spaceSpace and Physics

We Need To Protect Earth (And Space) From Interplanetary Invaders


Stephen Luntz

Stephen has a science degree with a major in physics, an arts degree with majors in English Literature and History and Philosophy of Science and a Graduate Diploma in Science Communication.

Freelance Writer


Image credit: Roman Chazov/

The Earth needs to be ready for invasion from other planets, scientists have warned, but the danger is not so much intelligent, malevolent aliens coming to conquer us. Instead, the danger we face is more in the form of microbes that could cause diseases for which we, and everything else on Earth, have no immunity. Likewise, we need to watch out for our own organisms hitchhiking on space missions to threaten any life that may exist on the worlds we visit.

The idea of interplanetary germ warfare goes back at least as far as HG Wells' War of the Worlds. However, the Univerity of Adelaide's Dr Phill Cassey and Dr Andrew Woolnough argue in BioSciences that it is time we moved it from the pages of science fiction to treating the problem as a serious concern.


“In addition to government-led space missions, the arrival of private companies such as SpaceX has meant there are now more players in space exploration than ever before,” Cassey. said in a statement. “We need to take action now to mitigate those risks. Risks that have low probability of occurrence, but have the potential for extreme consequences, are at the heart of biosecurity management. Because when things go wrong, they go really wrong.”

It's possible the rest of the Solar System is lifeless, with nothing to threaten us or be threatened. However, if there is life on (or in) Mars, Europa or Enceladus, we face what economists might consider the largest externality problem of all time. If any one country or company's mission to space were to return carrying a deadly virus (known as backward contamination) the consequences would be felt by everyone. Yet currently the costs of prevention fall only to those undertaking the mission, creating an enormous financial incentive to cut corners on sterilizing or containing anything brought back.

Similarly, if some future corporate exploration of Mars carries Earth-based bacteria that ends up displacing the local life forms (forward contamination) with them, the loss is to all of us but the price of avoidance falls only to the explorers.

To illustrate the dangers the authors point to the way humans have spread organisms to some of the most remote and hostile places on Earth. They note it is the isolated ecosystems with little experience of the outside world – or in this case Solar System – that are most vulnerable to new arrivals.


Australia, having suffered self-inflicted disasters such as the arrival of rabbits and cane toads has plenty of valuable lessons to teach the world about biosecurity, the authors argue. “It is far cheaper to prevent biological contamination by implementing protocols on Earth than it is on Mars, for example,” Casey said. 

Nevertheless, the international Committee on Space Research Planetary Protection has yet to call on the experience of invasion biologists, Australian or otherwise, raising the question of whose expertise they think is useful.


spaceSpace and Physics
  • tag
  • microbes,

  • humans