WEEKS after being billed as fit for growing asparagus, it now seems the red soil of Mars may not be quite so friendly after all.

After days of growing speculation about an important discovery, NASA finally revealed a secret yesterday.

Its Phoenix lander, which touched down in May, has found not the chemistry of life, but perchlorate - a toxic, highly corrosive compound used in household cleaners, explosives and rocket fuel that can destroy organic matter.