Astronomers compare Mars's weather patterns with those on Earth. (© Artsiom P - stock.adobe.com)
GREENBELT, Md. — In a groundbreaking discovery, scientists have uncovered evidence of extreme climate change on Mars billions of years ago. A recent study by NASA researchers reveals that carbonates found in Mars’ Gale Crater contain unusually high levels of heavy carbon and oxygen isotopes, painting a picture of a dramatically evolving Martian environment that left the planet virtually lifeless.
The research team, led by David G. Burtt from NASA’s Goddard Space Flight Center, analyzed data collected by the Curiosity rover, which has been exploring Gale Crater since 2012. The crater, once home to an ancient lake, provides a unique window into Mars’ past. The results are published in the Proceedings of the National Academy of Sciences.
Carbonates, minerals that form in the presence of water, are like time capsules that preserve information about the environment in which they formed. On Earth, we find carbonates in limestone and chalk. The carbonates discovered on Mars are a bit different – they’re rich in iron, forming minerals called siderite and ankerite.
What makes these Martian carbonates truly extraordinary is their isotopic composition. Isotopes are versions of the same element with different numbers of neutrons. The Martian carbonates contain unusually high amounts of carbon-13 and oxygen-18, the heavier isotopes of carbon and oxygen.
“The isotope values of these carbonates point toward extreme amounts of evaporation, suggesting that these carbonates likely formed in a climate that could only support transient liquid water,” explains Burtt in a media release. “Our samples are not consistent with an ancient environment with life (biosphere) on the surface of Mars, although this does not rule out the possibility of an underground biosphere or a surface biosphere that began and ended before these carbonates formed.”
To put this in perspective, imagine you have a bag of marbles where most are light, but a few are heavy. In normal circumstances, you’d expect to pull out mostly light marbles. In the case of these Martian carbonates, however, it’s as if someone reached into the bag and pulled out a surprisingly large number of the heavy marbles.
This isotopic enrichment is so extreme that it surpasses levels found in any other known Martian materials, including the current Martian atmosphere and other meteorites from Mars. It’s a scientific puzzle that demands an explanation.
The research team proposes two main mechanisms that could have led to this isotopic enrichment. The first is extensive evaporation, similar to what happens when a puddle dries up, leaving behind concentrated minerals. As water evaporates, it prioritizes removing lighter isotopes, leaving behind heavier ones.
The second proposed mechanism involves the formation of these carbonates in very cold, near-freezing conditions. This process, known as cryogenic precipitation, can cause unusual separation of isotopes due to the slow movement of molecules at low temperatures.
“The fact that these carbon and oxygen isotope values are higher than anything else measured on Earth or Mars points towards a process (or processes) being taken to an extreme,” Burtt explains. “While evaporation can cause significant oxygen isotope changes on Earth, the changes measured in this study were two to three times larger. This means two things: 1) there was an extreme degree of evaporation driving these isotope values to be so heavy, and 2) these heavier values were preserved so any processes that would create lighter isotope values must have been significantly smaller in magnitude.”
These findings suggest that Gale Crater experienced dramatic shifts between wet and dry conditions, possibly cycling between a water-filled crater and a parched, evaporative environment. This aligns with other evidence indicating that Mars transitioned from a wetter world to the cold, dry planet we see today.
Moreover, the study highlights how different Mars’ carbon cycle is from Earth’s. Without the influence of a biosphere – the collective term for all living things on a planet – Mars’ geochemical processes have taken a dramatically different path. As scientists continue to explore the Red Planet, each discovery is bringing humans closer to understanding Mars’ past, its ancient potential to harbor life, and what may have happened to it.
Paper Summary
Methodology
The study utilized data from two instruments aboard the Curiosity rover: the Chemistry and Mineralogy (CheMin) X-ray diffractometer and the Sample Analysis at Mars (SAM) instrument suite. CheMin analyzed the mineralogical composition of drilled rock samples, while SAM heated the samples and analyzed the gases released. The tunable laser spectrometer within SAM measured the isotopic composition of the evolved carbon dioxide. This combination of techniques allowed the team to identify the presence of carbonates and determine their unusual isotopic composition.
Key Results
The researchers analyzed samples from four different sites within Gale Crater. The carbon isotope values (δ13C) of the carbonates ranged from 72 to 110 parts per thousand, while the oxygen isotope values (δ18O) ranged from 59 to 91 parts per thousand. These values are significantly higher than those found in other Martian materials or in Earth’s carbonates. The team also observed variations in carbonate abundance and isotopic composition across the four sites, correlating with changes in the local environment from lacustrine (lake-like) to more arid conditions.
Study Limitations
The study is limited by the small number of samples analyzed and the restricted geographical area of Gale Crater. Additionally, the lack of precise dating for the carbonate formation makes it challenging to link these findings to specific periods in Mars’ history. The proposed mechanisms for isotopic enrichment are based on models and Earth analogs, which may not perfectly translate to Martian conditions.
Discussion & Takeaways
The extreme isotopic enrichment in these carbonates suggests that Mars underwent significant climatic changes, likely involving cycles of wet and dry conditions. The study proposes that a combination of evaporation and cryogenic precipitation could explain the observed isotopic values. These findings contribute to our understanding of Mars’ climate history and highlight the differences between Martian and terrestrial geochemical cycles. The research also underscores the value of in-situ measurements on Mars for unraveling its complex past.
Funding & Disclosures
This research was supported by NASA, with some authors receiving funding through the NASA Postdoctoral Program. The study utilized data from the Mars Science Laboratory mission, which is operated by NASA’s Jet Propulsion Laboratory. The authors declared no competing interests.
