Impact cratering: how holes in the ground shape planetary evolution and their landscapes

January 4, 2024

Impact cratering is the most fundamental geological process in the Solar System. It is a process that causes both destruction and creation — from the accretion and formation of planetary bodies, to the shaping of planetary landscapes, to its effects on biological evolution.

Impact craters are the dominant landform on the Moon, Mercury, Ceres, Vesta, the southern hemisphere of Mars, and many satellites of the giant planets in the outer Solar System. On Earth, however, they are not — our planet is simply too dynamic.

Plate tectonics, sedimentation, erosion, and weathering all contribute to reshaping the landscape and keeping it geologically young. The older a surface, the longer it has been exposed to impact cratering, accumulating craters over time — a younger surface will have fewer craters. Earth's atmosphere also acts as a shield and filter, protecting us from meteoroids heading towards our planet.

This may give the false impression that impact cratering is an ancient process that no longer affects our planet. But it is very much a present-day process. The Chelyabinsk meteor, for example, is the latest documented large meteor event: an 18-metre space rock that entered Earth's atmosphere on 15 February 2013 and fortunately exploded before reaching the ground, creating a large shock wave (watch a compilation here).

So how can we study such a fundamental process? We can rely on our planetary neighbours — Mars and the Moon — for which we have an excellent temporal imagery dataset. High-resolution cameras aboard the Mars Reconnaissance Orbiter (MRO) and the Lunar Reconnaissance Orbiter (LRO) have been returning repeated coverage of the martian and lunar surfaces since 2007 and 2009 respectively, allowing scientists to identify present-day surface changes including new impact craters.

Studying the Moon provides an incredible opportunity to understand the fundamentals of impact cratering, essentially in our own backyard. The Moon records the bombardment history of our corner of the Solar System — a record not well preserved on Earth. When we study the Moon, we look back at impacts that occurred billions of years ago, but also at impacts happening today, giving us a window into Earth's ancient past and present. The video below explains how new craters are found using the LRO's high-resolution camera, LROC NAC.

More than 200 new impact craters were discovered using LROC images between the start of the mission and 2016 — more than models of the current impact rate predicted. You can read more about this here.

There are several projects aimed at measuring the current lunar impact rate. One of them is the ESA-funded NELIOTA project, which has been running since 2017, detecting lunar flashes using an Earth-based telescope operated by the National Observatory of Athens near the Greek town of Kryoneri. Below is a gif generated from the NELIOTA database, updated to June 2023.

Understanding the present-day impact rate has important implications beyond scientific merit: it will help us assess how frequently Earth could be affected by meteoritic impacts, the size statistics of incoming objects, and the risk for future astronauts and lunar infrastructure. In short, we are buying down risk — both for life on Earth and for future lunar explorers.