Can We Recognize Alien Life? Ocean Worlds and the Search for Life

On a recent episode of SETI Live, host Beth Johnson spoke with astrobiologist Dr. Anastasia Yanchilina, the first recipient of the SETI Institute’s Frank Drake Postdoctoral Fellowship. Their conversation examined a central question in astrobiology: how can researchers distinguish true biosignatures from abiotic processes that only appear lifelike?

Dr. Yanchilina’s work combines several lab experiments with planetary science, particularly the study of ocean worlds such as Europa and Enceladus. These icy moons are believed to harbor subsurface oceans, making them key targets in the search for life beyond Earth.

Chemical Gardens: Structures That Mimic Life

In her Caltech laboratory, Dr. Yanchilina synthesizes mineral formations known as “chemical gardens.” These are self-organized, plant-like structures that form when a metal salt is introduced into an alkaline solution such as sodium silicate.

The reactions create hollow, semi-permeable tubes that resemble biological membranes. Through osmosis, these tubes transport fluids internally. Their lifelike morphology, however, is entirely abiotic – physical, rather than biological, in nature.

Recognizing such formations is critical, since false positives could easily complicate the interpretation of potential biosignatures on ocean worlds, Dr. Yanchilina explained.

Linking Lab Work to Hydrothermal Vents

On Earth, hydrothermal vents (fissures in the seafloor that release mineral-rich, heated water) are known to host thriving microbial ecosystems. In these environments, mineral precipitation produces chimney-like structures similar in appearance to chemical gardens.

Both processes involve self-assembly, chemical gradients, and the creation of compartmentalized environments that allow organic molecules to concentrate. These conditions may have played a role in the origin of life on Earth and could still exist today in the subsurface oceans of Europa and Enceladus.

Testing Origins of Life Hypotheses

Dr. Yanchilina’s experiments introduce additional factors that may shape prebiotic chemistry:

• pH levels: Early Earth’s oceans were alkaline, with values near pH 11. Laboratory tests at this alkalinity mimic both ancient terrestrial oceans and modern subsurface oceans of Europa and Enceladus.
• Simple organics: Amino acids, some of which were delivered to Earth via meteorites and comets, are introduced to observe whether they could concentrate within mineral membranes. Previous studies suggested this process could promote the formation of vesicles, precursors to living cells.
• UV exposure: Early Earth received significantly more ultraviolet (UV) radiation than it does today, due to the absence of an ozone layer. By exposing chemical gardens to varying UV intensities, researchers can assess whether radiation breaks down organic molecules or facilitates their assembly.

These factors combine to test a fundamental question: could abiotic structures and available organics assemble into increasingly complex molecules, i.e., the precursors of life?

Biosignatures and the Challenge of False Positives

Distinguishing true biosignatures from abiotic phenomena remains one of the most significant challenges in astrobiology. Dr. Yanchilina emphasized two well-established indicators:

• Isotopic fractionation: Biological systems preferentially process certain isotopes (e.g., lighter carbon isotopes) in ways that differ from abiotic chemistry.

• Chirality: Life on Earth uses left-handed amino acids and right-handed sugars, a property known as chirality. Abiotic processes typically produce equal mixtures of both orientations.

Incorporating these measurements into future missions could help confirm whether observed organic compounds are products of biology or chemistry alone.

Extending the Definition of Life

A recurring theme in the discussion was the difficulty of defining life. Many researchers adopt a working definition: a self-sustaining chemical system capable of Darwinian evolution. But life may not always fit into strict categories.

Experiments with abiotic chemical gardens blur the boundary between nonliving chemistry and systems with lifelike properties. This work suggests that life may be best understood as an emerging process rather than a fixed state.

Looking Ahead

Dr. Yanchilina outlined the next steps in her research:

• Testing the relative abundance of different isotopes (isotopic fractionation) in organic compounds within chemical gardens
• Introducing microorganisms to assess how life interacts with abiotic mineral structures
• Simulating planetary environments by varying conditions such as temperature, pH, and radiation exposure

She also expressed enthusiasm for upcoming planetary missions that would complement her laboratory studies:

• Europa Clipper (launched in 2024, arrival due in 2030): designed to investigate Europa’s subsurface ocean
• Dragonfly (launches in 2028): a rotorcraft mission to Titan, focused on prebiotic chemistry
• Mars Life Explorer (in its conceptualization phase): will be designed to assess habitability and search for biosignatures on Mars

These missions will carry advanced mass spectrometers capable of measuring isotopes and chirality, providing critical data in the search for extraterrestrial life. Dr. Anastasia Yanchilina’s fellowship represents an important step in advancing astrobiology. By recreating potential extraterrestrial environments in the lab, her work helps refine the methods used to distinguish true biosignatures from misleading abiotic structures. The research not only deepens scientific understanding of life’s origins on Earth but also sharpens the tools needed to identify life beyond it.

Learn more about the Frank Drake Fellowship and the SETI Institute’s research on ocean worlds.

Watch the full conversation with Dr. Anastasia Yanchilina on SETI Live: