A new study shows that Mars, which is now cold and dry, may have been under a warm and humid "tropical rainforest-like" climate for a long time billions of years ago. Some areas were even similar to tropical oases on Earth, with continuous rainfall and a rich liquid water environment. This judgment comes from the large pieces of light-colored "bleached" rock fragments discovered by the "Perseverance" Mars rover during its journey in Jezero Crater. Analysis has confirmed that they are rich in an aluminum kaolinite clay mineral, which is usually only formed in large quantities under long-term heavy rainfall leaching conditions.
The research team believes that these minerals not only provide key evidence for the ancient climate of Mars, but also further strengthen the possibility that Mars once had an environment suitable for life.
This result was recently published in the journal "Communications Earth & Environment" and was led by Adrian Broz, a planetary scientist at Purdue University. Members of his team are also involved in the long-term scientific planning of the National Aeronautics and Space Administration (NASA) "Perseverance" mission. The researchers pointed out that in the Mars orbit detection data, kaolinite rocks are extremely rare and are regarded as the most difficult type of alteration mineral to form, which means that extremely abundant and long-lasting water activity is required behind them. On Earth, this type of aluminum kaolinite mostly develops in areas with high temperature and humidity such as tropical rainforests, or in weathered zones exposed to heavy rainfall for a long time.
Based on the spectral and imaging data obtained by scientific instruments such as SuperCam and Mastcam-Z onboard Perseverance, the research team compared these light-colored fragments in the Jezero Crater with kaolinite samples near San Diego, California, and South Africa, and found that their mineral combinations and alteration characteristics are highly similar. This means that these rocks on Mars are likely to have experienced long-term rainfall leaching processes similar to those in Earth's tropical rainforests, rather than just being modified by local hydrothermal processes. The scientists further used data sets from three different locations to compare the differences in chemical fingerprints between the "high-temperature hydrothermal leaching" and "low-temperature rainwater leaching" scenarios, and ultimately preferred the latter.
However, the "life" of these kaolinite fragments is still an unsolved mystery. Currently, these light-colored rock blocks can be seen everywhere along the route of the "Perseverance", but no obvious large-scale parent rock exposures have been found in the nearby strata. The research team proposed two possibilities: First, these materials were originally developed in large kaolinite rock bodies in other areas of Mars, and were later transported by ancient rivers and deposited into the ancient lake where Jezero once existed; second, these rock blocks may have originated from one or more meteorite impacts, and were ejected and scattered on the surface of the crater.
Satellite remote sensing shows that large areas of kaolinite outcrops also exist in other areas of Mars, but it is currently not possible to conduct a close inspection by a Mars rover. Therefore, for these fragments ranging in size from small pebbles to large boulders in the Jezero Crater, they are currently the only kaolinite samples that humans can "personally" analyze, providing a valuable window for interpreting the evolution of the ancient Martian environment. Scientists emphasize that these rocks are like a "time capsule" that preserves the climate and hydrological conditions that Mars experienced billions of years ago, helping to deduce how the planet went from possible warmth and moisture to today's cold and arid conditions.
Broz pointed out that on Earth, kaolinite can not only be formed through long-term rainfall leaching in tropical rainforest-like climates, but it can also be formed by hot water transforming original rocks in high-temperature hydrothermal systems, but the latter will leave behind completely different chemical characteristics than low-temperature rainwater leaching. Comparative analysis shows that the chemical fingerprints of the samples in Jezero Crater are more consistent with the "long-term leaching of cold water" scenario, thus supporting the inference of continuous rainfall and stable water circulation in the early Mars. The research team believes that these rainfall processes may have continued for millions of years, enough to reshape the mineral composition of large areas of the Earth's crust.
The Jezero Crater is believed to have had an ancient lake about twice the size of Lake Tahoe in the early days of Mars. Its delta sedimentary landform has been regarded as a key area for searching for clues to ancient life as early as the mission planning stage. The fragments of kaolinite now discovered near the lake basin provide important support for the "ancient lake + rainfall" scenario, giving the idea that "Mars was once a tropical oasis" a more solid mineralogical foundation. The research team stated that if in-situ investigations of large kaolinite outcrops in other areas of Mars can be carried out in the future, it is expected to further clarify the origin and spatial distribution of these rocks, thus piece together a more complete picture of the ancient climate of Mars.
From the perspective of life potential, the "rain-fed environment" pointed by kaolinite is particularly interesting. Water is the basis for the existence of all known life forms, and a long-term warm, humid, and water-rich environment is regarded as a key condition for nurturing life and even maintaining the stability of ecosystems. Researchers believe that if Mars once had a long-term rainfall and humid environment similar to that in tropical areas on Earth, then what these kaolinites record is likely to be a period of climate that is extremely friendly to potential life; if life ever appeared on Mars, this may be one of the most likely stages for its prosperity and development.
Compiled from /ScitechDaily