Frozen worlds with underground oceans could be the incubation machines for organic life. But how did life get here?

Panspermia is a theory that suggests life may have come to Earth from space. According to this theory, life may have started on another planet or in an extraterrestrial environment, and life forms may have been transported to Earth through meteors, comets, or other space objects. The word "panspermia" is derived from the Greek term "panspermia" (seeds of everything), and this term expresses the idea that life could spread everywhere like a universal seed.

The theory of panspermia started gaining more attention in the scientific world in the 19th century and was developed through connections with various scientific research on the possibility of life existing in space. The theory offers an alternative perspective to traditional explanations of how life began on Earth. While many scientists have proposed theories such as "chemical evolution" or "abiogenesis" regarding the origin of life, the panspermia theory argues that the first signs of life could have existed in space and were carried to Earth.

Simplified diagram of the panspermia hypothesis. (Credit:  Astrobiology)

Foundations of Panspermia

The foundations of the panspermia theory are based on the existence of three main stages: the Origin of Life, the Spread of Life, and the Evolution of Life. These stages describe the processes that follow one another in relation to life originating in space, being transported to Earth, and undergoing an evolutionary process. Each of these stages presents different scientific perspectives when discussing whether the panspermia theory is valid.

The Origin of Life

The Origin of Life concerns the first emergence of life. According to traditional biological theories, life arose on Earth through abiogenesis, that is, through chemical reactions from non-living matter. However, the panspermia theory argues that the origin of life might have started on another planet or in space before it came to Earth. In this stage, it is suggested that the "seeds" of life (microorganisms or organic compounds) might have originated elsewhere, such as on planets like Mars or moons like Europa, or even in space. The fundamental components of life—organic molecules like amino acids, nucleic acids—could exist in space and be transported through interplanetary environments to reach Earth.

The Spread of Life

The Spread of Life describes the process through which life formed in one location is transported to another planet or into space. This stage is one of the most important aspects of the panspermia theory. The transport of life from one planet to another can occur in various ways. In particular, meteorites, comets, and other space objects have the potential to carry microorganisms. Meteors or comets can contain organic molecules or microorganisms and travel through space. These objects can move through interplanetary space, carrying life forms from one planet to another. Life could, for example, be transferred from Mars to Earth or from another planet to Earth. This stage is studied through experiments and observations to explore whether the space environment is suitable for transporting life.

The Evolution of Life

The Evolution of Life describes how life develops and diversifies over time on the planet to which it was transported. If life was brought from space to Earth, this stage is important for explaining how life adapted to Earth's environment and how evolutionary processes took place. Evolutionary biology and genetics play a key role in understanding the evolutionary processes of life. Organisms can diversify over time through mutations and natural selection in their environment. The panspermia theory discusses how life may have evolved on different planets, how organisms transported from space adapted to the conditions on Earth, and how evolutionary processes unfolded here. This stage involves the basic laws of evolutionary biology and how natural selection operates.

Panspermia Research

Since the panspermia theory suggests that life may have come from space, research in this field focuses on the existence of life in space, the transportability of life, and the ability of microorganisms to survive in space environments. Studies investigating panspermia have been carried out through various hypotheses, observations, and experiments aimed at testing the validity of the theory.

Microorganisms' Ability to Survive in Space

• Early Space Experiments (1970s): In the 1970s, the first experiments were conducted to determine whether certain microorganisms could survive in space. Under NASA's Biological Experiments in Space (BES) program, microorganisms and bacterial spores were sent into space. These experiments observed that some microbes managed to survive in space. Specifically, it was found that bacteria of the Bacillus and Clostridium genera could survive in space for extended periods.
• ExoMars 2016 Experiment: The European Space Agency's ExoMars mission tested whether microorganisms could survive in conditions similar to the surface of Mars. The mission, launched in 2016, conducted a series of experiments observing conditions to expose microorganisms to simulate the Martian surface. These experiments aimed to investigate the ability of microorganisms to sustain life in space and space-like environments.

Research on Meteors and Comets

• Meteor Composition and Life Molecules: Meteors are considered potential carriers of organic compounds transported through interplanetary space. The composition of meteors may contain the essential building blocks for life. For example, in 1969, the Murchison meteorite fell in Australia and was found to contain amino acids and other organic molecules. These findings raised the possibility that the fundamental components of life could spread in space and be transported to Earth.
• Cometary Panspermia: Studies on the idea that comets could carry organic components to Earth also support the panspermia theory. The organic compounds found in comets might be the building blocks of life. In 2004, NASA's Stardust mission collected samples from Comet Wild 2, providing crucial data suggesting that comets could transport organic components essential for life.

Laboratory Experiments

• NASA’s "Bio-Signature" Experiments: In the early 2000s, NASA expanded its research in astrobiology to search for signs of life in space. Through various space missions, experiments have been conducted to test how microorganisms and organic molecules can survive in space environments. These experiments explore the survival potential of microorganisms under conditions similar to those on Mars or in outer space.
• Microorganisms' Response to Space Conditions (2007-2009): Between 2007 and 2009, the European Space Agency (ESA) conducted experiments with microorganisms that survived in space. These studies observed that microorganisms were resistant to ultraviolet radiation, vacuum conditions, and temperature fluctuations. These findings provided significant evidence for the transportability of life in space.

Organic Compounds from Space and the Transport of Life

• Organic Compounds and Space "Seeds": Space research shows that organic compounds (such as amino acids and nucleic acids) can be transported to Earth via meteorites and comets. In a 2019 study, it was suggested that within the Oort cloud, organic compounds could create a life-sustaining environment similar to Earth’s conditions. Such organic compounds are one of the fundamental components of the panspermia theory.

Physical Panspermia and Transportability

• Physical Transport Experiments: Physical panspermia is based on the idea that microorganisms are transported by space objects. One of the experiments conducted on this topic was NASA's research on organisms that can survive in space. In 2005, an experiment showed that certain microorganisms sent into space survived despite exposure to very low temperatures and radiation. These types of experiments support the notion that microorganisms could be resistant to space conditions and that panspermia could be a valid theory.

Data Supporting the Panspermia Theory

The panspermia theory suggests that life is transported from one planet to another, allowing for the possibility of life existing at different points in the universe. Various pieces of evidence supporting this theory are based on findings from astrobiology, planetary science, biology, and space research.

Organic Molecules on Meteorites and Asteroids

Space objects, particularly meteorites and asteroids, may contain organic components. Analyses of many meteorites have revealed the presence of fundamental building blocks of life, such as amino acids, sugars, bases, and nucleic acids. These organic molecules are thought to form the foundation of life. In 2004, NASA’s Stardust mission discovered the presence of organic compounds in a sample collected from a comet. These findings suggest that organic molecules can spread through space and be transported to other planets.

Microorganisms Surviving in Space

It has been discovered that some microorganisms are resilient to the conditions in space. For example, organisms such as Deinococcus radiodurans and certain Bacillus species can withstand extreme radiation, high vacuum conditions, and low temperatures. In 2007, the European Space Agency (ESA) conducted the FOTON-M3 mission, where some microorganisms sent to space survived in the space environment. These findings support the idea that microorganisms can survive in space and potentially be transported between planets.

Comets and Meteors

Comets and meteors may play a crucial role in transporting organic compounds in space. Comets are icy bodies containing water and organic molecules. The presence of life’s basic components within comets supports the panspermia theory. Furthermore, some scientists suggest that comets could have the potential to carry organic compounds and microorganisms to other planets.

Microorganisms Traveling and Surviving in Space

A 2019 experiment demonstrated that bacteria sent from Earth could survive in the space environment. In ESA’s EXPOSE-E experiment, Bacillus and Clostridium species survived for extended periods under space-like conditions. This finding is considered critical for supporting the idea that life can be transported in space.

Microorganisms' Ability to Be Transported at High Speeds

For life to be transported in space, microorganisms must travel at high speeds from one planet to another. Collisions in space (such as asteroids or meteors striking planets) could enable the transfer of materials between planets. Several studies have shown that meteorites or asteroids have the potential to carry materials from Earth into space. These collisions could facilitate the transport of life or organic molecules.

The Possibility of Life Beyond Earth

The panspermia theory argues that life may exist not only on Earth but also on other planets or moons. For example, there are hints of microscopic life on Mars. In 1996, NASA discovered microscopic structures in the ALH84001 meteorite from Mars. These structures have been interpreted as possible signs of life. Additionally, the presence of water vapor under the surface of moons like Europa (Jupiter’s moon) and Enceladus (Saturn’s moon) suggests that these places could be habitable.

Galactic Conditions and Interstellar Environment

In the interstellar medium, tiny particles may spread through space. In this environment, microorganisms or organic molecules could be transported. Furthermore, some astronomical observations support the presence of organic compounds in the intergalactic medium. This increases the likelihood of organic molecules being transported between planets.

Discoveries Outside the Solar System

The Hubble Space Telescope and other space observatories have detected planetary systems around distant stars. Some of these planets may have conditions similar to Earth’s and may offer clues about the possibility of life existing there. These findings provide additional data supporting the panspermia theory and increase the likelihood that life could spread across the universe.

Advanced Microbial Evolution Theories

Some theoretical studies on microbial evolution propose that the evolutionary processes of life could occur similarly not only on Earth but also on other planets. These theories advocate for the intergalactic spread of life and strengthen the panspermia theory.

Bennu Asteroid and the Panspermia Theory

The Bennu asteroid is a discovery directly related to the Panspermia theory because the asteroid contains organic compounds and water, which have the potential to carry the fundamental components of life. NASA's OSIRIS-REx mission discovered this asteroid in 2016 and conducted a mission to collect samples from it in 2020. The study of Bennu at the beginning of 2025 has led to some significant findings supporting the Panspermia theory.

• Presence of Organic Molecules: Analysis of Bennu's surface has detected amino acids and other organic compounds. These molecules are the building blocks of life. The Panspermia theory suggests that life could spread through the interplanetary transport of such organic compounds. The presence of these organic compounds in Bennu strengthens the idea that life could spread through space and be transported to different planets.
• Water and Water Components: Data from Bennu indicate the presence of water components on the asteroid. Water is a critical component for sustaining life. The Panspermia theory assumes that the origin of life is associated with water. The presence of water components in Bennu could be seen as evidence that life could be transported to other planets and that water-based life might exist elsewhere.
• Interplanetary Transportability: Asteroids and meteors are key mechanisms in the Panspermia theory. Collisions in space allow asteroids and meteors to exchange material and transport it to other planets. Bennu's organic components and water content suggest that such transport could enable the spread of life to different planets.
• Transport of Microorganisms: Asteroids like Bennu are thought to demonstrate enough resilience for microorganisms to survive in space and be transported from one planet to another. A study conducted in 2020 suggested that asteroids could host microorganisms. If these microorganisms can be carried by asteroids like Bennu, it would provide crucial support for the Panspermia theory.
• Bennu's Role in the Origin of Life: The fact that Bennu carries organic molecules and water means it could provide information about the origin of life. The Panspermia theory proposes that life could have arrived on Earth from another planet. This asteroid might have played a carrier role, transporting the components of life. Additionally, Bennu's evolutionary processes and cosmic environment could offer clues about how life could spread across space.