the closest passes of the Lunar Reconnaissance Orbiter (LRO) over the Moon, during low-periapsis maneuvers in 2011. (Full resolution original image HERE.)  LROC NAC observation M168516400R, LRO orbit 9968, August 12, 2011; 36.11° incidence angle, resolution 39 cm from 22.92 km over 8.07°N, 312.38° [NASA/GSFC/Arizona State University].

The boulders along the walls of the rille probably were a coherent mass when the lava flows cooled, breaking up over billions of years of impacts into the boulders we see today. Gravity then pulled this material down the slope of the rille; this process is known as mass wasting. We see rock outcrops over the entire path of Rima Suess in the LROC NAC image M168516400R.

The very narrow, actually a 200 km-plus-long sinuous rille, apparently traced remarkably fast south from the Marius Hills "Yulu" double-volcano source nearly to Flamsteed P crater, through the bleak center of Oceanus Procellarum. Nearby Kepler crater (outside this view, to the right and east) added the bright ejecta rays. This view is distilled from a mosaic of LROC Wide Angle Camera (WAC) observations swept up over five sequential orbits during local early local morning, allowing long shadows to add some relief to this remarkably flat area of the lunar surface, all of it averaging below 2000 meters in elevation. LROC WAC mosaic from LRO orbits 6838 through 6842, December 18, 2010; 79° incidence angle, resolution 58 meters from 41.5 km [NASA/GSFC/Arizona State University].

Lunar rilles are exciting places for lunar scientists because they may cut through and expose the different layers of lava flows in the maria.  This gives scientists insight into the volcanic processes present during mare formation, and how they evolved with time.

Explore the winding path of this portion of Rima Seuss in the full resolution LROC NAC HERE.

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