A new chemical experiment carried out by NASA's Curiosity rover on the surface of Mars has revealed a rich variety of organic molecules for the first time on another planet, including key ingredients closely related to the origin of life on Earth. This discovery shows that the surface materials on Mars have the ability to preserve complex organic matter for a long time, providing important clues for assessing the past habitability of Mars, and laying the foundation for future missions to search for traces of ancient life.
The study was led by Amy Williams, professor of geology at the University of Florida and a member of the Curiosity and Perseverance science teams. Williams, who said the team believes the detected organic matter may have been preserved on Mars for about 3.5 billion years. "If we want to find evidence of life preserved in the form of organic carbon on Mars, we must first confirm whether ancient organic matter can be preserved for a long time in that environment, and this result shows that this is possibly." She pointed out that this is particularly critical for assessing whether the ancient Martian environment is suitable for microbial survival.
"Curiosity" landed in Gale Crater in 2012. Its main scientific goal is to determine whether Mars had an environment suitable for microbial survival billions of years ago. "Perseverance", which will arrive on Mars in 2021, is more directly focused on finding traces of ancient life. The new results announced this time are based on experiments carried out by Curiosity in an area called "Glen Torridon" in Gale Crater. This area is rich in clay minerals that form in aqueous environments and is considered the most promising place for organic molecules to be captured and preserved.
According to a paper published in Nature Communications, the experiment identified more than 20 different chemicals, including nitrogen-containing organic molecules whose structures are similar to compounds involved in building DNA-like molecules. Such structures have never been detected on Mars before. In addition, the team also discovered large sulfur-containing organic molecules such as benzothiophene. These bicyclic compounds were often transported to the surface of planets through meteorites in the early stages of planetary evolution and are considered to be one of the important "raw material packages" that constitute the precursors of life.
Williams pointed out that the meteorites that landed on Mars and Earth experienced a similar enrichment process in the early solar system. "The batch of materials that landed on Earth and may have provided the starting building blocks for life also landed on Mars." This means that, at least at the level of chemical raw materials, Mars and Earth had some commonality in their early days. The researchers emphasized that the current experiments still cannot answer whether these organic matter originated from ancient life activities, geological processes, or the input of foreign meteorites, but they confirmed that the shallow crust of Mars has the ability to preserve complex organic molecules.
The work relies on the Sampling and Analysis of Mars (SAM) science instrument suite, led by astrobiologist Jennifer Eigenbrode of NASA's Goddard Space Flight Center and others. Curiosity uses a chemical reagent called TMAH in its onboard laboratory to break large organic molecules in rock samples into smaller fragments for analysis by the SAM instrument. Since the total amount of TMAH carried by Curiosity is only about two cups, the scientific research team must carefully select the best drilling location early in the mission to maximize scientific return.
The experimental sample comes from rock powder drilled by Curiosity at the Mary Anning site. This site, named after 19th-century British paleontologist Mary Anning, is considered one of the most representative records of ancient lacustrine sediments in Gale Crater. Previous geological and mineralogical surveys have shown that liquid water once persisted here, and the sediments are rich in clay minerals, providing a "natural safe" for capturing and sealing organic molecules. The latest experimental results further prove that it is this type of clay-enriched area that is most likely to preserve important chemical and even biological stories that happened on Mars.
The research team emphasized that although the organic matter found is very close to some key components of life on Earth, existing airborne analysis capabilities cannot give a clear conclusion whether they are produced by biological processes. To confirm the true "biological characteristics", it is still necessary to bring Martian rock samples back to Earth and carry out multi-level comprehensive identification of isotopes, molecular structure and microscopic morphology under more complex and sophisticated experimental conditions. This is also highly consistent with the current "Mars Sample Return" concept: the orbiter and ascent rocket will try to return the samples cached by "Curiosity" and "Perseverance" to the Earth laboratory in future missions.
The success of this TMAH experiment not only reshaped the scientific community's understanding of the ability to preserve the Martian shallow environment, but also directly affected the design of experimental plans for future deep space missions. The article points out that the European "Rosalind Franklin" Mars rover mission and the "Dragonfly" mission to Saturn's moon Titan are expected to use similar chemical cracking and analysis techniques to systematically search for complex organic matter on more celestial bodies. In Williams’ view, “We now know that a huge amount of complex organic matter is preserved in the shallow underground of Mars, which provides very encouraging prospects for the future search for large organic molecules that can directly indicate the existence of life.”
TAGPH1 Although there is still no answer to the fundamental question of whether Mars once harbored life, this discovery by Curiosity proves that the ancient environment of Mars was rich in organic chemical resources, and that these resources can be locked in rocks and clay minerals on geological time scales. As subsequent rovers continue to drill samples in Gale Crater and other target areas, combined with Perseverance's exploration of delta sediments in Jezero Crater, humans are expected to give a much clearer answer to the "possibility of life" on Mars in the next few decades than now.