What did the Mariner reconnaissance spacecraft survey in the late 1990s?

The Mariner reconnaissance spacecraft, specifically Mariner 9, conducted a detailed survey of Mars in the late 1960s and early 1970s, providing the first comprehensive images of the planet's surface. While this spacecraft operated earlier than the late 1990s, it was crucial in the exploration of Mars, paving the way for future missions. The focus on Mars encompassed studying its geology, topography, and atmosphere, vastly increasing our understanding of the planet. This commitment to Mars exploration is the reason why Mars is the correct answer.

The other options refer to missions that involved different spacecraft and occurred in various timeframes. Venus and Jupiter have their respective missions, such as the Magellan spacecraft for Venus or the Galileo spacecraft for Jupiter, but they do not pertain to the Mariner program. Saturn, too, was explored by different missions, such as the Cassini spacecraft, which studied the planet in the more recent past. Hence, the Mariner spacecraft's dedicated mission to Mars is a significant milestone in the history of planetary exploration.