The unusual “leopard spot” markings on Mars’ rocks might finally indicate that alien microbes could have existed on the Red Planet.

A comprehensive analysis of these rocks has shown that the intricate patterns are “the clearest signs ever found on Mars,” as stated by Sean Duffy, a NASA representative.

These rocks, estimated to be about 3.5 billion years old, were discovered in July 2024 by NASA’s Perseverance rover. Since then, planetary scientists have been exploring various hypotheses to explain these markings.

Recent information from a Nature paper suggests that while the patterns may have a geological origin, the prevailing theory now points toward ancient Martian microbes as the likely culprits.

Perseverance collected rock samples, hoping to yield a more definitive answer. If all goes well, these samples will eventually return to Earth for a thorough examination of potential signs of past life.

Leopard Spots on Bright Angel

Currently, Mars is a barren, lifeless world, but this hasn’t always been the case. Until around 3 billion years ago, Mars’ surface was rich with flowing rivers and expansive lakes.

Wherever there is water on Earth, signs of life typically follow. For two decades, NASA’s rovers have been scouring Mars for evidence suggesting that the Red Planet could have once supported life.

The Perseverance rover is exploring a site known as Jezero Crater, which was a lake in Mars’ ancient history. Similar environments on Earth often serve as habitats for microorganisms.

Within rock formations referred to as the Bright Angel formation, Perseverance uncovered stunning patterns resembling leopard spots.

“We conducted extensive observations of the entire rock formation at Bright Angel,” said Professor Joel Hurowitz of Stony Brook University in the US, in an interview with BBC Science Focus.

While Perseverance’s cameras captured detailed images of the patterns, a spectrometer analyzed the mineral composition. The rover even utilized radar to map the structure of the subsurface outcrop.

“Essentially, we used every tool available on these rocks except for the kitchen sink,” Hurowitz remarked.

The analysis indicated that the patterns were formed by iron-rich minerals called vivianite and greygite. On Earth, these minerals typically arise from “redox reactions,” a process in which microorganisms exchange electrons with their environment.

“On Earth, these reactions are often facilitated by microorganisms residing in sediments, which derive energy from them for metabolic activity,” Hurowitz explained. The residuals from these processes create distinctive patterns in sedimentary rocks.

However, this doesn’t mean we should rush to celebrate the discovery of alien life just yet. There are other mechanisms that could account for the leopard spot patterns without any biological influence.

For instance, heat could have driven reactions between mud and organic matter, resulting in new minerals.

Yet, the research team did not find evidence indicating that the rocks were subjected to heat. Additionally, other methods they investigated also did not seem viable. Nonetheless, Hurowitz cautioned, “We cannot dismiss these entirely.”

One of the most surprising findings is the relatively young age of these rocks. At only 3.5 billion years old, the patterns formed while Mars was already entering a phase of decline, suggesting that the planet may have been habitable for much longer than previously assumed.

Unfortunately, Perseverance has an entire planet to explore and we continue our quest to find life beyond Earth.

“If I could revisit Jezero in the future, I would have follow-up questions that I would like to address using the rover’s instruments,” Hurowitz remarked.

“However, these follow-up analyses may not necessarily provide a more conclusive answer regarding whether these features were shaped by life.”

“Ultimately, determining whether life was involved will necessitate laboratory analysis back on Earth.”

Bringing Mars to Earth

Fortunately, Perseverance is part of the initial phase of Mars’ sample return mission. Not only is it studying the rocks on Mars, but it’s also preparing to bring samples back to Earth.

Before departing from Bright Angel, the rover collected and stored samples from the rocks along with numerous similar fragments obtained during its mission on Mars.

NASA aims to collaborate with the European Space Agency on follow-up missions to retrieve these samples and return them to Earth where they can be analyzed in top-tier laboratories.

After 3.5 billion years, finding definitive evidence is challenging. Instead, researchers will seek additional signs that microbes may have left behind.

“The first logical step is to analyze the isotopic composition of iron, sulfur, and carbon in the various mineral and organic components of the rock,” Hurowitz stated.

Isotopes can be thought of as different variants of the same element. Microorganisms tend to retain particular isotopes more than their non-biological counterparts, enabling researchers to narrow down their search for evidence of life.

“These variations in isotopic composition are essential tools for investigating biological signals in ancient rocks on Earth, and we aim to apply similar methods to this Martian sample,” Hurowitz noted.

The return mission is tentatively scheduled for the 2030s, although there is a risk of cancellation due to cuts to NASA’s planetary exploration budget during the Trump administration.

“NASA is examining strategies for retrieving these samples and others,” a NASA spokesperson told BBC Science Focus. “Having explored Mars for 60 years, we will continue to look into budgetary and timing considerations for a quick and cost-effective return of these samples.”

“We hope these findings will further motivate the sample return mission,” Hurowitz added. “This will allow us to scrutinize the sample with the detail necessary to determine its historical record of life on Mars.”

“If it’s indeed life, that would suggest our planet is not the only one where life has evolved,” Frowitz concluded. “If life originated twice, how many other places might it have occurred?”

About Our Experts

Joel Hurowitz is an associate professor in the Department of Geoscience at Stony Brook University in New York, USA. He investigates the early history of Mars through measurements taken from planetary studies and Earth’s similar topographies.

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