Tres Amicis

Three impact craters (125-180 m diameter) that may have formed in a contemporaneous impact event. NAC image M106827539L [NASA/GSFC/Arizona State University].

These three craters, located at 9.665°S, 7.646°E, appear to have formed more or less at the same time, certainly within a few minutes of each other. The southwest crater is 180 m diameter; the center crater is 150 m; and the northeast crater is 125 m across. From the northeast crater center to the southwest crater centers, they cover about 450 m. The projectiles were traveling from the east-northeast (the right side of the frame) and probably struck the surface at a relatively low angle, as indicated by the asymmetric ejecta patterns and the orientation of the ejecta rays. Bright ejecta extends as much as 1 km from the crater center.

Zoomed out view to include a larger area around the craters so that the long, thin bright ejecta rays are visible. Note that the ejecta is directed to the west (left side); little of it has gone to the east (right). NAC image M106827539L [NASA/GSFC/Arizona State University].

The morphology of the craters suggests that the southwest crater formed first, followed by the other two. The southwest crater may only have formed a few seconds or a few minutes before the other two; the timing is indicated by the ejecta from the middle crater that partly covers the southwest crater. The morphology of the two northeast craters (the low northwest-trending ridge between the craters) suggests that the projectiles hit the surface at the same time such that the excavation process of the two craters interacted, forming the ridge.

Same scene as above in afternoon lighting. The low Sun accentuates the subtle topography associated with the impact craters. NAC image M102107709R [NASA/GSFC/Arizona State University].

This same crater morphology was created in laboratory experiments where multiple projectiles were simultaneously fired from a high velocity gun. One of the distinctive features of the simultaneous impact is the presence of a ridge (or septum) of material between the craters.

Experimental double simultaneous impact crater in the Ames Vertical Gun, from Oberbeck et al. (1972) Apollo 16 Preliminary Science Report.

Explore the entire LROC NAC frame!

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Posted by Jeffrey Plescia on January 04, 2013 10:00 UTC.