WASHINGTON Why is Mars barren and uninhabitable, while life has always thrived here on our relatively similar planet Earth ? A discovery made by a NASA rover has offered a clue for this mystery, new research said on July 2, suggesting that while rivers once sporadically flowed on Mars, it was doomed to mostly be a desert planet. Mars is thought to currently have all the necessary ingredients for life except for perhaps the most important one: liquid water. However the red surface is carved out