Tuesday, December 18, 2012

LROC: Petavius

An outcrop exposed in the central peak of Petavius crater revealed in large fracture. From LROC Narrow Angle Camera (NAC) observation M1107889912LE, captured at 0.84 meters per pixel in LRO orbit 15552, November 18, 2012; field of view approximately 840 meters across [NASA/GSFC/Arizona State University].
Drew Enns
LROC News System

Petavius crater, a 177 km crater located at 25.28°S, 60.63°E, is one of an uncommon class of craters that have been modified by post-impact processes. What process could have produced the system of fractures that cut the floor, known as Rimae Petavius? Volcanism is the likely cause. Small patches of mare basalt exist in the north and south extents of the crater floor, which help cement this hypothesis. But unlike other mare filled craters, Petavius crater has only small patches of basalt.

Why did Petavius crater end up with such an extensive fracture system?

Context the LROC Featured Image, 100 km-wide field of view includes the cluster of the Petavius central peaks, composed of material tossed up from great depth when the crater formed in the lower Imbrium age, 3.9 billion years ago. Some darker basaltic material is in the northeast and southeast corners of this image, likely opportunistic intrusions of molten material that "seeped" to the surface following some global event, like the basin forming impact that formed Mare Orientale [NASA/GSFC/Arizona State University].

One hypothesis is that the fractures occurred as a result of volcanic modification. Uplift of the crater floor would occur as magma intruded beneath the floor and fracturing developed as the floor was pushed up. Because Petavius crater was not flooded completely, the fractures were never covered by basalt. The harder question is why is Petavius crater not flooded with basalt?

Wider still context LROC Wide Angle Camera (WAC) mosaic, showing the slumped walls of Petavius. Mosaic stitched from eight sequential observations during orbits 11232 through 11259, November 30, 2011; resolution averaged 70 meters at 68° angle of incidence, from 51 kilometers [NASA/GSFC/Arizona State University].

It is possible Petavius crater did not witness the same style of eruption as elsewhere on the Moon. Or maybe the magma underneath Petavius crater was not buoyant enough to completely flood the surface. Finally, it may simply be that the magma source region was relatively small, and thus only a modest amount of basalt was erupted.

Explore more of Petavius crater in the full LROC NAC observation HERE.

Related Posts:
Rock slide in Rima Hyginus
Pyroclastics and Vent
Archimedes - Mare Flooded Crater!

Petavius is a familiar telescopic landmark from Earth, after the Moon is 3 days old (or 2 days after a Full Moon), though fresher, rougher and less optically mature bright ejecta from smaller neighboring craters like Stevinus and Petavius B tend to overwhelm the scene as the region approaches mid-day. The simulated phase above shows the location of Petavius in relation to the Moon's appearance tonight. Virtual Moon Atlas v.6 using LROC WAC 100 meter textures [VMA].

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