An Unusual Two-Toned Rock on Mars

Explanation: How did this unusual Martian rock form? The atypical two-toned rock, visible in the lower right of the above image , was photographed a few days ago by the robotic Spirit rover currently rolling across Mars . For now, the environmental processes that created the rock remain a matter of speculation . Finding unusual rocks is not unusual for Spirit or its twin rover Opportunity , however. Over the past two years, for example, the rovers have unexpectedly discovered very small gray pebbles dubbed blueberries , and a rock out in the middle of nowhere now thought to be a meteorite . Having investigated alien terrain and having found clear evidence that part of Mars had a wet past , the Earth-launched Martian rovers are now entering their third spectacular year exploring the red planet.