Steve squyres, lead researcher of the Opportunity project team, said: "These objects look fragile on the outside, but soft in the middle. Their density, structure and composition are different, and their distribution is different. Therefore, we are faced with a very interesting geological mystery. " One theory is that the magma ejected from the volcano formed these spheres, not under the action of water. In "Mars Blueberries", scientists found a large number of hematite, indicating that they were formed in the process of groundwater passing through porous rocks. Water flow can lead to a series of chemical reactions, which can turn iron ore into pellets. However, this theory cannot explain why blueberries are smaller.

Scientists at the University of Hawaii pointed out in a research paper published in the journal Planetary and Space Science that meteorite impact is a more convincing explanation, which can explain the shape and composition of "Mars blueberry". In an interview with Joseph bennington Castro of National Geographic magazine, Anupam Misra, the research leader, said: "None of the physical characteristics of these spheres fit the solidification model, but meteorite theory can explain all their characteristics." The research papers of scientists from the University of Hawaii focus on the consistency of these Martian hematite ores. The vast majority of "Mars blueberries" are about 0. 16 inch (about 4 mm) in diameter, usually less than 0.24 inch (about 6.2 mm). Professor Misra pointed out that the size difference of "Mars Blueberries" can be explained by meteorite impact. The researchers found that a meteorite with a diameter of 1.6 inch (about 4 cm) can produce 1000 small balls with a diameter of 0. 16 inch (about 4 mm), which are distributed in a wide area.

However, these theories are also controversial. Some scientists point out that this theory fails to mention some key factors. Timothy Gloege, a geophysicist at the State University of New York at Stony Brook, told National Geographic: "Although some objects melt when passing through the atmosphere of Mars, these spheres are not formed in some high temperature events." Gloege pointed out that Opportunity's analysis of "Mars Blueberries" showed that these balls were formed in the process of low temperature.