Tag: geology

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Cool image time! The photo to the right, reduced and enhanced to post here, is an oblique view taken by Lunar Reconnaissance Orbiter (LRO) of the rays that were created when four million years ago an object smashed into the Moon’s far side and produced the 13.75 mile-wide Giordano Bruno crater.

Rays are formed as material ejected from an impact event slams into the surface and churns up local material. Rays are bright because they expose fresh material from depth (both the incoming material and locally churned soil). What is fresh material? Over time the lunar surface is impacted by micrometeoroids and bombarded by radiation; both processes work to darken the surface. The dark “mature” layer at the surface is often only about 50 cm (20 inches) thick, so energetic impacts can easily bring up fresh material from the subsurface. Eventually, the bright rays darken and fade into the background as the surface matures.

In this image, you can see where the ejecta blocks from Giordano Bruno hit the surface, creating a secondary crater, which dug up local material and spread that bright material downstream (so to speak).

The image itself is 4.78 miles wide, at its center, and was snapped from an altitude of 66 miles.

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Cool image time! The Lunar Reconnaissance Orbiter (LRO) science team today released the oblique image above and in close-up to the right, showing what they call a “silicic volcano.” From the release:

The Mairan T dome is a large silicic volcanic structure with a pronounced summit depression. Remote sensing indicates that the composition of the volcanic material (lava) making up the dome is enriched in silica (SiO2). This rock type would be classified as either rhyolite or dacite on Earth, and the composition starkly contrasts with the dark, iron-rich mare basalts that embay the Mairan T dome. Most of the volcanism on the Moon is basaltic or iron-rich. Still, silicic volcanism also occurred on the Moon. Indeed, bits and pieces of similar materials were found in the Apollo samples; however, all are small fragments delivered to the Apollo sites as material ejected from distant impact events.

One of the great questions for lunar science is how the silicic materials formed. On Earth, specific tectonic settings and higher water contents in the rocks favor the formation of such lavas; however, the Moon lacks plate tectonics and water-rich sediments. NASA is planning a Commercial Lunar Payload Services (CLPS) lander mission to another, larger silicic volcano, one of the Gruithuisen domes, to address this question.

The scientists also note that this volcano formed first, and then was partly covered by the dark flood lava that surrounds it.

Cool image time! The photo above, taken by Lunar Reconnaissance Orbiter (LRO), was released today by the orbiter’s science team, and provides us an oblique look at the mountains dubbed Montes Recti (lower right) and the wrinkle ridges near them (lower left). The highest point in this mountain range is about 5,900 feet high.

The image looks west across the northern part of the mare region dubbed Mare Imbrium, the dark area on the Moon’s visible hemisphere near its top. In the distance can be the mountains that form part of mare’s rim. The rounded peak in the top right is Promontorium Laplace (about 8,530 feet high). It is named this because it projects out (a promontory) into the mare a considerable distance from the rim. The crater at top center is Laplace D. As for the wrinkle ridges, the scientists describe them like so:

Tectonic landforms are those formed by forces that act to either contract or pull apart crustal materials. These forces develop faults or breaks in the crustal materials, and movement or slip along the faults form either positive or negative relief landforms. On the Moon, positive relief contractional landforms are the most common. The most significant contractional landforms on the Moon are wrinkle ridges, found exclusively in the dark mare basalts.

Essentially, something caused the ground to contract, which caused it to break at these ridges and be forced upward.