Mare basalts embayed ejecta structures formed by the massive Imbrium impact in this sub-scene of LROC Narrow Angle Camera (NAC) observation M131501983RE (2.2 km higher above, 902 meters in the LROC Featured Image field of view [full image HERE], immediately above). Arrows denote the contact between younger mare basalts and older Imbrium ejecta, image [NASA/GSFC/Arizona State University].
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Mare basalts fill most of the large impact basins on the Moon, and in many cases the pre-existing topography was buried by the huge outpourings of lava. However, sometimes pre-existing topography is not completely buried by the mare basalts. When lava flows around a topographic high and does not bury it completely, the resulting landform is called a kipuka, and may be used to tell scientists about the region before the lavas flowed across the landscape. In the case of today's Featured Image, this kipuka in southwestern Lacus Somniorum is probably ejecta from the impact that formed the Imbrium basin. When looking at a regional view, this knob and others form relatively linear chains which can be traced back to the Imbrium basin.
Preliminary Lunar Reconnaissance Orbiter (LRO) laser altimetry (LOLA) data showing Imbrium as seen from Earth, the most predominant, clearly identifiable feature on the near side seen with the naked eye from Earth. Imbrium is central to most of the Moon's mare phenomena and it's highest diversity of compounds. [NASA/GSFC].
Since the mare basalts are embaying this feature, the basalts postdate the formation of the Imbrium basin. Using remotely-sensed data to establish this kind of geologic relationship on the lunar surface helps to clarify the geologic history of the Moon, an important consideration for planning future lunar exploration.
LROC Wide Angle Camera view of southwestern Lacus Somniorum; arrow points to location of today's Featured Image. Subset of LROC WAC monochrome M117339055M [NASA/GSFC/Arizona State University].
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