A groundbreaking discovery has been made within a Martian meteorite, revealing the presence of water on Mars dating back an astonishing 4.45 billion years. This revelation comes from the analysis of a zircon grain, which may hold the oldest direct evidence of ancient, hot water on the red planet. Such an environment, reminiscent of Earth's hot springs, could have been conducive to life. This finding not only broadens our understanding of Mars' ancient habitability but also corroborates the observations made by spacecraft currently exploring Mars, which have detected signs of past rivers and lakes on its surface. However, the precise timing of water's emergence on Mars and its subsequent evolution and disappearance remain enigmatic.

Researchers delved into a sample from the "Black Beauty" meteorite, or NWA 7034, which was discovered in the Sahara Desert in 2011. This meteorite was ejected from Mars' surface following an impact with another celestial body between 5 and 10 million years ago. It has been a treasure trove for studying ancient Mars for several years. The recent study, published in the journal Science Advances on November 22, concentrated on a single zircon grain found within the meteorite. The findings indicate that water was present just 100 million years after Mars' formation, suggesting that the planet may have once been hospitable to life.

"The data we've gathered points to the existence of water in Mars' crust around the same time as the earliest evidence of water on Earth's surface, approximately 4.4 billion years ago," explained Jack Gillespie, the lead study author and a researcher at the University of Lausanne's Faculty of Geosciences and Environment in Switzerland. "This discovery sheds new light on Mars' planetary evolution, the processes that occurred there, and its potential to have supported life."

The quest to understand Mars' geological history and the possibility of past life on the planet is closely tied to the study of meteorites like Black Beauty. Carl Agee, a professor and director of the Institute of Meteoritics at the University of New Mexico, introduced this space rock to the scientific community in 2013. "The Black Beauty meteorite contains a multitude of rock and mineral fragments, each representing a different part of Mars' 4.5 billion-year history," said Dr. Aaron Cavosie, a co-author of the study and a planetary scientist at Curtin University's Space Science and Technology Centre. "It is the sole source for geological samples from the pre-Noachian era of Mars."

The Noachian period spanned from 4.1 to 3.7 billion years ago, and direct measurements from this era on Mars are scarce, yet understanding this period is crucial as it marks the beginning of Mars' history. Black Beauty has unveiled some of its secrets, with many rock fragments indicating that the Martian crust experienced numerous impacts, causing significant upheaval on the planet's surface. The meteorite also contains some of the oldest known pieces of Mars, including the oldest zircons, as stated by Cavosie.

Zircon, a mineral used in various products such as jewelry, ceramic tiles, and medical implants, is robust and can help scientists look back in time to determine the conditions present when it crystallized, including the temperature and interaction with water. "Zircon contains traces of uranium, which acts as a natural clock," Gillespie explained. "This element decays to lead at a precisely known rate. By comparing the uranium-to-lead ratio, we can calculate the age of the crystal formation."

The zircon in Black Beauty remained unchanged during its journey to Earth and its fiery entry into our atmosphere, thanks to its protected location within the meteorite's interior, according to Cavosie. During the analysis of the zircon grain, the team detected unusual amounts of iron, sodium, and aluminum, suggesting that water-rich fluids left these traces on the zircon as it formed 4.45 billion years ago. These elements are not typically found in crystalline zircon, but the researchers' atom-scale studies revealed the elements incorporated into the crystal structure, aligning like items in a market stall, as described by Cavosie.

"We could discern from the patterns of iron, aluminum, and sodium within the zircon that they were incorporated into the grain as it grew, much like the layers of an onion," Cavosie said. On Earth, zircons from hydrothermal systems, which form when water is heated by subsurface volcanic activity, exhibit similar patterns to those found in Black Beauty. If hydrothermal systems existed in the Martian crust 4.45 billion years ago, it is likely that liquid water reached the surface.

"Our experience on Earth demonstrates that water is essential for habitats capable of supporting life," Cavosie said. "Many environments on Earth host life in hot water systems, including hot springs and hydrothermal vents. Such environments may have given rise to the earliest life forms on Earth. Our new study indicates that Mars' crust was warm and wet during the pre-Noachian period, suggesting that habitable environments may have existed at that time."

Cavosie is eager to determine whether hydrothermal systems like hot springs were prevalent during the formation of Mars' crust between 4.48 billion and 4.43 billion years ago or if they were more sporadic. "If hydrothermal systems were a stable feature on early Mars, it would suggest that habitable conditions may have persisted over a significant period," Cavosie said. "This is now a testable hypothesis that can be addressed by collecting more data from Martian zircons."

Until samples can be directly returned from Mars, the Black Beauty meteorite remains one of the best windows into the formation of the Martian crust and the early surface conditions of Mars, according to Briony Horgan, a co-investigator on the Perseverance rover mission and a professor of planetary science at Purdue University in Indiana. Horgan was not involved in this study. Finding evidence of hydrothermal systems within the subsurface from a single grain of zircon aligns with scientific theories on the amount of water and volcanic activity that existed on ancient Mars, she added. These earliest potentially habitable environments would have been shielded from radiation by a strong planetary magnetic field, which Mars lacks today, Horgan noted. Scientists are still investigating how Mars lost its protective magnetic field.

Currently, the Perseverance rover is ascending the rim of Jezero Crater on Mars, an ancient lake that was once filled with water 3.7 billion years ago. Some of the rocks the rover has encountered may have been formed by hydrothermal systems, Horgan said. The rover will collect samples from these rocks, as they could preserve evidence of ancient microbial life. "As much as meteorites can inform us, we can achieve a more detailed understanding with carefully selected and intact rock samples from a known location on Mars with a clear geological context," Horgan said. "This paper is a strong motivation for bringing Mars samples back to Earth for in-depth study over the years to come."