Tracing Extraterrestrial Life: Scientific Evidence, Space Exploration, and Clues from Artificial Intelligence

With the advancement of space probes, robotic explorers, radio telescopes, and data analysis technologies, the amount of accessible information about the universe has increased dramatically. The integration of artificial intelligence has further enabled rapid organization and identification of complex cosmic signals and chemical data. Despite these developments, humanity has yet to confirm the existence of extraterrestrial life. However, a growing body of evidence from meteorites, space missions, radio signals, historical records, and AI-driven analyses is gradually assembling potential clues, suggesting that life may not be confined solely to Earth.

The first category of evidence comes from meteorites. The Orgueil meteorite, which fell in France in the 19th century, represents one of the earliest and most debated cases. This carbonaceous chondrite, rich in organic material and water, contains molecules considered strong biosignatures, including amino acids and chlorophyll degradation products. Under high magnification, numerous structures resembling microfossils have also been observed. Although early researchers questioned whether these features resulted from terrestrial contamination or mineral artifacts, subsequent studies ruled out pollen contamination and confirmed that both the organic compounds and structural features originated within the meteorite itself prior to its separation from its parent body.

Orgueil meteorite（Image source：Layalestani SSS et al. (2025)， CC BY 4.0 ）

Putative biological structures in the Orgueil meteorite（Image source：Layalestani SSS et al. (2025)， CC BY 4.0 ）

Putative bacterial microfossils in the Orgueil meteorite（圖片來源：Layalestani SSS et al. (2025)，採用 CC BY 4.0 授權）

Another significant meteorite, Murchison, has drawn attention due to its age, which predates Earth. Analyses have confirmed the presence of amino acids and nucleotides, fundamental components of life. Importantly, their structural characteristics differ from those formed under terrestrial conditions, supporting an extraterrestrial origin. If the building blocks of life existed before the formation of the solar system, the probability that life can emerge elsewhere in the universe is greatly increased.

Murchison meteorite（Image source：Layalestani SSS et al. (2025)， CC BY 4.0 ）

The most controversial case involves the Martian meteorite ALH 84001. This meteorite contains magnetite structures and nanoscale tubular formations resembling those produced by magnetotactic bacteria on Earth. Although these features cannot definitively exclude inorganic formation, the chemical processes required to form such minerals involve liquid water and moderate temperatures. This at least indicates that Mars once possessed environmental conditions compatible with life. Taken together, these three meteorites do not conclusively prove extraterrestrial life, but they demonstrate that biologically relevant organic compounds and life-supporting conditions can arise naturally on multiple celestial bodies.

Allan Hills meteorite 84001（Image source：Layalestani SSS et al. (2025)， CC BY 4.0 ）

Tubular structures in Allan Hills meteorite 84001（Image source：Layalestani SSS et al. (2025)， CC BY 4.0 ）

The second category of evidence comes from space probes. Over the past 60 years, missions from various countries have provided direct environmental data beyond Earth. Mars rovers have identified ancient lake sediments, dried river channels, and subsurface ice. The Cassini-Huygens mission revealed that Saturn's moon Enceladus may harbor a subsurface ocean beneath its icy crust. Meanwhile, the Voyager probes documented intense volcanic activity on Jupiter's moon Io. These findings do not constitute direct evidence of life, but they establish essential preconditions such as water, energy sources, chemical gradients, and environmental stability.

However, even if life exists, it may rely on biochemical systems entirely different from those on Earth, making detection significantly more difficult. On Earth itself, more than 99% of microorganisms remain uncultured and poorly understood in terms of metabolic requirements. Detecting extraterrestrial microbes is therefore an even greater challenge. While no direct evidence of life has yet been obtained, space missions have confirmed that multiple environments within our solar system could potentially support life.

Cassini-Huygens（Image source：NASA，CC0 1.0 ）

The third category of evidence arises from radio telescopes. Radio waves can penetrate cosmic dust, allowing detection of physical and chemical information from distant objects. Through spectroscopic analysis, scientists can identify organic molecules, atmospheric composition, and environmental conditions. To date, no signals with definitive characteristics of intelligent civilizations have been detected. However, radio observations have revealed more than one hundred organic molecules in interstellar space, including amino acids and nucleic acid components. These findings provide targets for further investigation and help identify celestial bodies more likely to support life.

The fourth category involves historical records and UFO-related claims. Although reports of unidentified flying objects and extraterrestrial beings have appeared repeatedly, none have passed scientific validation. For example, the alleged extraterrestrial bodies presented in the Mexican Congress in 2023 were later identified as likely human remains. The scientific consensus is that such cases reflect human expectations and interpretations of the unknown rather than credible evidence of extraterrestrial life.

Atacama Large Millimeter/submillimeter Array（Image source：Layalestani SSS et al. (2025)， CC BY 4.0 ）

In recent years, artificial intelligence has become increasingly powerful in analyzing scientific data. AI can detect subtle patterns in chemical spectra, gas signals, and imaging data, uncovering relationships that are difficult for human perception. For instance, machine learning has been used to reanalyze polycyclic aromatic hydrocarbons in meteorites, suggesting they are more consistent with volcanic rock processes than biological origin, thereby challenging earlier interpretations. In the future, AI may assist in analyzing extraterrestrial signals, processing probe-returned samples, filtering cosmic noise, and identifying potential biosignatures more efficiently than human researchers.

After decades of research, one conclusion is firmly established: the chemical conditions required for life are not unique to Earth. Organic compounds in meteorites, water-rich environments on other planets, chemical structures revealed by radio telescopes, and new insights from AI all indicate that the ingredients and processes associated with life are widespread in the universe. However, a vast gap remains between the possibility of life and its confirmed existence. The lack of direct observation of extraterrestrial organisms requires science to maintain a balance between caution and openness. The definitive answer may depend on future advances in detection technology, more sophisticated AI systems, or even human exploration of other worlds.

Author: Shui-Ye You

Reference:

Layalestani SSS et al. (2025). Evidence and traces of extraterrestrial life. International Journal of Astrobiology.

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