“This means that Mars has been dry for a long time,” said Eva Scheller, a graduate student of 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 been amazed at ancient evidence of flowing water carved into the Martian surface – giant ravines, tendrils of meandering river channels and deltas where the rivers have driven sediments into 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 more than three billion years ago how much water was on a younger Mars. But the hydrogen atoms floating in the atmosphere of Mars 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 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 one in every 700. NASA Goddard Space Flight Center scientists, who reported this finding in 2015, said it could be used to measure the amount of water Mars once had. to calculate. Mars probably began 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, says Renyu Hu, a scientist from NASA’s Jet Propulsion Laboratory and another author of the current Science article, is that 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 four billion years, can ‘make up only a small fraction of the water loss,’ said Dr. Hu said. “It’s not enough to explain the great drought of Mars.”