Directed Panspermia suggests that the seeds of life may have been purposely spread by an advanced extraterrestrial civilization, or can be spread from Earth to other planets by humans.

Ballistic panspermia, sometimes referred to as interplanetary panspermia, is a version of the panspermia hypothesis in which it is argued that impact-expelled rocks from a planet's surface serve as transfer vehicles for spreading biological material from one planet to another within the same solar system. It requires that the microorganisms survive (1) the impact ejection process from the planet of origin; (2) traveling through the solar system; (3) landing on a planet within the same solar system.

Lithopanspermia, sometimes referred to as interstellar panspermia, is a version of the panspermia hypothesis in which it is argued that impact-expelled rocks from a planet's surface serve as transfer vehicles for spreading biological material from one solar system to another. It requires that the microorganisms survive (1) the impact ejection process from the planet of origin; (2) travelling through space; (3) landing on a planet in another solar system.

The late Nobel prize winner Professor Francis Crick, OM FRS, along with British chemist Leslie Orgel proposed the theory of directed panspermia in 1973. A co-discoverer of the double helical structure of the DNA molecule, Crick found it impossible that the complexity of DNA could have evolved naturally.

Crick posed that small grains containing DNA, or the building blocks of life, could be loaded on a brace of rockets and fired randomly in all directions. Crick and Orgel estimated that a payload of one metric ton could contain 10¹⁷ micro-organisms organized in ten or a hundred separate samples. This would be the best, most cost effective strategy for seeding life on a compatible planet at some time in the future.

The strategy of directed panspermia may have already been pursued by an advanced civilization facing catastrophic annihilation, or hoping to terraform planets for later colonization.

During the 1830s Swedish chemist Jöns Jacob Berzelius confirmed that carbon compounds were found in certain meteorites "fallen from the heavens". Berzelius' finding contributed to theories propounded by later thinkers including the physician H.E. Richter and physicist Lord Kelvin (William Thomson) (1824–1907). Lord Kelvin declared in 1871, "[W]e must regard it as probable in the highest degree that there are countless seed-bearing meteoric stones moving about through space. If at the present instance no life existed upon this earth, one such stone falling upon it might, by what we blindly call natural causes, lead to its becoming covered with vegetation."

But it was the Swedish chemist and 1903 Nobel Prize winner, Svante Arrhenius, who popularized the concept of life originating from space in 1908. His theory was based on the notion that radiation pressure from the Sun and other stars "blew" microbes about like tiny solar sails, and not as the result of finding carbon compounds in stony meteorites.

During the 1830s Swedish chemist Jöns Jacob Berzelius (1779-1848) confirmed that carbon compounds were found in certain meteorites "fallen from the heavens". Berzelius' finding contributed to theories propounded by later thinkers including the physician H.E. Richter and physicist Lord Kelvin (William Thomson) (1824–1907). Lord Kelvin declared in 1871, "[W]e must regard it as probable in the highest degree that there are countless seed-bearing meteoric stones moving about through space. If at the present instance no life existed upon this earth, one such stone falling upon it might, by what we blindly call natural causes, lead to its becoming covered with vegetation."

But it was the Swedish chemist and 1903 Nobel Prize winner, Svante Arrhenius, who popularized the concept of life originating from space in 1908. His theory was based on the notion that radiation pressure from the Sun and other stars "blew" microbes about like tiny solar sails, and not as the result of finding carbon compounds in stony meteorites.

Directed panspermia from Earth to new solar systems has been proposed to expand life in the Universe. For example, microbial payloads launched by solar sails at speeds up to 0.0001 c (30,000 m/s) would reach targets at 10 to 100 light-years in 0.1 million to 1 million years. Fleets of microbial capsules can be aimed at clusters of new stars in star-forming clouds where they may land on planets, or captured by asteroids and comets and later delivered to planets. Payloads may contain extremophiles for diverse environments and cyanobacteria similar to early microorganisms. Hardy multicellular organisms (rotifer cysts) may be included to induce higher evolution. (Mautner, M. N. (1997), "Directed panspermia. 3. Strategies and motivation for seeding star-forming clouds", J. British Interplanetary Soc.)

There is a chance that humans, at some point in our space explorations, may unintentionally transport microorganisms on manned craft or unmanned probes to other other planetary bodies. Contamination such as this distorting data is a concern among space researchers seeking to find extraterrestrial life. Even the best sterilization techniques can not guarantee that organic materials will not be unintentionally spread.

Deliberate directed panspermia by humans would seed planetary bodies, securing the of future life. This intentional action would need to be balanced against interference with the quest to find extraterrestrial life. This interference can be minimized by targeting remote solar systems where life would not have evolved yet. Seeding a few hundred young solar systems would secure future life while leaving billions of stars pristine for exploration.

With the discovery of meteorites on Earth which almost certainly came from the Moon and Mars, it has become relevant to ask a logical question: Can life forms and/or chemical precursors of life be transported thus across the far reaches of the solar system? Can one planet infect another ballistically? An analysis by M.K. Wallis and N.C. Wickramasinghe is rather warm towards this idea:

"The mass of escaping ejecta from the presumed 10-km comet that caused the 180-km Chicxulub crater, with a radius of roughly 10 km and 1 m deep, amounted to ~300 Mm3, of which one third may have been rock and 10% higher-speed ejecta that could have transited directly to Mars. It may have taken 10 Ma to impact Mars but...the probability is not exceedingly low but 0.1-1%.

"The survival and replication of microorganisms once they are released at destination would depend on the local conditions that prevail. Although viability on the present-day Martian surface is problematical, Earth-to-Mars transfers of life were feasible during an earlier 'wet' phase of the planet, prior to 3.5 [billion years] ago. The Martian atmosphere was also denser at that epoch, with several bars of CO2, thus serving to decelerate meteorites, as on the present-day Earth. Since the reverse transfer can occur in a similar manner, early life evolution of the two planets may well have been linked." (Wallis, Max K., and Wickramasinghe, N.C.; "Role of Major Terrestrial Cratering Events in Dispersing Life in the Solar System," Earth and Planetary Science Letters, 130:69, 1995)

Exchange of material between the Earth and Mars may have been common during the first 800 million years of the Solar System's existence, that is, between 4.6 and 3.8 billion years ago, when major impacts with asteroids and comets were frequent. If simple organisms arose on either world during this time – and there is tentative evidence of terrestrial microbial life dating back 3.85 billion years – they may have been transferred inside ejected rocks to the neighboring planet and formed a colony on arrival. There are even plausible reasons to suspect that life may have evolved first on Mars and then, via ballistic panspermia, spread to the Earth. Or, there may have been a regular cross-fertilization of microorganisms between the two worlds. Conceivably, Venus, too, may have been involved in the transference of life when its surface conditions were more clement than they are today. One consequence of the possibility of such cross-fertilization is that if life, or evidence of past life, were found on Mars, it would not immediately imply independent biological evolution.

Some researchers believe that proof of ballistic panspermia has already been found:

• A meteorite originating from Mars known as ALH84001 was shown in 1996 to contain microscopic structures resembling small terrestrial nanobacteria. When the discovery was announced, many immediately conjectured that the fossils were the first true evidence of extraterrestrial life — making headlines around the world, and even prompting United States President Bill Clinton to make a formal televised announcement to mark the event. However, most experts now agree that these are not a definite indication of life, but may instead be formed abiotically from organic molecules. It has not yet conclusively been shown how they formed and recent advances in nanobe research has made the find interesting again.

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."