Ask A Scientist

Why does the moon look like it has a face? Why does the moon have craters and how were they formed?

Asked by: Liliana Carey, Katie Lee, Emm
School: Glenwood Elementary School, Vestal School Distric
Grade: 2

Answer from William Russell

Senior Counselor, Binghamton University

Interests/hobbies: Science, philosophy and reading
Family: Wife and one Australian Shepherd (named Alaska)  

The moon has been an object of great mystery and enchantment over the millennia. It’s light and dark surface features have suggested many things to the different peoples of the world over time.  For many, the moon presents a rotund and cheerful face; the famous Man in the Moon.  But in other lands and cultures, other things have suggested themselves: a hare to the ancient Aztecs, for instance; an old woman to the ancient Chinese; a stick-burdened witch to the Victorian English; and many other things.  This was the moon as viewed through the eyes of myth.

But what is the moon as viewed through the eyes of science?  What are those light and dark features, after all?   How did they originate?  What are those dark, smooth regions of the moon – the eyes, nose, and mouth of the Man in the Moon? Are they vast lunar seas washing up against the foothills of brighter, lunar mountain ranges, as the earliest astronomers once speculated?  And where did all those craters come from, and what are they?

The oldest regions of the moon’s surface appear to our earthly eyes as the bright lunar highlands or terrae (Latin for “earth”), which represent those regions on the moon’s crust that were repeatedly peppered by the plunge of large and small chunks of rocky bodies drifting about its immediate neighborhood during the formation of the solar system itself about 4.5 billion years ago.  The lunar highlands display countless, often overlapping scars of these earliest impacts and are bounded by the dark, significantly less cratered lowlands, the lunar maria (Latin, for “sea”).  Scientists have been able to infer by the fact that there are fewer craters in the lunar maria than the lunar highlands, as well as by the precise radiometric dating of lunar samples brought back to earth by the Apollo astronauts, that the thicker lunar crust of the highlands (composed mostly of the mineral anorthosite) are about 4.2 billion years old, whereas the shallower, mostly basaltic maria have an age in the range of 3.5 to 3.0 billion years old or younger.  The basaltic composition of the maria indicates that these “seas” formed as a result of lunar volcanism during the later stages of the moon’s formation: as the moon very slowly consolidated and compressed itself under the force of gravity, its molten interior often broke through to the surface in the form of volcanoes, erupting into spewing rivers of basaltic magma that pooled up within the lunar lowlands.  The first humans to land on the moon in 1969, in fact, set themselves down in one of these “seas,” the Sea of Tranquility.

So our modern science has brought us to the conclusion that the numerous mythological figures once seen upon the “face” of the moon are not cosmic deities at all, or any other supernatural being – they are, rather, the product of large-scale surface features of the moon which were created by natural geological processes and which can be found at work on and in any world in the cosmos. From the earth’s vantage-point, the varying shapes provided by these vast dark and bright regions on the lunar surface have allowed our ancestors to create people, animals, and stories that have meaning and significance to their lives. And they still do!  Not unlike the natural beauty of a sunset, or the sublimity embodied in a great work of art or musical masterpiece, the moon’s power to enchant us will never wan.

Last Updated: 9/18/13