Mars is the most studied planet in our solar system by dedicated landers and surveyors that have visited it since the 1970s. Although Mars is just half the size of the Earth, it has enough similarities to make it appealing for human exploration, including a solid surface, reasonable temperatures, a similar rotation period, 23.9 hours, and an orbit around the Sun that is almost two years, 687 Earth days. Its differences, however, are enough to make the dream of moving to Mars impossible unless we develop the right technology and the planet has the necessary elements to support a civilization like ours.
What elements are on its surface? How is the terrain?, and Where can we find water? are some of the questions scientists want to answer. The Mars Global Surveyor of NASA[1], operating from 1996 to 2006, the NASA Mars Odyssey[2], launched in 2001, and the Mars Express[3], developed by the European Space Agency (ESA) and starting work in 2003, are three missions that have been or are currently studying the planet. These Mars orbiters continuously survey the surface of the red planet, sending spectacular images that answer many questions about our neighbor.
Images taken by the Mars Global Surveyor reveal that Planum Boreum, the Martian north pole, is covered in layers and layers of fine dust and water ice several kilometers thick[1]. It has a permanent ice cap fixture approximately 1,000 kilometers (621 miles) across, that during the summer months, is mainly water ice, but during winter, it grows by almost two meters when about 30 percent of the carbon dioxide in the planet’s atmosphere freezes and falls down the polar caps[4].
Credit: ESA
Images derived from data taken by the Shallow Radar (SHARAD), one of six instruments on NASA’s Mars Reconnaissance Orbiter, revealed the subsurface geology in this region, allowing scientists to reconstruct the climate over the past few million years and the formation process of the spiral troughs.
The images of Chasma Boreale, the prominent dark feature that seems to cut this region in two, reveal an internal ice structure approximately 2 kilometers (1.2 miles) thick and 250 kilometers (155 miles) across, where the white lines show the reflection of the radar signal back to the spacecraft[5]. This information can be used to understand how the ice sheets evolved as each new layer was deposited.
The ice with a spiral-like shape in the Martian north pole is most likely the result of the strong winds that blow from the elevated center towards its lower edges by the same Coriolis force that causes hurricanes to spiral on Earth, shaping the ice cap over time. A higher resolution image taken by ESA’s Mars Express shows the spiral structure and the Chasma Boreale, the 310 miles long feature that is thought to be a relatively old feature formed before the ice–dust spiral features and is seemingly growing in depth as new ice deposits built up around it.
ESA’s Mars Express reveals a top view of dust layers, water-ice, and frost covering a region beyond the Planum Boreum[6]. A subtle wrinkling indicates where layers of material are starting to build up next to starkly cliffs of several kilometers in diameter, covered in frost and ice walls.
Credit: ESA/DLR/FU Berlin
Caption: In this color image, we can have a better idea of the topographic view of the region. The lowest altitude regions are blue/green, while the highest are red/white/brown.
Beyond the poles, Mars now appears to be an arid world; however, the planet’s surface is rich with signs that water was once abundant[7]. The images taken by the surveyors reveal what appear to be dried-up river channels, ancient ocean and lake beds, and water-carved valleys, so where has all this water gone?
As we will see, there is enough observational evidence that the water ice is underground; however, one mission landed on Mars and took a sample of this vital element. The NASA Phoenix Mars lander confirmed this on July 31, 2008, when it collected a soil sample containing water ice from a trench just two inches deep after touching down in the polar region[8].
The temperatures near the equator are not cold enough for exposed water ice to be stable, so if it is exposed at the surface, it will evaporate and escape the atmosphere; so here, the water is way down the surface. A study of the equatorial region called Medusae Fossae Formation (MFF) by the Mars Express, reveals massive deposits of this vital element underground, up to 1.6 miles deep[9].
Credit: ESA
The initial observations from ESA Mars Express showed the MFF to be relatively transparent to radar and low in density. These two characteristics could be due to features that are giant accumulations of windblown dust, volcanic ash, or sediment but also could indicate icy deposits[5]. More recent data reveals that ice-free materials cannot explain what scientists observe, suggesting instead layers of dust and ice 2.3 miles thick, all topped by a protective layer of dry dust or ash several hundred meters thick.
From these findings, the Mars Express team concludes that if the ice has melted and locked up in the MFF, it means that the entire planet is covered in a layer of water 5 to 8.9 feet deep, the most water ever found in this part of Mars, and enough to fill Earth’s Red Sea.
Credit: ESA
On the other side of the planet, the ESA Roscosmos ExoMars Trace Gas Orbiter studied the heart of the Mars’ canyon system called Valles Marineris. The spacecraft looks for water hidden beneath the surface with the Fine Resolution Epithermal Neutron Detector (FREND), which uses measurements of epithermal neutron flux to map the hydrogen – a measure of water content – in the uppermost meter of Mars’ soil.
Credit: ESA/Alexey Malakhov
Caption: ExoMars Trace Gas Orbiter maps water-rich region of Valles Marineris
Using FREND, the science team came to the conclusion that there is a central part of Valles Marineris packed full of water – far more water than expected — very much like Earth’s permafrost regions, where water ice permanently persists under dry soil because of the constant low temperatures.
Credit: NASA/JPL-Caltech/PSI
An independent test of the mapping results comes from observations taken by the High-Resolution Imaging Science Experiment (HiRISE), a camera aboard NASA’s Mars Reconnaissance Orbiter. HiRISE observed the locations of ice-exposing meteoroid impacts and showed the likely distribution of water ice buried within the upper 3 feet of the planet’s surface. Most craters are no more than 33 feet in diameter; however, a large crater, 492 feet wide, revealed a motherlode of ice hiding beneath the surface.
Scientists can use mapping data like this to decide where the first astronauts on Mars should land and find this vital resource for the first people to set foot on Mars. They need to find regions where astronauts can find water ice to convert into drinking water and to use as an ingredient for rocket fuel. These, however, have to be far from the Martian poles where, although there is plenty of ice, the temperatures are too cold for astronauts (or robots) to survive for long[10].
Credit: NASA/JPL-Caltech/ASU Caption: This map shows underground water ice on Mars. Cool colors represent less than one foot below the surface; warm colors are over two feet deep. Black zones on the map represent areas where a landing spacecraft would sink into fine dust. The outlined box represents the ideal region to send astronauts for them to be able to dig up water ice.
The map was created by combining data from multiple NASA orbiters, including the Mars Reconnaissance Orbiter and its Mars Climate Sounder instrument; Mars Odyssey and its Thermal Emission Imaging System; and the Mars Global Surveyor.
If you want to learn more facts about Mars, visit the NASA page [https://science.nasa.gov/mars/facts/#hds-sidebar-nav-5]
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