Mars and Exoplanets: When science glimpsed signs of life beyond Earth. A review of the findings that, at the time, paved the way for detecting biological activity on other worlds.
Astrobiology in Action: Discoveries on Mars and Beyond
At the beginning of the 21st century, scientists had adopted a clear strategy to find extraterrestrial life: identify chemical signatures that could betray biological processes in other corners of the universe.
A period emerged in which a new discipline, astrobiology, was born, transforming what once seemed like a topic of science fiction or mere speculation into a legitimate scientific objective. From Mars to planets in distant star systems, a methodical and rigorous search began to answer one of humanity’s oldest questions: Are we alone in the cosmos?
The Trace of Martian Habitability
During those years, NASA’s robotic missions to Mars provided data that surprised the scientific community. The Curiosity rover, which landed in Gale Crater in 2012, revealed evidence that the red planet once had stable aqueous environments suitable for sustaining living organisms.
In fact, samples drilled just a few centimeters below the surface showed the presence of the six fundamental chemical elements for life as it is known on Earth: carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur.
Nevertheless, what was truly revealing was that these chemical traces were located in an environment that, millions of years ago, maintained a pH and salinity balance that was not hostile to biology.
Consequently, scientists concluded that if microbial life had existed in that environment, it would have found ideal conditions to thrive. It was not determined whether such life actually appeared, but the finding consolidated the idea of a potentially habitable Mars.
Water on Distant Worlds
On the other hand, while Curiosity was investigating Martian sedimentary layers, spectroscopic measurements of exoplanets were being conducted from astronomical observatories on Earth. Additionally, around the star HR 8799—located approximately 130 light-years away in the constellation Pegasus—water was detected in the atmosphere of a gas giant then cataloged as HR 8799c.
Although this enormous gas sphere, with estimated temperatures close to a thousand degrees, was not suitable for life, the confirmation of water in its atmosphere represented a crucial technical step. It demonstrated that analyzing the chemical composition of distant planets was within reach, something that once seemed unachievable.
Meanwhile, the technique used for this remote analysis was spectroscopy, which by that period had already been established as a standard tool in astrophysics. Therefore, applying such a method to the faint radiation coming from exoplanets was a significant challenge.
The success in detecting water and carbon monoxide in HR 8799c was a technical advancement that, according to experts, could be replicated with other rocky, Earth-like planets in future observation projects.
From Skepticism to Scientific Strategy
The search for extraterrestrial life was no longer limited to a handful of theories or assumptions based on fantastical stories.
This shift was noticeable in hindsight: decades earlier, the scientific community was torn between skepticism and imagination; however, by the first half of the 21st century, the landscape was different. Moreover, there was the SETI (Search for Extraterrestrial Intelligence) project, which attempted to capture electromagnetic signals from advanced civilizations.
Although it had not reported any positive results, its existence reflected the growing interest in approaching the problem with scientific rigor, leaving behind the realm of simple conjectures. In fact, the emergence of astrobiology created a solid conceptual framework to explore the possibility of life in the universe.
This discipline integrated planetary geology, organic chemistry, molecular biology, and observational astronomy, combining efforts to understand how life could arise in other solar systems. Despite the complexity, a clear roadmap had been charted: first, confirm habitability; second, identify potential biosignatures; and finally, with new technologies, seek unequivocal evidence of the existence of living organisms outside Earth.
Mars: A Gentler Past Than Imagined
Subsequently, Curiosity played a central role in this scheme. Its findings corroborated that Martian water was not excessively acidic or alkaline, had some stability, and apparently contained an adequate concentration of salts.
The mission’s scientific director, John Grotzinger, had stated that if a human traveled back in time to that Martian period, they would have found potable water. These types of statements, based on concrete data, marked a substantial difference from the years when Mars was considered only a dusty, inhospitable wasteland.
That historical milestone sparked new questions: knowing that Mars was habitable did not imply that it had been inhabited.
Therefore, the scientific community continued to gather evidence, analyzing sedimentary layers, searching for complex organic molecules, and reconstructing the planet’s geological history. The aim was to elucidate whether that window of habitability coincided with a sufficiently long period for simple life to have had time to emerge.
Gas Giants and Atmospheric Chemistry
Observations of the planet HR 8799c were less promising regarding the search for life but were a technological and methodological milestone.
Additionally, that detection marked the beginning of a new era in which astronomers hoped to find not only water but also combinations of gases in exoplanet spectra. For example, if oxygen and methane were found coexisting in a distant world’s atmosphere, and geological processes that could produce them were ruled out, the hypothesis of extraterrestrial life would become tempting.
The key lay in chemical instability.
On a planet without biological processes, certain gas mixtures would not remain in equilibrium simultaneously for long periods. However, the joint and sustained presence of reactive gases would be a strong indication of a biological origin. This technique, in theory, would allow for the remote identification of the unmistakable signature of life.
The Long Road to Definitive Proof
Meanwhile, missions to Mars and exoplanet spectroscopy were not isolated efforts. Therefore, it was evident that a larger technological infrastructure was required, both in robotics and astronomical instrumentation, to make progress.
Curiosity was not designed to detect life directly but to assess the past habitability of the Martian environment. However, its success led to planning more ambitious missions, such as ExoMars, by the European Space Agency (ESA).
Launched after those years, this mission aimed to analyze the Martian subsurface for complex organic compounds potentially related to life. Simultaneously, more powerful space telescopes were projected, equipped with high-resolution spectrographs capable of separating the light signals of tiny planets from enormous and bright stars.
These instruments could scrutinize their atmospheres for molecules like oxygen, methane, or even ozone, which on Earth are linked to the metabolism of living beings.
The Historical Context of a Long-Awaited Announcement
Nevertheless, no one expected instant news about the confirmation of extraterrestrial life. While indirect evidence of habitability on Mars and the detection of water on exoplanets were essential steps, the scientific community understood that definitive confirmation would take time.
In fact, the interval between the first clues and irrefutable proof extended beyond what was initially imagined.
Moreover, scientific institutions, in light of the discussions held during those years, agreed on the importance of caution and rigor. It was not simply about finding any organic molecule but ensuring that their origin was not purely geological.
Therefore, Curiosity’s findings were interpreted as a springboard for more specialized investigations, while the analysis of HR 8799c’s atmosphere was understood as a successful test of the technical capabilities needed for future discoveries.
A Promise Guiding the Research
Meanwhile, public interest was growing. The media paid more attention to updates on Mars and candidate exoplanets with suitable conditions. Debates, documentaries, and international conferences were generated, bringing the general public closer to the complexity and scope of these scientific efforts.
The roadmap to detecting extraterrestrial life was laid out, and each finding, each instrumental improvement, and each new analysis provided another link in this long chain of research.
Similarly, experts emphasized the need for international collaboration and methodological diversity. Understanding life in the universe required combining multiple disciplines and sharing data among space agencies, universities, and research centers. This coordinated work laid the foundations of astrobiology as a global and multidisciplinary endeavor.
Towards a New Era of Cosmic Exploration
Ultimately, what began as a philosophical question took on a scientific aspect over time.
If Curiosity had demonstrated that Mars was habitable in the past, and spectroscopy had confirmed the presence of water on giant exoplanets, it was logical to think that, sooner or later, unequivocal signals of extraterrestrial life could be detected.
During that period, the scientific community maintained hope that technological advances, combined with growing experience in handling complex data, would lead to a groundbreaking announcement in the coming decades.
As research advanced, both NASA’s official portals and reports published by the ESA provided verified information, consolidating the credibility of these efforts.
Thus, a promising path was being paved toward the detection of life on other worlds, based on a rational strategy, long-term planning, and the shared enthusiasm of several generations of scientists. It was a time when humanity understood that the search was not just a romantic yearning but a tangible possibility grounded in scientific evidence.
