The DAN neutron detector, developed under an agreement between NASA and Russia's Roscosmos Federal Space Agency, will be activated within three to four days, project director Igor Mitrofanov said.
The detector is designed to search as deep as 20 inches for any water that might be bound into shallow underground mineral layers, he said.
"If we conclude that there is something unusual in the subsurface at a particular spot, we could suggest more analysis of the spot using the capabilities of other instruments," he said.
By measuring the energies of neutrons leaking from the ground, DAN can detect the presence of hydrogen, a possible sign of water, RIA Novosti reported.
The detector will help Curiosity determine whether Mars was ever a habitable planet and whether it has any suitable places for habitation now, scientists said.
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