MSGID: 1:317/3 649e5a6f   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Gullies on Mars could have been formed by recent periods of liquid   
   meltwater, study suggests    
      
     Date:   
         June 29, 2023   
     Source:   
         Brown University   
     Summary:   
         A study offers new insights into how water from melting ice could   
         have played a recent role in the formation of ravine-like channels   
         that cut down the sides of impact craters on Mars.   
      
      
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   A study led by Brown University researchers offers new insights into how   
   water from melting ice could have played a recent role in the formation of   
   ravine- like channels that cut down the sides of impact craters on Mars.   
      
   The study, published in Science, focuses on Martian gullies, which   
   look eerily similar to gullies that form on Earth in the Dry Valleys of   
   Antarctica and are caused by water erosion from melting glaciers. The   
   researchers, including Brown planetary scientist Jim Head, built a model   
   that simulates a sweet spot for when conditions on Mars allow the planet   
   to warm above freezing temperatures, leading to periods of liquid water   
   on Mars when ice on and beneath the surface melts.   
      
   The scientists found that when Mars tilts on its axis to 35 degrees, the   
   atmosphere becomes dense enough for brief episodes of melting to occur at   
   gully locations. They then matched the data from their model to periods   
   in Mars history when the gullies in the planet's Terra Sirenum region are   
   believed to have expanded rapidly downhill from high elevation points --   
   a phenomenon that could not be explained without the occasional presence   
   of water.   
      
   "We know from a lot of our research and other people's research that early   
   on in Mars history, there was running water on the surface with valley   
   networks and lakes," said Head, a professor of geological sciences at   
   Brown. "But about 3 billion years ago, all of that liquid water was lost,   
   and Mars became what we call a hyper-arid or polar desert. We show here   
   that even after that and in the recent past, when Mars' axis tilts to 35   
   degrees, it heats up sufficiently to melt snow and ice, bringing liquid   
   water back until temperatures drop and it freezes again."  The findings   
   help fill in some of the missing gaps on how these gullies formed,   
   including how high they start, how severe the erosion is and how far   
   they extend down the side of craters.   
      
   Previous theories suggest Martian gullies were carved by carbon dioxide   
   frost, which evaporates from soil, causing rock and rubble to slide   
   down slopes. The height of the gullies made many scientists theorize   
   that meltwater from glaciers had to be involved because of the distance   
   they traveled down the slopes and how eroded the gullies looked. Proving   
   liquid water could exist on Mars since it disappeared so long ago has   
   been difficult because temperatures typically hover about 70 degrees   
   below freezing.   
      
   The results from the new study suggest that gully formation was driven   
   by periods of melting ice and by CO2 frost evaporation in other parts   
   of the year.   
      
   The researchers found this has likely occurred repeatedly over the past   
   several million years with the most recent occurrence about 630,000   
   years ago.   
      
   They say that if ice was present at gully locations in the areas they   
   looked at when Mars' axis tilted to about 35 degrees, the conditions   
   would have been right for the ice to melt because temperatures rose   
   above 273 degrees Kelvin, equivalent to about 32 degrees Fahrenheit.   
      
   "Our study shows that the global distribution of gullies is better   
   explained by liquid water over the last million years," said Jay Dickson,   
   the study's lead author and a former researcher at Brown who's now   
   at California Institute of Technology. "Water explains the elevation   
   distribution of gullies in ways that CO2 cannot. This means that Mars has   
   been able to create liquid water in enough volume to erode channels within   
   the last million years, which is very recent on the scale of Mars geologic   
   history."  Despite doubts about meltwater being possible and scientists   
   never being able to model the right conditions on Mars for ice to melt,   
   the researchers were convinced that the meltwater theory was accurate   
   because they had seen similar features firsthand in Antarctica. There,   
   despite the cold temperatures, the sun is able to heat ice just enough   
   for it to melt and for gully activity to occur.   
      
   The new study is a continuation of previous research the team started   
   decades earlier looking at Martian gullies. In a 2015 study, for instance,   
   the researchers showed it was possible that there may have been past   
   periods on Mars when water was available to form gullies if Mars tilted on   
   its axis enough. The findings encouraged them to model what that tilt was   
   and match it with the locations and altitudes of gullies that have formed.   
      
   The paper raises anew the fundamental question of whether life could   
   exist on Mars. This is because life, as it's known on Earth, goes hand   
   in hand with the presence of liquid water. Mars will eventually tilt to   
   35 degrees again, the researchers said.   
      
   "Could there be a bridge, if you will, between the early warm and wet   
   Mars and the Mars that we see today in terms of liquid water?" Head   
   said. "Everybody's always looking for environments that could be conducive   
   to not just the formation of life but the preservation and continuation   
   of it. Any microorganism that might have evolved in early Mars is   
   going to be in places where they can be comfortable in ice and then   
   also comfortable or prosperous in liquid water. In the frigid Antarctic   
   environment, for example, the few organisms that exist often occur in   
   stasis, waiting for water."  The study also introduces the importance   
   of these gullies in terms of potential targets to visit during future   
   exploration missions on Mars.   
      
   The study included funding from the NASA Mars Data Analysis Program. Other   
   Brown-affiliated authors include former graduate students Ashley Palumbo   
   and Laura Kerber, former graduate student and postdoctoral researcher   
   Caleb Fassett and visiting researcher Mikhail Kreslavsky, a planetary   
   scientist at University of California, Santa Cruz.   
      
       * RELATED_TOPICS   
             o Space_&_Time   
                   # Mars # Solar_System # Space_Missions # NASA #   
                   Space_Exploration # Astronomy # Space_Probes # Mercury   
       * RELATED_TERMS   
             o Phoenix_(spacecraft) o Deimos_(moon) o Phobos_(moon)   
             o Solar_system o Mars_Exploration_Rover o Mars o   
             Exploration_of_Mars o Astronomy   
      
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   Story Source: Materials provided by Brown_University. Note: Content may   
   be edited for style and length.   
      
      
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   Related Multimedia:   
       * Terra_Sirenum_and_its_gullies   
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   Journal Reference:   
      1. J. L. Dickson, A. M. Palumbo, J. W. Head, L. Kerber, C. I. Fassett,   
      M. A.   
      
         Kreslavsky. Gullies on Mars could have formed by melting of water   
         ice during periods of high obliquity. Science, 2023; 380 (6652):   
         1363 DOI: 10.1126/science.abk2464   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/06/230629193235.htm   
      
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