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- Liquid water can\u2019t exist for long on Mars\u2019 surface<\/strong>. The atmosphere is far too thin and cold. But small amounts of brines \u2013 highly salty water \u2013 possibly could.<\/li>\n
- Brines could form under permafrost<\/strong>, or even help explain some of the unusual dark streaks on steep slopes.<\/li>\n
- But now a new study says brines are unlikely<\/strong> to be found on Mars, although it doesn\u2019t completely rule them out.<\/li>\n<\/ul>\n
Are there liquid water brines on Mars?<\/h3>\n
The surface of Mars is extremely dry, with no rivers, lakes or even puddles. The air is just too thin and cold for liquid water to be stable. But what about brines? Could brines \u2013 very salty water \u2013 exist on Mars? Perhaps in permafrost, or in the mysterious dark streaks seen to recur on steep slopes? Scientists have long debated their existence on this neighboring planet. And we still don\u2019t know for sure. But on December 16, 2024, researchers at the University of Arkansas said that even small amounts of brine would have difficulty forming in current Martian conditions. Their study didn\u2019t completely rule out brines on Mars. But, these researchers said, finding very salty water on Mars\u2019 surface won\u2019t be easy, even if such a thing exists.<\/p>\n
The researchers published their new peer-reviewed results in Proceedings of the National Academy of Sciences<\/em> on December 16, 2024.<\/p>\n
Recurring slope lineae and permafrost<\/h3>\n
Why speak of salty water on Mars at all? One place where scientists have thought brines might<\/em> exist are recurring slope lineae, weird dark streaks sometimes found on sun-facing slopes on Mars. They keep repeating in the same places. Could it be salty water that periodically comes to the surface?<\/p>\n
Another suggestion for brines on Mars centers around permafrost, such as that seen in the patterned ground at the Mars Phoenix landing site. <\/p>\n
But the new paper throws cold water on both possibilities for brines.<\/p>\n
The dark streaks of recurring slope lineae are seen more often on steep Martian slopes in warmer seasons. They fade in colder seasons. They do look a lot like streams of water. If they are, they would need to be briny in order to persist as long as they do.<\/p>\n
But \u2013 as some other papers have also suggested \u2013 the new study said the streaks are most likely flows of sand and dust. Vincent Chevrier, one of the two authors, is an associate research professor at the University of Arkansas\u2019 Center for Space and Planetary Sciences. He said:<\/p>\n
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I wanted to write this paper for a very long time, because I think there is a lot of confusion, a lot of misunderstanding, and a lot of erroneous interpretations of what the research papers are saying about the state of liquid water on Mars.<\/p>\n<\/blockquote>\n
And how about the regions under Martian permafrost? It\u2019s been suggested that small pools of brine might form beneath the Mars ice. This happens on Earth. Indeed, there are striped and polygonal features in the permafrost on Mars that could be attributable to brines.<\/p>\n
Again, however, the authors concluded there are probably too many limiting factors for the brines to exist. The researchers said that the relatively low amounts of the best types of salts, the pressure of water vapor and locations of ice \u2026<\/p>\n
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\u2026 strongly limit the abundances of brines on the surface or shallow subsurface.<\/p>\n<\/blockquote>\n
Is Mars\u2019 surface inhospitable for liquid water?<\/h3>\n
We know there used to be a lot of water on Mars\u2019 surface billions of years ago. There are ancient riverbeds, evidence for lakes, plus growing evidence for past oceans. The Mars rovers Opportunity and Spirit also found evidence of possible ancient hydrothermal systems as well as other water.<\/p>\n
But today, Mars\u2019 atmosphere is too cold and thin to sustain liquid water on the surface. In fact, the atmosphere is less than 1% as thick as Earth\u2019s. Any water that might appear would quickly freeze or boil away in the extremely tenuous atmosphere, even in the deepest canyons.<\/p>\n
What about brines on Mars?<\/h3>\n
Scientists have hypothesized that brines could still occur on Mars. Brines are water with a high salt content, like seawater. The salt can help keep the water from freezing or evaporating. Brines can freeze at much lower temperatures than pure water. We also know there are abundant salts on Mars\u2019 surface. Perchlorate salts in particular are common on Mars. A calcium perchlorate brine could remain liquid until the temperature reached -75 degrees Celsius (-100 F). And at Mars\u2019 equator, the average temperature is -50 degrees Celsius (-58 F). So brines should be theoretically possible.<\/p>\n
Indeed, in 2015, NASA said that results from the Curiosity rover supported the possibility of brines in the soil. Perchlorates could absorb water vapor from the atmosphere and allow brines to form in the soil.<\/p>\n
![\"Vertical](\"https:\/\/earthsky.org\/upl\/2024\/12\/polygonal-terrain-permafrost-Vastitas-Borealis-Mars-Phoenix-May-25-2008.jpg\")
View larger. | One of the 1st views from the Mars Phoenix lander of the polygonal terrain formed by permafrost, from May 25, 2008. As on Earth, brines could possibly form beneath permafrost on Mars. Image via NASA\/ JPL-Caltech\/ University of Arizona.<\/figcaption><\/figure>\n Could brines on Mars support life?<\/h3>\n
The researchers also noted that even if brines did form, they would \u2026<\/p>\n
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\u2026 remain highly unhabitable by terrestrial standards.<\/p>\n<\/blockquote>\n
Chevrier said:<\/p>\n
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Despite our best efforts to prove otherwise, Mars still remains a cold, dry and utterly unhabitable desert.<\/p>\n<\/blockquote>\n
But the paper does mention this caveat:<\/p>\n
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Despite these drawbacks and limitations, there is always the possibility that Martian life adapted to those brines and some terrestrial organisms could survive in them, which is a consideration for planetary protection because life on Mars might exist today in that case. Hence, detecting brines in situ remains a major objective of the exploration of the red planet.<\/p>\n<\/blockquote>\n
![\"3](\"https:\/\/earthsky.org\/upl\/2024\/12\/Mars-Phoenix-lander-brine-droplets-2008.jpg\")
View larger. | Possible droplets of briny water on one of the landing legs of the Mars Phoenix lander in 2008. Image via NASA\/ JPL-Caltech\/ UArizona\/ PNAS.<\/figcaption><\/figure>\n What about the Mars Phoenix lander?<\/h3>\n
NASA\u2019s Mars Phoenix lander touched down near the north pole of Mars on May 25, 2008. Exposed water ice could be seen in some of the trenches it dug in the ground. The ice evaporated within four days.<\/p>\n
But something else caught scientists\u2019 attention as well: small droplets of what looked like droplets of liquid water on one of the lander\u2019s legs. Scientists hypothesized that small amounts of briny water splashed up onto the leg during landing.<\/p>\n
Some other scientists, however, thought that small globs of frost or condensed water vapor were more likely. So even now, the jury is still out on that one.<\/p>\n
Even if<\/em> there aren\u2019t any brines on Mars, there is still growing evidence for them elsewhere in the solar system, such as the dwarf planet Ceres and the large asteroid Vesta. Where else might we find them?<\/p>\n
Bottom line: Scientists have hypothesized how liquid water brines on Mars could occur. A new study, however, suggested it is more unlikely than previously thought.<\/p>\n
Source: The elusive nature of Martian liquid brines<\/p>\n
Via University of Arkansas<\/p>\n
Read more: Dark streaks on Mars may be caused by salts and melting ice<\/p>\n
Read more: Are mysterious flows on airless worlds made by salty water?<\/p>\n
<\/div>\n
\n - Brines could form under permafrost<\/strong>, or even help explain some of the unusual dark streaks on steep slopes.<\/li>\n