Copernican period

The Copernican Period is a way scientists talk about the time on the Moon from about 1.1 billion years ago until now. It is named after the astronomer Nicolaus Copernicus, but it doesn’t mark the start of this time.

During this period, many craters on the Moon were formed by meteorite impacts.

One special feature of craters from this time 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 is still happening 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. 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, many other craters come from the Copernican period. On one side of the Moon, you can see big craters such as Tycho, Aristillus, Stevinus, Kepler, and Theophilus. On the other side, examples include Ohm, Jackson, King, and Necho.

Some craters visited by Apollo astronauts were found to be from the Copernican period. For example, North Ray and South Ray, explored during Apollo 16, were estimated to be about 50 million and 2 million years old.

Relationship to Earth's geologic time scale

The Copernican Period on the Moon matches a time when life was growing on Earth. This period began about 1.1 billion years ago and continues today. During this time, the Moon's geological activity was slowing down. On Earth, this time includes the later part of the Proterozoic eon, called the Neoproterozoic era, and the entire Phanerozoic eon, when animals first appeared.