article_snippet.sent: In total, what is now the planet's arid northern plains would have contained at least 12.4 million cubic miles (20 million cubic km) of water .
article_snippet.sent: Thanks to missions like Nasa's Curiosity rover, we know Mars once had water - but until now we didn't know how much.
article_snippet.sent: Scientists have provided the best estimates yet, claiming the best estimates once had more water than the Arctic Ocean - and the planet kept these oceans for more than 1.5 billion years.
article_snippet.sent: The findings suggest there was ample time and water for life on Mars to thrive, but over the last 3.7 billion years the planet has lost 87 per cent of the planet water - leaving the planet barren and dry.
article_snippet.sent: During Mars wet Noachian period - 4.1 to 3.7 billion years ago - Mars is estimated that Mars had enough water to cover the entire surface in a liquid layer 450 feet (137 metres) deep.
article_snippet.sent: However, it's likely that most of the water formed an ocean that occupied the northern hemisphere of Mars, which would have been as deep as one mile (1.6km) in places - comparable to the Mediterranean Sea on Earth.
article_snippet.sent: The research estimates that, in total, what is now the planet's arid northern plains would have contained at least 12.4 million cubic miles (20 million cubic kilometres) of water.