How do scientists measure water on Mars?

Question: I recently learned that water exists on Mars. How is water found and measured in such a dry, dusty place?

Image: NASA/JPL-Caltech/MSSS

Answer: Water on Mars isn’t as easily seen as in the oceans and rivers on Earth, but water is still there—in the soil. While Martian soils appear dry, water can be associated with different types of minerals, either attached to the surface of the mineral or used in its structure.

The Mars Science Laboratory rover named Curiosity is operating in the planet’s Gale Crater. It uses an onboard instrument called Sample Analysis on Mars (SAM) to evaluate the water in Martian sediments and small soil particles. SAM operates by heating sediment from 77 to 1535 degrees Fahrenheit (25 to 835 degrees Celsius) at a rate of 95 degrees F (35 degrees C) per minute. Water is released as the sample is heated, and that water flows from the oven chamber via tubing to an instrument called a mass spectrometer. A mass spectrometer measures the mass of particles, and from that information can determine what the particles are made of. In this case, it’s looking for water.

In this photograph from 2011, technicians and engineers inside a clean room at NASA’s Jet Propulsion Laboratory in California install the instrument SAM (yellow object) into the Mars rover, Curiosity. Photo: NASA/JPL-Caltech

SAM also keeps track of the temperatures at which water is released, and that information is combined with data from another piece of equipment, the Chemistry and Mineralogy (CheMin) instrument. The information from both instruments help researchers determine the type of material the water is associated with.

For example, phyllosilicates, a group of minerals that include materials like smectite, were detected on Mars. These minerals can contain water between their layers and in their structure. That water would be released upon heating in SAM, and CheMin would detect the presence of the phyllosilicate, giving scientists an idea of where and how the water was stored. As much as 3.0 weight percent (wt %) water was found in the sediment in Gale Crater, which means that for every 100 ounces of sediment, there are 3 ounces water.

This information helps researchers better understand the makeup of the soils on Mars and whether it is possible that life, which needs water, was ever present on the planet.

–Answered by Brad Sutter, Planetary Scientist at NASA

Have a question for Soils Matter? Post it as a comment below, or email us at

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s