During the last thirty years, our knowledge of Mars has been revolutionized by spacecraft missions and by studying Martian meteorites found on Earth. Some of the most intruiging discoveries have been that liquid water, and perhaps even life, were possibly present once on Mars' surface. The study of water on Mars - its availability for life, its role in the weather and climate, and its usefulness as a resource for future human exploration - is the crucial issue in the future of Mars exploration, and is a central focus of NASA's Mars Surveyor Program missions.

As the current lander mission in the Mars Surveyor Program, the Mars Polar Lander will focus primarily on Mars' climate and water. Its scientific instruments include the Mars Volatiles and Climate Surveyor (MVACS) package, the Light Detection and Ranging instrument (LIDAR), and the Mars Descent Imager (MARDI). The LIDAR and MARDI will study the atmosphere and geology near the landing site, while the MVACS package will study water and carbon dioxide at the landing site. These pages outline a history of Mars exploration, our present understanding of the roles of water and carbon dioxide, and how the Mars Polar Lander will add to our understanding.

• The Quest to Understand Mars - a brief history of telescopic and spacecraft exploration
• Volatiles: Substances Subject to Change - what are volatiles?
• Climate: A Brief Look at the Martian Almanac -seasonal and climatic cycles
• The Search for Water in All its Forms - how MVACS will study water
• Carbon Dioxide: The Air of Mars - how MVACS will study carbon dioxide
• An Expedition to the South Pole - why the South Pole?
• Science with MVACS - putting it all together