NASA / SCIENCE PHOTO LIBRARY NASA / SCIENCE PHOTO LIBRARY
Martian mineral sphere. Image from the Mars exploration rover Opportunity of an anomalous spherical ball found in a rock that has been named Robert E. The diameter of the ball is about four millimetres and it may be similar in composition to the haemetite (iron ore) balls found in the surrounding area and believed to be formed from water deposits.
Model release not required. Property release not required.