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

Today there is still water equivalent to a global ocean 65-130 feet deep, but it mostly freezes at polar peaks.

Planetary scientists have long marveled at ancient evidence of water flow carved from 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 explorerThat fell last month Crater LakeYou will head to a river delta on its edge hoping to find clues to past lives.

Without a time machine, there is no way to monitor how much water was present on younger Mars more than three billion years ago. But hydrogen atoms floating in Mars’ atmosphere today retain a ghostly signal to the ancient ocean.

On Earth, about one out of every 5,000 hydrogen atoms is a version known as deuterium and is twice as heavy because its nucleus contains both a neutron and a proton. (The nucleus of a common type of hydrogen atom contains only one 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 who I reported this result in 2015 He said that it could be used to calculate the amount of water on Mars. Mars may have started with a ratio of deuterium to hydrogen similar to that of 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 has not lost hydrogen fast enough, said Renew Hu, a scientist at NASA’s Jet Propulsion Laboratory and another author of the current science article. Dr Hu said measurements of the Martian atmosphere and the fluctuating orbital evolution of NASA, 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 drought. The Great on Mars. “