Could Galactic Cataclysms Be Recorded on the Moon?

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At the most recent Republican presidential candidate debate Mitt Romney pooh-poohed Newt Gingrich’s proposal that we should mine the moon’s resources as part of space commercialization.

Our only natural satellite has been considered an ideal place to dig up the isotope helium 3, which is rare on Earth, but embedded in the lunar regolith by the solar wind. Helium 3 could be used as fuel for nuclear fusion reactors of the far future — Gingrich therefore sees the moon as an untapped resource.

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But the moon is more than just a place to go strip mining. It is becoming increasingly apparent that the moon is an invaluable historical archive of what happened not only to Earth, but to the entire solar system, over the past 4.5 billion years.

It’s not just the fact that the solar system has evolved over billions of years, but that the sun and planets have also been on an interstellar journey. The sun completes a carousel circuit around the galactic center once every 200 million years.

It is a star trek fraught with perils that could have affected Earth and the other planets.

Along the journey the sun would have passed through dark, dusty molecular clouds in the galaxy’s spiral arms, and precariously near supernovae popping off inside brilliant young star clusters.

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When the solar system was at the “bow” of the galaxy, where it plows across intergalactic space like an ocean liner, we could have been deluged with cosmic rays.

The geologic record shows that Earth has undergone many upheavals during its history: completely freezing over nearly 700 million years ago, undergoing subsequent ices ages, as well as mysterious mass extinctions of most life forms.

But any evidence of why these disasters happened to Earth is murky at best. If they were triggered by a cosmic catastrophe, then the moon should have corroborating evidence recorded in its rocks.

For example, penetrating cosmic rays from a supernova would leave a clear calling card in the form of exotic isotopes embedded in lunar rock-like bullets. Sites of multiple lava flows would leave a layer cake structure that would be ideal for time tagging when a radiation surge happened. The next step would be to compare the era of the rock radiation damage to Earth’s fossil record to see if it syncs up with a mass extinction.

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Crossing a great galactic spiral arm, the solar system must have periodically drifted though dense molecular clouds of cold hydrogen laced with dust. Light from our sun would have been dimmed by the intervening dust. This may have entombed Earth in ice. The polluting interstellar dust should be stored away on the moon too, perhaps beneath a more recent impact lava flow from the heat of an asteroid impact.

The sun may also have had one or more close encounters with red dwarf stars or brown dwarfs that litter the galactic plane.

They would have gravitationally disrupted the hypothesized Oort comet cloud that encircles our solar system at a radius of one light-year. The effect of the intruder would be like shaking apples out of a tree. Comet storms would have pelted the inner solar system.

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Meticulous sampling of lunar craters might unveil telltale peaks in the cratering rate. Even ancient fragments of the comets or asteroids could be collected.

This is where Gingrich’s moon mining moon base comes in. Humans would be needed to go to the moon to operate a large drilling rig to burrow thorough lava layers and take core samples that carry the telltale isotopic record from the sun’s travels.

Perhaps only through the potential big bucks of commercial lunar mining could geologic science have an opportunity to hitchhike back to the moon’s surface. The geological exploration would hit an unintended pay dirt far more valuable than helium 3 — a history book of our sun’s galactic odyssey.

Source: New Scientist

Image credit: NASA

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