The team, Glen Cushing, Chris Okubo, Greg Vaughan, and Tim Titus were investigating ways to infer the material properties of the Entrada sandstone in the San Rafael Desert in southeast Utah.  Material properties would include things like the size of the grains of sand within the rock and its porosity (the amount of empty space between those sand grains). Using a thermal infrared camera, which measures light we cannot see, the team observed how sandstone heats up and cools off during the day and into the night. Knowing how quickly the rock heats and cools and making some assumptions about other rock properties, the team is then able to infer the porosity.

It’s easy to measure these things by touching them. You can feel the size of grains or determine porosity using tools. But when you can’t touch the surface of Mars or measure the pore space on an asteroid, it becomes important to be able to do this type of work from orbit or from far away. Inferring properties of something without touching it is called remote sensing and is a very important tool scientists use to learn a variety of things in the solar system – including the physical properties of a surface!

Sources/Usage: Public Domain. View Media Details

“We selected the Entrada Sandstone in Utah because it is a simple example of the types of rocks that we want to study on Mars and other planets,” said Dr. Chris Okubo. “The Entrada Sandstone is also studied by many other scientists investigating Earth-specific issues such as past environments, how water moves underground, and the ways that faults grow and cause earthquakes. Our team’s work can help to benefit these other separate but related investigations.”

It's important to be able to measure the porosity of rocks for a variety of reasons.

Did you know the strength or hardness of an asteroid depends on its porosity? A high porosity results in a softer rock, and a low porosity commonly result in a harder rock. Scientists want to know how strong an asteroid’s surface is because it can affect if and how we can land on an asteroid and explore it. NASA’s Near Earth Asteroid Rendezvous (NEAR) Shoemaker spacecraft landed on 433 EROS February 12, 2001, so we know 433 EROS was not a pile of loose rubble but one of a harder rock that NASA landed a car-sized spacecraft on.  

The strength would also affect options for altering an asteroid's orbit, which scientists would want to do if a dangerous asteroid were headed toward Earth. Although 433 EROS is not in the range to impact Earth, plenty others are, like Itokawa, which is a potentially dangerous asteroid should it impact Earth millions of years down the road. 

Knowing the porosity of a planetary surface could also be used to predict where resources such as water ice could be present on the Moon and asteroids. NASA’s ambitious Artemis program includes exploring the lunar south pole, by 2025, where astronauts will look for such resources in hopes of establishing a sustainable presence on the Moon and to take the next giant leap to Mars.  

Similarly, knowing the porosity of bedrock on Mars could be used to understand how groundwater flowed there in the past and where ancient underground habitable environments may have been located.

We’ve known about and used rocks since human’s early history to survive and assess the geology on other bodies. The difference is the degree of what we now know, what we can further discover, to advance the goals of the planetary science enterprise to the Moon and Mars.