On Earth chlorides are formed as the surfaces of large bodies of water such as lakes evaporate, leaving behind solid materials that had been dissolved in the water.
The minerals can also take shape as underground brines associated with volcanic activity evaporate.
Researchers think that saline minerals could have formed on Mars as acidic fluids evaporated during the weathering of volcanic rock known as basalt.
But there's more to be done to confirm the salt deposits and what they might mean for liquid water on the red planet, Osterloo said.
"In order to support the theory of an early wet Mars, I think we need to continue to send ground truth missions as well as orbital instruments," she said.
The study results are already getting a warm reception among Mars experts.
"It's about time they teased salt deposits out of the remote-sensing data!" Paul Knauth, a geologist at Arizona State University who was not affiliated with the new study, wrote in an email.
"Gary Brass showed over 25 years ago that concentrated brines could be stable there," he added. Brass, then a researcher with the University of Miami, published an oft-cited paper about brines on Mars in the April 1980 issue of the journal Icarus.
"Don Burt and I published papers several years ago showing why such brines should be there, possibly even seeping out today," Knauth continued, referring to an Arizona State colleague.
But salt didn't show up in the initial remote-sensing data, so the ideas didn't get much purchase, he said—until now.
"It is an extremely significant result, but is not surprising to those very few of us who have been howling in the wilderness about salt and brine on Mars."
Knauth hopes researchers will keep looking for more chlorides, particularly in the Hellas Basin, where he thinks dense brines could still be actively oozing.
A March 3 image of the basin taken by the Mars Reconnaissance Orbiter's HiRISE camera shows the distinctive swirling patterns of salt-marsh deposits.
"It's possible that some of these deposits are mushy right now," Knauth said, which could have "considerable astrobiological importance."
Study co-author Phil Christensen, also at Arizona State, agrees.
"The other good thing about salt is that it is an excellent preservative of organic material," he added.
"So if there was life, or even organic precursors to life, the organic molecules could be preserved in the salt deposits."
Free Email News Updates
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).
SOURCES AND RELATED WEB SITES