Is there Water on Mars?

Mars does have water, but it exists in markedly different forms and quantities than what we are familiar with on Earth.  The topic of water on Mars is particularly exciting because water is essential for life as we know it, and the presence of water is an important factor for any potential future human missions to the planet.

Current Forms of Water on Mars

• Polar Ice Caps:  Mars has two polar ice caps made up of layers of water ice and dry ice (frozen carbon dioxide).  These ice caps expand and contract with Mars’ changing seasons.  The water content in these caps would be substantial if spread over the planet’s surface, equivalent to a global water layer about 21 meters (69 feet) deep.

• Subsurface Ice:  There is evidence to suggest that significant deposits of water ice exist just below the Martian surface.  Instruments aboard the Mars Reconnaissance Orbiter have detected these subsurface ice deposits at higher latitudes.  They can be several meters deep and cover broad areas.

• Permafrost:  Mars has a layer of permafrost that extends from the poles to about 60 degrees latitude in both hemispheres.  This soil contains a considerable amount of water in frozen form.

• Water Vapor:  Although Mars has a very thin atmosphere, it does contain some water vapor.  The amount of water vapor varies depending on the time of day, geographical location, and altitude.

• Transient Liquid Water:  There is ongoing debate about the existence of transient flows of liquid water on Mars’ surface.  These are known as Recurring Slope Lineae (RSL).  Observations from orbiting spacecraft have shown dark streaks that appear to flow downhill in warm seasons and fade away in cooler seasons.  Some researchers interpret these as evidence of salty liquid water flows, although alternative explanations, such as dry flows of dust and sand, have also been proposed.

Past Presence of Water

Mars has geological features that strongly suggest a much wetter past:

• River Valleys:  The surface of Mars is covered with features resembling dried river valleys, which suggests that liquid water once flowed on the Martian surface.

• Lake Beds:  Some features, like Gale Crater, where the Curiosity rover has been exploring, appear to have once been lakes filled with liquid water.

• Potential Oceans:  There are hypotheses, backed by some geological evidence, that Mars may have once had an ocean covering a significant portion of its northern hemisphere.

Challenges and Constraints

• Atmospheric Pressure:  Mars’ thin atmosphere makes it impossible for liquid water to exist for extended periods on the surface; it would either freeze or evaporate quickly.

• Temperature:  Mars is much colder than Earth, with average temperatures around -80 degrees Fahrenheit (-62 degrees Celsius).  Such cold temperatures make it difficult for water to exist in a liquid state.

• Salinity and Acidity:  If liquid water does exist, it’s likely to be extremely salty or acidic, making it unsuitable for Earth-like life forms.

Implications

• Life:  The presence of water in any form increases the possibility that Mars could have supported life in the past, or might even contain microbial life now in some subsurface refuges.

• Human Exploration:  Water is a critical resource for human explorers, as it can be used for drinking, agriculture, and producing oxygen and fuel.

• Scientific Understanding:  Understanding the water cycle on Mars can offer insights into its climate history, geological activity, and the potential habitability of other celestial bodies.

Check out our 3D Mars Learning Center for more information on Mars.   You can also learn more at: NASA Mars Exploration.