panspermia

Panspermia is a hypothesis that life exists beyond Earth and can be distributed to planetary bodies, including Earth, by microscopic life forms or organic seeds carried by cosmic material such as meteoroids, comets, or dust. Several forms are distinguished: lithopanspermia, in which rocks ejected by impacts carry organisms to other planets; radiopanspermia, in which radiation pressure or solar wind could propel microbes; and interstellar or directed panspermia, which posits transfer over longer distances or by intentional seeding.

Current evidence does not confirm panspermia, and it remains one of several hypotheses about the origin and distribution of life. Indirect support includes the discovery of complex organic molecules in meteorites and DNA fragments; experiments show some microorganisms can survive extreme conditions for limited periods, including vacuum, radiation, and cold; however, the viability after the full journey through space and into a habitable environment is uncertain. The transfer efficiency between planets and star systems is thought to be low, and life would have to endure ejection, interplanetary transit, entry, and proliferation.

Historically, the idea was proposed by Svante Arrhenius in 1903 and has had occasional support and skepticism since. Modern discussions distinguish lithopanspermia as a physical transport mechanism from broader claims of life arriving from elsewhere in the galaxy or universe. Critics argue that while panspermia could explain the distribution of life’s building blocks, it does not solve the origin of the first biochemistry, and unresolved questions about survival and timing remain barriers to confirmation.