Mars lost more water than the volume of the Arctic Ocean

An ancient ocean on Mars held more water than is in the Arctic Ocean today, NASA scientists estimate, but 87% of it has been lost into space.

As a young planet, Mars would have had enough water to cover the entire surface in a liquid layer about 140 metres deep, but it would have formed an ocean occupying almost half of Mars’ northern hemisphere – in some places more than 1.5 kilometres deep with a volume of at least 20 million cubic kilometres.

It would have covered 19% of the planet’s surface, scientists believe – a huge ratio (the Atlantic Ocean covers just 17% of the Earth’s surface).

“Our study provides a solid estimate of how much water Mars once had, by determining how much water was lost to space,” said Geronimo Villanueva, first author of the paper and scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “With this work, we can better understand the history of water on Mars.”

The new estimate is based on observations of two different forms of water in Mars’ atmosphere. One is the familiar H2O, made with two hydrogen atoms and one oxygen. The other is HDO, in which one hydrogen is replaced by a heavier form, called deuterium.

The researchers distinguished the chemical signatures of the two types of water using the Keck Observatory’s 10-metre Keck II telescope; NASA’s Infrared Telescope Facility, both in Hawaii, and ESO’s Very Large Telescope in Chile. By comparing the ratio of HDO to H2O, scientists can measure the enrichment and determine how much water has escaped into space.

The results of the observations have been published in the journal Science.