European Space Agency (ESA) officials are heaving a sigh of relief following a report from the US National Research Council that says probes landing on Mars need not be sterilised if they are not conducting extraterrestrial biological experiments (Nature, Vol 358 No 6389). ESA was worried that stringent planet protection standards would extend the budget for its Marsnet project that will study the planet's meteorology and seismic activity.

The report says contamination from non-exobiological probes such as Marsnet is unlikely to spread beyond the landing site and stresses that more information from a range of Martian sites is needed to make decisions on landings for in-depth biological study.