Subsurface Liquid Water Lies Hidden Beneath Martian Poles
By Judith E Braffman-Miller
Out of all the mysterious and fascinating worlds inhabiting the bewitching Wonderland that is our Solar System, the Red Planet Mars has managed to sing the most haunting of all sirens’ songs to humanity. This small, rocky, rust-colored planet is our Earth’s near neighbor in space, as well as the world that has tantalized the imaginations of those among us who seek to answer the profound question of whether or not we are alone in the Cosmos. Nevertheless, despite its allure, Mars has not revealed itself to be inhabited, and Earth remains the only world that is actually known to host life. Of course, this does not mean that life isn’t out there somewhere in space–it only means that we have not as yet found it, and it apparently has not as yet found us. In July 2018, a team of astronomers announced that they have found evidence that deep beneath the frigid, frozen ice cap of the Martian south pole lies a hidden lake of liquid water–the first to be discovered pooling on the Red Planet. Life as we know it depends on the existence of liquid water.
The new discovery is based on data derived from the European Mars Express spacecraft’s radar instrument named Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS). The Italian Space Agency (ASI) led the development of the MARSIS radar. NASA contributed about 50% of the instrument, with management of the U.S. part led by the agency’s Jet Propulsion Laborator (JPL) in Pasadena, California.
The research paper, authored by the Italian MARSIS team, explains how a “bright spot” was discovered in radar signals approximately a mile beneath the surface of the ice cap in the Planum Australe region. This powerful radar reflection was determined by the study’s authors to be liquid water. This interpretation is important because where liquid water exists, life as we know it may also exist. The presence of liquid water indicates the possibility–though by no means the promise–of the presence of alien life on Mars.
“The bright spot seen in the MARSIS data is an unusual feature and extremely intriguing. It definitely warrants further study. Additional lines of evidence should be pursued to test the interpretation,” Dr. Jim Green commented in a July 25, 2018 JPL Press Release. Dr. Green is NASA’s chief scientist.
“We hope to use other instruments to study it further in the future,” Dr. Green added.
One of those new instruments will land on Mars late in 2018. The instrument, NASA’s InSight lander will carry a heat probe that is designed to burrow down into the Martian surface as far as 15 feet. InSight was built by the German Aerospace Center (DLR), and it is scheduled to provide important new data concerning how much heat manages to escape from the Red Planet and where the liquid water could possibly pool near its surface.
“Follow the Water” has long been one of the holy grails of NASA’s Mars program. The search for liquid water is currently the inspiration behind NASA’s exploration into the outer regions of our Solar System, where watery ocean-moon-worlds have the potential to host delicate life forms. Even dwarf planets, such as Ceres, the largest denizen of the Main Asteroid Belt between Mars and Jupiter, may help scientists gain a new understanding of how water is stored in rocky “buckets” that carry water across our Solar System.
A Hidden Lake
The hidden Martian lake is probably extremely cold and very salty. This makes it an improbable abode for life. However, the discovery, reported for the first time on July 25, 2018, in the online edition of the journal Science, is certain to bring new hope to those scientists who seek the presence of life on distant worlds. The search for other buried, hidden layers of water on Mars has now intensified, and the search is on for other bodies of water on Mars that might be more hospitable to delicate living creatures. “It’s a very exciting result: the first indication of a briny aquifer on Mars,” commented Dr. David Stillman in a July 25, 2018 Science Magazine Press Release. Dr. Stillman is a geophysicist at the Southwest Research Institute in Boulder, Colorado, who was not part of the study.
The team of scientists think that the lake is similar to one of the interconnected pools situated several miles under the ice sheets of Antarctica and Greenland, according to Dr. Martin Siegert in the same Press Release. Dr. Siegert is a geophysicist at Imperial College London (U.K.), who leads a consortium planning to drill into Lake Ellsworth under the ice of West Antarctica. However, the geophysical processes that created a deep lake on Mars are probably different. “It will open up a very interesting area of science on Mars,” Dr. Siegert added.
Planetary scientists generally think that water gushed across the surface of the Red Planet billions of years ago, when it possessed a warmer and thicker atmosphere. This water is believed to have carved gullies and channels that are still visible on Mars today. However, now low atmospheric pressures indicate that any surface water would boil away. In contrast, water manages to survive frozen in polar ice caps, as well as in subsurface ice deposits. Some of these ice deposits have been mapped by MARSIS.
On our own planet, microorganisms have been found swimming in the subglacial lakes of Antarctica. These hearty little microorganisms have managed to survive in isolation from the external Antarctica for as long as 35 million years–or even longer. This is because a large number of the 400 subglacial lakes that have been detected so far seem to be hydraulically tied to one another. Therefore, planetary scientists think that it is reasonable to conclude that microorganisms may swim around nearly everywhere beneath the Antarctic ice. Organisms, such as these, inhabiting regions generally considered to be inhospitable, are termed extremophiles. Extremophiles may be found on distant worlds dwelling in environments that seem to be hostile to life.
The discovery of tiny tidbits of life swimming around in the subglacial lakes of Mars would have profound significance for humanity. This is because it would be the first life to be discovered on a world other than Earth. In addition, discovery of these living tidbits would contribute to our scientific understanding of the prevalence of life in our Solar System. Ice-covered oceans are thought to slosh around beneath the frozen shells of Jupiter’s moons Europa and Ganymede, as well as Saturn’s moons Titan and Enceladus. In addition, Triton of Neptune, and several other bodies inhabiting our Solar System’s outer limits, hauntingly whisper some tantalizing hints of subsurface liquid water seas. On our own planet, wherever we find liquid water, we also find life. This indicates that the discovery of geologically persistent liquid water on so many distant planetary bodies raises the fascinating possibility that aquatic life-forms may be abundant throughout our Solar System.
The great Italian astronomer Galileo Galilei (1564-1642) made the first telescopic observation of Mars in 1610, using his primitive little “spyglass”, which was one of the first telescopes to be used for astronomical purposes. During that same century, other astronomers also observed the polar ice caps on Mars, using the tiny telescopes of that era. These early astronomers were nonetheless able to determine the Martian rotation period, as well as its axial tilt. These observations were mostly made when Mars was at its closest approach to Earth. Improved telescopes developed in the 19th century helped astronomers map permanent albedo features, and a crude map of the Red Planet was published in 1840. This very first map of Mars was followed by a series of increasingly improved maps from 1877 on.
The imaginative tale of “little green men” inhabiting Mars began when astronomers mistakenly believed they had observed the spectroscopic signature of water in its atmosphere. This captivating notion of Martian life became popular with astronomers and the general public alike, and it became especially popular when the American astronomer Perceval Lowell (1855-1916) thought that he had observed a network of artificial canals carved by intelligent beings on the Martian surface. However, these linear features were ultimately found to be mere optical illusions.
Also during the 1920s, astronomers were able to determine that the atmosphere of this rusty-red world harbors only tiny amounts of oxygen and water. Astronomers of that era also successfully found that the surface temperature of the Red Planet ranged from a truly frigid -121 degrees Fahrenheit to a comfortable 45 degrees Fahrenheit.
Two decades later, in 1947, the Dutch-American astronomer Gerard Kuiper (1905-1973) demonstrated that the thin atmosphere of Mars is composed primarily of carbon dioxide that added up to approximately double the quantity found in our own planet’s atmosphere.
Mars is the fourth planet from our Sun, and like the other solid inner planets–Mercury, Venus, and Earth–it basks in the brilliant sunlight streaming out from our Star. It is famous for its reddish hue that is caused by an abundance of iron sulfide coating its surface. In addition, the surface of Mars is scarred by a large number of impact craters that look very similar to those observed on Earth’s Moon.
Mars has a rotational period and changing seasons like our own planet. However, unlike our Earth’s large Moon (the largest moon in our Sun’s inner kingdom), Mars is orbited by a strange and intriguing duo of small potato-shaped moons. The Martian moons, dubbed Phobos and Deimos, are generally thought to be asteroids that escaped from the Main Asteroid Belt, only to be snared by the irresistible gravity of the Red Planet.
For the past two decades, cameras in orbit around Mars have sent back to Earth numerous revealing images. These images show that Mars sports a surface that is dotted with tiny valleys that have been formed into slopes that bear an eerie resemblance in their shape to gullies that resulted from gushing floods of liquid water on our own planet. The Martian gullies are thought to be relatively young geological features that are less than a few million years old–and some may even be more youthful than that. A few million years isn’t a very long time on geological time scales. These more recent observations give planetary scientists precious clues that great quantities of life-sustaining liquid water may still be lingering on Mars, and that this water may have been responsible for carving the surface gullies.
Even though the surface of the Red Planet isn’t particularly life-friendly today, there is sufficient evidence suggesting that very long ago its climate may have been such that water in its liquid phase pooled on its surface.
Martian Polar Ice Caps
Mars sports two permanent polar ice caps that are composed primarily of water ice. Frozen carbon dioxide builds up as a comparatively thin layer during a pole’s Martian winter. During that frigid season the poles are enshrouded in heavy blankets of relentless and continuous darkness. The extremely cold Martian winters freeze its surface, and cause the deposition of 25-30% of the atmosphere to freeze into slabs of carbon dioxide ice (dry ice). When the poles are again swept by warm sunlight during the spring and summer, the frozen carbon dioxide sublimates. These seasonal alterations transport great quantities of water vapor and dust. This results in Earth-like frost, as well as large cirrus clouds. Clouds composed of water-ice were imaged by NASA’s Martian rover Opportunity in 2004.
Both Martian poles display layered features, that are termed polar-layered deposits. These deposits are caused by seasonal melting and deposition of ice together with dust from the roaring Martian dust storms that sweep over the surface of the planet. Precious information concerning the past climate of Mars may eventually be revealed in these layers, that have been preserved in a kind of deep freeze since ancient times. This has been compared to the way that tree ring patterns and ice core data reveal climate changes over the passage of years on Earth. Both of the Martian polar caps also show grooved features that were likely caused by winds. The grooves are also influenced by the quantity of dust–in other words, the more dust there is, the darker the surface. This means that the darker the surface, the more frequent the melting. Dark surfaces absorb more light. However, there are other theories that have been proposed to explain the large Martian grooves.
The south polar ice cap of Mars sports large pits, troughs and flat mesas that give it a “Swiss cheese appearance.” In contast, the north polar ice cap displays a flat surface with smaller pits than those found at the south polar ice cap–giving the north polar ice cap the appearance of “cottage cheese”, rather than “Swiss cheese.”
Hidden Liquid Water Under Ice
The radar information obtained by MARSIS provides strong evidence that there is a pond of liquid water buried beneath layers of ice and dust in the south polar region of the Red Planet. Indeed, new evidence that Mars had an ancient watery past is scattered all over its surface in the form of enormous dried-out river valley networks and vast outflow channels. These tattle-tale features have been clearly imaged by the spacecraft. Orbiters, along with landers and rovers, have been exploring the Martian surface for years, discovering minerals that can only form in the presence of liquid water.
The Martian climate has changed significantly over the course of our 4.56 billion-year-old Solar System’s history. Liquid water cannot exist on the Red Planet’s surface today, so astronomers are on the hunt for subsurface water. Scientists have long suspected that liquid water is present buried beneath the Martian polar ice caps. This is because it is well known, based on studies of our own planet, that the melting point of water decreases under the pressure of an overlying glacier.
The potential existence of water in its liquid phase on Mars (which may have provided a habitable environment for delicate forms of life) was first predicted by Dr. Stephen Clifford back in 1987. Dr. Clifford’s theory was published in a paper titled Polar Basal Melting on Mars that appeared in the Journal of Geophysical Research on August 10, 1987. Dr. Clifford is a senior scientist at the Planetary Science Institute (PSI) in Tucson, Arizona.
In reference to the recent findings of ESA’s Mars Express, published in the June 25, 2018 issue of the journal Science, Dr. Clifford noted: “I believe that the evidence the paper’s authors have presented for the presence of liquid water at the base of the south polar layered deposits, at this location, is highly persuasive. It’s a finding that should be closely examined by the rest of the radar community to be sure we can rule out other alternative explanations–something I think the authors have already made an excellent effort of doing.”
Whatever the extent of polar basal melting on Mars today, it was almost certainly much greater in the past, added Dr. Clifford in a July 27, 2018 PSI Press Release. Geological evidence indicates that the south polar layered deposits blanketed a region that was approximately twice as large 2 billion years ago than it is today. This means that there was much more ice around to melt. The geothermal heat flux of Mars–which is caused by the decay of naturally occurring radioactive elements in the crust–is also thought to have been as much as three times greater during that ancient time. This would have reduced the necessary thickness of polar ice for basal melting.
Dr. Clifford continued to comment:
“The work I did 30 years ago was basically a theoretical exercise that considered what we then knew about the extensive network of subglacial lakes and channels that exist at the base of the Antarctic and Greenland ice sheets and examined its potential relevance to the Martian polar caps. It is certainly gratifying that the MARSIS radar team has now found evidence that demonstrates that this early theoretical work has some connection to reality.”
Judith E. Braffman-Miller is a writer and astronomer whose articles have been published since 1981 in various magazines, journals, and newspapers. Although she has written on a variety of topics, she particularly loves writing about astronomy because it gives her the opportunity to communicate to others some of the many wonders of her field. Her first book, “Wisps, Ashes, and Smoke,” will be published soon.
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