How does a Mars lander find a safe spot to land?

When you hop off a step, you look for clear ground beneath your feet. A Mars lander needs a clear place to touch down, too. How does a Mars lander find a safe spot to land?

The search begins long before the lander reaches Mars. Scientists study pictures from spacecraft flying around the planet. Those pictures help them find broad, flat areas without lots of large rocks or steep slopes.

From those pictures, scientists make a map, a picture showing where things are. They mark safer ground and places the lander should avoid. That map helps them plan a landing where the lander can stand steadily.

Some newer landers can also check their position while coming down. Let's follow one with a camera, a tool that takes pictures. The camera looks down at the ground as the lander gets closer.

Engineers give this lander a computer, an electronic tool that follows instructions. They teach the computer to match camera pictures with the map. Matching the shapes tells the lander which part of Mars lies underneath.

Suppose the pictures show a big bowl-shaped hollow beside a smaller one. Can you guess how those shapes help? Finding the same pair on the map helps the computer work out where the lander is.

Next, the computer follows the engineers' instructions to choose safer ground marked on the map. It picks a spot the lander can still reach. A clear patch far away would not help during these last moments.

The lander makes that choice without waiting for someone on Earth to answer. Messages take several minutes to travel between Earth and Mars. The engineers prepare its instructions ahead of time because landing decisions cannot wait that long.

Choosing a spot is not enough: the lander must move toward it. Following the engineers' instructions, the computer guides the lander's rockets. Their pushes steer it toward the chosen patch of ground.

The rockets also slow the lander's fall so it can touch down gently. Its landing feet meet the ground at the end of the journey. All that careful choosing has helped it reach a steadier place to rest.

Map, camera, computer. A lander with these tools matches pictures to a map, chooses reachable safe ground, and steers there.

As you settle into your own cozy spot, you can picture a lander resting on Mars.