Not only did this elicit a great deal of sympathy, the injury also led to one of Spirit"s greatest discoveries. As the rover limped along, her broken wheel dug a trench in the Martian soil revealing almost pure silica. On Earth, this kind of silica usually exists in hot springs or hot steam vents, a home for a rich diversity of microbial life. Now, thanks to Spirit, scientists think that could be a possibility on Mars as well.