🔗 Panspermia

🔗 Biology 🔗 Skepticism 🔗 Solar System

Panspermia (from Ancient Greek πᾶν (pan), meaning 'all', and σπέρμα (sperma), meaning 'seed') is the hypothesis that life exists throughout the Universe, distributed by space dust, meteoroids, asteroids, comets, planetoids, and also by spacecraft carrying unintended contamination by microorganisms. Distribution may have occurred spanning galaxies, and so may not be restricted to the limited scale of solar systems.

Panspermia hypotheses propose (for example) that microscopic life-forms that can survive the effects of space (such as extremophiles) can become trapped in debris ejected into space after collisions between planets and small Solar System bodies that harbor life. Some organisms may travel dormant for an extended amount of time before colliding randomly with other planets or intermingling with protoplanetary disks. Under certain ideal impact circumstances (into a body of water, for example), and ideal conditions on a new planet's surfaces, it is possible that the surviving organisms could become active and begin to colonize their new environment. At least one report finds that endospores from a type of Bacillus bacteria found in Morocco can survive being heated to 420 °C (788 °F), making the argument for Panspermia even stronger. Panspermia studies concentrate not on how life began, but on methods that may distribute it in the Universe.

Pseudo-panspermia (sometimes called "soft panspermia" or "molecular panspermia") argues that the pre-biotic organic building-blocks of life originated in space, became incorporated in the solar nebula from which planets condensed, and were further—and continuously—distributed to planetary surfaces where life then emerged (abiogenesis). From the early 1970s, it started to become evident that interstellar dust included a large component of organic molecules. Interstellar molecules are formed by chemical reactions within very sparse interstellar or circumstellar clouds of dust and gas. The dust plays a critical role in shielding the molecules from the ionizing effect of ultraviolet radiation emitted by stars.

The chemistry leading to life may have begun shortly after the Big Bang, 13.8 billion years ago, during a habitable epoch when the Universe was only 10 to 17 million years old. Though the presence of life is confirmed only on the Earth, some scientists think that extraterrestrial life is not only plausible, but probable or inevitable. Probes and instruments have started examining other planets and moons in the Solar System and in other planetary systems for evidence of having once supported simple life, and projects such as SETI attempt to detect radio transmissions from possible extraterrestrial civilizations.