It seems inevitable that humankind will eventually have to look further afield for natural resources as we deplete our own planet’s supply. There’s no shortage estimates that we’ll run out of everything from iron to platinum within the next century or so. The obvious place to look for new supplies is the asteroid belt.
Today, Duncan Forgan at the University of Edinburgh in Scotland and Martin Elvis at the Harvard Smithsonian Center for Astrophysics in Cambridge, MA, say this kind of thinking has important implications for the search for extraterrestrial intelligence.
They argue that any civilisation much more advanced than ours is likely to require natural resources from throughout its planetary system and that this kind of large-scale mining activity is likely to produce a signature that is visible to the current and next generation of telescopes studying exoplanets.
Forgan and Elvis begin by imagining how we might exploit our own system, arguing that extrasolar mining should produce three different kinds of signature.
First, moving certain substances from one part of a system to another should produce a chemical signature in the debris ring around a star. We know that debris discs should have certain ratios of elements, which we can measure using spectroscopy. Mining activities would distort these ratios.
Second, mining ought to change the size distribution of objects in the debris disc. There are various advantages to mining large bodies rather than smaller ones, so the numbers of these should drop artificially in a mined system. At the same time, mining activity can produce large amounts of dust, so this ought to increase.
What’s more, mining is likely to be done close to the home planet so this dust is likely to form in rings nearby. (Imagine our night sky, if this ever happens near Earth.)
Finally, Forgan and Elvis say there should be a significant thermal signature from mining activities, since dust is likely to absorb and emit thermal energy from the star. So these dust rings should be easily visible.
There’s a caveat to all this, of course. Forgan and Elvis are at pains to point out that these processes of chemical depletion and mechanical wear can also occur naturally. So these are by no means unique signatures of extraterrestrial mining activity.
Instead, they argue that we should use these signs, should we ever find them, as flags that more investigation is needed.
That seems sensible, especially since the kind of analysis that will reveal these kinds of disequilibria are likely to be done as a matter of routine on the data from planet hunting missions.
There is one important signature from mining that Forgan and Elvis do not discuss. This is related to the energy required to extract and process material on the scale they describe.
Whatever form of propulsion and machinery these civilisations use, it will require some form of power. And that’s likely to leave its own mark.
Perhaps the most visible signature will be clouds of exhaust gases encircling these systems and the glowing embers of spent reactors. In other words, pollution.
As we know to our cost on Earth, unwanted side-effects often leave the biggest scars.
Ref: arxiv.org/abs/1103.5369: Extrasolar Asteroid Mining as Forensic Evidence for Extraterrestrial Intelligence
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