# Liquids/Liquid objects/Mars

"Evidence of recent volcanic activity on Mars shows that eruptions could have taken place in the past 50,000 years."
"This may be the youngest volcanic deposit yet documented on Mars. If we were to compress Mars' geologic history into a single day, this would have occurred in the very last second."
"The volcanic eruption produced an 8-mile-wide, smooth, dark deposit surrounding a 20-mile-long volcanic fissure."
"When we first noticed this deposit, we knew it was something special. The deposit was unlike anything else found in the region, or indeed on all of Mars, and more closely resembled features created by older volcanic eruptions on the Moon and Mercury."
The "properties, composition and distribution of material match what would be expected for a pyroclastic eruption – an explosive eruption of magma driven by expanding gasses, not unlike the opening of a shaken can of soda."
"The majority of volcanism in the Elysium Planitia region and elsewhere on Mars consists of lava flowing across the surface, similar to recent eruptions in Iceland."
"This feature overlies the surrounding lava flows and appears to be a relatively fresh and thin deposit of ash and rock, representing a different style of eruption than previously identified pyroclastic features. This eruption could have spewed ash as high as 6 miles into Mars' atmosphere. It is possible that these sorts of deposits were more common but have been eroded or buried."
"The interaction of ascending magma and the icy substrate of this region could have provided favorable conditions for microbial life fairly recently and raises the possibility of extant life in this region."
"The ice melts to water, mixes with the magma and vaporizes, forcing a violent explosion of the mixture. When water mixes with magma, it's like pouring gasoline on a fire."
"The ages of the eruption and the impact are indistinguishable, which raises the possibility, however speculative, that the impact actually triggered the volcanic eruption."

## Surfaces

Liquid water on the surface of Mars cannot exist due to low atmospheric pressure, which is less than 1% of the atmospheric pressure on Earth, except at the lowest elevations for short periods. The two polar ice caps appear to be made largely of water. The volume of water ice in the south polar ice cap, if melted, would be sufficient to cover the planetary surface to a depth of 11 metres (36 ft). In November 2016, NASA reported finding a large amount of underground ice in the Utopia Planitia region. The volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior.
The Martian surface is primarily composed of tholeiitic basalt.

## Meteors

"Phoenix touched down on the Red Planet at 4:53 p.m. Pacific Time (7:53 p.m. Eastern Time), May 25, 2008, in an arctic region called Vastitas Borealis, at 68 degrees north latitude, 234 degrees east longitude."
"As the sun rises over Noctis Labyrinthus (the labyrinth of the night), bright clouds of water ice can be observed in and around the tributary canyons of this high plateau region of Mars. This color composite image, reconstructed through violet, green, and orange filters, vividly shows the distribution of clouds against the rust colored background of this Martian desert."

## Blues

The image at right shows "the eastern (west-facing) side of an impact crater in the mid-latitudes of the Northern hemisphere."
"Like many mid-latitude craters, this one has gullies along its walls that are composed of alcoves, channels, and debris aprons. The origins of these gullies have been the subject of much debate; they could have formed by flowing water, liquid carbon dioxide, or dry granular flows. The orientation of these gullies is of interest because many craters only contain gullies on certain walls, such as those that are pole-facing. This could be due to changes in orbital conditions and differences in solar heating along specific walls."
"Many of the other features observed in and around this crater however are indicative of an ice-rich terrain, which may lend credence to the water formation hypothesis, at least for the gullies visible here. The most notable of these features is the "scalloped" terrain in and around the crater. This type of terrain has been interpreted as a sign of surface caving, perhaps due to sublimation of underlying ice. (Sublimation is the process of a solid changing directly to a gas.)"
"Another sign of ice is the presence of parallel lineations and pitted material on the floor of the crater, similar to what is referred to as concentric crater fill. Parallel linear cracks are also observed along the crater wall over the gullies, which could be due to thermal contraction of ice-rich material."
"All of these features taken together are evidence for ice-rich material having been deposited in this region during different climatic conditions that has subsequently begun to melt and/or sublimate under current conditions. More recently, aeolian deposits have accumulated around the crater as evidenced by the parallel ridges dominating the landscape. Dust devil streaks are also visible crossing the aeolian ridges."
The second image at right shows layered rocks on the floor of McLaughlin Crater.
These "sedimentary rocks ... contain spectroscopic evidence for minerals formed through interaction with water. The High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter recorded the image."
"A combination of clues suggests this 1.4-mile-deep (2.2-kilometer-deep) crater once held a lake fed by groundwater. Part of the evidence is identification of clay and carbonate minerals within layers visible near the center of this image. The mineral identifications come from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), also on the Mars Reconnaissance Orbiter. The scene covers an area about one-third of a mile (about 550 meters) across, at 337.6 degrees east longitude, 21.9 degrees north latitude. North is up."

## Infrareds

At right is an image generated by detecting methane in the Martian atmosphere by carefully observing the planet throughout several Mars years with NASA's Infrared Telescope Facility and the W.M. Keck telescope, both at Mauna Kea, Hawaii. The methane "plumes were seen over areas that show evidence of ancient ground ice or flowing water. Plumes appeared over the Martian northern hemisphere regions such as east of Arabia Terra, the Nili Fossae region, and the south-east quadrant of Syrtis Major, an ancient volcano about 745 miles across."

## Astrognosy

"This artist's concept of the interior of Mars [on the right] shows a hot liquid core that is about one-half the radius of the planet. The core is mostly made of iron with some possible lighter elements such as sulfur. The mantle is the darker material between the core and the thin crust."
"Mars has not cooled to a completely solid iron core, rather its interior is made up of either a completely liquid iron core or a liquid outer core with a solid inner core."
"Earth has an outer liquid iron core and solid inner core. This may be the case for Mars as well."
"Mars is influenced by the gravitational pull of the Sun. This causes a solid body tide with a bulge toward and away from the Sun (similar in concept to the tides on Earth). However, for Mars this bulge is much smaller, less than 1 centimeter (0.4 inch). By measuring this bulge in the Mars gravity field we can determine how flexible Mars is. The size of the measured tide is large enough to indicate the core of Mars can not be solid iron but must be at least partially liquid."
"The tidal bulge is a very small but detectable force on the spacecraft. It causes a drift in the tilt of the spacecraft's orbit around Mars of one-thousandth of a degree over a month."
"The precession is the slow motion of the spin pole of Mars as it moves along a cone in space (similar to a spinning top). For Mars, it takes 170,000 years to complete one revolution. The precession rate indicates how much the mass of Mars is concentrated toward the center. A faster precession rate indicates a larger dense core, compared to a slower precession rate."
"Our results indicate the mass change for the southern carbon dioxide ice cap is 30 to 40 percent larger than the northern ice cap, which agrees well with the predictions of the global atmosphere models of Mars."
"The amount of total mass change depends on assumptions about the shape of the sublimated portion of the cap. The largest mass exchange occurs if we assume the cap change is uniform or flat over the entire cap, while the lowest mass exchange corresponds to a conically shaped cap change."

## Craters

Catenae on Mars, represent chains of collapse pits associated with grabens (see, for example, the Tithoniae Catenae near Tithonium Chasma).
"Near the lower left corner of this view [at right] is the three-petal lander platform that NASA's Mars Exploration Rover Spirit drove off in January 2004. The lander is still bright, but with a reddish color, probably due to accumulation of Martian dust."
"The High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter recorded this view on Jan. 29, 2012, providing the first image from orbit to show Spirit's lander platform in color. The view covers an area about 2,000 feet (about 600 meters) wide, dominated by Bonneveille Crater. North is up. A bright spot on the northern edge of Bonneville Crater is a remnant of Spirit's heat shield."
The shield volcano, Olympus Mons [shown in the second image at right] (Mount Olympus), at 27 km is the second highest known mountain in the Solar System. It is an extinct volcano in the vast upland region Tharsis, which contains several other large volcanoes. Olympus Mons is over three times the height of Mount Everest, which in comparison stands at just over 8.8 km.
Rampart craters are a specific type of Martian impact crater which are accompanied by distinctive fluidized ejecta features. A Martian rampart crater displays an ejecta with a low ridge along its edge. Usually, rampart craters show a lobate outer margin, as if material moved along the surface, rather than flying up and down in a ballistic trajectory. The flows sometimes are diverted around small obstacles, instead of falling on them. The ejecta look as if they move as a mudflow. Some of the shapes of rampart craters can be duplicated by shooting projectiles into mud. Although rampart craters can be found all over Mars, the smaller ones are only found in the high latitudes where ice is predicted to be close to the surface. It seems that the impact has to be powerful enough to penetrate to the level of the subsurface ice. Since ice is thought to be close to the surface in latitudes far from the equator, it does not take too strong of an impact to reach the ice level. So, based on images from the Viking program in the 1970s, it is generally accepted that rampart craters are evidence of ice or liquid water beneath the surface of Mars. The impact melts or boils the water in the subsurface producing a distinctive pattern of material surrounding the crater.
At the second left down is an image of a "newly formed impact crater, observed by HiRISE on Mars Reconnaissance Orbiter. The impact that formed the crater exposed the water ice beneath the surface. Some of the ice can be seen scattered at the adjascent area in the subimages. The blast zone (excavated dark material) is almost 800 meters (half a mile) across. The crater itself is just over 20 meters (66 feet) across".
"This crater is one of a special group that have excavated down to buried ice. This ice gets thrown out of the crater onto the surrounding terrain. Although buried ice is common over about half the Martian surface, we can only easily discover craters in dusty regions. The overlap between areas that both have buried ice and surface dust is unfortunately small. So even though we have discovered over 100 new impact craters we have only discovered 7 new craters that expose buried ice."
"When craters excavate this buried ice it tells us something about the extent and depth of buried ice on Mars (controlled by climate); this information is used by planetary scientists to figure out what the recent climate of Mars was like. It has also been a surprise that this ice is so clean. Scientists expected this buried ice to be a mixture of ice and dirt; instead this ice seems to have formed in pure lenses. Yet another surprise that Mars had in store for us!"
The ice (presumably water ice) is white in the image, but take note of the blue dust or regolith also exposed.
The third image at right is a subimage of the one at left. It is natural color and shows in better detail both the ice (white) and the blue material.
At third left is an image showing an impact crater on Planum Boreum, or the North Polar Cap, of Mars, as observed by HiRISE on Mars Reconnaissance Orbiter in natural color.
"Impact craters on the surface of Planum Boreum, popularly known as the north polar cap, are rare. This dearth of craters has lead scientists to suggest that these deposits may be geologically young (a few million years old), not having had much time to accumulate impact craters throughout their lifetime."
"It is also possible that impacts into ice do not retain their shape indefinitely, but instead that the ice relaxes (similar to glass in an old window), and the crater begins to disappear. This subimage shows an example of a rare, small crater ( approximately 115 meters, or 125 yards, in diameter). Scientists can count these shallow craters to attain an estimate of the age of the upper few meters of the Planum Boreum surface."
"The color in the enhanced-color example comes from the presence of dust and of ice of differing grain sizes. The blueish ice has a larger grain size than the ice that has collected in the crater. The reddish material is dust. The smooth area stretching to the upper right, away from the crater may be due to winds being channeled around the crater or to fine-grained ice and frost blowing out of the crater."
The fourth image at right shows a freshly formed impact crater that occurred on Mars between February 2005 and July 2005. Note the blue material expelled from the crater rock onto the nearby Martian landscape.

## Astroglaciology

The discoveries of water ice on the Moon, Mars and Europa add an extraterrestrial component to the field, as in "astroglaciology".
Extinct "Martian rivers indicate an ice-age climate for Mars coincident with the earth’s Pleistocene epoch, which further suggests the existence of extraterrestrial controls."
"This is the south polar cap of Mars [on the right] as it appeared to the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) on April 17, 2000. In winter and early spring, this entire scene would be covered by frost. In summer, the cap shrinks to its minimum size, as shown here. Even though it is summer, observations made by the Viking orbiters in the 1970s showed that the south polar cap remains cold enough that the polar frost (seen here as white) consists of carbon dioxide. Carbon dioxide freezes at temperatures around -125° C (-193° F). Mid-summer afternoon sunlight illuminates this scene from the upper left from about 11.2° above the horizon. Soon the cap will experience sunsets; by June 2000, this pole will be in autumn, and the area covered by frost will begin to grow. Winter will return to the south polar region in December 2000. The polar cap from left to right is about 420 km (260 mi) across."
"The western Utopia Planitia in the Northern mid-latitudes of Mars is marked by a peculiar type of depression with scalloped edges [on the left] and by a network of polygonal fractures."
"The scalloped depressions are typical features; a smooth layered terrain located between 40 and 60 degrees in both hemispheres. Scalloped depressions probably form by removal of ice-rich subsurface material by sublimation (ice transforming directly from a solid to a gaseous state), a process that may still be active today. Isolated scalloped depressions generally have a steep pole-facing scarp and a gentler equator-facing slope. This asymmetry is interpreted as being the result of difference in solar heating. Scalloped depressions may coalesce, leading to the formation of large areas of pitted terrain."
"The polygonal pattern of fractures resembles permafrost polygons that form in terrestrial polar and high alpine regions by seasonal-to-annual contraction of the permafrost (permanently frozen ground). On Earth, such polygons indicate the presence of ground ice."
"These landforms most likely show that sub-surface ice is present or has been present geologically recently at these latitudes, and they may slowly be continuing their development at the present time."

## Gaseous objects

"Four hydrogen (H$_2$) lines have been detected in a spectrum of Mars observed with the Far Ultraviolet Spectroscopic Explorer. ... The line intensities correspond to [an] H$_2$ abundance ... above 140 kilometers on Mars. ... Analysis of [deuterium] fractionation among a few reservoirs of ice, water vapor, and molecular hydrogen on Mars implies that a global ocean more than 30 meters deep was lost since the end of hydrodynamic escape. Only 4% of the initially accreted water remained on the planet at the end of hydrodynamic escape, and initially Mars could have had even more water (as a proportion of mass) than Earth."