I remember being intrigued as a boy by the idea that there might be other worlds out there, including some with intelligent life. Imagine my surprise to read recently that the search for planets outside our own solar system has found more than 4,000 of them so far.
New techniques in planetary astronomy now in development will vastly increase the count and give us more detailed information about the objects we discover. We will recognize not just their masses and sizes but their temperatures and the composition of their atmospheres. Atmospheres are especially significant in the search for alien life. That’s because they might be affected by biological processes, the way photosynthesis on Earth produces nearly all of our planet’s oxygen. The search for signs of life is a core subject in astrobiology, the study of life beyond Earth.
But less consideration has been given to a more spectacular possibility. Could future planetary exploration turn up evidence of advanced technology outside our solar system? What would such evidence look like?
A technologically advanced civilization born on one planet might want to diversify its portfolio by colonizing other planets nearby. Elon Musk and Jeff Bezos, among others, have advocated that we Earthlings get to work on it. To make such colonies habitable on a large scale, it would probably be necessary to re-engineer the new planet’s atmosphere to mimic the old one. Such cloned planets, with an otherwise inexplicable resemblance between their atmospheres, could be one signature of astrotechnology.
Another possibility is that an alien civilization might deliberately trigger a greenhouse effect to raise a planet’s temperature. A runaway greenhouse effect caused by an accumulation of water vapor and carbon dioxide is what turned Venus into a hellish wasteland. Closer to home, an accumulation of carbon dioxide is currently warming Earth’s climate.
An advanced alien civilization could use this technique in a more controlled fashion to raise the temperature of a cold planet, making it more favorable for life by allowing it to support liquid water.
Alternatively, it might be possible to use atmospheric engineering to produce cooling effects.
Unusually high temperatures on a distant planet could also be a sign that it is using artificial energy sources. Manufacturing powered by nuclear fission could look like that.
Closely related to this concept is the Dyson sphere, a hypothetical structure named after the physicist Freeman Dyson. It involves deploying solar panels in space, on a colossal scale, to trap a significant fraction of a star’s energy output and beam that energy to manufacturing centers.
The classic strategy in SETI, the Search for Extraterrestrial Intelligence, is to look for signals that an advanced technology might broadcast. The pursuit of planetary astronomy suggests a different approach. An alien species that wants to communicate could draw the gaze of astronomers by effectively using its parent star to focus attention. This might turn out to be the most practical way to open communications across the universe.
My childhood dream of intelligent life on another planet could still turn out to be accurate.