Lunar Reconnaissance Orbiter images are reshaping our understanding of the Moon. We can now view the surface at amazing resolution and have a better understanding of how impact cratering, volcanism, and reshaping of the crust by tectonic (internal) forces reveal the Moon as a dynamic place. The "Dynamic Moon" could be the theme of future lunar exploration.
Wrinkle Ridges Reveal Recent Activity
After the mare basins were flooded with basalt lava, they contracted. As they contracted, the basalt broke and folded, forming wrinkle ridges. Scientists believe that the fields of boulders on the ridge slopes, possibly shaken loose by moonquakes, could be related to recent shrinking of the Moon. The Moon, it seems, is not "dead" but still geologically active.
Image ID: M135507772R
Image width: 1.85 m (1.1 mi.)
Random Scarps Show the Moon Is Shrinking
The thousands of small cliff-like features discovered in LROC images throughout the lunar highlands provide evidence of a shrinking Moon. Planetary geologists call them lobate scarps. Here, one cuts across a large impact crater. Lobate scarps are faults formed when the lunar crust breaks as it shrinks and thrusts blocks of rock upward. The shrinking occurs as more of the Moon's interior slowly cools and thus takes up less space.
Image ID: M156626383LR
Image width: 4.3 km (2.7 mi.)
Young Craters Cut by Even Younger Scarps
Small, sharp lobate scarps (winding cliff-like features) are among the youngest lunar landforms. Scientists know this because small features on the Moon don't survive billions of years of steady bombardment by meteors. Also, these scarps cut through existing craters that are also very young. The scarps are so young they may even still be actively forming on the Moon today.
Image ID: M103460280LR
Image width: 4.8 km (3 mi.)
Lunar Stretch Marks
A series of small, narrow troughs (upper half)—so small they could only be found in high-resolution images—formed where the lunar crust is stretching. As it stretches, the crust breaks apart along faults, and sections drop down into narrow troughs called graben. Chains of circular pits, formed when the lunar soil drains into voids, are found within these troughs. Like many other fault features on the Moon, these graben are very young. They show that the shrinking Moon is not shrinking everywhere.
Image ID: M104756463R
Image width: 4.8 km (3 mi.)
Recent Volcanic Activity
Scientists had thought that volcanic activity ended on the Moon over a billion years ago. However, they have discovered more than 60 small volcanic flows in LROC images that appear relatively young (10 to 100 million years old). The smooth blobs within this D-shaped volcanic crater bear few impact craters—evidence of their young age.
Image ID: M1108203502LR
Image width: 5.2 km (3.2 mi.)
Young Lava Flows
Smooth volcanic flows cover the floor of this shallow depression. They came from the circular raised feature that may be a small volcano. Many of the smaller flows appear unconnected to the central volcano, so the lava must have emerged from multiple vents. Future volcanic eruptions might still be possible.
Image ID: M1123370138R
Image width: 2.4 km (1.5 mi.)
Overlapping Features Tell a Story
Scientists can tell the relative ages of lunar features by how they overlap or crosscut. Here, a wide flat-bottomed trough, or graben, first opened (left to right), then large areas collapsed into pits (lower left to upper right), and finally lava erupted very recently within the pits. Lava moving beneath the surface may have caused these events.
Image ID: M1108117962LR
Image width: 13 km (8 mi.)
Young Features Hint at Hidden Depths
Lava flows have spread across the floor of this large collapsed area. Their lack of impact craters and steep sides show that they erupted relatively recently. Discoveries such as these are causing scientists to rethink their ideas about the Moon's internal composition. Perhaps a large reservoir of radioactive elements is generating heat deep within the Moon and keeping it volcanically active.
Image ID: M1142616950LR
Image width: 1.9 km (1.2 mi.)
A Lunar Cavern
Collapse pits, where the near-surface lunar crust has caved in, can provide a window into the shallow subsurface. They are somehow related to the volcanic plumbing system that lava moved through when it flooded the mare basins early in the Moon's history. Could they be openings into a system of hollow lava tubes? These images, taken at different times, reveal that a cave extends at least 25 meters (82 feet) under the surface here. Arrows connect the same features.
Image IDs: M126710873R, M155016845R, M152662021R
Image width: 200 m (660 ft.)
A Natural Bridge on the Moon
The most extraordinary collapse pit found in LROC images is this one in King crater. What appears to be two closely spaced pits is actually one spanned by a natural bridge. It formed when a resistant or stronger portion of the roof remained when both sides caved in. The enlargement (right) shows light that passed under the bridge shining on the pit floor to the left of the bridge.
Image ID: M113168034R
Image width: 500 m (1,640 ft.)
Lunar Pits on the Far Side
Collapse pits can show the structure of shallow subsurface lava flows. This pit reveals layer upon layer of lava flows that flooded Mare Ingenii on the Moon's far side.
Image IDs: M171835900L, M184810830L, M1135454764R
Fresh Impact Craters
Scientists can identify newly formed craters by comparing images of the same area taken over time. Using LROC images, they have found more than 200 new craters ranging from 1.5 to 43 meters (5 to 141 feet) across. The images here show three sets of examples. The images to the left were taken before an impact. The middle images were taken after an impact. The right images (called ratio images) combine aspects of the before and after images to highlight changes caused by the impacts.
Image IDs: M1105837846LR, M1121160416LR, M1104273380LR, M1180855200LR, M1101866147LR, M1132496422LR