Explore Rocks Using Core Sampling

Watch this video to learn about the three classes of Earth rocks – igneous, sedimentary, and metamorphic – and the three types of rocks found so far on the Moon: basalt and anorthosite, which are igneous rocks, and breccia, a type of sedimentary rock. We can tell what type of rock we're looking at, how it formed, and how old it is by studying its characteristics. These characteristics include the rock’s appearance (both inside and outside) and composition.

About the image: A Moon rock sample collected by the Apollo 14 mission. › Full image and caption

Scientists are still learning about the igneous, sedimentary, and metamorphic rocks on Mars. Sedimentary rocks can give us a glimpse into the history of Mars if we are able to analyze the layers and the materials inside the rock. Because humans haven’t yet been to Mars, we rely on robots, like Mars rovers, to explore and report back on their findings.

Scientists are especially interested in a type of sedimentary rock called a conglomerate. These rocks are made up of small pebbles of other rock types cemented together. Conglomerates are interesting to scientists because the rounding of the pebbles indicates that water once eroded, or ate away at, these rocks. And where there was once water, there might have once been life. (Scientific evidence indicates that life forms, if they existed on Mars in the past, would likely have been microscopic.)

NASA’s Perseverance rover is specially designed to investigate rocks like conglomerates as part of its mission to seek signs of ancient microbial life and collect rock and soil samples for possible return to Earth.

About the image: The image above, captured by NASA's Curiosity rover on Mars, shows an outcropping – an area where ancient bedrock underneath the surface is exposed. Outcroppings on Earth are known to form as a result of running water and create gravel that's a similar size and shape. By comparing this image of Mars to similar features on Earth, geologists have been able to theorize that Mars might have also once had running water. › Full image and caption

The Martian atmosphere has weathered the exterior of rocks on Mars for billions of years, erasing much of the information we might gather from simply looking at a picture of a rock. To gather more information from a given rock sample, we need to drill into the rocks and retrieve samples from inside. Scientists call this process core sampling.

A core sample is a long narrow piece of rock obtained by drilling into a rock with a special tool that lifts out an intact part of the rock. In-depth study of core samples requires a science lab full of equipment – something we don’t yet have on Mars. So, we must return these samples to Earth for study.

NASA’s Perseverance rover will be taking core samples of Mars rocks that could be brought to Earth someday and studied in more detail. Mars rock core samples will be stored in special caching tubes that Perseverance will leave on the surface for a future mission to collect and bring to Earth.

About the image: This image shows core samples collected from the Moon. › Full image and caption

1. Choose one color of play dough that will make up most of your rock and cement your other rock pieces together.
2. From the other colors of play dough, form pea-size and marble-size spheres of play dough to represent inclusions, or material trapped inside a rock during its formation.
3. If you have cake sprinkles, ground pepper or sand, mix some into one or more colors of play dough. Mix a lot into one or more small spheres of play dough until it becomes stiff and grainy, then form it into a cube – this will represent harder rocks.
4. Grab a chunk of your main color of play dough that will become the bottom of your rock. Flatten it onto the piece of paper. Add the spheres and cubes of other colors and chunks of the main color and press them all together to form a rock.
5. Cover your rock with the main color of play dough so it looks like the rock is one color. This represents the weathering that can oxidize, or change the surface by chemically reacting with oxygen, rock surfaces on Mars.

If possible, trade your rock with another person, so you can investigate one that is unknown! If you can't trade with anyone, find a family member who didn’t watch you make the rock and challenge them to do the next steps.

Cut a plastic straw into thirds or fourths or disassemble an old ballpoint pen and retain the straw-like cylinder.

Push an open end of the straw or cylinder straight down into the rock, all the way to the paper. Twist the straw or cylinder in place and lift out a sample.

This is a core sample of your rock. Use a toothpick, chopstick or short stick to push your core sample out of the cylinder for inspection.

Examine your core sample. Can you see inclusions or layers underneath the surface of the rock?

Use your core sample to investigate how the rock formed over time and how many different materials it’s made of.

Compare the size and roundness of any inclusions in your core sample. The larger an inclusion, the closer to its source it is. Smaller inclusions will have traveled farther, perhaps in moving water or in a landslide or other geologic event. Rounder inclusions indicate a more active body of water that smoothed them during tumbling.

Repeat steps 6 and 7 several times. Think about the best places to collect samples so that you can get as much information about your rock as possible.

• Video: Seeking Signs of Life in Ancient Martian Rocks
• Video: Mars 2020 Rover Sample Collection Animation