The water on Mars is gone. This could be where he went.

“This means that Mars has been dry for quite a long time,” said Eva Scheller, a Caltech graduate student who was the lead author of the scientific article.

Today, there is still water equivalent to a 65-130-foot-deep global ocean, but which is mostly frozen in the polar ice caps.

Planetary scientists have long marveled at ancient evidence of the flow of water carved into the Martian surface – gigantic canyons, twists of winding channels, and deltas where rivers disgorged sediment into lakes. NASA’s latest robotic explorer on Mars, Perseverance, which landed in Jezero Crater last month, will head to a river delta aboard in hopes of finding signs of past life.

Without a time machine, there is no way to directly observe the amount of water contained on a younger Mars more than three billion years ago. But the hydrogen atoms floating in Mars’ atmosphere today retain a ghostly hint of the ancient ocean.

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

But on Mars, the concentration of deuterium is significantly higher, around one in 700. Scientists at NASA’s Goddard Space Flight Center who reported the discovery in 2015 said it could be used to calculate the amount of water. that Mars once had. Mars likely started with a deuterium to hydrogen ratio similar to Earth’s, 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 the atmosphere.

The problem with this story, said Renyu Hu, a scientist with NASA’s Jet Propulsion Laboratory and another author of the current science article, is that Mars did not lose hydrogen quickly enough. Measurements by NASA’s Mars Atmosphere and Volatile Evolution orbiter, or MAVEN, have shown that the current rate, extrapolated over four billion years, “may only represent a small fraction of the water loss.” , said Dr Hu. “This is not enough to explain the great drying up of Mars.”