Evidence has accumulated that some bacteria and archaea are more resistant to extreme conditions than previously recognized, and may be able to survive for very long periods of time even in deep space. These extremophiles could possibly travel in a dormant state between environments suitable for ongoing life such as planetary surfaces.
- The exchange of matter in the form of meteorite impacts has existed and will exist within solar systems. Some argue that anomalies resembling bacterial life found within Martian meteorite ALH 84001 indicate that bacteria can travel from planet to planet without intelligent help.
- In 1995, researchers at California Polytechnic State University reported reviving Bacillus bacteria spores from the gut of a bee stuck in amber. The bee was estimated to be 25 million to 30 million years old.
- In October of 2000 scientists revived a 250 million-year-old unit of bacteria found buried 1,850 feet underground near Carlsbad, New Mexico.
- In the 1960s it was reported that live bacteria more than 500 million years old were discovered in salt. The report was dismissed as impossible at the time but is being seriously considered now.
- On May, 2001, two researchers from the University of Naples claimed to have found live extraterrestrial bacteria inside a meteorite. Geologist Bruno D'Argenio and molecular biologist Giuseppe Geraci claim the bacteria were wedged inside the crystal structure of minerals, but were resurrected when a sample of the rock was placed in a culture medium. They believe that the bacteria were not terrestrial because they survived when the sample was sterilized at very high temperature and washed with alcohol. They also claim that the bacteria's DNA is unlike any on Earth. They presented a report on May 11, 2001, concluding that this is the first evidence of extraterrestrial life, documented in its genetic and morphological properties. Some of the bacteria they discovered were found inside meteorites that have been estimated to be over 4.5 billion years old, and were determined to be related to modern day Bacillus subtilis and Bacillus pumilus bacteria on Earth but appears to be a different strain.
Planets such as Earth and Mars are occasionally blasted by asteroids and comets large enough to hurl rock at speeds exceeding escape velocities. Minerals in rocks can shield microbes from shock and radiation (associated with impact craters) as well as hard radiation from the Sun as stony meteors move through space. The hardiest forms of life also have the ability to survive in a cold vacuum by going into stasis - reducing chemical interactions to zero while maintaining biological structure well enough to later thaw and multiply in more salubrious environments.
In a paper entitled "Lithopanspermia in Star Forming Clusters" published April 29, 2005, cosmologists Fred C. Adams of the University of Michigan Center for Theoretical Physics and David Spergel of the Department of Astrophysical Sciences of Princeton University consider the lithopanspermia hypothesis in star forming groups and clusters, where the chances of biological material spreading from one solar system to another is greatly enhanced due to the close proximity of the systems.
Suppose that life can be seeded into one solar system in a young cluster, either by direct biogenesis or through a chance encounter with bio-invested material from outside the birth aggregate. Subsequent dynamical interactions among the constituent solar systems can then allow life to spread throughout the birth cluster.
Adams and Spergel conclude that "...young star clusters provide an efficient means of transferring rocky material from solar system to solar system. If any system in the birth aggregate supports life, then many other systems in the cluster can capture life bearing rocks."