L51 Catena Davy
A neat line of small craters strung across the floor of Davy crater, most plausibly the scar of a chain of comet or asteroid fragments striking in quick succession — a lunar echo of Shoemaker-Levy 9’s fall into Jupiter.
Source: IAU/Gazetteer & Sky & Telescope Lunar 100 (Wood, 2004)
L51 Davy Crater Chain
Mare Nubium · Catena Davy📉 Vital Statistics
🔭 Field Notes
Catena Davy lies on the floor of Davy Y, a satellite crater largely overlain by the crater Davy itself on the eastern edge of Mare Nubium. Roughly 23 craters string out along a line about 50 km long, ranging from the bright 15 km Davy G at one end down to craterlets barely large enough to cast a shadow. Several of the smaller pits bear historical names — Susan, Osman, Priscilla, Alan, Delia, Harold — inherited from an old topographic map that happened to chart just that stretch of the chain in detail, rather than from any modern or systematic naming scheme.
- ▶ Three Rival Origins: Crater chains like this one are generally explained one of three ways: a line of secondary craters thrown out from a much larger impact elsewhere, a chain of collapse or explosion pits along a volcanic fissure, or the scars left by an impactor that broke apart into a string of fragments before striking the surface — the same mechanism later observed directly when comet Shoemaker-Levy 9 broke up and struck Jupiter in a line of impacts.
- ▶ A Natural Test Case: Catena Davy’s remarkably regular spacing and size distribution — more uniform than a typical secondary-crater chain — is precisely why a fragmented-impactor origin gets taken seriously here, and why the chain is one of the better lunar examples for weighing all three hypotheses against each other. That’s a large part of why Wood included it on the Lunar 100 — not for a single settled answer, but as an invitation to compare the evidence yourself.
- ▶ A Once-Considered Landing Site: Catena Davy was studied as a possible early Apollo landing site, and it was photographed in detail by Ranger 9 during its final approach — by the time Apollo 12 and 14 flew, it was no longer a serious landing candidate, but their crews still captured additional orbital photography of the region.
📍 Nearby L100 Targets
- L15 Straight Wall: The famous Rupes Recta fault, roughly 340 km south-southwest, is a 110 km linear scarp on the eastern edge of Mare Nubium. It appears in some of the same wide-field photographs as Catena Davy, making the pair a natural one-session pairing for observers working through the same stretch of Mare Nubium.
- L47 Alphonsus Dark Spots: The large walled plain Alphonsus sits roughly 140 km southeast, close enough that it appears in the very same orbital photographs used to study the Davy chain. Its dark-halo craters are the Moon’s best-known candidate sites for actual volcanic vents, a useful contrast to Davy’s more ambiguous, still-debated origin.
- L61 Mösting A: A small, sharp-rimmed crater roughly 240 km north-northeast, historically important as the reference point once used to define the lunar coordinate system. It’s a good example of a simple, textbook impact crater to set against the ambiguity of the Davy chain nearby.
🚀 Mission Log
Target Acquisition — L51 Davy Crater Chain
Anchor on Davy, then look east onto Davy Y’s floor
Start at Davy, a small but conspicuous crater on the eastern edge of Mare Nubium — Davy itself overlies the western rim of the larger, lava-flooded Davy Y directly beside it, and the chain sits on Davy Y’s floor to the east. The prominent crater Alphonsus lies to the southeast as a secondary landmark, and the chain itself curves gently east-northeast, extending generally toward the Ptolemaeus region further along.
Time it for low, grazing sunlight
Most of the chain’s craterlets are shallow — only a few hundred meters deep — so they need real shadow relief to read as distinct little craters rather than a single blurred groove across Davy Y’s floor. Plan your session for whichever terminator pass puts this part of Mare Nubium under low, raking light.
Work up in power to count the chain and find Davy YA
At moderate-to-large aperture, with steady seeing doing more work here than raw power, locate Davy YA first — at about 2.6 km across, it’s the largest and deepest single member, sitting near the middle of the chain, and makes a good anchor for working outward in either direction. From there, see how many of the roughly 23 craterlets you can pick out strung across the chain’s 50 km length, and look for the tighter “peas in a pod” cluster of similarly sized craterlets between Davy YA and Davy Y’s wall.
Pair it with the Alphonsus neighborhood
Alphonsus (L47), with its dark-halo craters on the floor, sits just southeast of Davy and is a natural companion stop on the same session — both targets reward the kind of close, patient look that casual glancing at Mare Nubium tends to skip past.
📝 Observation Log — L51 Davy Crater Chain
0/4 CompleteIs Catena Davy visible tonight?
Catena Davy crosses the floor of Davy crater on the northern edge of Mare Nubium, southwest of Alphonsus, at 11.0°S, 7.0°W — close enough to the meridian to be a reliably easy target once the light angle is right. Best viewing falls around First Quarter (roughly Day 8), when a low sun casts individual shadows from each small crater in the chain, making the string of impacts easiest to trace. Libration has little influence at this longitude; a well-placed terminator does the real work.
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When to Observe the Davy Crater Chain
This is one of the smallest-scale targets on the Lunar 100 — a string of craterlets, most only a few kilometers across, stretched over roughly 50 km. Finding the chain is easy once you’re oriented; resolving it into individual craters takes some patience.
- For Orientation: Locate Davy crater first, on the eastern edge of Mare Nubium, with Alphonsus and Ptolemaeus nearby to the southeast and east. The chain sits on the floor of Davy Y, a large, lava-flooded ghost crater whose rim Davy itself overlies to the west.
- For the Individual Craterlets: You’ll want low, grazing sunlight — most of the chain’s members are shallow, on the order of a few hundred meters deep, so they need real shadow relief to stand out as distinct craters rather than a single blurred groove.
- Aperture and Seeing: Moderate-to-large aperture and steady seeing both help here — the reward for resolving the chain is seeing roughly two dozen similarly sized craters lined up almost like beads on a string.
What to Look For
Catena Davy contains roughly 23 small craters strung across about 50 km of Davy Y’s floor. What sets it apart from an ordinary cluster of impacts is how similar in size most of the craters are, and how neatly they line up — a pattern that strongly suggests formation in a single episode, even though exactly what kind of episode is still debated.
Near the middle of the chain sits Davy YA, at about 2.6 km across the most prominent single member, and one of the deepest at several hundred meters. It’s a good anchor point for working outward along the rest of the chain in either direction.
Between Davy YA and the wall of Davy Y sits a tight cluster of similarly sized craterlets, informally studied and named individually by amateur lunar researchers. Depths here vary — some cast a full shadow at low sun, while the shallowest members barely register at all.
Catena Davy has a strong observational pedigree: it was photographed by Ranger 9 on its final approach, imaged repeatedly by Apollo 12 and Apollo 14 from orbit, and captured by the Soviet Luna 22 probe. It was even considered at one point as a candidate early Apollo landing site.
The Science: A Moon-Sized Echo of Shoemaker-Levy 9
Most crater chains on the Moon have mundane origins — chains of secondary craters thrown out by a single big impact, or collapse pits along a volcanic or tectonic crack. Catena Davy has been proposed as the exception, one of the strongest lunar candidates for something more dramatic, though its origin isn’t fully settled.
The Tidal Disruption Hypothesis
In a 1995 paper, Wichman and Wood proposed that Catena Davy records the impact of a comet or asteroid that was torn apart by the Moon’s tidal forces shortly before impact — the same mechanism, on a much smaller scale, that shredded Comet Shoemaker-Levy 9 into a “string of pearls” before it struck Jupiter in 1994. They argued the chain’s setting and appearance don’t match ordinary secondary-impact or volcanic crater chains, but instead resemble the tidal-disruption catenae seen on Jupiter’s moons Ganymede and Callisto.
Why It’s So Much Smaller Than the Jovian Chains
Catena Davy is far shorter than the crater chains seen on Ganymede and Callisto, but the disruption models say that’s expected — the strength of tidal disruption scales with the mass of the body doing the pulling, and Earth is enormously less massive than Jupiter. A weaker tidal field naturally produces a shorter, more modest fragment train.
An Orbital Puzzle That’s Still Open
Wichman and Wood’s own modeling raised a genuine complication: many typical Earth-crossing trajectories appeared difficult to reconcile with a chain as long as Catena Davy, since fragments from a disruption event moving at typical Earth-crossing speeds wouldn’t have time to spread out enough before impact. That led them to suggest the impactor’s original orbit may have been unusual compared to typical Earth-crossing objects, though exactly what kind of orbit would fit isn’t settled. The same paper predicted that similar tidal-disruption chains, if this mechanism is right, might exist on Iapetus, Titan, Titania, or Oberon — a prediction that hasn’t led to a widely accepted identification of comparable chains there so far.
Most Lunar 100 crater chains are explained by processes that happen often and locally — volcanism, or debris from one big nearby impact. Catena Davy is the one that reaches off the Moon entirely, tying a modest string of small craters to the same violent physics that shredded a comet in front of Jupiter.