Final answer:
The Second Expedition to Mars was driven by a renewed focus on Martian exploration that began in the 1990s with smaller, cost-effective missions such as Pathfinder, which successfully landed and operated on Mars and demonstrated the planet's potential for further study.
Step-by-step explanation:
The Second Expedition to Mars was motivated by the desire to continue exploring and understanding the Martian environment despite previous mission failures. Following a period during which Mars had been unvisited, NASA initiated a new era of Martian exploration in the 1990s. The successful Pathfinder mission, which included the deployment of a solar-powered rover, marked a significant milestone, demonstrating that smaller and less costly spacecraft could accomplish meaningful science and exploration on Mars. This success was buoyed by the subsequent missions, such as the Mars Global Surveyor and the Mars Odyssey orbiter, which provided valuable data on the Martian surface and subsurface, including evidence of gullies potentially formed by surface water and signs of subsurface frozen water. These findings encouraged further exploration, and satellites such as the Mars Reconnaissance Orbiter and the Mars Atmosphere and Volatile EvolutioN (MAVEN) orbiter followed suit, continually enhancing our understanding of Mars. This steady stream of data and the promise of new discoveries provided the impetus for additional missions to brave the journey to Mars despite the mystery surrounding the fate of earlier expeditions.