North Ray (crater)

North Ray crater is a small crater in the Descartes Highlands of the Moon visited by the astronauts of Apollo 16. The name of the crater was formally adopted by the IAU in 1973.[1] It is the largest crater sampled by astronauts during the Apollo program.

North Ray
Apollo 16 image
Coordinates8.82°S 15.48°E / -8.82; 15.48
Diameter950 m[1]
Depth240 m
EponymAstronaut-named feature
LRO image

The Apollo 16 Lunar Module (LM) Orion landed between North Ray and South Ray craters on April 21, 1972. The astronauts John Young and Charles Duke explored the area between the craters over the course of three EVAs using a Lunar Roving Vehicle, or rover. 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, which is approximately 3 km south of North Ray.

North Ray crater is approximately 1 km in diameter and approximately 240 m deep.[2] The astronauts observed that the upper 50 m of the slope is gentle, but that it 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 (10 m high x 20 m long) boulder, known as House Rock, lies near the southeastern rim. A smaller boulder that is almost certainly a fragment of House Rock is officially known as South Boulder, but unofficially known as Outhouse Rock.[3] The ray system, which can be seen from orbit, was not obvious on the ground.

North Ray cuts into the Cayley Formation of Imbrian age,[4] but the crater itself is much younger, of Copernican age, based on the presence of rays. (See also section on age below.)

Panorama of North Ray Crater from the south rim. House Rock is at right edge. Compare with the map below.
Planimetric map of Station 11 from the Apollo 16 Preliminary Science Report. X indicates sample locations, 5-digit numbers are LRL sample numbers, rectangle is lunar rover (dot indicates TV camera), black spots are large rocks, dashed lines are crater rims or other topographic features, and triangles are panorama stations.
  • Geologic map of North Ray crater
    Geologic map of North Ray crater
  • Oblique Apollo 14 image, facing east
    Oblique Apollo 14 image, facing east
  • Telephoto image of rocks in the interior walls of the crater
    Telephoto image of rocks in the interior walls of the crater
  • John Young using the rake tool to collect a sample (67700) at the southeast rim, with the rover at the central horizon, and white breccia boulders at the right horizon
    John Young using the rake tool to collect a sample (67700) at the southeast rim, with the rover at the central horizon, and white breccia boulders at the right horizon
  • White breccia boulder along the south rim of the crater, showing typical dark-clast population, rounded, unjointed surfaces, and well-developed fillet
    White breccia boulder along the south rim of the crater, showing typical dark-clast population, rounded, unjointed surfaces, and well-developed fillet
  • House rock as viewed from the white breccia boulders (looking northeast)
    House rock as viewed from the white breccia boulders (looking northeast)
  • East side of House Rock
    East side of House Rock

Age
Lunar sample 67955 was used to date the impact at about 50 million years ago.

Based on sample 67955,[5] a noritic anorthosite collected from Outhouse Rock, the impact that created North Ray crater was about 50 million year ago. This is based on the measured duration of the rock's exposure to cosmic rays.[6] The rock itself is dated at 4.20 ± 0.07 b.y. by Sm/Nd radiometric dating.[7]

Samples
Lunar sample 67016, found lying on the ground next to the rover
Lunar sample 67475, a clast was removed from one of the white breccia boulders shown above
Lunar sample 67559, found within rake sample 67510
Lunar sample 67729, found within rake sample 67710

The following samples were collected from North Ray Crater (Station 11), as listed in Table 6-II of the Apollo 16 Preliminary Science Report,[3] which does not include samples smaller than 25 g weight (of which there were many). Sample type, lithology, and descriptions are from the Lunar Sample Atlas of the Lunar and Planetary Institute.[8]

SampleSample TypeIn Situ PhotoLithologyDescription
67015rakebrecciaFragmental matrix breccia, mostly feldspar, but with a wide range of highland lithologies represented as loose clasts in the matrix; have been dated at 3.9 b.y. and the breccias, itself, has had an exposure to cosmic ray of 51 m.y.
67016rockbrecciaFeldspathic fragmental breccia with both light and dark clasts, and is 3.95 b.y. old with an exposure age of 50 m.y.
67035rock-Fragmental brecciaVery friable, light matrix breccia; was found to be 3.95 b.y.
67055rockbrecciaBlack and white breccia; high trace element content, but has not been dated.
67075rockanorthiteLunar sample 67075 is very friable. Detailed petrographic description showed that the sample may be a mixture of closely related anorthositic rocks from a layered igneous intrusion, and it has been shown to be 4.47 b.y. old, with about 50 m.y. exposure to cosmic rays
67095rockimpact melt brecciaA glass-coated basaltic impact melt or "bomb" that has not been dated.
67115rakebrecciaGlass coat is rather thick, but has been fractured and broken off by micrometeorite bombardment
67210 (67215)rakebrecciaWhite polymict breccia made up of mostly calcic plagioclase and a few relict lithic clasts and has many zap pits on top and bottom
67230 (67235)rockimpact melt breccia67235 is a large special sample that was collected to study the outer surface of a lunar rock
67415rakebrecciaAccording to Lindstrom and Lindstrom (1986), 67415 is a lightly-shocked, granulitic breccia with a cataclastic matrix.
67435rockbrecciaGrey matrix breccias with both dark and light clasts
67455rockbrecciaVery friable, white polymict feldspathic breccia
67475rockbrecciaA tough purplish-grey, glassy breccia
67515rake-brecciaFriable, chalky white rock containing lithic fragments of cataclastic anorthosite and feldspathic granulite
67549rake-brecciaPorous and rounded with a light matrix and both light and dark clasts
67556rake-brecciaA friable micropoikilitic impact melt with intrusive glass veins. It has a micrometeorite crater.
67559rake-basaltIgneous texture indicating that it cooled from a liquid, albeit, highly aluminous. It contains a trace of Ni, Ir and Au and has been dated at 3.76 ± 0.04 b.y., which makes it a critical sample.
67605rake-brecciaRelatively large friable, white particle about the size, shape and color of a golf ball
67627rake-brecciaGlass-cemented aggregates
67628rake-brecciaGlass bombs (renumbered to 4 separate samples 67685-67688)
67629rake-brecciaGlass-cemented aggregates (renumbered to 4 separate samples 67629, 67695, 67696, 67697)
67647rake-brecciaRelatively coherent with many zap pits and has glass clasts, and glass in the matrix
67718rake-brecciaAbundant clasts of plagioclase set in an aphanitic matrix
67729rake-brecciaVesicular glass breccia with significant clasts, and has the appearance of a "glass bomb". It has zap pits on all sides
67915rock-brecciaComposed of white and grey breccias; both are polymict (Taylor and Mosie 1979), cemented by shock-melted glass and is also cut with thin black glass veins
67935rockbrecciaThin veins of black glass, texture of fine-grained subophitic basalt
67936rock-brecciaThin veins of black glass, texture of fine-grained subophitic basalt
67937rock-brecciaThin veins of black glass, texture of fine-grained subophitic basalt
67955rockbrecciaExterior surface has a thin brown patina with micrometeorite pits; has been dated at 4.2 b.y. with exposure to cosmic rays for ~ 50 m.y. (age of North Ray Crater)
67975rockfragmental brecciaIrregularly shaped rock with approximately equal amounts of pale gray, fragmental, friable breccia and a coating of frothy, clast-rich glass.

References
  1. North Ray, Gazetteer of Planetary Nomenclature, International Astronomical Union (IAU) Working Group for Planetary System Nomenclature (WGPSN)
  2. Apollo 16 Landing Area, 78D2S1(50), NASA Lunar Topophotomap. Published by The Defense Mapping Agency, November 1974. Available from Lunar and Planetary Institute.
  3. Apollo 16 Preliminary Science Report (NASA SP-315), 1972
  4. Geologic Map of the Apollo 16 (Descartes) Landing Area by Apollo Field Geology Investigation Team (D. P. Elston, E. L. Boudette, J. P. Schafer), United States Geological Survey, April 1972
  5. 67955 Summary Sheet available from Lunar and Planetary Institute
  6. Drozd R.J., Hohenberg C.M., Morgan C.J. and Ralston C.E. (1974) Cosmic-ray exposure history at the Apollo 16 and other lunar sites: lunar surface dynamics. Geochim. Cosmochim. Acta 38, 1625-1642.
  7. Norman M.D., Shih C.-Y., Nyquist L.E., Bogard D.D. and Taylor L.A. (2007) Early impacts on the moon: Crystallization ages of Apollo 16 melt breccias (abs#1991). Lunar Planet. Sci. XXXVIII Lunar & Planetary Institute, Houston. (LPSC 2007 web page)
  8. Lunar Sample Atlas, Lunar and Planetary Institute
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