Mars Pathfinder
Pathfinder’s view of Sojourner. Credit: NASA

Mars Pathfinder

30/06/2022Written by Catherine Muller

Celebrating Mars Pathfinder - 25 years since the spacecraft delivered a lander and rover to study the Red Planet.

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On 4 July 1997 Mars Pathfinder bounced onto the Red Planet. The pioneering spacecraft delivered both an instrumented lander and a robotic rover to study the Martian surface in greater detail than ever before. 25 years on, we take a closer look at Pathfinder and its incredible discoveries.

About Pathfinder

About Pathfinder
Composite self-portrait of Pathfinder. Credit: NASA

Launched on 4 December 1996, Pathfinder was the first mission to touch down on the Martian surface in over 20 years. Officially renamed the Carl Sagan Memorial Station upon arrival, the lander made its home on Ares Vallis, a rocky flood plain in the northern hemisphere of Mars.  

Deployed from the lander was Sojourner, the first roving vehicle on another planet. Named after Sojourner Truth, an American civil rights crusader, the rover cruised with a maximum speed of one centimetre per second. Sojourner was the size of a small microwave (65cm by 48cm by 30cm) and weighed approximately 10kg. Despite scientists only planning for Sojourner to be active for a week, it spent 83 days exploring Mars and returning data to Earth. 

Objectives and Experiments

Objectives and Experiments
Engineers testing Pathfinder’s airbags in 1995. Credit: NASA

Developed and constructed in under three years, with a total cost of $256 million, Pathfinder was the second mission in the Discovery Program – NASA’s programme with the aim of producing of low-cost, science-oriented missions to test new technology and unlock the mysteries of our Solar System. Pathfinder was used to demonstrate new airbag technology – as the spacecraft entered the Martian atmosphere it was slowed by a parachute until finally, as it approached the surface, a giant system of airbags inflated, protecting the lander from impact. 

Pathfinder was equipped with the following instruments: 

  • Imager for Mars Pathfinder (IMP) – colour cameras, used to capture images of the lander’s surroundings. 
  • Atmospheric Structure Instrument/Meteorology Package (ASI/MET) – studied Mars’ atmosphere as the spacecraft descended to the surface. 
  • Alpha Proton X-ray Spectrometer – used to determine the composition of soil and rock samples. 

Scientific Findings

Scientific Findings
Sojourner studying the surface of the rock “Yogi”. Credit: NASA

Over the course of its 85 days on the Martian surface, Mars Pathfinder sent back 2.3 billion bits of information. This included 550 images from Sojourner and 16,500 images from the lander. Making use of this, as well as the analysis of 15 rock and soil samples, Pathfinder’s main discoveries included: 

  • Measurement of the radius of Mars’s metallic core using radio tracking.  
  • Identification of round stones around the lander, suggesting that they were formed in running water and, therefore, that Mars may have had a much warmer, wetter past. 
  • Sensors spotted dust devils and water ice clouds in the lower atmosphere. 
  • Characterisation of airborne dust, suggesting it is made of maghemite, a magnetic form of iron oxide. 



Image of the “Twin Peaks” captured by Pathfinder. Credit: NASA

Mars Pathfinder was a resounding success. Both the lander and Sojourner surpassed their designed lifetimes, by three and 12 times respectively. Right until its final transmission on 27 September 1997, Pathfinder sent back ground-breaking data used by scientists to begin to piece together the story of Mars’ history. Inspiring scientists and the public alike, the accomplishments of Pathfinder and Sojourner paved the way for future missions to the Red Planet.

About the author: Catherine Muller is a Space Communications Presenter at the National Space Centre.