Astromic's Backyard: History of Solar System Buried on the Moon

Unlike the Earth's surface, which is being constantly scrubbed dean by erosion and plate tectonics, the face of the moon is ancient and scarred, sporting some of the largest impact craters in the Solar System.

Meteorites on Moon

This lunar cratering tells the story of the Late Heavy Bombardment, and the pounding of the planets of the inner Solar System shortly after their formation. This period of intense bombardment probably delayed the earliest lime Ilia! life could take hold on our planet. But there are plenty of other hazards in our Galaxy that have posed a threat throughout the history of life on Earth. This new research suggests that the Moon may hold a record of some of them.

In October's Cutting Edge column i took a look at a research paper reporting the likely effects of a gamma-ray burst on the Earth's marine ecosystems. Less energetic, But closer, supernovae could also seriously disrupt Earth's ecosystems. A further threat is presented by the interstellar molecular clouds drifting through the Galaxy. These dense clumps of gas and dust would spell havoc for the delicate balance of Earth's environment if the Solar System were to pass through one on its stately orbit around the galactic center.

Some of the greatest mass extinctions of life on Earth may have been caused by cosmic catastrophes like these. But we don't really know how frequent these events are, or how this might have changed over billions of years. The record preserved on the Moon may be able to help here, too, Ian Crawford, and his colleagues describe how the regolith (a layer of loose, mixed material) covering the lunar surface serves to trap tell-tale isotopes blasted out by supernovae or particles of interstellar dust. Samples of moon dust could show this record and so reveal crucial details of the history of external events affecting our Solar System.

This is all well and good, but a patch of lunar soil exposed to the space environment would accumulate these informative dues over time. and so the record of different events would become hopelessly smeared together. The situation is made worse by the constant rain of micrometeorites onto the airless Moon, which steadily mixes up the surface regolith - known as 'impact gardening'.

The trick, says Crawford, is to search for places on the Moon where an earlier patch of surface regolith has since been buried, smothered by a lava now rolling across it. Now hidden under meters of solid rock this 'palaeoregolith', and the history it holds, becomes preserved. These lunar regions could be seen with high-resolution imaging and ground penetrating radar: Crawford hopes that a shortlist of the most promising sites could be drawn up.

Future robotic or even human missions would then land at these target locations and drill down to the level of the palaeoregolith, revealing the secrets it holds. Different sites would have been buried by lava flows at different times, allowing researchers to peer into Solar System history to follow the evolution of the Sun, or the timings of extreme astrophysical events, over billions of years.