Featured Image - (04/22/2008)
The multifaceted nature of the lunar mare is apparent in this Apollo 15
metric mapping photograph (Figure 1, below) showing a region in Mare Imbrium
northwest of Euler crater (diameter: 28 km) under low Sun conditions. Euler is in the lower right of this image and the ejecta blanket of the crater Diophantus is barely visible in the upper left of the image.
The Complex Lunar Mare
Figure 1. Region
of Mare Imbrium between Euler and Diophantus craters under low Sun
conditions. Numerous secondary craters that postdate the formation of the mare dot the surface. (Apollo Image AS15-M-1702 [NASA/JSC/Arizona State University])
Figure 2. Region of Mare
Imbrium between Euler and Diophantus craters under low Sun conditions
with specific lunar geomorphology features highlighted. A
close-up view of the region highlighted with the rectangle is provided
as Figure 3. (Apollo Image AS15-M-1702 [NASA/JSC/Arizona State
Close-up view of a lunar sinuous rille in Mare Imbrium northwest of
Euler crater. The dendritic nature of sinuous rilles is evident in this image. (Apollo Image AS15-M-1702 [NASA/JSC/Arizona State University])
Although the lunar mare look uniform to the naked eye from
Earth, the low Sun angle in this close-up photograph shows the
complex geomorphological features on this mare surface. Three of
the most prominent features are highlighted in Figure 2 (above), and
During stays at a lunar outpost, astronauts will make extended
exploration traverses across complex lunar terrain like this one. In order for lunar geoscientists to fully understand the complex geology of regions such as this, we will have to combine the absolutely unsurpassed field geological abilities of highly-trained astronauts, the collection and analysis of lunar samples with known
geologic contexts, and the detailed remote sensing data returned by the
armada of spacecraft (Kaguya, Chang'e, Chandrayaan-1, and the
Lunar Reconnaissance Orbiter) that are going to be orbiting the Moon by the end of 2008.
- Multiple lava flows.
Many lava flows can be distinguished in this image. The edges of mare lava flows often have lobate morphology and are sometimes referred to as "lobes." The outline of one of these lobes is shown in the upper right of Figure 2.
All of these lava flows point to the northeast (in the approximate direction of the arrow in the upper right of this image), which indicates that the mare materials that filled this part of the Imbrium basin flowed from the lower left to the upper right.
- Mare ridges, which are
caused by the subsidence
and contraction of mare lavas.
- Numerous small sinuous rilles
that with dendritic branching that resembles the shape of terrestrial rivers. These look very similar to terrestrial rivers formed by the erosion of
water. However, these sinuous rilles were actually carved into the
lunar surface by very hot and thus very fluid flowing lavas that thermally eroded the lunar surface . Figure 3 shows a close up view of one of these sinuous rilles. Notice how the rille weaves and branches off in different directions.
For more information, please see: Apollo over the Moon: The View from Orbit, H. Masursky, G. Colton, and F. El-Baz, editors, NASA SP-363, United States Government Printing Office, pg. 192.