What Can We Actually Find on an Exoplanet? Part 4: Looking For Us

Exoplanets offer a wealth of information from a single observation. This dot can reveal what's in its atmosphere, sketch a rough map of its surface, pinpoint areas of oceans and continents, and even hint at signs of photosynthesis and how life adapts to seasonal changes. Furthermore, this dot can provide evidence of not just life, but potentially intelligent life.

If life exists on a planet, it might be accompanied by a civilization that leaves distinct atmospheric signatures known as technosignatures. These signatures, primarily technological in nature, can be easier to detect than biological ones. Technosignatures include substances like chlorofluorocarbons (CFCs), sulfur hexafluoride, nitrogen trifluoride, and perfluorocarbons, which have no natural sources and can linger in an atmosphere for thousands of years after release.

Recent events, such as the 2020 pandemic-induced reduction in nitrogen dioxide from reduced industrial activity, demonstrate how tightly pollution tracks industrial activity. This level of atmospheric detail can potentially allow an alien astronomer to discern a planet's economic indicators, such as its GDP. While Earth's technosignature phase, predominantly from 1960 to 2050, is short compared to the planet's four-and-a-half billion-year history, the window of detectability is particularly narrow.

If civilizations tend to outgrow their pollution phase, the odds of detecting them through their technosignatures may be higher than finding a settled, clean civilization. Regardless of whether we encounter a polluted civilization, we can still glean valuable insights about a world's geography, oceans, photosynthesis, and atmospheric conditions.