Planners of the first human mission to Mars will have to worry more about hexavalent chromium – the toxic waste in the movie Erin Brockovitch – than about hostile Martians. To assess that danger, NASA should measure levels of hexavalent chromium in Martian dust, says a new report from the US National Research Council. Other measurements the report recommends to assure astronaut safety include the stickiness of the dust, radiation levels on the Martian surface and the strength of Martian soil. Human expeditions to Mars are currently only a hope in the hearts of space enthusiasts. NASA has no plans at present, but asked the National Research Council to identify what data it would need to collect before it could begin planning a human mission.