Tech UPTechnologyMars had multiple sources of water

Mars had multiple sources of water

One of the biggest mysteries in reconstructing the history of the past of Mars is summed up in a key question: where did the water come from? Analysis of two Martian meteorites that fell to Earth, containing samples of the planet’s crust, Northwest Africa (NWA) 7034 – discovered in Antarctica in 1984 – and Allan Hills (ALH) 84001 – discovered in the Sahara desert in 2011-, shows that Mars likely received water from at least two very different sources early in its history. This variability implies that Mars, unlike Earth and the Moon, never had a global magma ocean.

The crust is the place where the largest reservoir of water on Mars is believed to exist, containing 35% of the estimated total water below the surface of the red planet. Fortunately, meteorites detached from the Martian crust, from time to time, reach Earth and here, using state-of-the-art techniques, scientists can carefully study them.

The experts looked at the hydrogen isotopes locked inside the rocks of Mars. Taking into account that hydrogen is one of the components of water, the proportion of this isotope enclosed in the rock can help us understand the history of water: as if it were a water fossil.

The results in previous research were inconsistent and quite scattered, but the current team focused on meteorites that they knew with the highest certainty originated in the Martian crust.

The Northwest Africa 7034 meteorite, nicknamed Black Beauty, has an estimated age of 2 billion years, and formed and separated from the planet when a massive impact hit Mars, capturing material from different points along the line of Martian time. Alan Hills, interacted with the fluid of the Martian crust about 3.9 billion years ago.

 

By looking at the two meteorites, the researchers conducted a chemical analysis looking for two types of hydrogen isotopes. They were specifically looking for “light hydrogen” and “heavy hydrogen”, because the ratio of these two isotopes can be used to understand the origin of traces of water found in rocks.

Their observation, published in the journal Nature Geoscience , showed that Mars likely received water from at least two very different sources in its earliest stage since both samples had similar isotope ratios, sitting comfortably within the ratio found in water on Earth. and the proportion found in the Martian atmosphere. Even more peculiar, this relationship was similar to the younger rocks analyzed by the Curiosity rover right there on Mars. This indicates that the chemical composition of water has been constant for about 3.9 billion years, a completely unexpected result, given previous studies.

“These two different sources of water in the interior of Mars could tell us something about the types of objects that were available to merge on the rocky inner planets,” said Jessica Barnes, assistant professor of planetary sciences at the University’s Lunar and Planetarium Laboratory. from Arizona (USA). Two different planetesimals with very different water contents could have collided and never completely mixed. ” This context is also important to understand the habitability and astrobiology of Mars ‘ past,” he clarifies.

Planetesimals were the building blocks of the planets that make up our solar system today. They are made up of traces of gas and dust from the formation of our sun. Over time, they grew in size and collided with each other, forming planets.

“We thought, ok, this is interesting, but also a bit strange. How do we explain this dichotomy where the Martian atmosphere is splitting up, but the crust basically stays the same during geologic time? Barnes wondered. “If you try to explain this very constant isotopic ratio of the crust of Mars, you can’t really use the atmosphere to do it. But we know how crusts form. They are formed by molten material from within that solidifies on the surface,” he continues.

 

“The prevailing hypothesis before starting this work was that the interior of Mars was more like Earth .”

However, when they analyzed the chemical composition of the Martian meteorites, they found something fascinating: the meteorites in the mantle fit into two different groups of igneous rocks called shergotite. (enriched and depleted, containing water with varying proportions of hydrogen isotopes). “It turns out that if you mix different proportions of hydrogen from these two types of shergotites, you can get the value of the crust,” says Barnes.

Those two chemical signatures indicate two water reservoirs of different origin and unmixed in the Martian mantle. Which may mean that, unlike on Earth, a global ocean of liquid magma below the mantle did not homogenize the layer above.

“We believe that shergotites are recording the signatures of two different reservoirs of hydrogen and, by extension, water within Mars. The large difference suggests to them that more than one source could have contributed water to Mars and that Mars did not have a global magma ocean, “the expert concludes.

Reference: Multiple early-formed water reservoirs in the interior of Mars, Nature Geoscience (2020). DOI: 10.1038 / s41561-020-0552-y, https://nature.com/articles/s41561-020-0552-y

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