L45 Maurolycus
Deep in the southern highlands, a region battered so thoroughly that older rims are barely traceable beneath the newer craters overlapping them — about as saturated a stretch of terrain as the Moon has to offer.
Source: IAU/Gazetteer & Sky & Telescope Lunar 100 (Wood, 2004)
L45 Maurolycus
Southern Highlands · Saturation Cratering📉 Vital Statistics
🔭 Field Notes
Maurolycus is a fine complex crater in its own right — tall terraced walls, a central peak, a broad, flat floor — but it isn’t on the Lunar 100 for its own features. It’s here as the anchor point for a stretch of southern highlands so relentlessly battered by impacts that it illustrates what planetary scientists call crater saturation: terrain so densely cratered that new impacts erase old ones about as often as they add new ones.
- ▶ Craters Overlapping Craters: Maurolycus itself overlaps the ruined remains of an older, larger crater along its southern rim, and is in turn joined at its own southeast rim by the smaller Barocius. That’s at least three overlapping impacts stacked into one small patch of highland — a pattern that repeats across the whole surrounding region.
- ▶ Saturation, Not Randomness: Once a surface reaches saturation equilibrium, its crater count stops climbing — every new impact is roughly balanced by an older crater it destroys or buries. The southern highlands around Maurolycus are one of the regions researchers point to when studying this equilibrium and its role in resurfacing ancient lunar terrain.
- ▶ An Oddly Smooth Floor: The floor is unusually smooth for such an ancient highland crater. Various explanations have been proposed, including impact-related resurfacing and ejecta infill, but no single interpretation has gained universal acceptance.
📍 Nearby L100 Targets
- L40 Janssen Rille: Rimae Janssen, a rare highland graben cutting across the floor of the 201 km walled plain Janssen, roughly 580 km to the southeast. Both targets sit in unflooded highland crust, but where Maurolycus tells a story of relentless impact overprinting, Janssen’s rille tells one of crustal extension happening somewhere volcanism doesn’t obviously reach.
- L55 Baco: A 65 km crater roughly 300 km to the south-southeast, whose terraces have been worn smooth and whose floor is unusually flat and featureless. It’s a smaller-scale, single-crater echo of the same erosional forces at work across the whole Maurolycus neighborhood, just concentrated on one rim rather than spread across a whole region.
- L96 Leibnitz Mountains: A informal name for peaks glimpsed along the Moon’s southern limb, roughly 1,300 km south near the pole itself, believed to mark the rim of the immense South Pole–Aitken basin. A genuinely difficult target that rewards favorable libration — a reminder of how much rougher the highlands get the further south you look from Maurolycus’s own crowded neighborhood.
🚀 Mission Log
Target Acquisition — L45 Maurolycus
Find one crowded corner of the southern highlands
Maurolycus is joined at its southeast rim by the smaller crater Barocius, with the overlapping pair Stöfler and Faraday just to its west — four craters piled against one another in a single crowded neighborhood. Maurolycus itself is a fine complex crater — tall terraced walls, a central peak complex, a broad floor — but it isn’t on the Lunar 100 for its own features. It’s the anchor point for a stretch of terrain so relentlessly battered that it’s become a textbook example of crater saturation.
One lighting window covers the whole neighborhood
Around first quarter, with the terminator nearby, low sun angle brings out the full drama of the crater’s massive terraced rim and throws long shadows across the floor. That same window is best for tracing where Maurolycus cuts into older, underlying terrain and where younger craters like Faraday cut into their neighbors in turn.
Read the layers, then catch the floating peaks
Compare the height and terracing of Maurolycus’s eastern wall, which stands roughly 4.5–4.7 km above the floor, against its lower, more broken southeastern rim where it joins Barocius. Working outward, see how many generations of overlapping craters you can identify — Maurolycus over older terrain to its south, its own rim breached by Maurolycus F, Faraday cutting into Stöfler’s rim next door. Near sunrise, watch for the crater’s central peaks catching light well before dawn reaches the floor around them — they appear to float in darkness.
Pair it with the wider southern highlands
Janssen Rille (L40), roughly 580 km southeast, sits in the same unflooded highland crust but tells a story of crustal extension rather than impact overprinting. Baco (L55), roughly 300 km south-southeast, is a smaller-scale, single-crater echo of the same erosional forces — just concentrated on one rim rather than spread across a whole region. And the Leibnitz Mountains (L96), roughly 1,300 km south near the pole, are a reminder of how much rougher the highlands get the farther south you look from Maurolycus’s own crowded corner.
📝 Observation Log — L45 Maurolycus
0/4 CompleteIs Maurolycus visible tonight?
Maurolycus lies deep in the southern highlands near Barocius and Stöfler, at 42.0°S, 14.0°E — a longitude close to the meridian, so its viewing window is set almost entirely by its far-southern latitude. Best viewing falls around First Quarter (roughly Day 6), when the terminator crosses this stretch of highlands and long shadows expose just how densely one crater overlaps the next. A favorable southerly libration tips the region further into view and is worth watching for, since at 42°S the terrain is already somewhat foreshortened even under ideal conditions.
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When to Observe Maurolycus
Maurolycus sits in one of the most heavily battered stretches of the southern highlands, a region where craters overlap craters so many times over that it’s become a textbook example of what happens when a surface runs out of room for new impacts.
- For Orientation: Maurolycus is joined at its southeast rim by the smaller crater Barocius, with the overlapping pair Stöfler and Faraday just to its west — four craters piled against one another in a single crowded neighborhood.
- For the Terraced Walls: Around first quarter, with the terminator nearby, low sun angle brings out the full drama of the crater’s massive terraced rim and throws long shadows across the floor.
- For the Overlapping Structure: The same low-sun window is best for tracing where Maurolycus cuts into older, underlying rings and where younger craters like Faraday cut into it in turn.
What to Look For
Maurolycus is about 114 km across, with tall, wide, terraced walls that are especially prominent along the eastern rim. The crest of that rim stands roughly 4.5–4.7 km above the crater floor, making Maurolycus one of the more impressive deep-walled craters in the southern highlands.
Maurolycus overlies portions of older, heavily degraded terrain to its south, while its own northwestern rim has been breached by the smaller crater Maurolycus F. A few kilometers west, Faraday cuts into the rim of the larger crater Stöfler, and Faraday’s own rim has in turn been chewed up by still smaller, later impacts.
Large portions of the crater floor are relatively level, but the area near the breach at Maurolycus F is noticeably more rugged. Rising from the floor is a complex of central peaks, tall enough that their summits catch sunlight well before dawn reaches the surrounding floor — a striking sight through a telescope near sunrise, when the peaks appear to float in darkness.
Just west of Maurolycus, Stöfler is a large, comparatively flat-floored crater whose southeastern rim has been overrun by Faraday. Because Faraday clearly cuts across Stöfler’s rim rather than the other way around, it’s straightforward to tell which crater came second — a clean, nearby example of the same layering of impacts that makes Maurolycus itself so visually chaotic.
The Science: When a Surface Runs Out of Room
This stretch of the southern highlands is one of the best places on the Moon to see what geologists call crater saturation — a surface so thoroughly bombarded that it has essentially reached a steady state.
Saturation Equilibrium
Early in lunar history, impacts fell fast enough that some ancient surfaces became so densely cratered that new impacts started erasing or overprinting existing craters about as often as they added new, distinguishable ones. Once a surface reaches this rough equilibrium, simply counting visible craters stops giving a reliable readout of how many impacts have actually occurred — the surface has effectively filled up.
A Living Record of the Late Heavy Bombardment
The tangle of overlapping rings around Maurolycus, Stöfler, Barocius, and Faraday is thought to preserve the aftermath of the intense, chaotic bombardment that reshaped much of the ancient lunar crust more than 4 billion years ago. Surfaces this heavily saturated are generally understood to date to roughly the end of that early bombardment period, though pinning an exact age on any one surface from crater counts alone gets harder precisely because it’s saturated.
What Hasn’t Been Resolved
Exactly how crater populations behave once they approach saturation — how quickly new impacts start erasing old ones, and how that process varies with crater size — is still an active area of study, refined through statistical modeling and comparison with other cratered bodies. Maurolycus and its neighbors remain a useful real-world testbed for that work rather than a fully settled case.
Where Regiomontanus turned on a single, misleading impact crater, Maurolycus is shaped by thousands of them — a crowded, ancient landscape that shows what the Moon looks like once a surface has taken about as many hits as it can hold.