Recent analyses and interpretations of geochemical data found on other planets and asteroids – within our solar system and beyond – reveal the presence of organic molecules that could be associated with life.
There has been no unequivocal proof of life – yet. But the findings are tantalizing and beg for further study in the form of sample return missions to Earth labs and other continued exploration.
Mars Perseverance Rover Discovery
NASA’s Perseverance rover successfully landed on Mars in early 2021 and is currently exploring the rim of Jezero Crater. We last reported the rover’s progress in the August 2024 EXPLORER.
A Martian day, or “Sol,” is about 40 minutes longer than a day on Earth. As of April 28, 2025, Sol 1478, Perseverance has traveled 20.9 miles and drilled 25 core samples out of 38 total sample tubes for the entire mission. The rover has returned more than 820,000 raw images that are publicly available in the mission multimedia catalog.
On the crater rim, the rover has cored five rocks, sealing samples from three of them in sample tubes. It has also performed up-close analysis of seven rocks and analyzed another 83 from afar by zapping them with a laser. This is the mission’s fastest science-collection tempo since the rover landed on Mars four years ago. The next stage is to get them to back for detailed study only possible in Earth labs. However, the planned Mars Sample Return Mission has had huge cost overruns and budget cuts.
In 2022, Perseverance detected aromatic organic compounds at Wildcat Ridge in the Jezero delta front. The geologic sediments there formed in a lake environment in Jezero Crater and interacted with water long after their deposition.
Morgan Cable is a research scientist in the Laboratory Studies group at the NASA Jet Propulsion Laboratory in Pasadena, Calif. In a video released by NASA, she describes a recent sample that contains organics and possible biosignature.
“Sample 25 is called Sapphire Canyon. This is a core that was collected from the Cheyava Falls rock in the Neretva Vallis. The Cheyava Falls rock is really neat. If you look at it, it’s got all sorts of cool features. It has these small black spots that we call ‘poppy seeds’ and also these larger spots that we call ‘leopard spots.’ This is the only place we’ve found on Mars so far where we have chemical evidence that chemical reactions associated with life could have been happening as well as organic molecules,” she said. “The SHERLOC (Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals instrument) detected an organic signature, so both of those together in the same rock is really compelling because these similar types of features, when we find them on Earth, oftentimes they’re associated with biology, with microbes.”
“And so those pieces of evidence combined together, we believe, justify calling it a potential biosignature,” she added.
This underscores the importance of returning these carefully selected Mars samples to Earth labs where the detail and detection limits far exceed any of the instruments sent to Mars on robotic rovers. Consider this with the example of asteroid Bennu biochemistry, to be discussed in what follows. A revised, more cost-effective Mars sample return mission is still being defined. The collected Perseverance samples will be launched from the Martian surface using a Mars ascent vehicle, with the European Space Agency providing the Earth Return Orbiter to capture the samples in orbit and bring them back to Earth. The mission is expected to be completed in the 2030s.
SHERLOC uses a deep ultraviolet laser to excite the sample and analyze the emitted light (Raman and fluorescence), revealing information about the molecules and minerals present.
Katie Stack-Morgan, Perseverance deputy project scientist, elaborated on Sapphire Canyon to explain that the rover’s SHERLOC instrument observed a Raman peak at the so-called “G band.” Raman spectroscopy is used to analyze materials by measuring the specific bands of light scattered in reflection. A Raman peak at the G-band (“G” stands for “graphite”) is suggestive of macromolecular carbon. As reported in March 2025 at the Lunar and Planetary Science Conference, on Sol 1159, Perseverance began exploring Neretva Vallis, an ancient river channel that served as the primary inlet on Jezero crater’s western margin delta. From Sols 1180–1218, the SHERLOC instrument collected 18 spectral maps (totaling 1,800 spectra) from four targets including Sapphire Canyon across three rocks. They report Raman G-bands are diagnostic of macromolecular carbons, which include large and complex, reduced carbon molecular structures. MMC is a complex mixture of hybridized carbons bonded in aromatic rings and aliphatic chain structures. They can include carbohydrates, lipids, proteins and nucleic acids essential for life. Discriminating these details will have to wait until the samples are analyzed in labs on Earth.
The Most Significant Find
Curiosity landed in Gale Crater on August of 2012. Besides a great many chemical analyses, the rover has returned 689,849 images of Mars as of April 23, 2025, Sol 4519 for Curiosity.
Scientists studying crushed rock with NASA’s Curiosity rover have discovered the largest organic molecules ever detected on Mars. The findings, published on March 24, 2025, in the Proceedings of the National Academy of Sciences, indicate that prebiotic chemistry on Mars might have progressed further than previously believed. Using the rover’s Sample Analysis at Mars (SAM) Gas Chromatography-Mass Spectrometry (GCMS) mini-laboratory, researchers re-examined a previously collected rock sample and identified long-chain aliphatic molecules – decane, undecane, and dodecane – which contain 10, 11 and 12 carbon atoms, respectively. These molecules are likely remnants of fatty acids, which on Earth are key organic components involved in the formation of cell membranes and other life-related processes.
Fatty acids are created by living organisms to build cell membranes and support other biological functions. However, they can also form through non-biological means, such as chemical reactions caused by geological processes – for example, when water interacts with minerals in hydrothermal vent environments.
An environment with seasonally wet and dry cycles could have spurred the evolution of cell membranes on Earth. Wet and dry cycles on early Earth are thought to have played a crucial role in the evolution of cell membranes and the development of protocells. These cycles, involving periods of water evaporation and rehydration, could have concentrated amphipathic compounds, the building blocks of early cell membranes, on surfaces like clay minerals. This concentration facilitated the formation of lipid vesicles, which are precursors to modern cell membranes.
Curiosity scientists had previously discovered small, simple organic molecules on Mars, but finding these larger compounds provides the first evidence that organic chemistry advanced toward the kind of complexity required for an origin of life on Mars.
Experiments conducted by the SAM instrument onboard the Curiosity rover have previously reported several classes of chlorinated and sulfur-containing organic compounds in Gale crater sedimentary rocks, with chemical structures of up to six carbons. The SAM pyrolysis sample revealed in the chromatogram the presence of the long-chain alkanes decane (C10H22), undecane (C11H24), and dodecane (C12H26. The mass spectrum of decane corresponds to that expected based on laboratory data from the SAM Earth-based testbed. SAM GCMS measurements are being performed using a unique instrument on Mars. Perseverance rover is not equipped with a SAM GCMS. The SAM experiment on Cumberland rock has been worked and optimized over the last 13 years of Curiosity’s mission. The origin of these molecules remains uncertain, as they could be derived from either abiotic or biological sources.
Asteroid Discoveries
As reported in the November 2023 EXPLORER, the OSIRIS-REx mission collected asteroid Bennu samples in October 2020 when the OSIRIS-REx probe executed the “Touch-and-Go” sample collection maneuver. The spacecraft descended to Bennu’s surface, briefly touched down, while firing a burst of nitrogen gas to stir up regolith, collecting samples in a specialized container. OSIRIS-REx completed its return journey to Earth in September 2023, delivering the collected samples back to Earth on a parachute in the Utah desert. The mission collected a total of 121.6 grams of material from asteroid Bennu. That is more than twice the mission goal of 60 grams.
The detailed sample analyses are nothing short of amazing.
Organic material found in meteorites offers insights into the early chemical processes of the solar system and the origins of life-related molecules, but interpreting these clues can be difficult due to contamination from Earth’s environment. However, samples collected from the B-type asteroid Bennu by NASA’s OSIRIS-REx mission allowed scientists to analyze pristine, carbon-rich material untouched by Earth’s biosphere. The analysis revealed that Bennu’s samples contain high levels of volatile elements – such as carbon, nitrogen and ammonia – exceeding those found in Japan’s asteroid Ryugu samples and most meteorites. Enrichment in nitrogen-15 isotopes suggests these nitrogen compounds, including ammonia, originated in a cold, molecular cloud or the distant regions of the early solar system’s protoplanetary disk. Researchers identified numerous organic compounds, including amino acids (14 of the 20 used in Earth biology), amines, formaldehyde, carboxylic acids, poly-aromatic ring hydrocarbons (PAHs), nitrogen-containing rings and all five nucleobases found in DNA and RNA (adenine, guanine, cytosine, thymine and uracil). In all they discovered around 10,000 carbon and nitrogen-based molecules. All detected amino acids had equal amounts of left- and right-handed molecules, as opposed to the left-handed bias seen in life on Earth. The types and proportions of amino acids and other soluble organics suggest they formed and changed through low-temperature chemical reactions, likely in ammonia-rich liquids. This implies Bennu’s parent body either formed in, or incorporated, material from a distant, cold region of the Solar System where ammonia ice could exist.
Exoplanet K2-18b
K2-18b is an exoplanet that orbits the red dwarf star K2-18, situated 124 light-years from Earth in the constellation Leo. An “exoplanet” or “extrasolar planet” is a planet orbiting a star outside our solar system.
The K2-18 star is too faint to be visible without a telescope. K2-18b, the planet, has a radius roughly 2.6 times that of Earth and completes one orbit every 33 days. It orbits within the star’s habitable zone where it receives a similar amount of light as Earth does from the Sun. First identified by the Kepler space telescope, K2-18b’s atmosphere was later examined in more detail using the new James Webb Space Telescope.
Analyses reported from JWST on K2-18b in The Astrophysical Journal Letters, April 20, 2025, has spurred news headlines such as “Alien Life Discovered on a Distant Planet!”
In contrast, let’s approach this with a note of caution.
In 2019, scientists reported the detection of water vapor in the atmosphere of exoplanet K2-18b, sparking significant interest in the system. By 2023, the JWST had identified carbon dioxide and methane in its atmosphere, which some researchers interpreted as evidence that K2-18b might be a water-rich world with a hydrogen-dominated atmosphere.
In 2025, further analysis suggested the presence of dimethyl sulfide (DMS), a compound potentially linked to life, at levels 20-times higher than those found on Earth. Since DMS is short-lived, its presence in such concentrations may indicate an active source. However, some scientists questioned the reliability of this conclusion, citing flawed analysis and laboratory studies that show DMS can also be formed through non-biological processes (synthesized in a laboratory, for instance). On Earth, DMS mostly comes from the breakdown of dimethylsulfoniopropionate (DMSP), a substance produced by certain marine algae. It is the most common biological sulfur compound released into the atmosphere and is also produced by marine bacteria and through the microbial conversion of dimethyl sulfoxide (DMSO).
On Earth, DMS and dimethyl disulfide (DMDS) are exclusively produced by living organisms, especially microbes like marine phytoplankton. While it’s possible that an unknown non-biological process is responsible for these gases on K2-18b, their presence represents the most compelling hint so far that life might exist beyond our solar system. The researchers claim that detections have reached a statistical confidence level of three sigma, meaning there’s only a 0.3-percent chance the result is due to random fluctuations. However, for the claim to qualify as a scientific discovery, it must reach five sigma – indicating a probability of less than 0.00006 percent that the observation happened by chance.
Lead researcher Nikku Madhusudhan of Cambridge’s Institute of Astronomy made a particularly striking comment: “The levels of DMS and DMDS in K2-18b’s atmosphere appear to be thousands of times higher than on Earth. This has fueled speculation that K2-18b may belong to a special class of exoplanets known as Hycean worlds – water-rich planets with hydrogen-heavy atmospheres.”
“Previous theoretical models predicted the potential for high levels of sulfur-based gases like DMS and DMDS on Hycean planets. Now we’ve observed exactly that, matching those predictions. Based on current data, the most consistent explanation is that K2-18b is a Hycean world with a life-filled ocean,” he added.
The ‘Sobering Reality’
Planetary scientist Sara Seager from MIT, along with her colleagues from the United States, United Kingdom and Europe, emphasized the challenges involved in using the JWST to conclusively identify signs of life on distant exoplanets. They point out that interpreting the data from transmission spectroscopy is highly complex and that this field of research is still in its infancy – though scientists are steadily improving their methods.
Seager and her team outline three essential criteria for confirming a potential biosignature:
- Detection: Is the signal strong and reliable?
- Attribution: Are the observed spectral features accurately linked to the right gases?
- Interpretation: Are the estimated planetary characteristics sound and well-understood?
According to the authors, the recent claims of detecting DMS or DMDS in the atmosphere of K2-18b do not satisfy any of these standards.
They write, “The proposed detection of DMS in K2-18b’s atmosphere is the exoplanet community’s first encounter with a potential biosignature that fails to meet all three critical criteria.”
Their conclusion is blunt: “We must face the sobering reality that JWST may never be able to definitively identify a biosignature gas in an exoplanet’s atmosphere.”
Despite this, the authors acknowledge the JWST’s importance in advancing the field. With more data and repeated observations, scientists are gradually building a clearer picture of distant planets and their atmospheres. As more potential biosignature detections emerge, each one will contribute valuable insights.
Looking ahead, the team notes that JWST will continue to be the centerpiece of this era of exploration and will likely be remembered as the telescope that laid the groundwork for answering one of humanity’s greatest questions: Are we alone in the universe?
But, as noted in previous EXPLORER astrogeology articles, famed astronomer Carl Sagan cautioned on the search for alien life, «Extraordinary claims require extraordinary evidence.»
These discoveries of complex organic molecules in many extraterrestrial settings is amazing and set the stage for the evolution of life, but as yet does not provide proof that life exists on other worlds. We now know that most star systems host planets. With at least 200 billion stars in our galaxy alone and probably over three trillion galaxies in the universe, what are the odds?
In this article, we have seen some of the strongest evidence of organic biosignatures from NASA’s recent flagship missions: sophisticated robotic rovers on Mars, sample returns from an organic rich asteroid and peering into the atmospheric chemistry of an exoplanet 124 light years from Earth fulfilling a goal of the sophisticated James Webb Space Telescope. The current NASA budget proposal includes unprecedented cuts to every sector of NASA.
Doug Wyatt, chair of AAPG’s Astrogeology Committee and NASA senior program manager and advisory scientist said, “(Perseverance) Mars sample return mission is in serious doubt.”
Meanwhile China is planning a Mars sample return mission for launch in 2028 or 2030. They are inviting international partners. This sounds like an opportunity for diplomatic cooperation. Let’s hope that congressional action on NASA’s budget continues to support science in the quest of the meaning of our existence in a nearly infinite universe.