Water vanished on the surface of Mars. This may be where he went.

“This means Mars has been dry for a long time,” said Eva Schiller, a graduate student at California Institute of Technology and lead author of the science paper.

Today, there is still water equivalent to a global ocean 65 to 40 meters deep, but most of it is frozen in the polar ice caps.

Planetary scientists have long marveled at ancient evidence of water flow carved into the surface of Mars – giant canyons, solutions of meandering river channels and deltas as rivers push sediments into lakes. Perseverance is NASA’s newest robotic Mars explorerIt landed in the last month Crater LakeShe goes to a river delta on its outskirts, hoping to find clues to past lives.

Without a time machine, there is no way to control how much water was on smaller Mars more than three billion years ago. But hydrogen atoms floating in the Martian atmosphere today retain a ghostly hint of the ancient ocean.

On Earth, about one in 5,000 hydrogen atoms is a version known as deuterium and is twice as heavy because the nucleus contains both a neutron and a proton. (The nucleus of a common type of hydrogen atom contains only a proton and no neutrons.)

But on Mars, the concentration of deuterium is significantly higher, about one in 700. Scientists at NASA’s Goddard Space Flight Center said that I reported this result in 2015 This, he said, could be used to calculate how much water Mars once had. Mars may have started with a similar ratio of deuterium to hydrogen as Earth, but the fraction of deuterium increased over time as water evaporated and hydrogen was lost in space, because heavier deuterium is less likely to escape from the atmosphere.

The problem with this story is that Mars wasn’t getting rid of hydrogen fast enough, said Renew Hu, a scientist at NASA’s Jet Propulsion Laboratory and another author of the current scientific paper. Doctor. Hu said NASA measurements of the Martian atmosphere and the fluctuating orbital evolution or MAVEN showed that the current rate, extrapolated over a period of four billion years, “could represent only a small fraction of the water loss.” “This is not sufficient to explain the great dryness of Mars.”