A study of water from the Martian interior shows that Mars was originally formed from similar building blocks to Earth, but evolved differently later on.
The finding implies that both planets got their water from chondritic meteorites; unlike on Earth, though, Martian rocks containing atmospheric volatiles such as water don't get recycled into the planet's deep interior.
Scientists at NASA's Johnson Space Center in Houston, Carnegie, and the Lunar and Planetary Institute in Houston, reached their conclusions after studying water concentrations and hydrogen isotopic compositions trapped inside crystals within two Martian meteorites. Known as shergottites, one of these meteorites was rich in elements such as hydrogen, and the other depleted.
One meteorite, with a hydrogen isotopic composition similar to that of Earth, appears to have changed little on its way from the Martian mantle up to the surface. The other appears to have sampled Martian crust that had been in contact with the atmosphere.
Thus, the meteorites represent two very different sources of water: one sampled water from the deep interior and represents the water that existed when Mars formed as a planet, whereas the other sampled the shallow crust and atmosphere.
"There are competing theories that account for the diverse compositions of Martian meteorites," says researcher Tomohiro Usui. "Until this study there was no direct evidence that primitive Martian lavas contained material from the surface of Mars."
Because the hydrogen isotopic compositions of the two meteorites are different, the team believes that Martian surface water has had a different geologic history than water from the interior. Most likely, atmospheric water has tended to lose the lighter hydrogen isotope to space, retaining the heavier hydrogen isotope.
The concentrations of water in the meteorites are also very different. The fact that one has a rather low water concentration implies that the interior of Mars is rather dry. The enriched basalt has 10 times more water than the other one, though, suggesting that the surface of Mars could have been very wet at one time.