Extraterrestrial Life May Defy Earthly Expectations: Astrobiologists Are Developing New Frameworks to Study Complex Systems

Humanity currently has only one example of biology in the universe: life on Earth. But what if life can form through entirely different processes? How do scientists search for alien life when its appearance or chemistry might be completely unlike anything we know?

These are the questions at the forefront of astrobiology, the field dedicated to investigating life beyond Earth. Astrobiologists are working to establish universal principles that might govern the emergence and evolution of complex systems—both biological and physical—on Earth and elsewhere in the cosmos.

I am an astronomer with a strong interest in astrobiology, having written extensively on the subject. My research suggests that the most likely form of extraterrestrial life is microbial, as single-celled organisms are simpler and more likely to form than large, complex beings. However, considering the possibility of advanced civilizations, I am part of an international advisory council developing messages intended for potential alien intelligences.

Detecting Life Beyond Earth

Since the groundbreaking discovery of the first exoplanet in 1995, astronomers have identified more than 5,000 exoplanets—planets orbiting stars outside our solar system. Many of these exoplanets are Earth-like: small, rocky, and located within their star’s habitable zone. This zone represents the range of orbital distances where liquid water—a key ingredient for life as we understand it—could exist.

This sample of exoplanets implies the existence of up to 300 million locations in the Milky Way galaxy where conditions might allow life to emerge. These include exoplanets, their moons, and even free-floating bodies in interstellar space.

A key challenge in astrobiology begins with defining life itself. While recognizing life seems intuitive—whether it’s a bird flying through the air or a microbe in a water droplet—scientists remain divided on a precise definition. NASA defines life as “a self-sustaining chemical system capable of Darwinian evolution,” meaning organisms with complex chemistry that adapt to their environment through natural selection.

The evolution of life on Earth has progressed over approximately 4 billion years, from primitive microbes to multicellular organisms, large animals, and eventually humans. Astrobiologists use spectroscopy—a method that analyzes light spectra—to study the atmospheres and surfaces of exoplanets, searching for chemical indicators of life. For example, oxygen in a planet's atmosphere might suggest photosynthetic microbes, while the presence of chlorophyll could indicate plant life.

Evolution and Complexity

All terrestrial life, from bacteria to whales, shares a common microbial ancestor. Despite their diversity, the chemical and biological processes underlying life on Earth are universal. However, extraterrestrial life may follow entirely different biochemical pathways.

In October 2024, a multidisciplinary group of scientists convened to explore the origins of order and complexity in the universe, extending their inquiry beyond biological systems. The goal was to identify general principles governing the emergence of complex systems.

Some researchers proposed that complex systems—whether chemical, mineral, or biological—evolve in environments where certain configurations are more stable than others. Over time, these systems increase in diversity, complexity, and functionality, a process akin to natural selection.

Information plays a central role in understanding complexity. In biological terms, information is encoded in DNA, the molecule that dictates an organism’s structure and functions. From an information-theoretic perspective, complexity grows as organisms store more information about their environment.

Interestingly, complexity does not equate to sophistication. Primitive organisms like bacteria often have genomes with higher information density—meaning a greater proportion of functional genes—than those of more complex organisms like humans.

Expanding the Search for Life

Researchers are exploring alternative biochemistries that could support life. On Earth, water is the universal solvent, enabling the chemical reactions necessary for life. But other solvents, such as ammonia, liquid methane, or even sulfuric acid, could potentially play similar roles on other worlds.

Astrobiologists like William Bains and Sara Seager have identified thousands of molecules that could signify life. Furthermore, life elsewhere might not be carbon-based, as it is on Earth. Alien life might thrive on moons like Saturn’s Titan, where liquid methane lakes replace water, or exist on free-floating planets that lack stars altogether.

Advanced alien life forms might be so different from Earthly organisms that they would be unrecognizable to us. To address this, scientists are developing creative approaches to detect life. One strategy is to analyze the mineral composition of exoplanets. Life on Earth has influenced the diversity of minerals; for instance, early Earth had around 100 minerals, while today there are over 5,000. Some minerals, like apatite—a component of bones and teeth—are directly linked to biological activity.

Another strategy involves searching for technosignatures, which are signs of advanced civilizations. Examples include artificial light, atmospheric pollutants like nitrogen dioxide, or radio signals that could indicate communication.

The Road Ahead

The search for extraterrestrial life is far from straightforward. It spans disciplines—from chemistry and biology to astronomy and information theory—and challenges humanity to think beyond Earth-centric paradigms. Life might be detected within our solar system, through the study of exoplanet atmospheres, or via signals from distant civilizations.

Ultimately, finding life beyond Earth, whether microbial or advanced, will require both ingenuity and patience. For life as we don’t know it, the possibilities are endless—and the search has just begun.

Key Facts Added:

1. Exoplanet discoveries as of 2024 exceed 5,000 confirmed planets.
2. The concept of habitable zones is tied to liquid water but is being expanded to include other solvents like ammonia or methane.
3. The mineral diversity on Earth has grown significantly due to biological evolution, a factor astrobiologists are considering for exoplanets.
4. The use of spectroscopy to detect specific biosignatures such as oxygen, chlorophyll, or industrial chemicals is critical in exoplanet research.