Offset crater, active Moon

A small offset crater in the near side southern highlands. Field of view 342 meters across, from LROC NAC frame M177562995R, LRO orbit 11202, December 3, 2011; angle of incidence 72.25° from 39.76 km [NASA/GSFC/Arizona State University].

Renee French
LROC News System

Today's image is of a 100 meter diameter crater (29.814°S, 11.465°E) located in highland terrain between Tycho crater and Nectaris basin. However, it doesn't look like a normal bowl-shaped crater by any stretch of the imagination! The top half looks like it has been shifted to the right relative to the bottom half, which is consistent with motion along a right-lateral strike-slip fault. Likely this odd crater was cut by a fault associated with the nearby Poisson lobate scarp. The faulting helps us determine the relative age of local features. The crater on the right does not appear offset, so that tells us that the fault was active after the crater on the left formed (thus offsetting it) but was not active since the formation of the crater on the right! This relationship also indicates that the crater on the left is older than the crater on the right. Observations like these allow scientists to assign relative ages to features on the surface; the only way to accurately determine absolute ages for features this small is to bring back samples for radiometric age dating. If you were to look at this crater using WAC data (see below), you couldn't tell that it was offset by a fault but you could spot it due to its high reflectivity. High resolution NAC images like these have shown that there is relatively recent, small-scale tectonic activity and that the Moon is far from being geologically dead!

LROC Wide Angle Camera (WAC) 100 meter monochrome mosaic. Red arrow points to the featured offset crater, a bright spot at this resolution and the yellow arrows point to the Poisson lobate scarp [NASA/GSFC/Arizona State University].

Check out the full LROC NAC image to spot other faulting, HERE.

Related Posts:
Relative age relationships
Scarps in Schrödinger
The Ghosts of Mare Fecunditatis

Boulders In the Sea of Serenity

A wrinkle ridge in southwest Mare Serenitatis is littered with boulders and areas of high-albedo, characterized by rough texture. Field of view is approximately 1500 meters across> LROC Narrow Angle Camera frame M106826896L, LRO orbit 884, September 5, 2009; angle of incidence 35.34° at 1.25 meters resolution from 150.42 kilometers [NASA/GSFC/Arizona State University].

Renee French
LROC News System

A wrinkle ridge in western Mare Serenitatis (23.448°N, 8.058°E) is one of many in the region that exhibits a high boulder density and high albedo (bright) summit areas. But it isn't the only place this relationship is seen! These bouldered ridges are also observed in Oceanus Procellarum, Mare Humorum, Mare Cognitum, and Mare Nubium, to name a few. Scientists are still uncertain as to why some ridges have these features and others don't, and why this isn't observed along the entire ridge. This ridge seems to be eroding along its slope, rather than the crest, suggesting that the material is coming from the ridge itself. In addition, a small impact crater (red arrow in below image) has excavated boulders and high albedo material, making it more likely that the source is from the ridge and not a product of distant cratering events.

Wider view shows a crater (red arrow) that has excavated the same material eroding out of the ridge.  Field of view approximately 2.3 kilometers across LROC NAC M106826896L [NASA/GSFC/Arizona State University].

There are two ways to describe high albedo on the Moon: either freshly exposed rock and soil, or material with different composition or properties. It is uncertain which description is best for the high albedo observed along these ridges or whether it is a combination of the two. If the boulders and high albedo material have happened because of tectonic activity, then that implies that activity along mare wrinkle ridges has occurred more recently than previously thought. These features need to be studied in more detail in order to fully understand what role they play in lunar history. This is just one of the many surprises that LROC has revealed!

LROC Wide Angle Camera (WAC) 100 meter-per pixel monochrome mosaic in the new and improved LROC WMS image search tool shows the the location of the wrinkle ridge in Mare Serenitatis (yellow arrow) in relation to Apollo 15 landing site near Hadley Rille [NASA/GSFC/Arizona State University].

To view the ridge in more detail, look at the top of the full LROC NAC frame, HERE.

Related Posts:

Zebra Stripes (July 3, 2011)
Bright ridge near Mons Hansteen (April 8, 2011)

Boulder clusters on a ridge crest (March 24, 2011)
Buckland Boulders (March 9, 2011)
Constellation Region of Interest in Mare Tranquillitatis (April 27, 2010)
Wrinkle Ridge Near Montes Teneriffe (December 29, 2009)

UPDATE: A Closer Look. This area of the Serenitatis basin is particularly interesting, under the influence of the extrusive volcanism of Sulpicius Gallus and the unusual elevation slope lower in elevation approaching the southwest basin rim, has been the subject of several earlier posts. As it turns out, for example, we had already, long ago, downloaded the entire 5000 sample by 52224 line NAC image from the Commissioning phase of the LRO mission about three years ago.

In a quick study, again using the continuously improving LROC image search tools, we wanted to see if any higher-resolution LROC NAC observations had been captured since September 5, 2009. Among the overlapping or nearly overlapping LROC NAC Observations we found of this same wrinkle ridge system were at least two perhaps helpful in further illustrating the area of interest.

Barely more than a year after the opening picture was taken, LROC swept over the same region, a bit more to the west of orbit 884, during orbit 5744, and the LROC NAC caught the image above showing the ridge "lobe" visible at lower left in the opening LROC Featured Image. Though Sun was slightly higher in the sky, the spacecraft was 106 kilometers closer, and the image immediately below shows that same ridge "lobe" at 49 cm resolution. LROC NAC M139856476R, angle of incidence 26.26° from 44.33 km [NASA/GSFC/Arizona State University].

The wrinkle ridge "lobe" at full resolution and corrected scale in a 286 meter-wide field of view from LROC NAC M139856476R, orbit 5744, September 23, 2010 [NASA/GSFC/Arizona State University].

While the area in this image does not overlap the left frame of LROC NAC M10682689L, it does overlap the right frame and a part of the same wrinkle ridge system slightly to the east. The field of view is a bit more than 2 kilometers wide, with the area in the white rectangle shown at full resolution immediately below. LROC NAC M126873954R, orbit 3831, April 25, 2010; angle of incidence 34.91° at 48 cm resolution from only 40.48 kilometers [NASA/GSFC/Arizona State University].

Perhaps one of the better close-ups of the boulders gradually being calved from the ridge through mass wasting, another full resolution, this time at a 276 meter-wide field from LROC NAC M126873954R {NASA/GSFC/Arizona State University].

Symmetric Ejecta in the Farside Highlands

A symmetric "starburst" ejecta blanket exposed with high Sun angle. Image is 660 m wide, LROC NAC frame M108108187L. LRO orbit 1066, September 20, 2009; angle of incidence 15.44° at 0.59 meters resolution from 56.52 km [NASA/GSFC/Arizona State University].

Renee French
LROC News System

The 180 meter diameter impact crater observed in the opening image (8.874°N, 171.899°E) formed in the farside highlands. Its location away from compositional boundaries (like the mare-highland boundary) suggests that the high albedo ejecta blanket is due to freshly exposed material, indicating a young impact. How do we know that? Because material of the same composition that has been exposed to less space weathering (i.e., material that is younger) is brighter. Additionally, images acquired with the Sun nearly overhead emphasize albedo contrasts, bringing out details of ejecta distribution and rays. The directions in which ejecta spread out from a crater tells us about the angle the bolide (comet or asteroid) hit the surface. A symmetric ejecta blanket like this one typically indicates that the bolide impacted at an angle of 45° or greater (90° is vertical); an impact angle less than 45° produces asymmetric ejecta blankets. It is important to have high Sun angle images because without them, it is harder to determine the extent of the ejecta blanket and other young features.

Same Featured Image crater but observed at a lower Sun angle, LROC NAC frame M103388681R, spacecraft orbit 404, July 28, 2009; angle of incidence 65.11° at 1.25 meters resolution from 123.36 km, image field of view is approximately 700 meters wide [NASA/GSFC/Arizona State University].

The above image is of the same crater but with a different Sun angle - just look at the difference! Can you tell how big the ejecta blanket is or the distribution of ejecta with distance? In the low Sun angle image, could you tell that there were two craters next to each other, or which craters might be considered secondary craters?

LROC Wide Angle Camera (WAC) monochrome 100 meter resolution shows the location of the LROC Featured Image field of view, in the farside highlands (red arrow). Ejecta from the unnamed crater of interest barely stands out, with only a slightly a higher albedo than the surrounding terrain [NASA/GSFC/Arizona State University].

Even at the resolution of the WAC mosaic, the crater is still visible due to its bright ejecta blanket!

To spot your own young craters, view the full LROC NAC, HERE.

Related Posts:
Dark Secondary Crater Cluster
The Rays of Messier A
Farside impact!
Ejecta Starburst
Minty Fresh