Mars was once wet, with an ocean of water on its surface.
Today, most of Mars is as dry as a desert, except for ice deposits in its polar regions. Where did the rest of the water go?
Some of it disappeared into space. Water molecules, which are pumped by particles of solar wind, break out into hydrogen and oxygen atoms, and especially the lighter hydrogen atoms rushed out of the atmosphere and lost in outer space.
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But most of the water, according to a new study, went down and sucked into the rocks of the red planet. And there it remains, trapped in minerals and salts. About 99% of the water that once flowed over Mars could indeed still be there, the researchers estimate in an article published in the journal Science this week.
Data from the past two decades of robotic missions to Mars, including NASA’s Curiosity Rover and the Mars Reconnaissance Orbiter, have shown a wide distribution of what geologists call hydrated minerals.
“It became very, very clear that it was common and not uncommon to find evidence of water change,” said Bethany Ehlmann, a professor of planetary science at the California Institute of Technology and one of the authors of the article. .
Ehlmann, who spoke at a news conference at the Lunar and Planetary Science Conference on Tuesday, said that if rocks are changed by liquid water, water molecules are absorbed into minerals such as clay. “Water is effectively trapped in the crust,” she said.
To get a sense of the amount of water, planetary scientists are talking about a “global equivalent layer” – that is, if Mars were ironed out into a uniform, functional ball, how deep would the water be?
The scientists estimated that the depth would have been 100 to 1,500 meters, or 330 to 5,000 feet.
According to them, the deepest probability is about 2000 feet, or about a fourth as much water as in the Atlantic Ocean.
The data and simulations also indicated that the water disappeared almost 3 billion years ago, around the time when the earth was composed of unicellular microbes in the oceans.
“This means that Mars has been dry for a long time,” said Eva Scheller, a graduate student at Caltech, the lead author of the Science article.
Today, there is still water equivalent to a world sea 65 to 130 feet deep, but it is mostly frozen in the ice sheets.
Planetary scientists have long marveled at ancient evidence of flowing water carved into the Martian surface – giant ravines, tendrils of meandering river channels and deltas where the rivers suffocate sediments in lakes. NASA’s latest Mars explorer, Perseverance, which landed in the Jezero crater last month, will go to a river delta on its edge in hopes of finding signs of past life.
Without a time machine, there is no way to directly observe how much water was on a younger Mars more than 3 billion years ago. But the hydrogen atoms floating in the atmosphere of Mars today retain a ghostly hint of the ancient ocean.
On Earth, about 1 in 5,000 hydrogen atoms is a version known as deuterium that is twice as heavy because the nucleus contains a neutron and a proton. (The nucleus of an ordinary hydrogen atom has only a proton, no neutrons.)
But on Mars, the concentration of deuterium is significantly higher, about 1 in 700. Scientists from the NASA Goddard Space Flight Center, who reported this finding in 2015, said it could be used to measure the amount of water Mars once had. to calculate. Mars probably started with a similar ratio of deuterium to hydrogen as Earth, but the fraction of deuterium increased over time as the water evaporated and hydrogen was lost in space because the heavier deuterium is less likely to escape the atmosphere. .
The problem with the story, Renyu Hu, a scientist at NASA’s Jet Propulsion Laboratory and another author of the current Science article, said Mars did not lose hydrogen fast enough. Measurements by NASA’s Mars Atmosphere and Volatile Evolution orbit, or MAVEN, have shown that the current rate, which has been extrapolated over 4 billion years, can ‘make up only a small fraction of the water loss,’ Hu said. “It’s not enough to explain the great drought of Mars.”
This led to the new research concluding that a large majority of water goes into the rocks.
“This is a very interesting new study in which many processes are put together to provide alternative scenarios for the fate of water on Mars,” Geronimo Villanueva, one of the NASA scientists who conducted previous deuterium measurements, said in an e- post written. “It offers the possibility of an even wetter past, and that rocks on Mars now contain more water than we initially thought.”
However, the water will probably not be very useful to settlers of the earth. “The amount of water in a rock is very small,” Scheller said.
To release water trapped in minerals, it must be heated to high temperatures. “We’ll have to cook a very large amount of rocks to have something that will be useful,” Scheller said.
Elon Musk, the founder of SpaceX, who dreams of one day sending colonists to Mars, reflected on the explosion of nuclear bombs on Mars to melt the ice sheets and warm the planet, making it more hospitable. These explosions would also release the water into the hydrated minerals, though Scheller would not speculate how much.
Michael Meyer, the lead scientist of NASA’s Mars reconnaissance program, said, “I would just mention that a planet is not usually a good way to make it habitable.”
On earth, water is also absorbed into rocks, but it does not remain indefinitely. The motion of the earth’s crust pushes rocks into the mantle, where it melts, and then the molten rock – and water – rises again through volcanoes. On Mars, it appears that volcanism, like liquid water, has long since disappeared.
This article originally appeared in The New York Times.
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