L22 Aristarchus Plateau
A tilted crustal block roughly 200 km across, rising out of Oceanus Procellarum like an island of older crust mantled in dark volcanic glass — uplifted and tipped during the Imbrium impact, the plateau is now home to the Moon’s densest tangle of sinuous rilles, the cobra-headed gash of Vallis Schröteri, and a deep blanket of pyroclastic ash that has made this the single most reported site of Transient Lunar Phenomena anywhere on the Moon.
L22 Aristarchus Plateau
Oceanus Procellarum📉 Vital Statistics
🔭 Field Notes
The Aristarchus Plateau is a tilted crustal block — rectangular in outline, rising steeply on its southeastern edge and sloping gently down to the northwest — that projects more than 2 km above the surrounding lava plains of Oceanus Procellarum. It is one of the most geologically diverse regions on the Moon: ancient noritic highland crust, multiple generations of mare basalt, the largest pyroclastic deposit on the lunar surface, and the greatest concentration of sinuous rilles anywhere on the Moon, all concentrated within a remarkably compact region.
- ▶ Pyroclastic Mantle: Almost the entire plateau surface is blanketed by a dark deposit of iron-rich volcanic glass beads — the product of ancient fire-fountain eruptions that spread material across more than 49,000 km². Radar studies show the deposit is highly variable in thickness, from less than a metre in some areas to an estimated 20–30 m in others. Under good seeing, this mantle gives the plateau its characteristically dark appearance, noticeably distinct from the surrounding Procellarum mare.
- ▶ Imbrium Origin: The plateau is thought to be a block of ancient pre-Imbrian crust that was structurally uplifted, tilted, and fractured when the Imbrium basin formed roughly 3.85 Ga ago. Its long northeast-trending borders run approximately radial to Imbrium, while its northwest borders are roughly concentric to the basin — a geometry that reflects the crustal reorganisation driven by that impact.
- ▶ Transient Lunar Phenomena: The Aristarchus region has more reported transient lunar phenomena than any other location on the Moon, accounting for roughly one-third of the highest-confidence observations. Apollo 15’s alpha particle spectrometer detected elevated radon-222 emissions passing 110 km overhead, later confirmed by the Lunar Prospector mission, suggesting episodic release of gases from the lunar interior. The plateau is also anomalously enriched in thorium, consistent with the concentration of KREEP-rich materials and a prolonged volcanic history.
📍 Nearby L100 Targets
- L17 Schröter’s Valley (Vallis Schröteri): The largest sinuous rille on the Moon, stretching over 160 km across the plateau and out into Oceanus Procellarum. It originates at the “Cobra Head” — a broad collapse depression roughly 6 km across that marks the primary volcanic vent and is widely regarded as one of the Moon’s largest volcanic vent complexes. The primary channel reaches roughly 4 km wide and 500 m deep; winding along its own floor is a second, inner rille carved by a later eruption episode, adding another layer of complexity that becomes visible only in good seeing. Under low morning illumination the Cobra Head casts a distinctive shadow, making it the easiest first fix when sweeping the plateau from its northern edge.
- L11 Aristarchus Crater: The single brightest crater on the Moon, sitting on the southeastern edge of the plateau at 23.7°N, 47.5°W. At roughly 40 km across and 3.5 km deep, the Copernican-age impact punched through both the plateau’s noritic highland crust and the surrounding Procellarum mare, exposing a cross-section of over 3 km of stratigraphy in its walls. LROC imagery reveals complex stratified wall materials exposing mare basalt, highland crust, impact melt, and volcanic deposits. Herodotus, a similarly-sized but lava-flooded and featureless companion crater, sits immediately to the west, making the contrast between freshly excavated highland material and ancient mare geology immediately legible even at modest magnification.
- L86 Prinz Rilles (Rimae Prinz): A fan of sinuous rilles spread across the Procellarum mare roughly 100 km east of the plateau, originating on and around the lava-flooded remnant of Prinz crater (46 km, 25.5°N, 44.1°W). The primary rille, Rima Prinz, snakes roughly 75 km from its source vent — the small volcanic depression Vera, just north of Prinz’s rim — first westward then sharply northward, before fading into the mare. At least four distinct rilles make up the system, several converging near the low hills of Montes Harbinger. Modelling using LROC topography suggests Rima Prinz formed largely by thermal erosion from sustained, high-volume lava flows, though other mechanisms may also have contributed — making it one of the most studied examples of lunar lava channel formation.
🚀 Mission Log
Target Acquisition
Find Aristarchus crater — the brightest spot on the Moon
Start with Aristarchus crater (L11), which sits on the southeastern edge of the plateau and is effectively self-marking. It is the single brightest crater on the near side and is can often be detected with the naked eye during crescent phases as an unusually bright point in the otherwise dark expanse of Oceanus Procellarum. Under any magnification, it announces itself. Once you have Aristarchus, the plateau stretches to its north and west — a broad, noticeably darker elevated terrain rising above the surrounding mare.
Read the plateau as a dark elevated block, not a crater
The L22 target is the plateau itself — roughly 170 × 220 km of uplifted ancient crust containing extensive dark pyroclastic deposits. Near the terminator, the steep southeastern scarp rising more than 2 km above Procellarum throws a broad shadow that defines the plateau edge clearly at 50x – 75x. Under high Sun, the pyroclastic mantle takes over: the plateau reads as a distinctly darker elevated block against the grey mare, noticeably different in tone from both Oceanus Procellarum to the south and the surrounding lava plains. Either lighting condition makes it visible — they just reveal different things.
Locate the Cobra Head and Schröter’s Valley along the northern edge
With the plateau established in the field, move to its northern edge and look for Schröter’s Valley (L17) — the largest sinuous rille on the Moon. The entry point is the Cobra Head, a roughly 6 km collapse depression widely interpreted as the principal volcanic source region of the valley. Near the terminator at 75x – 100x, the Cobra Head casts a distinctive shadow that makes it the easiest first fix in this part of the plateau. From there the valley snakes northward and westward, eventually widening as it descends off the plateau edge and out onto the Procellarum mare.
Push magnification to hunt the inner rille of Schröter’s Valley
Inside the main channel of Schröter’s Valley, a second narrower rille runs along the valley floor — generally interpreted as a younger volcanic channel within the larger valley. This inner rille requires 150x or more, good seeing, and patience; it is not visible in every session. Confirming it is one of the more rewarding fine-detail challenges the plateau offers. While you are in the area, Herodotus crater — immediately west of Aristarchus, similar in size but heavily lava-flooded and relatively featureless — provides a striking comparison to its brilliant neighbour and helps frame the southeastern corner of the plateau.
📝 Observation Log — L22 Aristarchus Plateau
0/4 CompleteIs the Aristarchus Plateau visible tonight?
The plateau rewards two separate sessions. The dark pyroclastic tone is best seen near Full Moon when albedo contrast is highest. Schröter’s Valley, the Cobra Head, and the southeastern scarp need the terminator — aim for Waxing Gibbous (Day 10–11) or Last Quarter (Day 21–22).
Check Moon Phase TodayReturn to the List
Ready to find the next target? Go back to the full map to see what else is visible tonight.
← Back to Lunar 100 Map
When to Observe the Aristarchus Plateau
The Plateau is unusual among Lunar 100 targets in that nearly every one of its features depends on a different kind of light. The dark pyroclastic mantle is an albedo effect that reads best under moderate, slightly oblique sun — too high and the color contrast flattens out, too low and the deposit just looks like one more dark shape in shadow. The rilles, by contrast, are pure relief features that need a low, raking terminator to show at all. There isn’t a single best night for this target; it rewards repeated visits at different phases.
- Dark Mantle Contrast: Best around Day 6–8 (waxing) or Day 19–21 (waning), when the sun is high enough to suppress shadow but oblique enough to preserve the reddish-brown tonal contrast between the pyroclastic deposit and the brighter plateau crust around it.
- Rille Network (Vallis Schröteri and Rimae Aristarchus): Best around Day 7–9 or Day 18–20, when the terminator crosses the plateau directly. Under a low sun, Vallis Schröteri’s “Cobra Head” and the narrower rilles to the north throw sharp, continuous shadow lines that vanish entirely under high sun.
What to Look For
At 50x–75x, look for the Plateau’s distinctive shape: a roughly rectangular slab about 200 km across, standing 1–2 km above the surrounding Oceanus Procellarum on its southeastern edge and sloping gently down to the northwest. Unlike most lunar highlands, this block sits stranded in the middle of a mare, an island of older crust that mare lava never managed to bury. Aristarchus crater itself sits right on its southeastern corner, bright enough to be the first thing your eye catches before you notice the broader plateau beneath it.
Under moderate sun at 75x–100x, scan the plateau for a broad reddish-brown haze overlying the brighter terrain — one of the largest pyroclastic deposits on the Moon, estimated at tens of thousands of square kilometers. This is fine volcanic glass, sprayed out during a long-lived, Hawaiian-style fire-fountain eruption centered on the “Cobra Head” vent at the head of Vallis Schröteri. A color or deep-yellow filter can help separate the deposit’s distinct reddish hue from the surrounding crust for visual observers.
With the terminator nearby at 100x–150x, look for the largest sinuous rille on the Moon: it begins at a wide, bulbous depression nicknamed the Cobra Head just north of the crater Herodotus, then narrows and winds roughly 160 km across the plateau. At its widest, near the source, it spans up to 11 km; by its end it has tapered to barely 1 km.
North of the Cobra Head, look for a dense tangle of narrower sinuous rilles cutting across the plateau — the densest concentration of this rille type found anywhere on the Moon. Many appear to originate at their own small source vents, where low-viscosity lava broke through the surface and then channeled or tunneled across the terrain before partially collapsing.
The Science: An Uplifted Block, Not a Simple Mare
Almost everything distinctive about the Aristarchus Plateau traces back to two separate events, roughly half a billion years apart: first the basin-forming Imbrium impact that lifted and tilted an ancient slab of highland crust, and later a long period of explosive and effusive volcanism that mantled, channeled, and scarred the surface of that same slab.
Explanation 1 — Uplift and Tilting by the Imbrium Impact
The leading interpretation is that the Plateau is a large block of ancient highland crust that was displaced, uplifted, and tilted during the Imbrium basin-forming impact, roughly 3.9 billion years ago. Altimetry data shows the slab tilted downward to the northwest while staying elevated on its southeastern margin — exactly the geometry expected from a crustal block jolted and rotated by a nearby basin-scale impact, rather than slowly built up by later volcanism. Margins of the Plateau line up radially and concentrically with the Imbrium basin itself, reinforcing the connection.
Explanation 2 — A Partially Buried Shield Volcano
A minority interpretation, proposed by Spudis et al. (2013), argues instead that the Plateau is largely a large, partially developed shield volcano complex that simply never finished burying the older highland block beneath it. Under this view, much of what looks like an uplifted crustal slab is actually volcanic construction sitting on top of, rather than displacing, the original crust. A 2024 gravity-inversion study by Liang et al. found buried, ring-shaped low-density structures within the plateau consistent with older crater rims preserved beneath the surface — evidence that at least part of the original crust survives intact beneath whatever volcanic material was added later.
What the Pyroclastic Deposit Adds
Whichever uplift story is correct, the volcanism that followed is reasonably well constrained, though not fully resolved. Spectral and thermal data show the dark mantling deposit is fine-grained, glass-rich, and largely free of entrained rock fragments — consistent with a prolonged, Hawaiian-style fire-fountain eruptive episode rather than a single violent blast. The glass is enriched in iron, giving the deposit its distinctive reddish color in visible light, a hue observers have noted since the 17th century. Spatter-cone-like features near the Cobra Head vent suggest the pyroclastic mantle is thought to have contributed to the same broad eruptive activity that helped form Vallis Schröteri, though the rille’s own formation — likely a staged process involving lava channeling, thermal erosion, and possibly older fault structures — is not yet fully understood.
Seen together, the Plateau tells a layered story: an ancient slab of crust, wrenched upward and tilted by a distant basin-forming impact (or, on the minority view, built up by volcanism that never fully buried it), later scarred and draped by a sustained period of local volcanic activity — making it one of the few places on the Moon where both a basin-scale impact event and a prolonged volcanic episode have left their fingerprints on the same patch of ground.