Major discoveries and colorful characters are helping the agency launch a public-relations offensive as it seeks to maintain a record of impressive achievements on a shoestring budgetAs space exploration goes, it looked like a good week for Nasa. The revelation that scientists had discovered water on Mars – or more accurately uncovered evidence of certain chemicals in rocks that suggested recent liquid flows – piqued interest in the Red Planet ahead of this weekend’s launch of the sci-fi blockbuster The Martian.