The disappearance of water on Mars

NASA researchers have created a series of unique maps of the distribution of atmospheric water on Mars from which emerge new clues on what was to be the primitive ocean of the red planet. The results suggest that about 4.5 billion years ago, Mars had enough water to cover at least 20% of its surface and then it was lost in space in the course of geological time. This paper provides insight into the evolutionary history of water on Mars, and provides a useful investigative tool to identify potential water deposits underground.
A series of maps of the distribution of atmospheric water on Mars, made by a group of NASA researchers led by Geronimo Villanueva thanks to some of the largest ground-based telescopes, have allowed us to determine that there was an ocean on Mars primitive characterized by a volume d ‘ water of at least 20 million cubic kilometers, higher than that of the Arctic Ocean here on Earth, and then over time, 87% ended up in space.


Credit: Science/Villanueva et al. 2015

As a young man, the planet would have enough water to cover the entire surface to form a liquid layer about 137 meters deep. Not only that, but the water would also form an ocean occupying almost half of the northern hemisphere and in some regions of reaching greater depths of several kilometers.
“Our study provides a solid estimate of what was the content of water on Mars,” says Villanova, author of the paper published in Science. “This work provides insight into the evolutionary history of water on Mars.”
The observations conducted by researchers are based on a series of detailed measurements of two slightly different compounds of the water present in the Martian: one is familiar to us, that is, the H2O, while the other is a form isotopic (HDO, heavy water), in which a hydrogen atom is replaced by heavier version called deuterium. To do this, scientists have collected data over a period of seven years, from 2008 to 2014, using the high resolution spectrometers, which CRIRES, NIRSPEC and C shell that are installed respectively at the Very Large Telescope (VLT), the telescope Keck and InfraRed Telescope Facility (IRTF). Comparing the relationship HDO / H2O, the scientists were able to determine the concentration and thus to estimate how much water is lost in space during the life of the planet.


Credit: Science/Villanueva et al. 2015

The maps of the distribution of atmospheric water on Mars, which are the first of this type, show how varied the content of the water and its ordinary counterpart isotopic depending on the season and region of Mars, despite the red planet today is essentially a desert and a hostile environment. In particular, researchers are interested in the regions near the poles as the polar caps of ice are the main water deposits known. It is believed that the polar ice caps represent a kind of historical Martian water from 4.5 to 3.6 billion years ago, when they had to be present abundant underground water reservoirs.
The most important result that emerges from this study is that the new maps reveal a remarkable concentration of deuterium than the average global whose observations showed the relationship between the ordinary and heavy water D / H of 5-6, as defined by the standards VSMOW (Vienna Standard Mean Ocean Water). In fact, the researchers found the values of D / H higher near the Polar Regions, also seven times higher than what is measured in the case of the Earth’s oceans. In other words, the results suggest that about 4.5 billion years ago, Mars had enough water to cover at least 20% of its surface (for comparison the Atlantic Ocean occupies 17% of the Earth’s surface). This implies that the planet must have lost a volume of water equal to 6.5 times greater than that which is currently available in the polar caps to justify a D / H ratio so high.


Credit: Science/Villanueva et al. 2015

Moreover, even large variations of the inclination of the axis suffered from Mars at intervals of millions of years would cause vaporization and the subsequent formation of the main deposits of ice, a process that, according to the authors, the water would reshuffled by different basins at regular intervals. If this is true, almost all the water basins and polar surface should have a D / H ratio relatively equal. But because of the values observed are even higher (up to 9-10) in some regions, this mixing of the water might suggest that existing water deposits on Mars contain a ratio even higher than assumed, a process that could imply a higher estimate of the loss of water during the life of the planet.
“The fact that Mars has lost a lot of water indicates that the planet has hosted for long periods favorable conditions for the development of life,” adds Michael Mumma of NASA and co-author of the study. In short, it is possible that the red planet has had even more water in the past, and that part of it is subsequently came under the surface. Since these new maps reveal the presence of a series of micro-climates and variations in the atmospheric content of water in the course of time, they could provide a survey instrument useful for identifying potential water basins in the surface of Mars. Finally, more realistic estimates of the distribution of the compounds refer to the water current and the oldest epochs could be realized, for example, by the mission MAVEN NASA in order to better define the water content of Mars both today and in the past.

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