It is a scientific consensus that water once flowed on Mars , and that it had a denser atmosphere, meaning that it was once habitable. Unfortunately, roughly 4.2 to 3.7 billion years ago, Mars' rivers, lakes, and global ocean began to disappear as solar wind slowly stripped its atmosphere away. For scientists, the question of how long it remained habitable has been the subject of ongoing inquiry. Where some scientists maintain that Mars ceased being habitable billions of years ago, recent