Copernican period

The Copernican Period is a way scientists describe the time on the Moon from about 1.1 billion years ago until today. It is named after the famous astronomer Nicolaus Copernicus, but it doesn’t mark the start of the period. During this time, many craters on the Moon were formed by meteorite impacts.

One special feature of craters from this period is their bright ray systems. These rays look like lines spreading out from the craters and are made of material thrown out during impacts. A well-known example is the crater Copernicus, which has these bright rays, showing it is young in lunar terms.

Even though most of the Copernican Period is marked by these crater features, some areas of dark, smooth lunar rock called basalt have covered parts of the rays. This basalt is still considered part of the Copernican Period because it is younger than the rays it covers, like in the area near the crater Lichtenberg.

Definition

The Copernican period began about 1.1 billion years ago and continues to today. It is defined by looking at impact craters on the Moon that have bright rays of material spreading out from them. These bright rays appear when fresh material is brought up from below the Moon’s surface during an impact. Over time, these rays darken due to space weathering.

Scientists originally used the loss of these bright rays to mark the start of the Copernican period. However, they have found that some rays stay bright because of the materials they are made of, not just because they are fresh. For example, bright materials from the lunar highlands can stay visible even after space weathering.

Examples

Besides Copernicus, there are many other craters from the Copernican period. On the side of the Moon we can see large craters such as Tycho, Aristillus, Stevinus, Kepler, and Theophilus. On the far side, examples include Ohm, Jackson, King, and Necho.

Several craters visited by Apollo astronauts were found to be Copernican in age. For instance, North Ray and South Ray, explored during Apollo 16, were estimated to be about 50 million and 2 million years old, respectively.

Relationship to Earth's geologic time scale

The Copernican Period on the Moon corresponds to a time when life was thriving on Earth. During this period, which lasts from about 1.1 billion years ago to today, the Moon's geological activity was winding down. On Earth, this time matches the later part of the Proterozoic eon, called the Neoproterozoic era, and includes the entire Phanerozoic eon, when animals began to flourish.