Hopes of finding life on Mars, at least on the surface, were dealt a blow Thursday by a study revealing that salt minerals present on the Red Planet kill bacteria. In lab tests on Earth, the compounds known as perchlorates killed cultures of the bacteria Bacillus subtilis, a basic life form, a research duo from the University of Edinburgh’s School of Physics and Astronomy reported. Perchlorates, stable at room temperature, become active at high heat.