Mars Rovers: Robots Exploring the Red Planet

On Mars, robots have driven across dusty plains, drilled into bedrock and read the story written in layers of ancient rock.

Those rovers have ranged from a machine the size of a microwave oven to laboratories on wheels as big as a small car.

Here you will learn why scientists send rovers instead of just orbiters,

how they survive the plunge through the Martian atmosphere,

what it takes to drive on a planet many millions of kilometers away and what the rovers discovered along the way.

Why Send Robots to Mars?

Orbiting spacecraft can map an entire planet, but they cannot pick up a rock, drill into it or sniff its chemistry.

Rovers act as robotic field geologists.

They carry cameras, spectrometers, drills and small laboratories that let scientists study individual layers of rock and grains of soil up close.

Mars is an especially tempting target because it seems to have been much wetter billions of years ago.

Where there was liquid water, there may once have been conditions suitable for life.

The central goal of most rover missions has been to find evidence of that watery past and to judge whether ancient Mars could have supported microbes.

Surviving the Seven Minutes of Terror

Landing on Mars is notoriously hard.

A spacecraft slams into the thin atmosphere at around 20,000 kilometers per hour (12,000 miles per hour) and must slow to a gentle touchdown in about seven minutes.

Radio signals take several minutes to cross between the planets,

so by the time engineers on Earth learn that the landing has started, it is already over.

Everything must happen automatically, which is why engineers nicknamed it the seven minutes of terror.

The sequence goes roughly like this: a heat shield absorbs temperatures that can reach about 1,300 degrees Celsius (2,370 degrees Fahrenheit),

a supersonic parachute opens, and then rockets or other systems handle the final descent.

Different missions used different tricks for the last step:

• Airbags: The landers carrying the first three NASA rovers were wrapped in giant cushions and dropped, bouncing across the surface 15 to 28 times before rolling to a stop.
• Sky crane: The heavier Curiosity and Perseverance rovers were lowered on cables from a hovering rocket stage, which then flew away to crash at a safe distance.
• Smart navigation: Perseverance compared camera images with onboard maps as it descended, steering itself away from hazardous terrain.

Driving on Another Planet

Depending on where Earth and Mars are in their orbits, a radio signal takes anywhere from about 3 to 22 minutes to travel one way.

Joysticks are useless across that kind of delay.

Instead, teams on Earth study the latest images, plan a day's drive and experiments, and send the commands in a single batch.

Much of the data comes home through spacecraft orbiting Mars, which relay signals from the surface.

The rovers also make their own decisions.

Using stereo cameras, they build 3D maps of the ground ahead and pick safe routes around rocks and slopes.

Even so, they move slowly and carefully, with top speeds of only a few centimeters per second,

because getting stuck or damaging a wheel millions of kilometers from a mechanic can end a mission.

A Martian day, called a sol, lasts about 24 hours and 40 minutes.

During the first months of several missions, team members lived on Mars time, shifting their schedules later each day to keep pace with their rovers.

Meet the Rovers

Between 1997 and 2021, six rovers from two countries landed on Mars:

Spirit and Opportunity were designed for missions of about 90 sols. Spirit worked for more than six years,

and Opportunity kept going for about 14 years before a planet-wide dust storm in 2018 blocked the sunlight it needed.

What the Rovers Discovered

Clear Evidence of Ancient Water

Opportunity landed near layered rocks studded with tiny, BB-sized spheres rich in the mineral hematite, nicknamed blueberries.

Along with the rocks' chemistry and textures, they showed that liquid water had once soaked the area.

Years later, the rover found bright veins of gypsum, a mineral deposited by water flowing through cracks.

Spirit, on the opposite side of the planet, found soil almost pure in silica, a sign of hot springs or steam vents.

A Lake That Could Have Hosted Life

Curiosity landed in Gale Crater in 2012 and soon drove across rounded pebbles that had been tumbled by a flowing stream.

Drilling into a nearby mudstone,

it found that the crater once held a lake with water that was neither too acidic nor too salty,

containing the chemical ingredients that microbes on Earth use.

It was the first time a rover had confirmed an environment on Mars that could have supported life.

Curiosity later detected complex organic molecules preserved in ancient rocks and found that the small amount of methane in the air near the ground rose and fell with the seasons.

Neither finding proves life ever existed, but both gave scientists new questions to chase.

Rock Samples, a Helicopter and Oxygen

Perseverance landed in 2021 in Jezero Crater, the site of an ancient lake fed by a river delta.

It drilled and sealed rock cores in tubes,

setting some of them down on the surface in case a later mission could bring them to Earth for study.

It also carried Ingenuity, a small helicopter that made the first powered, controlled flight on another planet in April 2021,

and went on to fly 72 times over nearly three years.

Another experiment aboard Perseverance, called MOXIE, showed that oxygen could be produced from the carbon dioxide in the Martian air,

a technology that could one day help astronauts.

Power, Dust and Survival

Mars receives less than half the sunlight Earth does, and fine dust slowly coats solar panels.

Spirit and Opportunity survived longer than expected partly thanks to gusts of wind that occasionally swept their panels clean, boosting power overnight.

Curiosity and Perseverance avoided the problem by using nuclear power sources that turn heat from decaying plutonium into electricity, day or night, in any season.

Every rover also battles bitter cold, with nighttime temperatures that routinely plunge far below freezing.

Heaters, insulation and careful energy budgets are just as important as wheels and cameras.

The Takeaway

Mars rovers have turned the Red Planet from a distant red dot into a place with a readable history.

They proved that liquid water once flowed there,

that ancient lakes held the ingredients for life and that machines can land, drive and even fly on another world.

The next time Mars glows orange in your evening sky, remember the robots that have left their tracks across its dust.