19
Nov 2012

The Atmospheric Mirror

POSTED BY: ANDREW RUSHBY
 

The Blue Marble Space Institute for Science is a not-for-profit research organisation that is using PetriDish.org to fund a modelling project that seeks to identify the signs of industrial activity in the atmospheres of extra-solar planets. Find out more about the project, including more about the authors, their methods, the possible outcomes of the project and a breakdown of the costs, here:   

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When viewed from space, the Earth glows like a blue marble under the light of the distant Sun, bobbing gently in an unimaginably vast sea of darkness. Oceans of azure water lap against the winding, jagged coastlines and pure-white clouds swirl gracefully across its face, temporarily obscuring from view the extensive brown-green landmasses below. At first, there is little to suggest that beneath the clouds, scuttling around the coasts, intelligent* bipedal apes are busying themselves with their daily activities; most utterly absorbed by their own inflated sense of self-importance and certain of their centrality to all the workings of the cosmos. However, with the exception of a couple hundred satellites, a permanently occupied human outpost and sea of debris in low Earth orbit, we have remarkably little effect on the environment of space outside the Earth. We assume that not much of our global civilisation can be detected from astronomical distances, excluding the banality of 1960s television that is currently washing across star systems 50 light years from here, carried outwards from the Earth by radio waves.

If however, somewhere out there in the menagerie of stars that is the Milky Way, an alien astronomer was perched at his (or her) telescope one night staring out into dark, and our Solar System happened to come into view, what would they see? The blinding glare of the Sun would obscure our family of planets from direct view**,  but perhaps some information could be gleamed via other methods nonetheless. Using radial velocity measurements or transit timings for example, a whole host of planets seem to be present around this particular G-type star:  four gas or ice giants and possibly four smaller bodies. If our exo-astronomer ran their evening’s observations through their superior spectrometer however, chances are they may be surprised by the results returned from one tiny planet in the orbit of this humdrum star.

Spectrometers measure the properties of light, at first emitted by stars (in the this case, the Sun) but then altered by the constituent gases of the planetary atmospheres through which the beam passes on the way to the receiving instrument. Different gases absorb light at different wavelengths to produce characteristic spectra, and the composition of the atmosphere can be teased out of the noise with sufficient skill and instrument capabilities. The high levels of oxygen, methane and other gases associated with biological or industrial activity detected in the atmosphere of this planet should result in the alien equivalent of a raised eyebrow or two. Methane and other reducing gases are usually rapidly oxidised in the presence of oxygen, meaning that detecting an appreciable amount in the atmosphere of an otherwise relatively oxidised planet may suggest that a biological mechanism is responsible for its continual replenishment. This kind of atmospheric disequilibrium is termed by astrobiologists a ‘biosignature’ for this very reason.

Planetary atmospheres are something we are all intimately familiar with; the Earth’s is the medium in which all of our lives play themselves out. Ours is filled with life-giving oxygen, greenhouse gases essential (in the right balance) to maintaining planetary climate and ozone that shields us from the Sun’s harmful rays. If humans are to ever colonise Mars, atmospheric engineering on a global scale would be essential to provide a clement climate. Without the thin envelope of gases that clings to the surface of our planet, life as we know it would be unlikely to exist, and the advanced civilisations of intelligent species like humans would be impossible. However, we probably take for granted the atmosphere’s ability to act as a mirror of our industrial and technological activities detectable at light-year distances, able to preserve the unique signatures of the gases associated with these processes and hold them there for those with the correct instruments to see.

Under the watchful eye(s) of our distant alien astronomer’s stern but fair supervisor, and following a long and arduous proposal to the relevant funding bodies of their world during which detractors on the committee would openly balk at the possibility of advanced life outside of their star-system, more observing time would be begrudgingly allocated to collecting data about this strange planet in obvious thermodynamic disequilibrium. A soup of exotic chemicals are now detected: high and increasing amounts of CO2 and constantly replenished methane along with a suite of more harmful and industrially produced compounds like chlorofluorocarbons (CFCs). There is no known biological mechanism for producing CFCs, so their detection in the atmosphere of this planet is a strong indication of the activities of industry, termed a ‘technosignature’ in line with the naming conventions of the field. The exo-astronomer has struck gold (or the equivalently rare element on their planet); they have detected strong evidence of a technologically advanced species at work, despite having never seen the surface of their planet itself. In doing so, they have forever altered the way their civilisation views itself – one of perhaps many in a vast, galactic family. Whilst they are given a passing mention in the local paper, statues of the members of the funding committee are erected in a square of their nation’s capital, for the whole project was their idea from the outset.

Ignoring the thinly-veiled allegorical critique of science funding on Earth, this is the theory that lies behind the most recent proposal out of the aptly-named not-for-profit Blue Marble Space Institute of Science (BMSIS). Their project, currently seeking funding at PetriDish.org, aims to use computer modelling techniques to simulate the hypothetical spectra of planets that have elevated levels of CFCs in their atmospheres. Whilst out of our reach at present, the hope is that instruments of the future will be able to examine the atmospheres of these planets to search for signs of life, and these hypothetical signatures would be readily available for comparison against data received from the planet of interest. They will form a standard by which to determine whether the received spectra are the result of accidental or intentional alteration by another global civilisation light years distant.

Acquiring science funding from kickstarteresque sites like PetriDish.org is ideal for this kind of small project; perhaps too close to the politically-charged line that NASA is willing to tread when it comes to funding SETI projects, but with sufficient outside interest to attract funding and a mandate directly from the public. The four BMSIS investigators are looking for $24,000  to cover their costs, with a minimum donation of $1. Addressing a resolvable problem within the field with admirable foresight, optimism and cost-effectiveness and detached from the bureaucracy of tax-payer funded science institutions, surely this is the kind of research that should be at the forefront of astrobiological research?

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* – whether humans are truly ‘intelligent’ or not is open for debate, as this video of a ‘haunted toaster’ illustrates all too well.

** – assuming a similar level of observational technology to that of the astronomers of contemporary Earth, which remains statistically unlikely.

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