'Nasa launched the Mars exploration mission to check whether at least one part of the planet had a persistently wet environment that could have been hospitable to life,' the agency said in a statement. 'Today, we have strong evidence for an exciting answer: Yes.' Lead scientist Steve Squyres said rock formations near the landing site showed water once flowed there, changing the rocks' chemistry and composition. 'We've been able to read the tell-tale clues the water left behind, giving us confidence,' he added.