Explanation: What if a rock that looked like a jelly donut suddenly appeared on Mars? That's just what happened in front of the robotic Opportunity rover currently exploring the red planet. The unexpectedly placed rock, pictured above , was imaged recently by Opportunity after not appearing in other images taken as recently as twelve Martian days ( sols ) before. Given the intriguing mystery, the leading explanation is somewhat tame -- the rock was recently scattered by one of the rover's tires. Even so, the rock's unusual light tones surrounding a red interior created interest in its composition -- as well as causing it to be nicknamed Jelly Donut . A subsequent chemical analysis showed the rock has twice the abundance of manganese than any other rock yet examined -- an unexpected clue that doesn't yet fit into humanity's understanding of the Martian geologic history. Opportunity , just passing its 10th anniversary on Mars , continues to explore the Murray Ridge section of the rim of 22-kilometer wide Endeavor Crater .