Mars, often called the “Red Planet” due to its distinctive color, is a desert-like, rocky planet with a very thin atmosphere. Understanding the resources present on Mars, from its buried ice to the gases in its atmosphere and the minerals making up its surface, is important for scientific understanding and for considering future human presence. The planet’s unique geological history and current conditions have shaped the availability and forms of these various resources.
Water on Mars
Water on Mars exists predominantly as ice. Water ice is present in the polar ice caps, which also contain frozen carbon dioxide. The northern polar cap, for example, has a diameter of about 1000 km during Mars’s northern summer and holds approximately 1.6 million cubic kilometers of ice, enough to cover the cap with a 2 km thick layer. The southern polar cap has a diameter of 350 km and a thickness of 3 km.
Beyond the poles, substantial amounts of subsurface water ice have been detected at mid-latitudes, often just a few meters below the surface. Radar data from missions like the Mars Reconnaissance Orbiter and Mars Express have revealed extensive underground water-ice sheets, with some deposits as thick as 100 meters, typically covered by a layer of soil one to two meters thick. This shallow ground ice is present under approximately one-third of the Martian surface, particularly poleward of 60° latitude where ice concentrations can exceed 20%. Recent findings also suggest that significant water ice deposits, potentially several kilometers deep, exist buried beneath the planet’s equator in features like the Medusae Fossae Formation.
While liquid water is not stable on the Martian surface due to the thin atmosphere, small amounts of water vapor are present in the atmosphere. Water is also chemically bound within hydrated minerals found in the Martian regolith and rocks. These hydrated minerals, such as clays and sulfates, trap water within their crystalline structures. Estimates suggest that the volume of water stored in these hydrated minerals could be substantial, potentially equivalent to a global layer between 8 and 234 meters deep.
Gases in the Martian Atmosphere
The Martian atmosphere is considerably thinner and colder than Earth’s, with an average surface pressure that is less than one percent of Earth’s sea-level pressure. It is primarily composed of carbon dioxide, which makes up about 95% to 96% of its volume.
Other significant components include molecular nitrogen, accounting for about 2.7% to 3% of the atmosphere, and argon, present at around 1.6% to 2%. Trace amounts of other gases, such as oxygen (0.13% to 0.174%), carbon monoxide (0.0747% to 0.08%), and water vapor, are also present. The thinness of the atmosphere means that even with a high percentage of carbon dioxide, the greenhouse effect on Mars is weak, contributing only about 5°C of warming.
Seasonal changes on Mars affect the atmospheric pressure, as carbon dioxide gas freezes out of the atmosphere to form a layer of dry ice at the poles during winter. This process can cause the global atmospheric pressure to drop by 25% to 30%. The Martian atmosphere is also dusty, with particulates that give the sky a hazy, tawny, or reddish appearance.
Martian Surface Materials
The surface of Mars is primarily characterized by its regolith, which is a layer of finely broken-up rock fragments and dust that covers most of the planet. This regolith is rich in iron oxides, which are responsible for Mars’s distinctive reddish color through a process similar to rusting. The global dust cover and wind-blown sediments contribute to a remarkably uniform soil composition across the Martian surface.
The underlying rocks of Mars are largely basaltic, a type of igneous rock formed from rapidly cooled lava. While basalt is dominant, studies have also identified a diversity of igneous materials, including more evolved lavas like dacite and even granitic rocks in certain areas.
Various minerals have been identified on the Martian surface. These include mafic minerals such as olivine, pyroxene, and plagioclase feldspar, which are common in basaltic compositions. Magnetite is also present.
Hydrated minerals, specifically clays (phyllosilicates) and sulfates, are widespread and indicate past interaction with water. Sulfates like jarosite, kieserite, and gypsum have been detected. Silica has also been found. Sedimentary formations, including sandstone, are also widespread.