“This means that Mars has been dry for a very long time,” said Eva Scheler, a Celtic graduate student who was the lead author of the science paper.
Even today, the global ocean has water similar to 65 to 130 feet deep, but it is mostly frozen in caps of polar ice.
Planetary scientists have long been amazed by the ancient evidence of flowing water carved on the surface of Mars – vast valleys, river basins and deltas where rivers turn into lakes. NASA’s latest robotic Mars explorer, Perseverance, who landed in the Jezero crater last month, will lead the 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 tiny Mars more than three billion years ago. But the hydrogen atoms floating in the atmosphere of Mars today preserve the haunting sign of the ancient ocean.
On Earth, there is a version of deuterium called hydro atoms in about 1,000 hydrogen atoms that is twice as heavy because its nucleus contains both neutrons and protons. (The structure of a normal type of hydrogen atom contains only protons, not neutrons.)
But on Mars, the concentration of deuterium is significantly higher, one in about 700. Scientists at NASA’s Goddard Space Flight Center, who reported the discovery in 2015, say it could be used to calculate the amount of water on Mars. Probably Mars started with the same ratio of deuterium to hydrogen as Earth, but the amount of deuterium increased with time as water evaporated and hydrogen was lost in space, as heavy deuterium is less likely to escape from the atmosphere.
The problem with that story, said Renu Hu, a scientist at NASA’s Jet Propulsion Laboratory and second author of the current science paper, is that Mars is not losing hydrogen rapidly. Da Hu said measurements made by NASA’s Mars Atmosphere and Volatile Evolution Orbiter, or Maven, showed that the current rate, an additional four billion years, was “only responsible for a small fraction of the water loss.” “This is not enough to explain the great drying up of Mars.”
