In-Class Exercise Solutions: Mapping on the Moon

Astronomy 23/223 In-Class Exercise:

Solution: Mapping on the Moon

The image below comes from a Lunar Orbiter IV image of the lunar surface. Four craters (A, B, C, and D) and the dark mare (E) are indicated. Arrange these in chronological order, with the youngest unit first and the older unit last, and label the young and old ends of your list.

If you look carefully at crater D, you will realize that it is flooded by basalt E. Therefore, crater D is older than basalt E.

Examine the area around crater C. Notice that its ejecta lie on top of basalt E. So crater C must be younger than basalt E.

Note that both craters A and B lie on top of the ejecta blanket around C, so they must be younger than it is. If you look even more carefully, you'll notice that crater B lies on top of crater A. So A must be older than B.

So, the order of events shown here is as follows:

oldest D > E > C > A > B youngest