Scientists reported on Monday definitive signs of liquid water on the surface of present-day Mars, a finding that will fuel speculation that life, if it ever arose there, could persist to now.

“This, I think, gives a focus of where we should look more closely,” said Alfred S. McEwen, a professor of planetary geology at the University of Arizona and the principal investigator of images from a high-resolution camera on NASA’s Mars Reconnaissance Orbiter.

In a paper published in the journal Nature Geoscience, Dr. McEwen and other scientists identified waterlogged molecules — salts of a type known as perchlorates — in readings from orbit.

“That’s a direct detection of water in the form of hydration of salts,” Dr. McEwen said. “There pretty much has to have been liquid water recently present to produce the hydrated salt.”