In its quest to discover the presence of life outside our planet, NASA employs sophisticated instruments like the James Webb Space Telescope. The primary goal is to identify biosignatures, and a scale is being devised to aid the interpretation of the obtained evidence. Crucial indicators of potential life consist of evolving chemical systems, the existence of liquid water, sources of energy, and imbalances in atmospheric gases. Environmental “gradients” also signal the possibility of environments suitable for life.
The future might bring revelations from a distant planet, providing subtle clues of possible life forms, but these insights might not be easily deciphered.
Our astronomical telescopes could spot an atmospheric gas mixture resembling ours on another planet. Computer simulations could help assess the potential of the planet to harbor life. Experts may argue over the validity of the evidence for life’s existence, or endeavor to gather more supportive proof for such a monumental inference.
“We are in the dawn of a remarkable period,” stated Ravi Kopparapu, a researcher at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, specializing in habitable planets. “For the first time in human history, we might be close to answering: Is there life beyond Earth?”
The journey towards this epoch starts with NASA’s James Webb Space Telescope, investigating exoplanets – planets orbiting other stars. The spacecraft’s onboard tools are determining the atmospheric composition of these exoplanets. As telescopic technology advances, future superior instruments could detect possible biosignatures – potential indicators of life – even from a planet many light-years away.
Illustration of a potentially life-sustaining rocky world, orbiting a red dwarf star, as seen by an incoming observer. Credit: NASA/JPL-Caltech/Lizbeth B. De La Torre
Within our solar system, Mars’s Perseverance rover is collecting rock samples for future analysis on Earth, potentially revealing signs of life. Moreover, the forthcoming Europa Clipper mission intends to visit Jupiter’s icy moon to ascertain if its conditions could sustain life in its global ocean, covered by a global ice shell.
However, any indication of life beyond Earth raises another significant question: How confident can we be about the drawn scientific conclusions?
“The challenge is determining what is life – and when to declare, ‘I found it,’” expressed Laurie Barge from NASA’s Jet Propulsion Laboratory’s Origins and Habitability Lab in Southern California.
Astrobiologists, faced with the challenge of identifying a definitive “sign of life,” are constructing a novel framework to comprehend the quality of the evidence. A provisional scale suggested in 2021, ranges from 1 to 7, with 1 indicating hints of extraterrestrial life, to 7 signaling certain evidence of life elsewhere. This evolving framework acknowledges that the scientific pursuit for life’s existence is a complex journey rather than a linear path.
Identifying conclusive signs of “life as we know it” is a significant challenge. Detecting evidence of life forms with unfamiliar molecular structures or based on a solvent other than water, would be even more uncertain.
Yet, as the search for life intensifies within our solar system and beyond, NASA researchers and their global counterparts have devised several preliminary concepts.
The Evolution of Life
NASA offers an informal, non-binding yet constructive definition of life: “A self-sustaining chemical system capable of Darwinian evolution.” This encapsulates the essence of Charles Darwin’s natural selection theory, where characteristics inherited across generations lead to species evolution over time.
Formulated in the 1990s by a NASA exobiology working group, this definition doesn’t influence mission designs or research plans. However, it serves as a guide to set expectations and steer discussion around the intricate query: When does non-life become life?
“Biology is chemistry with history,” explains Gerald Joyce, a member of the group that created the NASA definition and currently a research professor at the Salk Institute in La Jolla, California.
This implies that history is recorded chemically – in our case, through DNA, which encodes genetic information that gets translated into our physical structure and processes.
A complex, robust, self-replicating, and open-ended DNA record, Joyce suggests, is crucial for survival and adaptation across billions of years.
“Identifying a molecule recording information would be an undeniable piece of evidence,” Joyce explained.
Such a molecule, whether DNA, RNA, or something else, could potentially be discovered in a Mars sample from a future NASA mission or among the “ocean worlds” in the outer solar system – Jupiter’s moon, Europa, Saturn’s Enceladus, or other moons hiding vast oceans beneath ice shells.
Due to the astronomical distances, it’s impractical to obtain samples from planets outside our solar system. Instead, we’ll rely on remotely identifying potential biosignatures by analyzing types and quantities of gases in exoplanet atmospheres to determine if they were produced by life forms. This will likely necessitate a deeper understanding of the requirements for life to originate and persist long enough to be detectable.
Life’s Origin and Habitat
There’s no agreed-upon checklist for life requirements, be it within our solar system or in distant stars. However, Joyce, who studies the origins and evolution of life, suggests a few essentials.
Foremost is liquid water. Despite the wide range of environments hosting life on Earth, it appears all life forms require it. Liquid water provides an environment for life’s chemical components to persist and interact, unlike air or rock surfaces.
An important consideration is an energy source, necessary for structural chemical reactions and to maintain “order” against the universal propensity for “disorder” – entropy.
An imbalance in atmospheric gases could also hint at life’s presence.
“In Earth’s atmosphere, oxygen and methane quickly react with each other,” Kopparapu explained. Left unchecked, they would soon neutralize each other.
“They should not coexist,” he stated. “So why do we observe methane and oxygen? Something must be continually replenishing these compounds.”
On Earth, life is that “something,” incessantly adding to the atmospheric imbalance. A similar imbalance in a distant exoplanet’s atmosphere, whether due to these or other compounds, might indicate a living biosphere. However, scientists would also need to eliminate geological processes, like volcanic or hydrothermal activities, that could produce life-associated molecules.
Rigorous laboratory work and precise modeling of potential exoplanet atmospheres will be essential to distinguish between the two.
Life’s Evolutionary Changes
Barge also emphasizes the concept of “gradients,” changes over time and space, like wet to dry, hot to cold, and various other environments. Gradients offer energy pathways, generating molecules or chemical systems that may eventually become part of life forms.
Earth’s plate tectonics and the cycling of gases like carbon dioxide – absorbed into Earth’s crust or released back into the atmosphere – exemplify one type of gradient.
Barge’s expertise, the chemistry of hydrothermal vents on the ocean floor billions of years ago, is another. It represents a potential path towards primitive metabolism – converting organic compounds into energy – possibly preceding the advent of true life forms.
“What gradients existed before life?” she questions. “Given life’s reliance on gradients, could life’s origin also have been influenced by these gradients?”
Better mapping of potential life pathways could influence future space telescope designs, assigned with analyzing the gases in potentially habitable exoplanet atmospheres.
“We not only need to detect gases but also ascertain their emission patterns from the planet, if they’re emitted in appropriate
The NASA James Webb Space Telescope and other advanced instruments are in the process of examining signs of extraterrestrial life. The central attention is on identifying biosignatures, with the development of a scale to interpret the gathered evidence. The indicators for potential life include evolving chemical systems, the presence of liquid water, accessible energy sources, and an imbalance in atmospheric gases. Also, environmental “gradients” signify possible environments suitable for life.
The possibility of unearthing hints of life on a distant planet in the foreseeable future cannot be ruled out. This discovery, however, might not be immediate or easy.
Our space telescopes may identify a mixture of gases in its atmosphere similar to that of our own planet. Computer simulations would then provide insights into the planet’s potential to host life. Experts would discuss if the evidence strongly suggests life or if more evidence is needed to back this monumental interpretation.
Ravi Kopparapu, a scientist at NASA’s Goddard Space Flight Center who studies habitable planets, believes that we are in the dawn of a new age. He said, “For the first time in the history of civilization, we might be able to answer the question: Is there life beyond Earth?”
This new age of exoplanetary exploration has begun with NASA’s James Webb Space Telescope. The telescope’s onboard instruments are deciphering the compositions of exoplanet atmospheres. With the continuous improvement of telescopic power, advanced future instruments may be able to discern possible biosignatures from planets light-years away.
Within our solar system, the Mars rover Perseverance is collecting rock samples for analysis on Earth, looking for signs of life. Furthermore, the upcoming Europa Clipper mission aims to explore one of Jupiter’s icy moons to determine if its subglacial ocean could support life.
However, any indication of extraterrestrial life prompts a consequential question: How definitive can any scientific conclusion be?
“The challenge is deciding what is life – when to say, ‘I found it,’” said Laurie Barge from the Origins and Habitability Lab at NASA’s Jet Propulsion Laboratory in Southern California.
Astrobiologists, grappling with the ambiguity of what even constitutes a “sign of life,” are devising a new framework to comprehend the strength of the evidence. A proposed model includes a scale from 1 to 7, where level 1 signifies possible signs of life and level 7 confirms its existence elsewhere. This scale, still under discussion and refinement, recognizes that the quest for extraterrestrial life is a complicated journey, not a direct route.
Finding definitive signs for “life as we know it” is a daunting task. Discovering evidence of unknown forms of life, with unfamiliar molecular combinations or based on solvents other than water, is even more challenging.
Nevertheless, the search for life, both in our solar system and in distant star systems only known by their emitted light, is proceeding in earnest. NASA scientists and global collaborators have some starting points in mind.
For starters, NASA proposes an informal, non-binding, yet useful definition of life: “A self-sustaining chemical system capable of Darwinian evolution.” This principle, formulated by a NASA exobiology working group in the 1990s, helps set expectations and focus discussions on the critical transition from non-life to life.
Gerald Joyce, a research professor at the Salk Institute, considers biology as “chemistry with history.” The history is inscribed in our DNA, which carries the genetic data that instructs the formation of our bodies. For such history to endure and adapt over billions of years, Joyce argues, it needs to be robust, complex, self-replicating, and open-ended.
Evidence of these attributes in a molecule from another world, like DNA, RNA or something else, could be obtained from a Mars sample or the icy moons of gas giants in our solar system.
However, securing such samples from exoplanets is out of our reach as their sheer distance would require tens of thousands of years of space travel. Consequently, we must rely on remote detection of possible biosignatures and in-depth understanding of life’s prerequisites for initiation and enduring existence.
Although there isn’t an established list of requirements for life, both within our solar system and beyond, several likely “must-haves” are suggested. Liquid water tops this list, given its universal necessity for life on Earth. Another essential requirement is an energy source, for structural creation and for maintaining order against universal entropy. Also, an imbalance in atmospheric gases could potentially indicate life.
Barge emphasizes the significance of “gradients” or changes over time and distance, like the shift from wet to dry, hot to cold, among many possible environments. These changes create sites for energy transformations and the production of molecules or chemical systems that could eventually be incorporated into life forms.
A better understanding of these possible life pathways could shape the design of future space telescopes, enabling them to more confidently analyze the gases in the atmospheres of potentially habitable exoplanets.
Kopparapu states, “With future telescopes, we’ll be more confident because they’ll be designed to look for life on other planets.”
This search for life continues as we delve deeper into our understanding of life on Earth and possible life on other planets.
Table of Contents
Frequently Asked Questions (FAQs) about Extraterrestrial Life
What is the primary tool NASA is using in the search for life beyond Earth?
NASA is using the James Webb Space Telescope, alongside other advanced tools, to search for signs of life beyond Earth.
What are the key markers of potential life that NASA is focusing on?
Key markers of potential life include chemical systems capable of evolution, liquid water, energy sources, and atmospheric gas imbalances. The presence of environmental “gradients” also indicates potential life-hosting environments.
Who is Ravi Kopparapu and what does he do at NASA?
Ravi Kopparapu is a scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. He studies habitable planets and believes that we are currently in the beginning of a golden era for this kind of research.
What is the James Webb Space Telescope’s role in the search for life on exoplanets?
The James Webb Space Telescope has instruments that can detect the composition of atmospheres on exoplanets. As the power of telescopes increases in the future, more advanced instruments could potentially capture signs of life, or “biosignatures”, from a planet light-years away.
What is NASA’s working definition of life?
NASA’s working definition of life is “a self-sustaining chemical system capable of Darwinian evolution”. This definition helps set expectations and focuses debate on the critical question of when non-life becomes life.
What missions within our solar system are currently searching for signs of life?
Within our solar system, the Perseverance rover on Mars is gathering rock samples to be analyzed for signs of life. Additionally, the upcoming Europa Clipper mission will visit one of Jupiter’s moons to determine whether conditions there would allow life to thrive.
What is the proposed framework for understanding the strength of evidence for extraterrestrial life?
A sample framework proposed in 2021 includes a scale ranging from 1 to 7, with hints of other life at level 1, to increasingly substantial evidence, up to certainty of life elsewhere at level 7. This framework is still being discussed and revised.
More about Extraterrestrial Life
- NASA’s Search for Life
- James Webb Space Telescope
- NASA’s Perseverance Rover
- Europa Clipper Mission
- Understanding Biosignatures
- Exoplanet Exploration
- Astrobiology at NASA
