Moon Mission Could Reveal the Story of Earth’s Journey around the Milky Way

A researcher’s proposal for an ESA mission to return to the Moon could lay the groundwork for a full-surface geological survey from a permanent lunar base. Ian Crawford, a professor of planetary science and astrobiology at Birkbeck College, University of London, believes the data collected would rewrite our understanding of the solar system’s voyage through the galaxy, and even link nearby supernovae with ancient mass extinctions on Earth.

Earth-Moon system. Image credit: Comfreak.

Since its formation, our solar system has orbited the Milky Way 20 times, passing through various environments including star-forming regions with enhanced rates of supernovae. Theories abound as to how this journey has affected the Earth.

“There’s been a long, controversial history of looking for patterns in mass extinctions to correlate them with astronomical events like supernovae,” Prof. Crawford says. “None of these are very convincing.”

This is in part because a record of these events, consisting of either radiation damage to surface materials from galactic cosmic rays, or direct collection of unusual supernovae isotopes, has been sparing.

“The Earth is very efficient at getting rid of this material in just a few millions years old,” Prof. Crawford says.

Also the quality of the Earth’s record is hindered by shielding from our atmosphere and magnetic field, preventing cosmic rays from reaching the surface. As a results attention has turned to rocky, airless bodies with ancient surfaces – such as the Moon.

Not only is the Moon accessible, it also offers an ideal environment for time-stamping evidence of supernovae due to the covering of an optimally low but consistent rate of re-surfacing by occasional impact ejecta, or geological activity creating localized lava or pyroclastic flows.

And we know this cosmogenic material is there. Just this year scientists found supernovae ejecta on Apollo samples, hinting at huge galactic events in our neighborhood in the last few million years.

This study, led by Dr. Gunther Korschinek at the Technical University of Munich, looked for iron-60 created in supernova explosions. This isotope can also be produced by cosmic rays bombarding surface nickel.

However using known half lives of other products produced during this process the team were confident in estimating the Apollo samples contained 10 times more iron-60 than would be expected from nickel alone – a disparity that they propose must be accounted for by recent, local supernovae.

Gunter describes Prof. Crawford’s proposal, and the geology-enabled time signature method in particular, as “very interesting”, and suggests India and China’s interest in lunar missions may provide a route to return.

However he warns of the challenge of collecting samples containing sufficient amounts of the exotic isotopes with longer half lives required to piece together a history beyond the last few million years.

“We collected 80 milligram of iron-60. You could need as much as 10,000 times that for plutonium and the other isotopes,” Prof. Crawford suggests. “Though if we can improve the efficiency of the collection method this would be less.”

Prof. Crawford will be submitting his ideas as part of a proposal to the European Space Agency that he sees as building on recent technological investments in ExoMars, the Philae Drill on Rosetta and the PROSPECT drill designed to bury through layers of ice.

“Initially this would involve sending a small lander to drill into these layers. A full moon survey can only been facilitated by a moon based operations but we can start incrementally,” Prof. Crawford says.

“There are multiple reasons to want to return to the Moon beyond charting the history of the Earth-Moon system,” he adds.

“The far side presents a good place to do astronomy, and there could even be biological studies of how life adapts to the Moon’s gravity. We need to go back.”

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Ian A. Crawford. 2016. The Moon as a Recorder of Nearby Supernovae. Chapter for forthcoming book ‘Handbook of Supernovae,’ edited by Athem W. Alsabti and Paul Murdin (Springer International Publishing, in press); arXiv: 1608.03926

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Moon Mission Could Reveal the Story of Earth’s Journey around the Milky Way