Secrets of Schröteri

Vallis Schröteri is a magnificent sinuous rille and of particular interest is its inner rille, which diverges from the primary rille near the arrow. This nested form indicates that multiple eruptive events occurred or there was a large change in the volume of a single eruption over time. LROC WAC mosaic, 100 m/pixel.

LROC NAC close-up of a bend in the inner rille of Vallis Schröteri; the rille walls are visible in the upper left and lower right corners of this image. The arrow in the LROC WAC mosaic above denotes the location of this image; image width is 600 m.

Photo credit: NASA/GSFC/Arizona State University

Note: The large crater in the top image is Herodotus Crater.

Impact Melt Features on Tycho Crater's Floor

Depressions and positive relief features in Tycho crater were caused by a complex mixture of granular material and impact melt settling to the floor. Image width is 370 m, LROC NAC M119923147L.

LROC WAC mosaic with arrow noting the location of the melt features within Tycho crater seen in the NAC image above. Image width is 150 km.

Impact melt creates a wide variety of features on the Moon. These include melt ponds, draped ejecta, viscous flows, linear and nonlinear depressions, and positive relief features. As impact melts mix with loose rock during crater formation, solid pieces of rock stick above the surface of the ponding melt to form little peaks (positive relief features). The depressions are possibly cooling fractures in the melt that result as the melt slowly solidifies and contracts (the opposite of how water behaves when it freezes), however they could also be part of an impact melt drainage network. We don't know for certain know the origin of all of these features, the best way to find out is to have astronauts traverse this terrain while exploring the Moon.

Photo credit: NASA/GSFC/Arizona State University

Block of Ejecta in Tycho Crater

320 meter (1,050 feet) block of ejecta in Tycho crater covered by a veneer of impact melt. Image width is 370 meters (1214 feet), LROC NAC 142334392RE.

LROC WAC context mosaic of Tycho, arrow points to the ejecta block within Tycho. Image width is 150 km.

Tycho crater is a Copernican age crater (85 kilometers, or 53 miles, diameter) located at 43.3° South, 11.2° West. It is named for the 16th century Danish astronomer Tycho Brahe and is one of the most visible features on the near side of the Moon. Its ray system is so obvious and widespread that Apollo 17 astronauts sampled its ejecta, over 2,000 kilometers (1,243 miles) away from the crater. Scientists dated the Tycho samples at about 110 Ma. We also have surface views of Tycho's ejecta blanket taken by the Surveyor 7 soft lander.

Notice the smooth areas on the top of the ejecta block in this NAC frame. Most likely the smooth area is a thin sheet of impact melt. The large block was probably flung up during the impact event, fell back down into the crater, and subsequently covered by impact melt. This series of events must have occurred quickly after the impact, as the melt would solidify soon after forming.

Photo credit: NASA/GSFC/Arizona State University

Rilles As Far As The Eye Can See

LROC WAC mosaic of the rille-rich Prinz crater region. Bench-like features are visible in the Prinz B depression and two flows originating in Prinz B converge just west of the arrow.

The bouldery, higher-reflectance mound in the central portion of this image is an island near the source region, Prinz B, for a short sinuous rille. The two rilles join at the triangular tip of this kipuka-like structure and flow northwestward for ~10 km. Image width is 500 m.

Photo credit: NASA/GSFC/Arizona State University