Wednesday, April 17, 2013

The Fourth Marian Dome

A volcanic dome in northeastern Oceanus Procellarum., west of Rima Sharp. LROC Narrow Angle Camera (NAC) observation M1119207667R, spacecraft orbit 17144, March 29, 2013, resolution 1.5 meters over a field of view 3.1 km across [NASA/GSFC/Arizona State University].
Sarah Braden
LROC News System

The volcanic dome in the Featured Image (located at 43.673°N, 310.145°E) rises above the mare basalt of Oceanus Procellarum. This dome is another example of silicic volcanism on the Moon, much like the nearby Mairan Domes, the Gruithuisen Domes, and the Lassell Massif.

Each of these features were originally identified as "red-spots," meaning they are spectrally anomalous compared to surrounding mare and highlands material, with strong ultraviolet absorptions that are responsible for their red color.

New data from the Diviner Lunar Radiometer Experiment instrument on the LRO spacecraft confirmed that all four domes (see the WAC context image below) are highly silicic compared to mare and highlands compositions. The Diviner team's work included this fourth dome as part of the Mairan Domes and dubbed it Mairan "northwest." In terms of size and shape, Mairan "northwest" has the most in common with the smallest Mairan dome, Mairan "south." Mairan "northwest" is ~3.2 km in diameter, just slightly smaller than Mairan "south" at ~4.2 km in diameter. However, Mairan "south" is about 400 meters in height (relative to the surrounding mare) while the structure in the Featured Image has a height of only ~180 meters (measurements taken from the WACGLD100 DTM). Regardless of their height relative to the mare, both domes may be greater in size that their surface expressions due to embayment by mare basalt.

LROC Wide Angle Camera (WAC) context image of northeastern Oceanus Procellarum shows the location of the area surrounding the LROC Featured Image field of view (white box) in relation to the more prominent named Mairan Domes. Field of view is about 120 km across [NASA/GSFC/Arizona State University].
The dome of interest (lower right) and its relation to points north and a lengthy segment of Rima Sharp. LROC WAC monochrome (643 nm) observation M117827780ME, orbit 2498, January 11, 2010; spacecraft and camera slew -11.15° resolution 59 meters per pixel from 40.72 km [NASA/GSFC/Arizona State University].
Oblique view south over Rima Sharp from the JAXA planetary camera on-board SELENE-1 (Kaguya) in 2007. The small dome of interest can be seen as small white blur, between the horizon and the bend region of Rima Sharp at lower center. The named Marian Domes and the crater Marian G are visible half way between the horizon and the small dome of interest [JAXA/SELENE].
The dome of interest (yellow arrow) as seen from Earth, photographed by Lunar Picture of the Day (LPOD) contributor Stephan Lammel, June 11, 2003. The massive Mons R├╝mker effusive dome is visible at high relief at left. The largest crater in the highlands at right is Marian, 40 km across.
Examples of extrusive silicic materials are rare in the collection of Apollo samples and the origins of these materials are not known. However, it is thought that silicic domes like the Mairan domes may be the source locations. Studies of the Compton-Belkovich region have shown that highly silicic lunar rocks are more volumetrically important in the lunar crust than would be implied by their near absence in the Apollo samples. A sample return mission to the region of today's Featured Image would finally answer questions about the origin of these highly silicic rocks - how they were created as part of the Moon's late stage magmatic evolution.

Explore the entire NAC frame, HERE.

Related Images:
New Views of the Gruithuisen Domes
Gruithuisen Domes Constellation Region of Interest
Marius Hills Constellation Region of Interest
Compton-Belkovich: Farside Highlands Volcanism!

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