NASA’s Astrobiology Program is dedicated to unraveling the mysteries of life’s origins and existence in the universe, aiming to answer the profound question, “Are we alone?” The program embarks on its research by delving into the emergence of life on Earth, starting from the formation of our Sun.
To understand the genesis of life on Earth and extend our knowledge to the cosmos, NASA’s Astrobiology Program conducts comprehensive research. This includes investigating the formation and positioning of Earth within the habitable zone, studying the chemical evolution that led to life, and employing advanced telescopes to explore exoplanets for potential signs of life. These endeavors enhance our capabilities to address the universal query of whether life exists beyond our planet.
Where should we begin?
In charting the path of life in the cosmos, we might commence with the first cells, thriving and harnessing energy in environments such as hollows on Earth’s nascent surface or scorching vents at the depths of ancient seas.
However, a genuine comprehension of life, whether on Earth or elsewhere, necessitates delving into even earlier origins: the ignition of stars carrying the essential building blocks of life, the formation of planets from protoplanetary disks, and the intricate interplay between energy, chemistry, and celestial bodies.
With over 5,000 confirmed exoplanets and potentially billions more within our Milky Way galaxy, the prospects for other habitable worlds have skyrocketed in recent years. Furthermore, with the advent of more advanced telescopes currently in development or scanning the skies, we possess better tools than ever before to investigate these distant realms.
To seek answers to the timeless question of whether we are alone in the universe using these new tools, what must we learn?
“We cannot identify where or what to search for if we lack an understanding of what transpired on Earth,” explains Mary Voytek, the director of NASA’s Astrobiology Program.
Unraveling the puzzle of Earth’s journey to life
Much of NASA’s astrobiology research, focusing on the origins and prerequisites of life in the cosmos, originates from our own planet. It traces back to the birth of our star, the Sun, within a swirling cloud of gas and dust.
This cosmic cloud contained the essential ingredients for life: carbon, water, ammonia, methane, and other building blocks—molecules forged primarily in the hearts of previous generations of stars. Their explosive deaths scattered these elements throughout the universe.
By observing these same components in distant star systems and planets, we confirm the first condition for habitability.
“The journey begins with the star,” remarks Voytek. “The reason it culminated in life on Earth lies in the intricate details: the formation of planets from the swirling disk of dense gas surrounding a newborn star, the interplay among the star, the other planets in the system, and Earth that rendered our planet habitable and fostered the emergence and evolution of life.”
An artist’s rendering envisions Earth’s surface approximately 3.8 billion years ago, during the early stages of life. Credit: NASA/JPL-Caltech/Lizbeth B. De La Torre
The next condition for habitability revolves around Earth’s positioning within our solar system. Earth resides within the “habitable zone,” an orbital region around a star where a planet can maintain liquid water on its surface under suitable atmospheric conditions. Life on Earth thrives in a remarkably diverse range of environments, spanning from extreme cold to caustic boiling pools, all of which require liquid water. Scientists anticipate that water is similarly crucial for life on other worlds.
Venus, Earth’s rocky sibling in terms of size and composition, orbits too close to the Sun, just inside the inner edge of the habitable zone. On its surface, which is scorching enough to melt lead, liquid water is out of the question, although it might have existed in the past. As for Mars, its surface is frozen and exposed beneath an exceedingly thin atmosphere at the outer edge of the habitable zone, making persistent liquid water highly improbable.
The icy moons within our solar system’s outer reaches, harboring hidden oceans of liquid water, may also provide habitable conditions despite existing well beyond the traditional habitable zone.
While environments akin to those found on our planets and moons could prevail in other systems throughout the galaxy, certain possibilities, such as potentially habitable “exomoons,” lie beyond the reach of our present remote sensing technology. Therefore, the habitable zone and the presence of surface water serve as rough guidelines to aid astronomers in sifting through the multitude of exoplanets in search of potential life-supporting targets.
Unlocking the Secrets of Chemistry
Scientists who seek to understand life’s origins and explore the question of life beyond Earth also delve into the realm of molecules and chemistry. How did microscopic interactions on an early and volatile Earth, around four billion years ago, give rise to a complex package of material that we would define as “alive,” capable of consuming energy and producing waste?
Various potential scenarios have been proposed by scientists to explain the initiation of life. Betül Kaçar, a professor at the University of Wisconsin-Madison, leads the Molecular Paleobiology Laboratory and the NASA Interdisciplinary Consortium for Astrobiology Research (ICAR) project known as Metal Utilization and Selection across Eons (MUSE). Kaçar’s team takes an experimental approach, focusing in part on enzymes, the proteins responsible for triggering chemical reactions within cells. These enzymes, which play a role in metabolism, can help build or break down cellular components.
“We revive multiple crucial enzymes to explore ancient biological systems that trace back to the origins of these metabolic innovations—how life learned to utilize available resources in its environment, including the atmosphere,” explains Kaçar. “Using available DNA, we rewind the clock and venture billions of years into the past.”
According to Kaçar, recent astrobiology research has witnessed a shift towards studying the behavior of ancient aggregations of molecules that exhibit life-like properties, rather than solely synthesizing chemical compounds associated with early life. These life-like structures may include “proto-molecules” that can store information or catalyze reactions, albeit in a more primitive and less efficient manner than the RNA and DNA familiar to us today.
“We consider these structures as life-like but not exactly life,” Voytek adds.
Voytek and Kaçar also note a shift in our understanding of the history of life on Earth, encompassing environments ranging from the depths of the ocean at hydrothermal vents—an conceivable location for the origin of life—to the earliest land surfaces, where chemistry might have contributed to the emergence of life. The components and functions of life may have emerged gradually at different times and places over hundreds of millions of years, eventually converging to form recognizable living organisms.
Chemistry across this spectrum explores a wider range of energy sources, mineral diversity, and the presence of wet-dry cycles, Kaçar explains. When it comes to the origin of life, location and chemistry are key.
Learning from Other Planets
As our understanding of the universe deepens, so does our ability to discover exoplanets and gather information about them.
Telescopes have already revealed a multitude of exoplanets with varying compositions, some rocky and others gaseous. These include “super-Earths,” which may or may not be scaled-up versions of our own rocky world, and “mini-Neptunes,” smaller counterparts to Neptune that do not exist in our solar system. The exoplanet menagerie also includes “hot Jupiters” and “hot Saturns,” massive gas giants orbiting their stars at close proximity, as well as rogue planets drifting alone in space without a parent star.
Our knowledge of other worlds continues to be profoundly influenced by increasingly powerful space telescopes. Surveys conducted by NASA’s retired Kepler spacecraft and the currently active Transiting Exoplanet Survey Satellite (TESS) have led to the discovery of numerous planets. The James Webb Space Telescope, which has begun providing a wealth of images and atmospheric data, and the Roman Space Telescope, scheduled for launch in 2027, are expected to uncover around 100,000 more distant worlds while also testing novel technologies for directly imaging exoplanets.
Future space telescopes, even more advanced than the current ones, could directly analyze the atmospheres of exoplanets for signs of life, known as biosignatures.
However, if Earth serves as the model for identifying evidence of life among exoplanets, we must not only learn to detect biosignatures from planets resembling our present-day Earth but also recognize signs of life on planets resembling Earth’s distant past, when conditions were vastly different.
Timothy Lyons, a biogeochemistry professor at the University of California, Riverside, leads the Alternative Earths Team, formerly funded through the NASA Astrobiology Institute and now operating as an ICAR project. The team investigates how Earth might have appeared at various stages of its 4.5-billion-year history to a distant observer.
“Earth is the only planet we know with life, but Earth has taken on different forms throughout its history. Those are the alternative Earths,” explains Lyons.
For instance, would we recognize a living Earth before oxygen accumulated sufficiently in the atmosphere to be detected? Life forms that do not rely on oxygen flourished for billions of years before an oxygenated atmosphere could have been observed from afar. Additionally, after life began producing oxygen, its presence in the atmosphere might have remained undetectable for billions of years.
Lyons’ research team aims to use chemical measurements of ancient rocks, which serve as a historical record, along with computer models, to create a catalog of gaseous profiles corresponding to Earth’s various stages. This platform allows them to imagine possibilities on distant planets, even if they differ significantly from anything found in Earth’s archives. If the James Webb Space Telescope and future telescopes capture matching atmospheric profiles on an exoplanet, it could be a compelling indication of a “biosphere”—a world characterized by environmental conditions that foster and are influenced by some form of life.
“The ultimate goal is to comprehend how a planet can develop and sustain a detectable biosphere—not only to acknowledge that life could exist, but to confirm its presence,” emphasizes Lyons. “We hope our work will inform the design of new telescopes and the interpretation of initial data on atmospheric composition from planets within habitable zones.”
In the pursuit of understanding life beyond Earth, researchers must also be aware of non-biological processes that could generate gases mimicking biosignatures. Photochemistry and specific atmospheric properties, for example, could produce abundant oxygen on a lifeless planet.
Such a holistic perspective on the potential for life elsewhere necessitates multidisciplinary collaborations involving biologists, geochemists, geologists, exoplanet researchers, and other experts.
“It’s like a biologist, a geologist, and an astronomer walk into a bar, and life happens,” quips Kaçar. She compares the collaborative effort to a “smoothie,” blending various scientific disciplines to unravel the mysteries of life detection, whether it be on neighboring planets or exoplanets scattered throughout the galaxy.
“There’s an incredible level of interest right now, more than I’ve ever seen, in tackling this problem and an amazing number of students pursuing it,” she shares. “It’s an exhilarating and inspiring time. That’s why I believe we are getting closer to solving this puzzle. It’s truly thrilling.”
Table of Contents
Frequently Asked Questions (FAQs) about Astrobiology
What is NASA’s Astrobiology Program?
NASA’s Astrobiology Program is a scientific initiative aimed at understanding the origins and requirements of life in the cosmos. It focuses on researching the emergence of life on Earth and extends this knowledge to explore the possibility of life on other planets.
What does the Astrobiology Program investigate?
The Astrobiology Program investigates various aspects related to the origins of life and the existence of life beyond Earth. It studies the formation and positioning of Earth within the habitable zone, the chemical evolution of life, and uses advanced telescopes to search for potential signs of life on exoplanets.
How does the Astrobiology Program search for signs of life?
The program employs sophisticated telescopes to analyze exoplanets for potential biosignatures, which are indicators of life. It also studies the chemical composition and environments of ancient Earth to understand how life may have originated and evolved.
What is the habitable zone?
The habitable zone refers to the orbital region around a star where conditions are suitable for liquid water to exist on a planet’s surface under the right atmospheric conditions. It is considered a key factor in determining the potential habitability of exoplanets.
How do scientists study the history of Earth’s life?
Scientists study the history of Earth’s life by examining ancient rocks and fossils, analyzing chemical signatures, and using computer models to reconstruct past environments. They aim to understand the different phases Earth has gone through and how life adapted and evolved during those times.
What are biosignatures?
Biosignatures are indicators or traces of life that can be detected in the atmosphere or surface of a planet. These could include the presence of certain gases, such as oxygen or methane, or the detection of complex organic molecules.
What is the role of space telescopes in astrobiology research?
Space telescopes, such as the James Webb Space Telescope and the Roman Space Telescope, play a crucial role in astrobiology research. They provide powerful tools for observing exoplanets, capturing images, and collecting data on atmospheric compositions, which helps scientists search for potential signs of life beyond Earth.
Why is multidisciplinary research important in astrobiology?
Astrobiology is a multidisciplinary field that requires collaboration among scientists from various disciplines, such as biology, chemistry, geology, and astronomy. This collaboration allows researchers to approach the complex questions of life’s origins and existence from different perspectives and gather a comprehensive understanding of the subject.
More about Astrobiology
- NASA Astrobiology Program
- NASA Exoplanet Exploration
- NASA James Webb Space Telescope
- NASA Roman Space Telescope
- University of Wisconsin-Madison Department of Bacteriology
- University of California, Riverside Biogeochemistry
