The US space agency and an international team of planetary scientists have found evidence in meteorites on earth that indicate Mars has a distinct reservoir of water or ice near its surface.
The discovery helps resolve the question of where the "missing Martian water" may have gone.
"There have been hints of a third planetary water reservoir in previous studies of Martian meteorites but our new data require the existence of a water or ice reservoir that also appears to have exchanged with a diverse set of Martian samples," explained lead author Tomohiro Usui from Tokyo Institute of Technology in Japan.
Until now, there was no direct evidence for this surface reservoir or interaction of it with rocks that have landed on the earth from the surface of Mars, he said.
For the study, a team from Tokyo Institute of Technology, the Lunar and Planetary Institute in Houston, the Carnegie Institution for Science in Washington and NASA's Astromaterials Research and Exploration Science Division studied three Martian meteorites.
The samples revealed water comprised of hydrogen atoms that have a ratio of isotopes distinct from those found in water in the Red Planet's mantle and current atmosphere.
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Researchers emphasise that the distinct hydrogen isotopic signature of the water reservoir must be of sufficient size that it has not reached isotopic equilibrium with the atmosphere.
"The hydrogen isotopic composition of the current atmosphere could be fixed by a process that involves rapid loss of hydrogen to space and the sublimation from a widespread ice layer," said co-author John Jones, member of NASA's Mars Curiosity rover team.
Curiosity's observations in a lake bed in an area called Mount Sharp indicate Mars lost its water in a gradual process over a significant period of time.
"In the absence of returned samples from Mars, this study emphasises the importance of finding more Martian meteorites and continuing to study the ones we have with the ever-improving analytical techniques at our disposal," said co-author Conel Alexander, a cosmochemist at Carnegie Institution for Science.
The reservoir's existence also may be a key to understanding climate history and the potential for life on Mars.
The findings were reported in the journal Earth and Planetary Science Letters.