We're not prepared for contamination between worlds

The year is 2034.

Humans have sent a probe to Jupiter’s moon Europa to drill through the icy surface and photograph the ocean beneath. In the few hours before it stops functioning, the probe returns images of shapes that could be some form of life. Scientists quickly organize a followup mission that will collect samples of that spot and bring them back to Earth. But, unknown to anyone, the first probe wasn’t sterile—it carried a hardy bacteria that had survived even the mission’s clean rooms. By the time the samples finally reach Earth years later, they’re dominated by this bacteria, which has happily set up shop in Europa’s dark, salty waters. Just like that, our first opportunity to study a truly alien ecosystem has been destroyed.

This is a nightmare scenario for NASA and other space agencies, and it’s one they’ve worked intensely to avoid with every mission to another orb. But some researchers from a lesser-known branch of ecology argue that even the current strict standards aren’t rigorous enough, and as more ambitious missions to other planets and moons get ready to launch, the risk of interplanetary contamination becomes more dire. They say we need to better plan for “forward contamination,” in which our technology disseminates Earth microbes, as well as “back contamination,” in which life from elsewhere hitches a ride to Earth. In fact, we already have a playbook to lean on: the discipline of invasion science, the study of how species on our planet invade each other’s ecosystems.