Flag (crater)

Lore & Background

Flag crater is located about 1.5 km west of the Apollo 16 Lunar Module Orion landing site, which touched down on April 21, 1972. The astronauts John Young and Charles Duke explored the area over three EVAs using the Lunar Roving Vehicle. They drove to Flag on EVA 1. The adjacent crater Plum is only about 30 m in diameter, while the slightly larger crater Spook lies less than 1 km to the east.

Reader's Guide

Flag crater served as Geology Station 1 during the Apollo 16 mission, where astronauts collected samples from its vicinity and that of the adjacent Plum crater. The samples, listed in Table 6-II of the Apollo 16 Preliminary Science Report, include various lithologies described in the Lunar Sample Atlas. The crater cuts into the Cayley Formation of Imbrian age, providing geological context for the lunar highlands. Its exploration contributed to understanding the Moon's geological history, though the article does not specify broader scientific conclusions.

Did You Know?

• Flag crater is approximately 240 m in diameter and over 20 m deep.
• The astronauts drove to Flag crater on EVA 1 of Apollo 16.

Landing in the Descartes Highlands

On April 21, 1972, the Apollo 16 Lunar Module named Orion touched down in the Descartes Highlands region of the Moon, settling roughly 1.5 kilometers to the east of a small impact feature that would become known as Flag. The landing site was situated between two prominent ray craters—North Ray on one side and South Ray on the other—giving the area a distinctive visual character. The two astronauts assigned to this mission, John Young and Charles Duke, spent their surface stay conducting three separate extravehicular activities, traveling between sites aboard a Lunar Roving Vehicle. Flag itself became one of their first destinations, reached during the very first EVA. The Descartes Highlands setting placed the crew in a region of ancient lunar highland terrain, making the area scientifically rich and visually striking against the surrounding landscape.

Physical Profile and Geological Context

Flag is a modest impact structure measuring approximately 240 meters across and plunging more than 20 meters into the lunar surface. Its dimensions place it in a middle range among the craters the Apollo 16 crew encountered in the immediate vicinity. Just beside it sits Plum, a dramatically smaller bowl barely 30 meters in diameter, while the somewhat larger Spook crater rests less than a kilometer to the east. All three features were visited by the astronauts during their surface operations. Geologically, Flag is significant because its rim and walls cut into the Cayley Formation, a unit of Imbrian age. This means the crater's impact event postdates the formation of those underlying rocks, providing a natural cross-section that reveals the stratigraphy of the highland terrain. The contrast in size between Flag and its tiny neighbor Plum makes the pair a striking visual and scientific pairing in the Descartes Highlands landscape.

The Apollo 16 Exploration Campaign

During their three extravehicular activities, John Young and Charles Duke used the Lunar Roving Vehicle to traverse the terrain around their landing site, and Flag was among the first stops on their itinerary, reached during EVA 1. The crater and its immediate surroundings were designated Geology Station 1, a formal scientific waypoint anchored at the adjacent Plum crater. At this station the astronauts collected rock and regolith samples from the vicinity of both Flag and Plum. These specimens were later catalogued in Table 6-II of the Apollo 16 Preliminary Science Report, though that listing omits any fragments weighing less than 25 grams, of which there were numerous. Detailed descriptions of sample type, lithology, and physical characteristics are preserved in the Lunar Sample Atlas maintained by the Lunar and Planetary Institute. The work at Station 1 represented one of the earliest and most focused geological investigations of the highland terrain during the Apollo era.

Naming, Designation, and Scientific Record

The name "Flag" was formally adopted by the International Astronomical Union in 1973, cementing the crater's place in the official nomenclature of the lunar surface. This designation followed the Apollo 16 mission and reflected the feature's role as a key reference point in the Descartes Highlands. The crater's proximity to the LM landing site, its position between the well-known North Ray and South Ray craters, and its association with Geology Station 1 all contributed to its selection as a named landmark. Today, Flag endures in the scientific record as a site where Imbrian-age Cayley Formation material was examined in situ, where samples were gathered and later analyzed, and where the interplay of impact geology and highland stratigraphy was documented by two astronauts in a rover. Its modest size belies the depth of data it contributed to our understanding of the Moon's ancient crust.

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