Mars Rovers

A Mars rover is a robotic vehicle sent to drive across the surface of Mars. Mars rovers have transformed our knowledge of the Red Planet over the last quarter of a century. They have found rivers and lakes that dried up billions of years ago, signs that Mars once had a thick atmosphere, and the first preserved organic chemicals (the building blocks of life) found on another world. The four NASA rovers that have driven on Mars have lasted far longer than planned: one was supposed to last 90 days and ran for 15 years.

  • NASA rovers on Mars4Sojourner, Spirit, Opportunity, Curiosity, Perseverance (5 with original)
  • First Mars roverSojournerJuly 1997, 11 kg, the size of a microwave
  • Longest-lived roverOpportunityOperated for 15 years (planned: 90 days)
  • Currently activeCuriosity, PerseverancePlus the small helicopter Ingenuity
  • Total drive distanceOver 50 kmAcross all rovers combined
  • Time radio signal takesapprox. 4 to 22 minutesOne way between Earth and Mars

Why send rovers to Mars?

Mars is the most Earth-like planet in our Solar System. It has a day almost the same length as Earth's, polar ice caps, seasons and weather. But it is also a freezing-cold desert with a thin atmosphere of mostly carbon dioxide and no surface liquid water. Astronomers want to know two big things: was Mars ever like Earth? And could life have lived (or maybe even still live) there?

You cannot answer those questions from orbit; you need to be on the ground, picking up rocks, looking at layers of sediment, drilling into the surface and chemically analysing what you find. That is what Mars rovers do.

Sojourner (1997): the first Mars rover

The first rover on Mars was Sojourner, which arrived in July 1997 as part of NASA's Pathfinder mission. Sojourner was tiny by modern standards (just 11 kg and about the size of a microwave) and was meant to last 7 days. It ran for 83 days and travelled about 100 metres around its landing site, returning thousands of pictures and chemistry readings from a dozen Martian rocks.

Spirit and Opportunity (2004): the twin rovers

NASA followed up Sojourner with two identical larger rovers, Spirit and Opportunity, which landed on opposite sides of Mars in January 2004. Each was the size of a small golf cart and was designed to operate for 90 Martian days (about 92 Earth days). Spirit ran for 6 years before getting stuck in soft sand. Opportunity ran for an astonishing 15 years before a 2018 global dust storm covered its solar panels and ended the mission. The two rovers together found extensive evidence that liquid water had once flowed across the surface of Mars billions of years ago.

Curiosity (2012): a roving laboratory

Curiosity landed in August 2012 inside Gale Crater. About the size of a small car (900 kg, 3 m long), Curiosity is a roving science laboratory packed with cameras, drills, spectrometers and even a laser that can vaporise rock 7 metres away to analyse the smoke. It is powered by a small radioactive heat source instead of solar panels, so it does not have to worry about dust storms.

Curiosity has found that Gale Crater used to contain a lake of liquid water with conditions friendly to life. It has drilled into Martian rocks and found organic molecules (the chemical building blocks of life). It is still operating in 2025, and is now climbing the slopes of a 5-km-high mountain (Mount Sharp) in the centre of Gale Crater.

Perseverance (2021): looking for fossils

Perseverance landed in February 2021 in Jezero Crater, an ancient lake bed with a river delta visible from orbit. About the same size as Curiosity, Perseverance carries upgraded instruments designed specifically to look for signs of past microbial life: tiny chemical or visual signatures that might be left by microbes that lived in Mars' lakes billions of years ago.

Perseverance is also collecting samples of Martian rock and storing them in carefully sealed metal tubes. A future joint NASA/ESA mission, called Mars Sample Return, hopes to pick up those tubes later this decade or in the 2030s and bring them back to Earth, where laboratories far more advanced than anything carried on a rover can study them in detail.

Fact Perseverance carried a tiny helicopter called Ingenuity tucked under its belly. Ingenuity made the first powered flight on another planet on 19 April 2021, hovering for 39 seconds in the thin Martian atmosphere. Ingenuity was meant to make 5 test flights but ended up making 72 flights over almost 3 years, scouting routes for Perseverance from the air. Ingenuity's mission ended in January 2024 when it damaged a rotor blade during landing.

How rovers cope with Mars

Driving on Mars is unusually slow. Radio signals take between 4 and 22 minutes to travel one way between Earth and Mars (depending on where each planet is in its orbit). That means rovers cannot be remote-controlled in real time: drivers on Earth plan a day's drive in advance, send the commands at the start of the Martian morning, and check back at the end of the Martian day to see what happened. Perseverance has driven up to 200 metres in a single Martian day; Spirit and Opportunity managed about half that.

Mars is also brutally cold: average -60 °C, dropping to -125 °C at the poles in winter. Rovers carry small heaters and are designed to survive freezing temperatures. They also have to cope with global dust storms, low gravity (38% of Earth's), and an atmosphere only 1% as dense as Earth's.

Did you know? Each Mars rover ever sent has cost a lot less than people often think: Curiosity cost about $2.5 billion (£2 billion) over its entire 10-year project, including all the science the team has done. For comparison, that is roughly the cost of a single new aircraft carrier, spread over a decade, and it has given us decades of science about a whole other planet.
Deeper dive: the search for life on Mars

The biggest question driving Mars exploration is whether life has ever existed on Mars. Today's rovers cannot give a definite yes or no, but they can build a strong case one way or the other.

Mars was once a much warmer, wetter planet. Around 3.5 to 4 billion years ago (during a period scientists call the Noachian), Mars had a thicker atmosphere, liquid water lakes and rivers, and probably a magnetic field that protected the surface from solar radiation. This is precisely the same period when life was just getting started on Earth. If life could begin on one of these planets, why not the other?

Curiosity has already shown that ancient Mars had all the basic conditions life needs: liquid water, organic molecules, the right elements (carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur) and energy sources. The next step is finding biosignatures: chemical or structural patterns that only living things produce. Perseverance is hunting for those right now in Jezero Crater, and the samples it caches will be analysed back on Earth, where much more sensitive tests are possible.

Even if Mars never had life, the question of why not is interesting. Mars and Earth started out as twins, but Mars lost its atmosphere when it lost its magnetic field; the solar wind stripped the gases away into space. Studying Mars helps us understand the conditions that make a planet habitable, and what could go wrong.

For other landmark missions see Voyager 1 and 2, the Hubble Space Telescope and the James Webb Space Telescope. For Mars itself, see planet Mars.