North Ray (crater)
Largest crater sampled by Apollo astronauts, visited in 1972.
NASA/John Young/Charlie Duke · Public domain
North Ray is a lunar crater located in the Descartes Highlands, and it was explored by the Apollo 16 crew. It holds the distinction of being the biggest crater from which astronauts collected samples during the entire Apollo program. The International Astronomical Union officially gave it its name in 1973.
The Apollo 16 Lunar Module, named Orion, touched down between North Ray and another crater called South Ray on April 21, 1972. Astronauts John Young and Charles Duke spent three extravehicular activities (EVAs) driving a Lunar Roving Vehicle across the area between these two craters. They reached North Ray during their third EVA, at a site called Station 11, roughly 4.4 kilometers north of where they landed. Along the route, they drove along the rim of Palmetto, a crater of similar size but older age, located about 3 kilometers south of North Ray.
The crater measures about 1 kilometer across and goes down roughly 240 meters. The astronauts noted that the top 50 meters of the slope are gentle, but below that the incline becomes steep, and they could not see the bottom. The inner walls are littered with boulders up to 5 meters wide. Near the southeastern rim sits a massive boulder, 10 meters high and 20 meters long, known as House Rock. A smaller boulder, almost certainly a piece broken off House Rock, is officially called South Boulder but is unofficially nicknamed Outhouse Rock. Although the crater’s ray system is visible from orbit, it was not obvious to the astronauts on the ground.
North Ray cuts into the Cayley Formation, which dates to the Imbrian period, but the crater itself is much younger. Based on the presence of its rays, it is classified as Copernican in age.
**Age**
Analysis of sample 67955, a noritic anorthosite collected from Outhouse Rock, indicates that the impact forming North Ray occurred about 50 million years ago. This age comes from measuring how long the rock was exposed to cosmic rays. The rock itself has been radiometrically dated using the samarium-neodymium method to 4.20 ± 0.07 billion years.
**Samples**
The samples gathered at North Ray (Station 11) are listed in Table 6-II of the Apollo 16 Preliminary Science Report, which excludes any specimens weighing less than 25 grams (though many such small samples were also collected).
Quick Facts
- Diameter
- 950 m
- Depth
- 240 m
- Formation
- Copernican
- Eponym
- Astronaut-named feature
Facts from the source article.
Lore & Background
North Ray crater is approximately 1 km in diameter and 240 m deep. The astronauts observed that the upper 50 m of the slope is gentle, but becomes steep below 50 m, and they could not observe the bottom. The inner slopes are covered by boulders up to 5 m across. A huge boulder, known as House Rock (10 m high x 20 m long), lies near the southeastern rim. A smaller boulder, almost certainly a fragment of House Rock, is officially known as South Boulder but unofficially called Outhouse Rock. The ray system, visible from orbit, was not obvious on the ground.
Reader's Guide
North Ray crater is significant as the largest crater sampled by astronauts during the Apollo program, providing key insights into lunar impact processes and the age of the lunar surface. The Apollo 16 Lunar Module Orion landed between North Ray and South Ray craters on April 21, 1972. Astronauts John Young and Charles Duke explored the area over three EVAs using a Lunar Roving Vehicle. They visited North Ray on EVA 3, at station 11, about 4.4 km north of the landing site. On the way, they drove along the rim of the similar-sized but older crater Palmetto, approximately 3 km south of North Ray. The crater cuts into the Cayley Formation of Imbrian age, but the crater itself is much younger, of Copernican age, based on the presence of rays. Sample 67955, a noritic anorthosite collected from Outhouse Rock, indicates the impact occurred about 50 million years ago, based on cosmic ray exposure. The rock itself is dated at 4.20 ± 0.07 billion years by Sm/Nd radiometric dating. The samples collected at Station 11 are listed in Table 6-II of the Apollo 16 Preliminary Science Report.
Did You Know?
- A huge boulder near the southeastern rim, known as House Rock, is 10 m high and 20 m long.
- The crater's ray system is visible from orbit but was not obvious on the ground.
- Sample 67955 from Outhouse Rock dates the impact to about 50 million years ago.
Gallery
Frequently Asked Questions
What is North Ray crater?
North Ray is a small impact crater sitting in the Descartes Highlands on the Moon, positioned just north of its twin, South Ray. It became a major science target when the Apollo 16 crew made it a primary sampling site in 1972.
How big is North Ray crater?
The crater spans roughly one kilometer in diameter and drops about 240 meters from rim to floor. Despite that modest footprint, it is the largest crater from which Apollo astronauts ever collected rock and regolith samples.
How old is North Ray crater?
Cosmic-ray exposure dating of sample 67955, gathered by the Apollo 16 crew, places the crater's formation at roughly 50 million years ago. That makes it a relatively young feature in lunar geological terms.
Why is North Ray crater significant in Apollo history?
It holds the program-wide record as the biggest crater ever sampled by astronauts, a milestone that underscored Apollo 16's geology objectives. The International Astronomical Union formally approved the name in 1973 to cement its place in official lunar nomenclature.
Who explored North Ray crater and when?
Astronauts John Young and Charles Duke reached North Ray during the third EVA of Apollo 16 on April 21, 1972, driving the Lunar Roving Vehicle up from the Orion landing site in the valley between the two Ray craters. Their stops there yielded the samples that still anchor our understanding of the Descartes Highlands' history.
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