Lithopanspermia

Lithopanspermia is a hypothesis about the interplanetary transfer of life via rocks ejected from a planetary body by impacts. In this view, rocks reaching another world can shield microorganisms during space transit, allowing them to survive long enough to seed life upon landing. It is a rock-based mechanism within the broader idea of panspermia.

The proposed process involves several stages. First, a planetary surface is bombarded by a large impact, ejecting rocks at velocities sufficient to escape the body's gravity. During transit through space, organisms inside the rock may be shielded from radiation and extreme temperatures by the rock’s interior and, in some cases, by ice or other insulating materials. If the rocks later collide with another planet or moon and release viable organisms into a suitable environment, life could potentially establish there. Transit times could range from thousands to millions of years, depending on orbital dynamics and fragments involved.

Evidence and challenges surround lithopanspermia. Experiments have shown that certain microorganisms and spores can survive exposure to space-like conditions for limited periods, and some meteorites carry organic compounds. However, there is no direct evidence that life has been transferred between planets. Calculations of transfer rates and survival probabilities remain uncertain, and critical steps—ejection, long-term survival, atmospheric entry, and successful colonization—pose substantial challenges.

The hypothesis informs astrobiology and planetary protection, influencing how scientists think about life’s distribution in the Solar System and the implications for life-detection missions and future sample-return endeavors.