LROC: Hyginus and Pyroclastics

A 145 meter crater on the north rim of Hyginus Crater uncovered dark, most likely pyroclastic material. A 504 meter-wide field of view under a relatively high sun (angle of incidence = )from LROC Narrow Angle Camera (NAC) observation M155193272R, LRO orbit 8005, March 19, 2011; resolution 0.48 meters from 40.33 kilometers. View the larger, original LROC Featured Image HERE [NASA/GSFC/Arizona State University].

Sarah Braden

LROC News Center

A crater on the northern rim of Hyginus crater (exact location: 7.896°N, 6.229°E, diameter of 145 meters) excavated low reflectance material.

Deposits of pyroclastics are located around Hyginus Crater, so the low reflectance material is most likely from a layer of pyroclastics buried beneath the lunar surface. 

The same eruption that emplaced the pyroclastics also likely created an empty cavity beneath the surface, which then collapsed, forming Hyginus Crater!

A 1.38 kilometer-wide field of view from the LROC NAC frame stepped back to 2 meter resolution shows the subject of the Featured Image emplaced on the north rim 600 meters over the caldera interior. Dark material excavated by the impact appears to have streamed over the rim and down the wall [NASA/GSFC/Arizona State University].

A small, fresh crater on the southern exterior of Hyginus has high reflectance, optically immature ejecta rays instead of dark rays caused by uncovering pyroclastic material.  LROC NAC M155193272R. View a larger version of this 420 meter-wide field of view HERE [NASA/GSFC/Arizona State University].

Another crater in the image above (located at 7.608°N, 6.221°E) found on the southern rim of Hyginus is a perfect contrast to the crater in the Featured Image. The rim of the crater is hard to see in this image, but the diameter is ~20 m. This crater is smaller, so it excavated material from a shallower depth compared to the Featured Image crater, and therefore did not sample the buried pyroclastic deposit. The rays from the crater on the southern rim are high reflectance, which is typical of immaturity rays made of fresh material, in comparison to rays made from material compositionally different from the surrounding area.

In this LROC Wide Angle Camera (WAC) context image the yellow arrow marks the location of the crater in the Featured Image and the white marks the location of the fresh rayed crater. LROC WAC observation M177596018C, LRO orbit 11308, December 3, 2011; angle of incidence 70.31° at 52.82 meters resolution from 38.98 kilometers  [NASA/GSFC/Arizona State University].

Explosive eruptions of basaltic magma form lunar pyroclastic deposits, which are associated with the eruption of the mare deposits on the near side of the Moon. In remote sensing data pyroclastic deposits appear smooth and low in reflectance. Pyroclastic deposits are valuable since measurements of pyroclastic beads returned from the Apollo missions show that the material is enriched in volatile elements such as sulfur, lead, fluorine, and zinc (compared to other more common lunar materials such as mare basalt and highland anorthosite). On the Earth all of these materials are relatively common. However, if you were living on the Moon, pyroclastic deposits are the best place to find these materials! Pyroclastics are also typically high in iron oxides and some contain titanium oxides.

Explore more of the Hyginus caldera inside and out with the full LROC NAC image, HERE.

Related Images:

Inside Hyginus

Rock slide in Rima Hyginus

Dark streaks in Diophantus crater

Alphonsus crater mantled floor fracture

Read more about the Hyginus region in the Icarus paper, "An igneous origin for Rima Hyginus and Hyginus crater on the Moon."