Wednesday, February 9, 2011

LROC: Rupes Recta

Artful Lunar Picture of the Day (LPOD) contributor Maurice Collins of New Zealand created this mosaic of LROC Wide Angle Camera images, swept up at local sunrise, and demonstrates why Rupes Recta is easier to spot when the Moon is just past First Quarter as seen from Earth. The change in elevation is not unusually high, for the Moon, but the rift is consistent (even if segmented) throughout its more than 100 kilometer length. The Straight Wall is consistent with a change in topography, if not age and stratigraphy, dividing an eastern zone from a western slope, both within an inundated crater broken in half by the weight of later melt pressing down on the interior of Mare Nubium. This gentle rift casts a long shadow at sunrise, however, one that gradually thins until the Moon waxes Full, and afterward it stays visible in modest telescopes [NASA/GSFC/Arizona State University/MoonScience].

EDITOR'S NOTE: Every 90 days, each time Dr. Mark Robinson's Lunar Reconnaissance Orbiter Camera (LROC) team at Arizona State University releases its latest voluminous batch of low-orbit lunar photography, one of several bench mark locations we immediately search for updates has been the familiar "Straight Wall," Rupes Recta. LROC Featured Image February 9, 2011 examines and better explains a feature discussed here in a post originally uploaded July 8, 2010.

For a review of our many posts (and images) featuring Rupes Recta, we recommend the reader take a side trip HERE, or simply examine the list of relevant Lunar Pioneer links below the list of LROC "Related Posts" below.

In July, when after we first began manipulating the same frame LROC released below, we described the image above as, a "closer look at the crater straddling the Straight Wall near 21.6°S, 352.2°E, The character of each half of the plain divided by the rift appears similar. Also, at this point in this montage, consisting of both the right and left frames of LROC Narrow Able Camera observation M122264663. For a Wallpaper-sized view of the above image, click HERE [NASA/GSFC/Arizona State University].

Rupes Recta is a well-known linear rille over 100 kilometers long, familiar in amateur telescopes, west of the central meridian in the Nearside southern hemisphere, seen here in an annotated portion of LROC Wide Angle Camera (WAC) monochrome mosaic; illumination from the west (left), the asterisk denotes the location where LROC Narrow Angle Camera (NAC) observation M122264663 intersected the fault, in the LROC Featured Image below [NASA/GSFC/Arizona State University].

Lillian Ostrach
LROC News System

Several weeks ago LROC featured a series of WAC monochrome mosaics of some of the most spectacular sinuous rilles on the Moon (Rimae Posidonius, Vallis Schröteri, and Rimae Prinz). Unlike sinuous rilles, linear rilles (or graben) are not believed to primarily result from lunar volcanism. Linear rilles are surface manifestations of structural faulting that formed when the lunar crust was pulled apart. The widths of these linear rilles range from as little as a few meters to kilometers across; Rupes Recta is between 1 - 3 km wide across its length. In addition, Rupes Recta is composed of several en echelon segments - the linear rille is not a single, uninterrupted 100 km length fault! There are at least 5 large fault segments visible at the LROC Wide Angle Camera scale (100 meters/pixel) ranging from around 8 to 50 kilometers in length.

Cross-cutting relations between Rupes Recta and an impact crater are evident in this subset of LROC NAC observation M12264663R (LRO orbit 3151, March 3, 2010). The cliff-face of Rupes Recta is noted by the arrows on the right side of the image. At some point after the formation of Rupes Recta an impact occurred and excavated material from the fault wall. The arrows on the left side (forming a somewhat-curvilinear path) denote the crater wall. Subsequent down-slope movement of eroded debris and blocks is visible. Image field of view is 840 meters, illumination from the left, and a low-incidence angle highlights albedo variations [NASA/GSFC/Arizona State University].

What cross-cutting relationships can you determine in the LROC WAC monochrome mosaic? How does the full LROC NAC image change your view of Rupes Recta?

Related posts:
Linear Graben

Lunar Pioneer Posts:
A second NAC cross-section of Rupes Recta
More on that second Rupes Recta close-up
Rima Birt and Rupes Recta
LOLA/LROC: Hunting for ancient impact basins (LROC)
More Kaguya Terrain Camera images
Paul Spudis: Caves on the Moon
Google Moon, Limited (Part One)
A New Era of Lunar Exploration

Segment from the really outstanding LROC WAC monochrome mosaic of the >100 km-long segmented fault east of Mare Nubium in the Nearside southern hemisphere. The northern half of the feature is set apart here to note a cross-fault (upper arrow) first brought to our attention by Charles A. Wood in a discussion posted to his essential Lunar Picture of the Day (LPOD) website. The nearly perpendicular rille is often difficult to pick out in Earth-side photography but unmistakable in the LROC image. The lower arrow, again identifies the location of the impact crater in extreme close-ups above. The image field of view is approximately 40 kilometers [NASA/GSFC/Arizona State University].

No comments: