The chances of an alien invasion have increased as a result of missions to Mars.
Aliens
A new report from Professor Anthony Ricciardi, an expert in the ecology of invasive species, has revealed that "extra-terrestrial organisms" could have a devastating impact on ecosystems.
It is said that bacteria, fungi and other invisible stowaways could attach themselves to spacecraft and survive the mission back to Earth.
Professor Ricciardi said: "Owing to their massive costs to resource sectors and human health, biological invasions are a global biosecurity issue requiring rigorous transboundary solutions.
"The era of space exploration brings with it a new risk - invasion.
"The peril comes not from little green men arriving on flying saucers but, rather, from microbiological contamination of Earth from extra-terrestrial environments and vice versa.
"Bacterial strains exhibiting extreme resistance to ionising radiation, desiccation and disinfectants have been isolated in NASA 'clean rooms' used for spacecraft assembly."