Panspermia

Panspermia is a hypothesis in astrobiology that suggests that life exists throughout the Universe, distributed by space dust, meteoroids, asteroids, comets, planetoids, and also by spacecraft in the form of unintended contamination by microorganisms.

Overview

Panspermia proposes that life forms that can survive the effects of space, such as extremophiles, become trapped in debris that is 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. If met with ideal conditions on a new planet's surfaces, the organisms become active and the process of evolution begins. Panspermia is not meant to address how life began, but merely the method that may cause its distribution in the Universe.

Mechanisms

The mechanisms proposed for interstellar panspermia are radiation pressure and directed panspermia. The survival of microorganisms has been studied extensively in laboratories with the result that many different types can survive the harsh conditions of space.

History

The first known mention of the term was in the writings of the 5th century BC Greek philosopher Anaxagoras. In the 19th century it was again revived in modern form by several scientists, including Jöns Jacob Berzelius (1834), Kelvin (1871), and finally reaching the level of a detailed scientific hypothesis through the efforts of the Swedish chemist Svante Arrhenius (1903).

Criticism

Critics argue that the hypothesis of panspermia, while not disproven, is speculative. It only shifts the problem of the origin of life to another location or to another time, and it does not actually solve the problem.

See also

• Astrobiology
• Extraterrestrial life
• Drake equation
• Fermi paradox
• Rare Earth hypothesis