Liquid Water on Mars

Additional content for this article is from Margaret Lattke.

Introduction

Scientists have carefully studied and tracked the history of water on the Red Planet. It is now widely accepted due to the geomorphological evidence that Mars had an ocean of liquid water billions of years ago. This ocean covered the northern hemisphere. This is indicated by the lower altitude of the surface, smoother and geologically newer surface of the northern hemisphere, as opposed to the higher altitude and the more jagged appearance of the highlands of the southern hemisphere. An ocean covering most of the northern hemisphere has consequences such as a thicker atmosphere and warmer temperatures. It is clear by photographic evidence that volcanic activity was very active in Martian history. In close proximity to ancient volcanoes are areas of catastrophic flooding, caused when volcanic heat rapidly melted the subsurface ice. This evidence can still be seen today. (Nature6) Mars has a significant CO2 atmosphere, which would have been important to sustaining a warmer and wetter planet in the past. This thicker atmosphere could have been in place for 10 million to a billion years. Volcanism and cycling of carbonate rocks would have helped to keep the atmosphere intact for this lengthy geologic time. (Icarus) Current science indicates Mars was once a warm and wet planet and currently has liquid water on the surface for short periods of time. Data consistent with liquid water has been observed. It is proposed water appears seasonally as minerals are mixed with water that erupts through the surface and runs down the sides of craters, keeping it liquid at temperatures below freezing. There is ample evidence, morphologically and spectroscopically, from the fleet of spacecraft that have been and are now presently working on and around Mars.

History

Water on Mars makes headlines often and has been debated for over a century. Astronomer Giovanni Schiaparelli’s observations in approximately 1877 started the frenzy over water on Mars. When Schiaparelli observed what he thought were channels on Mars, he called them canali which means channels. (See Figure 1)[1] When his findings were published, the term was misinterpreted as canals which led many people to believe intelligent life existed on Mars. Channels and canals are distinctly different. A channel is a naturally occurring groove in the ground where water or some other fluid has eroded the soil away to make a riverbed. A canal is made by sentient beings, for water to flow through. (Chaisson & McMillan) Schiaparelli declared his disbelief for water on Mars in a letter to Professor Holden in April 1893, in which he rejected the idea of water on Mars. This was based on his study of the planet and the colors he observed. He states that when you view water on Earth from a higher point, it appears black which he did not observe. (Pacific)(Willett)

For nearly two decades in the late 19th and early 20th Century, Percival Lowell utilized a telescope he built specifically to observe Mars. He was intrigued with the findings of Schiaparelli. The Lowell Observatory was built in Flagstaff, Arizona, USA and still stands. Lowell’s sketches show many features that were considered to be evidence of intelligent beings on Mars. He authored three books on the subject, which included references to canals and oases. Many people disagreed with Lowell’s observations and he was ostracized by some. (Chaisson & McMillan)(Willett) Studies searching for water on Mars continued. From February to April 1937 observations at the Mount Wilson Observatory using a plane grating spectrograph on the telescope detected water vapor in the Martian atmosphere. The spectrograph indicated that a wavelength of 7200. The peaks on the spectrogram were consistent with H2O. The data was determined not to be of Earthly origin. (Pacific2) The Modern Era Seeks Water on Mars As technology advanced, we discovered that some of these geological features were present, but not in the exact state recorded by Lowell. The Mariner 4 and 9 were launched in the 1960’s and early 1970’s. These spacecrafts proved that the drawings Lowell made were not accurate. (Chaisson & McMillan) Each spacecraft that visited the Red Planet added to the data set being compiled regarding water on Mars. During the latter half of the 20th Century, the fleet of spacecraft orbiting, landing, and roving Mars increased. Geologic periods on Mars have been established as: Pre-Noachian which was a period lasting from 4.5 billion years ago (bya) to 4.1 bya,, Noachian from 4.1 bya to 3.7 bya, Hesperian from 3.7 to 3.0 bya, and Amazonian which started 3.0 bya to present day. As the data came in Martian geologists identified two types of channels carved by water, runoff channels and outflow channels. Runoff channels formed during the Hesperian Period are often found in the southern highlands and can be hundreds of miles long. They appear nearly identical to interconnecting riverbeds on Earth. Outflow channels are found in the equatorial region and appear to be relics of catastrophic flooding during the late Hesperian. They are not interconnected and are thought to be paths of huge volumes of water. (Chaisson & McMillan)(Willett) As the 21st Century has brought increased technology and data, the estimates for the period when water existed in liquid form on the surface of Mars has changed dramatically. In the last decade alone, the estimates have gone from billions of years ago to millions, thousands, hundreds, decades ago and more recently it has been said there may be water on the surface now. (NASAtv)(Willett) Geological Conditions and Observations Mars does not have the appropriate global conditions for liquid water to sit on the surface for extended periods of time. The triple point on Mars for liquid water is 0oC with a pressure of 0.088 pounds per square inch (psi) at the average surface altitude. The average temperature is below the freezing point of water and the pressure is 0.087 psi. Typically, these conditions are inconsistent with sitting liquid water, unless we explore areas of lower altitude or add certain molecules to water. No vast areas of liquid water sit on the surface and no rivers flow today. As specific conditions are met, it is possible that liquid water can flow and puddle on Mars. (Chaisson & McMillan) During the late-Noachian and early-Hesperian periods ice sheets were laid down on Mars. In 2018, it was reported that vast water ice sheets were discovered that are at least 100 meters thick. The ice sheets appear to have been laid down over different time periods, some may be as recently as 100 million years ago. The team analyzed eight ice sheets that were semi-exposed for the study. All of the ice sheets were within 55o of the equator. It is suspected by the unique layering pattern that the ice was laid down by periods of H2O snow. This would be an essential part of a planet wide water cycle, whereby meltwater would recharge any aquifers beneath the surface and likely still exists on Mars. Spectroscopy indicates the water ice is pure enough for Martian astronauts to melt and utilize for drinking water and other human necessities. The purity of the water ice causes sublimation into vapor, thus causing further collapse of the ice sheets. (Icarus2)(Science5) The vapor can then be deliquesced into the salts in the regolith causing dampness on the surface as photographed by the rovers. Amateur astronomers on Earth can see the polar ice caps on Mars on a clear night from a small telescope. The ice caps on Mars are made up of CO2 and H2O ice. They grow and recede throughout the year. CO2 and H2O are present in the Martian atmosphere as well. CO2 makes up 96% of the atmosphere and H2O only exists in trace amounts.(Science)(NASA) The interest in water on Mars has influenced the scientific community to further study the planet searching for clues to verify or debunk the mystery.

Mariner Missions

In 1965, NASA’s Mariner 4 spacecraft flew by Mars and sent images back to Earth. After many arduous hours, scientists received the signal and had 22 small crude images of the rocky and barren surface of Mars.(NASATech) To the scientists it was an incredible feat of engineering, however to the public, it was a disappointing confirmation of the lack of anything very interesting, including water, on Mars. In 1969 the Mariner 6 and 7 flew by Mars taking hundreds of pictures and other data and sending them back to Earth. The spacecraft confirmed the canali on Mars were merely an optical illusion and misinterpretation of data from Earth based telescopes. (NASATech)

Viking

The Viking I and II missions by NASA were composed of two landers and two orbiters. The orbiters imaged the entire planet while taking scientific data readings, including an infrared spectrometer, to seek and track water vapor in the atmosphere. The landers took images from the surface and sampled the soil and atmosphere on opposite sides of the planet. Viking I landed at 22.27°N 47.95°W and Viking II at 47°38′24″N, 225°42′36″W. They were also tasked with seeking evidence of life, which would need a source of water to survive. (NASANatl) The Viking Orbiters’ instrument, called the Mars Atmospheric Water Detector, detected upwards of approximately 100 microns of atmospheric H2O. (Geo) Atmospheric water is an important discovery in order to establish a baseline for a planetary water cycle. Rampart craters were photographed by the Viking orbiters. The craters are surrounded by what appear to be muddy flows. This is called fluidized ejecta, a type of muddy mixture, and is the result of the friction from an impact of a meteorite and the subsurface ice which interacted. The melted ice and regolith mixed together during the event and created the fluidized ejecta that is seen surrounding the rampart craters. (dePater & Lissauer) Scientists examined and reexamined the Viking data trying to piece together some semblance of a story regarding the history of Mars’ water. Some were adamant that water could not exist on Mars today, but if water ever existed on Mars it had to be billions of years ago. Other scientists were starting to speculate that it may have existed more recently. As the scientific method goes, more data needed to be collected. Pathfinder Sojourner Mission On July 4, 1997 the two-part spacecraft, Pathfinder-Sojourner, landed on Mars at 19°7′48″N 33°13′12″W. The pair was made up of a lander and the first rover to ever be deployed on another planet. The Sojourner Rover, a small solar-powered rover, at about a meter in length. Its planned lifespan was 30 sols (Martian days) but lived to transmit valuable information back to Earth for 83 sols. Part of the scientific mission of the lander-rover complement included finding evidence of past liquid water on Mars. The mission findings included round pebbles near the landing site. Round pebbles occur in running water that has a strong enough flow to tumble jagged rocks over and around each other, dulling the edges and metamorphosing the jagged rocks into small round pebbles. The suggestion is that Mars was warmer with a thicker atmosphere that allowed for liquid water to flow and stand on the surface. (NASAPS) The visible evidence from Pathfinder in Chryse Planitia indicated an area of ancient catastrophic flooding equaling a volume of hundreds of km3. The images of the rocks themselves showed some to be rounded and others sharp and stacked. Geologists state that these features indicate catastrophic flooding as seen by analogues on Earth. The sharp and stacked rocks appear to have been shoved on top of each other by flood water. Some evidence of rock conglomeration was imaged, but the results were inconclusive to whether this was caused by water. (NASAGeo) More data needed to be collected.

Mars Global Surveyor

Orbiters have continued to fly to and orbit Mars for decades providing photographic evidence of riverbeds, channels, flooding, ice cap growth and recession. The evidence for water flowing on Mars was not only growing but appeared to be indicative of a more recent existence.

The Mars Global Surveyor (MGS) orbiter reached orbital insertion in September 1997, shortly after the Pathfinder mission arrived it was tasked with many things, some of which were determining the geological processes that occur; imaging the surface seeking evidence of past water erosion; examining the physical properties of ice; monitoring the polar ice caps; and tracking weather patterns and the seasons. MGS had a suite of scientific instruments which included cameras, a laser altimeter, and a spectrometer. The instruments worked together to give planetary scientists a clearer picture of the history of water on Mars. One such instance occurred when MGS imaged the same crater six years apart. To the surprise of the scientific community, there had been a change in the crater wall. The crater lies in the Centauri Montes region at 38.7o S 263.3o W. The image in 1999 showed a non-distinct crater. In 2005 when the crater was imaged again, a sediment trail was identified. Spectroscopy indicated that the sediment was made up of salts and minerals that could be the result of briny water that flowed down the slope of the crater. When the water evaporated, a dry sediment of minerals would have been left behind, as indicated by the bright material imaged by MGS. (NASA) Some scientists stated the sediment could have been caused by water erupting through a weak spot on the crater wall, staying liquid due to the salt and minerals, flowing down the side of the crater, the water evaporating, and leaving remnants of minerals behind. (See Figure #2) Over the duration of the MGS mission, many more gullies were discovered. (NASA)

Another interesting clue to the history of water on Mars was when the Thermal Emission Spectrometer (TES) on board the MGS discovered vast amounts of hematite consistent with forming in water. Hematite is found abundantly on Earth and has been widely researched and found to be formed when the interaction of iron and water occur over long periods of time. Hematite forms in spherule shapes, concreting over time. (Geo2) Mars Odyssey In late 2001, the Mars Odyssey entered the Martian orbit. This spacecraft mapped and verified the water ice that exists beneath the surface of Mars. (UofA) As the evidence mounts for liquid water existing on Mars today, some scientists insist this is not the case. It has been suggested that the evidence put forth for water on Mars today is instead moving sand or deliquescence of perchlorate salts. Perchlorates act as a natural antifreeze on Mars. Deliquescence is the act of water vapor from the atmosphere being absorbed by the salts in the regolith and forming sitting liquid water, which in itself is contrary to the proposition that sitting liquid water does not exist on the surface.(Brit) Hundreds of features have been imaged in crater walls and slopes of canyons named recurring slope lineae (RSL). Part of the astronomical community believes RSLs are swaths of water moving down the slopes and other scientists disagree vehemently. Others believe the moving sand theory which is due to the slope of the crater walls that have been studied. The incline of the slopes has been found to be 27o or more which during testing of similar materials, shows that sand can move down a slope moving the surrounding materials. (Science4) A 2016 study of RSLs by Odyssey’s Thermal Emission Imaging System were shown to be as dry as the Atacama Desert, yet this did not contradict the hydrated salts data collected in 2011. (NASAOdyssey) Mars Reconnaissance Orbiter The Mars Reconnaissance Orbiter (MRO) entered the orbit of Mars in March 2006, a few months before NASA lost contact with MGS. The MRO also carried cameras and spectrometers. The HiRISE camera has imaged many RSLs. (See Figure 3) In 2015 NASA announced MRO had discovered hydrated minerals in the area of the dark streaks on steep slopes. The RSLs grow and recede with the temperature and seasonal changes and appear more commonly at mid-latitudes where the temperature is warmer.(NASAjpl) The streaks appear more often as Mars’ axial tilt aims the areas toward the Sun and the temperature reaches -23oC. This is below the freezing point for fresh water on Mars. (Nature4) However, water that contains perchlorates and other minerals, dubbed hydrated salts or briny water, can exist at the temperature and pressure on Mars. (NASAjpl)(Nature4)

Other scientists have proposed water is not the cause at all but instead blocks of CO2 ice moving down the slopes are causing the linear gullies. The theory proposes that as the seasons change blocks of CO2 ice are loosened by sublimation. Blocks of carbon dioxide ice then fall down the steep slopes carving gullies that appear to be evidence of flowing water. (ScienceDirect)

Spirit and Opportunity

The Mars Exploration Rovers Spirit and Opportunity (MER) landed on Mars a few weeks apart in January 2004. Each rover contributed greatly in the search for evidence of water. Steve Squyres, Principle Investigator for MER, stated the mission was a “follow the water” mission. (NASA) Early in the history of Mars a large planetesimal hit the planet and melted the entire surface, this is known as the Borealis Impact. Any water or life that existed on the Red Planet would have been vaporized. The “follow the water” mission of the MER was tasked with finding out if water existed on the surface of Mars after the Borealis Impact. The Opportunity Rover landed at 1.94°S 354.47°E and explored Eagle Crater at Meridiani Planum shortly after landing on Mars. As images from the area were processed and viewed by the geologists on the team, it was discovered that a vast field of hematite had been discovered. The hematite was nicknamed “blueberries” due to the bluish hue in the images and the appearance of a spattering of blueberries on the ground. (Universe) The Opportunity Rover used the Rock Abrasion Tool (RAT) to grind and examine a blueberry. The team next used a spectrometer to determine the mineral content of the nodule. The spectroscopic analysis revealed the concretion to be hematite and jarosite.(See Figure 4) (Science3) The Utah desert is home to a vast region of fossilized sand dunes that is a perfect analog to Eagle Crater and the surrounding Meridiani Planum on Mars with its own vast area of fossilized sandstone and hematite. Hematite only forms in the presence of water. Water penetrates the sandstone and pours through the cracks. As the water contacts the rock it brings with it minerals, like iron, that forms concretions around the sand. The dense iron nodules fall out of the sandstone as wind erosion dissipates the rock around the nodules. Over millennia, more blueberries fall out of the sandstone and pile up on the surface of the planet. For the tens of thousands of hematite nodules found by the Opportunity Rover, vast amounts of water must have existed on the surface of Mars. The water could only be sustained in liquid form with a much thicker atmosphere. The atmosphere also must have been much denser in order to cause the amount of wind erosion seen that caused the hematite to fall out of the sandstone. (Universe) Spirit landed in January 2004 at 14.56°S 175.47°E in a dry lake bed. By March the Spirit Rover found evidence of past water in a rock named Humphrey. The MER team instructed the rover to examine Humphrey with the RAT which ground 2mm into the surface of the rock. It was discovered that the crystalline structures inside Humphrey had been in contact with water in order for the crystal to form. (NASAPress)

Spirit roved Mars for over 1200 sols when she was nearly crippled by a wheel that was no longer operational, but continued to rove and drag the wheel behind her. As the wheel drug through the regolith, a white powdery substance was revealed. The substance was examined by the X-ray spectrometer and determined to be 90% pure silica. Squyres stated that via teleconference, this was a “remarkable discovery”. Silica is often found on Earth in areas where hot springs exist. The silica discovered by Spirit may have formed in a hot spring and later have flowed to an area further from the source. Another option for the formation of silica in the region is possibly the interaction with acidic vapors from volcanic activity combined with the regolith and water. (NASAmer) At Gusev Crater in the Columbia Hills, Spirit examined a grouping of rocks, including a rock named Clovis. The team investigated Clovis utilizing the Mossbauer spectrometer which revealed the presence of eight iron bearing minerals including goethite, which only forms in the presence of water. (See Figure 5)(AGU)

Phoenix

The Phoenix Lander landed near the north polar region at 68.22oN 125.7oW on Mars in May 2008. The lander used a parachute and reverse thruster, retrorockets landing method. (Phoenix) Notable images from Phoenix included a vast panorama of polygon shaped regolith which were indicative of ices beneath the regolith that had frozen and thawed, thus leaving behind a polygon shape. The polygons are formed by the freezing and thawing process as the regolith is blown by the wind and into the cracks in the ices. (See Figure 6) The camera on the underneath of the lander took an image of a block of a frozen white substance that was later identified as water ice. This was the first surface observation of water ice on Mars. (Chaisson & McMillan) The thrusters had blown away the regolith and revealed the ice. The most intriguing photos were taken over a period of approximately 30 days and revealed globules on the landing struts of Phoenix. The globules grew and receded then eventually completely disappeared. They were found to be liquid water mixed with perchlorates. (SpaceSci) This elemental composition was later proven to be the reason the water could stay liquid at sub zero temperatures and pressures far below that of Earth. (Astrobio2)(Science2) The Phoenix lander also imaged, for the first time, water ice clouds and snow falling. The temperatures at the time were not cold enough to form CO2 clouds which requires -120o C. Instead the temperatures hovered between -97.7 o C and -19.6 o C, and would be conducive to H2O clouds and snow. (Science2)(Geoscie)

Mars Science Laboratory - Curiosity

As technology improved, images sent to Earth by various spacecraft had better resolution and scientific instruments have been able to gather more detailed information. Rovers, orbiters and landers have benefitted from the technological advancements in miniaturization of instruments, allowing more scientific equipment to be carried on each craft. The implementation of the sky crane landing method has allowed for the landing of unprecedented payloads on the surface of Mars. The Mars Science Laboratory Curiosity (MSL) is an 899 kg rover that landed via the sky crane landing method. The rover has an entire laboratory on its back, many cameras, and a versatile arm. When NASA was deciding on a landing spot for Curiosity it was important to find an area with evidence of previous water activity in order to assess habitability. Gale Crater is only 4.5o south of the equator and is the site of a significant alluvial fan from previous water activity. Within a few days after Curiosity landed at 4.58°S 137.44°E, it was announced by John Grotzinger, Project Scientist for MSL, on a NASA telecast, that Curisoity had landed in an ancient riverbed that had flowed vigorously with fresh water up to waist deep. Grotzinger explained the water was so pure, based on chemical analysis of the surrounding area, that a person could have scooped up the water and drank straight from the river. This discovery was made initially by the photographs of the area that showed what appear to be concretions of rocks that would have been arranged in the position by the flow of water over a long period of time. (See Figure 7) Another clue to the ancient riverbed was the rounded pebbled seen jutting out of the edge of the compacted rocks and pebbles. The rounded pebbles show that the water had to have persisted for a period of time long enough for rocks to tumble over each other and reshape them from their former jagged appearance. (NASANews)

The Curiosity team also discovered perchlorates in Gale Crater. Perchlorates allow water to be liquid at temperatures below freezing. Liquid brines can form in the pre-dawn hours on Mars. It has been proposed that within 5 cm of the surface, liquid brines form in Gale Crater. This liquid evaporates after sunrise. Studies up to 15 cm beneath the surface indicate that an exchange of atmospheric vapor interacts with the surface regolith and through deliquescence liquid water forms. (Nature5) Desiccated mud cracks have also been discovered in Gale Crater. (See Figure 8) This implies liquid water stood for a period of time, around 3 billion years ago, and mixed with the regolith making mud. The water evaporated from the mud and what was left were polygon shaped muddy cracks. The cracks were buried over time by sediment that was blown across the surface. In more recent geologic history, the sediment was eroded away and what we see now are the remnants of dried mud cracks that were filled with sand. In close proximity to the mud cracks were layers of mudstone and sandstone. This indicates periods of time when a body of water was sitting in the area. The water would have moved somewhat tidally over the boundary of the lake and what is left behind are areas that appear to be a lakeshore. Another point of view is that the mud cracks could have been formed during a dry period of blowing sediment. Either way, indicating a dry period is by default pointing to a period of water in the area. (JPLnews) The data collected will continue to be studied.

Is it Water?

It is a fact that water has previously flowed on Mars and that frozen water exists in the polar caps, beneath the regolith, and chemically bound to the regolith. The major issue is; does liquid water exist on Mars now for any period of time? Some scientists have looked at the evidence and come to the position that Mars is now dry and liquid water does not exist on the surface. The evidence against liquid water on Mars comes in various forms. A percentage of scientists are diligently working to prove the evidence set forth regarding liquid water on Mars currently, is not water at all. This is the way science is performed. Scientists need to thoroughly look at every aspect of a scenario to attempt to disprove a theory only to try to prove it is a fact. The major evidence supporting liquid water on Mars currently are the RSLs. However, some evidence suggests this may not be water at all but consists of sand flows. The explanations given are: the RSLs do not exist on any crater wall with less than a 27o gradient downslope and the MRO has not detected a signature for H2O at the RSLs in question. (JPL) The Knudsen pump effect explains that the amount of water present in the Martian atmosphere and beneath the surface of Mars in the area of RSLs is not sufficient for RSLs to be liquid water. The mechanism thereby would be gases pushing the sand up due to heating from the Sun and the particles then fall down the slope of the crater. (Nature3) The MRO has taken measurements and the results indicate a lack of H2O in the area of the RSLs has been detected by the spectrometers onboard. (arXiv) Colin Dundas and his team at the U.S. Geological Survey’s Astrogeology’s Science Center in Flagstaff, Arizona created models of the RSLs, after studying over 150 of the phenomena, out of the thousands that have been discovered. Dundas’ models indicated that the RSLs are more consistent with sand flowing down the side of a slope than liquid water. (JPL) The aforementioned information appears to prove water is not in liquid form on the surface of Mars today. However, these data do not explain all of the aspects of the RSLs. These features fade quickly, which would be more consistent with water. The RSLs grow over a period of time gradually and appear during the warmer season. Hydrated salts have also been detected in the areas of RSL appearance. Hydrated salts can form as, though a miniscule amount has been detected, water vapor does exist in the Martian atmosphere, and the salts absorb H2O from the atmosphere. This process may be creating salty water droplets. The amount of water absorbed into the salt molecules would be small, but enough to cause the seasonal flows we see on the slopes of Mars. Over 50 areas have been identified thus far to include RSLs. The location of the RSLs that have been identified stretch from the equator to approximately 45o N and S. Astrobiology The implications for finding liquid water on Mars cannot be stated strongly enough. Through the years astronomers have stated in various iterations the number one reason we study astronomy is to find out if we are alone in the universe. Water is an essential ingredient to life as we know it. Steve Squyres, has stated many times NASA’s mission was to follow the water to try to build up evidence of finding a habitable environment on Mars. Each mission has discovered that Mars has water in some form. Dr. John Grotzinger, project scientist for the Curiosity mission, when speaking about the discovery of an ancient freshwater riverbed in Gale Crater, went so far as to state, “We have found a habitable environment. The water that was here was so benign and supportive of life that if a human had been on the planet back then, they could drink it." (NASArsl) If liquid water exists on Mars today, extant life could exist. Our studies on Earth of extreme organisms show that anywhere liquid water exists, we find life. Extermophiles in the Atacama Desert can lie dormant for many years until a small amount of moisture encounters them. Suddenly they wake up and reproduce and return to dormancy. (PNAS2) Extreme organisms, called halophiles, have been studied on Earth which can also tolerate salty environments, including perchlorates. (PubMed) This model can be used analogously to RSLs and small damp areas on Mars.

Conclusion

Water on Mars has been well established for decades. Every few months, NASA will release a statement ‘confirming’ water on Mars, due to the evidence collected from Martian spacecraft and Earth-based spectroscopy. Water can remain in liquid form on the surface of the Red Planet for short periods of time when mixed with perchlorates and other salts. When Christian Huygens looked through his telescope at Mars, he saw what he interpreted as definitive evidence of the polar ice caps. Many astronomers tried to disagree and state another explanation. This is how the history of finding water on Mars has proceeded since that time. Science is in the business of disproving to prove. In the 1990’s Michael Carr wrote a book called Water on Mars, and in it stated that a water table must exist on Mars and to reach it, one should look about one-half of a kilometer underground. If this is true, then water could break through the sides of craters and flow down the sides, bringing with it salts and minerals to be left behind and imaged by spacecraft. Another fact that leads science to conclude liquid water exists on Mars is the age of the volcanoes on Mars. Many of the volcanoes were active 4 x 108 years ago. This is about ten percent of the age of Mars. Geologically the volcanoes are young, thus heat still exists beneath the crust of Mars. If Mars is hot on the inside and cold on the outside, the temperature in the middle would be suitable for liquid water to exist and move toward the surface. As we have seen briny water remains liquid at temperatures below freezing. The Curiosity Rover has imaged damp regolith on the surface of the Red Planet, this is sitting water mixed with the molecules in the dirt and causing dampness to occur. “Since the 1990’s debunkers have said liquid CO2 or rivers of sand were the cause of the channels on Mars. People are trying to come up with theories and ignoring the most obvious, these channels were created by transient water on the surface of Mars.” (Zubrin)

References

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