By The Great Courses Staff

After sending data from the red planet for 15 years, NASA’s Mars rover, Opportunity, has signed off for the last time. The exploratory robot captured over 200,000 images during its stay. The findings during its record-breaking mission added priceless new information to our knowledge of Mars.

The rover far exceeded expectations that it would only last 90 days on the red planet. It lasted over 5,000 Martian days and traveled over 28 miles. But without the capacity to send back physical samples from Earth’s neighbor, what did Opportunity do to further our studies? Also, how was the mission even possible?

New Findings Confirm Martian Water Theories

According to NASA’s Mars Exploration Program website, the rover Opportunity made several major discoveries since it landed on Mars with its twin, Spirit, in January 2004. On Mars, Opportunity—which earned the nickname “Oppy” from its team—encountered the mineral gypsum, which proved that underground water once flowed. Oppy found further evidence supporting this claim when it discovered clay minerals that usually form in pH-neutral water. These findings suggest that Mars once had an environment that could have supported life during the same time life on Earth began.

So where did the water go? The red planet’s thin atmosphere is likely to blame. “It’s important to understand that planets—the inner rocky planets in the solar system—when they formed, their interiors were very hot due to the process of formation,” said Dr. David M. Meyer, Professor of Physics and Astronomy at Northwestern University. “If you’ve got a bigger rocky planet, you can insulate that heat and keep it there longer, but Mars is a smaller planet. It led to more rapid cooling of its interior. As its interior cooled off, the volcanic activity slowed. Thus, there’d be less out-gassing of the carbon dioxide which helps keep the atmosphere thick. You put in less carbon dioxide and also, very importantly, you’d have lost the magnetic field.”

Without a magnetic field, Mars has no protection from solar winds, Dr. Meyer said. Charged particles from solar winds then stream down to Mars and strip its atmosphere. This chain reaction combines with the sun’s ultraviolet rays to break up water molecules into hydrogen and oxygen atoms and send the hydrogen off into space. No water means no life.

Persevering Rovers Make History

Oppy and Spirit entered the Martian atmosphere in a landing craft at “five times the speed of a rifle bullet,” Dr. Meyer said. Before it hits the surface, however, atmospheric friction reduces the speed of the lander by 90 percent. Then parachutes open in the lander and rockets fire to further slow it down. Airbags deploy and the rovers make a cushy landing before getting to work.

NASA said that Oppy traveled an exact total of 28.06 miles during its mission, setting the world record for the longest drive on another world. Oppy also made the first confirmed identification and characterization of rocks on another planet. It couldn’t have done all this without a great team and a bit of luck. According to NASA, Oppy’s wheels slipped multiple times while driving out of its landing site at Eagle Crater. A team of NASA employees once had to discover how to free the rover from a sand trap.

When Oppy finally lost power for good, a June 2018 dust storm was the cause—but it was expected to happen 14 years earlier. Oppy and Spirit were both solar-powered rovers, and frequent Martian storms potentially caused multiple operational problems for them. “As the dust built up on these solar panels, you begin to cut the amount of electricity they would receive,” Dr. Meyer said. “The dust would cover the solar panels and it would be hard to get power to them.” However, despite the thin air on Mars, wind kept the solar panels clean for far longer than their initial 90-day mission plan.

Opportunity and Spirit confirmed many scientific theories about life on Mars. They shattered records and exceeded expectations. Their contributions to the scientific community will live on in the more than 340,000 images they sent to us, and in future Mars rover expeditions.

Dr. David M. Meyer, Ph.D., contributed to this article.
Dr. Meyer is Professor of Physics and Astronomy at Northwestern University, where he is also Director of the Dearborn Observatory and Co-Director of the Center for Interdisciplinary Exploration and Research in Astrophysics.