Signatures of Planetary Computation

The Earth and planetary sciences are increasingly incorporating systemic paradigms. We already talk about Earth system science and solar system science. At a recent workshop on a proposed mission to the planet Uranus someone asked why we weren’t thinking of Uranus as a system of the planet, its moons and rings, Uranus system science. The SETI community is also taking into consideration systems approaches.

For example, civilizations and intelligence can be thought of as emerging out of planetary systems. In this paradigm, intelligence doesn’t just happen on a planet. It happens to a planet. One way to think of planetary intelligence is to consider it as computation by analogy to AI systems. Life may not form on all planets, but where life does take over a planet, a planetary stack may evolve with technological and biological layers. Technosignatures (indications or evidence of technology) are essentially signatures of the postbiological planetary stack and how it evolves over time. Technosignatures measure the development of the planetary stack.

The solar system has a large range of planets, from worlds that have changed little in billions of years, such as the planet Mercury, to planets which are constantly changing due to their geology and atmosphere, such as Earth itself. In fact, Earth may be the most dynamic planet in the solar system with its hundreds of active volcanoes, active plate tectonics, weather, and of course the mysterious phenomena of life and intelligence. Earth is not just dynamic, but has also evolved numerous layers including a biosphere, all living things, and now a technosphere, the technosystems that cover the planet (e.g., cities). Artificial intelligence could be considered the latest layer of planetary intelligence. The question you might ask relevant to planetary exploration whether this has happened to other planets. Could other planets have become developed stacks to drive planet-wide computation?

Intelligence could be considered a planetary process if defined as the information processing within a system. In nature, most information is processed very slowly, think of how long it takes an ecosystem to respond to a change like the introduction of a new species. Through induring mass extinctions and events like asteroid impacts and returning to a stable equilibrium, Earth’s biosphere can be seen slowly taking in information over time and responding to it, so it could be argued that there is a distributed low level planetary intelligence. The processing of information is most efficient and dense, for the moment, within the human brain.

Human intelligence emerged the intelligence of primates and it appears that artificial intelligence is growing out of human intelligence. Could this lead to the emergence of a higher planetary intelligence? For example, satellite networks have allowed humanity to see itself from space and observe what is happening to the Earth system and respond to threats ranging from natural disasters to climate change. Could this not be an example of the planet itself becoming intelligent through collective human intelligence? Perhaps, humans are the layer through which the planet comes to know itself.

We only have a sample of n = 1, so it is not clear that all civilizations advance in the same way as humanity, but a generalized understanding of what is happening as humans spread across the planet could be the emergence of a new planetary intelligence where intelligence is acting as a geologic process re-shaping metal, carbon, and silicon into cities, computers, and ultimately infrastructure to support agents in the cloud.

This complexity has also spread to other planets as humans have sent probes to observe other planets and even land on their surfaces, but this explosion of intelligence remains concentrated on Earth. Mars and the Moon are still yet to become planetary intelligences themselves. Even with all the orbiters at Mars, it is still more correct to say that Mars’s satellite array is a way that Earth observes Mars, not a way that Mars observes itself. The complexity of Earth’s interconnected systems stands in contrast to the relatively inert, geologically dead terrestrial worlds of the solar system, such as Mars, Venus, Earth’s Moon, Mercury, and the icy moons of the outer planets.

Earth with its green-blue color and abundant clouds stands in contrast to the relatively uniform geologically dead worlds of the solar system. Upper left is the dwarf planet (1) Ceres. All images credit: NASA, Gregory Rivera (Moon), and the European Organization for the Exploitation of Meteorological Satellites (Earth image).

An exception to this is Jupiter’s moon Io with more active volcanoes than Earth, tectonic mountain ranges (most planetary bodies other than Earth are not geologically active enough for mountains to form this way), and a surface that is constantly churning.

Jupiter's volcanically active moon Io. Image credit: NASA.

Life on Io would not be life as we know it, but if life is the result of complex chemistry, I would not be surprised if we did find some sort of weird life on Io which could evolve a form of weird computational intelligence, weird from our perspective anyways.

A silicon-based life-form out on a stroll in the countryside on Io? Image credit: Dickinson and Schaller from the book "Extraterrestrials: Field Guide for Earthlings" (1994).

Of course, since we only have a sample of n = 1, we cannot know for certain how this planetary stack evolves and emerges. This is where the tools of SETI could help to answer the question of how this stack evolves.

How would we detect emergent complexity or planetary computation over interstellar distances? Commonly cited ways include the detection of industrial pollutants in exoplanetary atmospheres, which would indicate the activity of a civilization, such as CFCs. Another example is the search for alien megastructures, such a Dyson spheres, a hypothetical construct built to enclose entire an star and capture its energy. There is also the familiar approach of listening for alien radio signals.

Two recent papers suggest it might even be possible to map compute distribution on a planetary and even sub-planetary scale across interstellar distances. In one recent paper, the author develops a model that uses Doppler drift of radio signal due to planetary rotation to create a crude map of the distribution of signal across Earth (modeled as if an exoplanet) which could be used to roughly map population centers on an exoplanet using signal strength as a proxy for population size.

Another paper uses a similar approach where specular reflection is used to map the surface of Earth observed as an exoplanet to demonstrate that specular reflection can potentially be used to detect subplanetary scale structures (e.g., cities built of glass and steel) on a planetary surface and create a crude map of the distribution of urban centers on an exoplanet. Although still new and yet to be applied to actual exoplanet data, these approaches are promising. They have the potential to not only determine whether or not planetary computation is happening but actually provide clues to the distribution and possible development of compute across a planetary surface.

We might be able to detect specular reflection off the buildings of an alien city on an exoplanet. Image credit: Gemini.

Planetary computation is a speculative concept, but it can be useful in making predictions about the development of other civilizations and how they might be detectable. It also has implications for our own civilization. If other centers of planetary computation have survived long enough to be detectable by our current methods, it shows that there may be a future for our own planetary stack.

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