When was Mars habitable? Much more recently than we thought

The notion that Mars once teemed with life billions of years ago continues to intrigue scientists. Today, the red planet’s cold, dry landscape, stripped of its once-strong magnetic field, poses questions reminiscent of a cosmic forensic investigation. 

Researchers are particularly interested in understanding whether Mars was habitable, and if so, during what period.

Mars’ magnetic field

A research team at Harvard’s Paleomagnetics Lab, within the Department of Earth and Planetary Sciences, has been at the forefront of exploring this timeline. 

A recent paper in Nature Communications presents their strongest evidence yet that Mars‘ life-protecting magnetic field, or “dynamo,” could have lasted until about 3.9 billion years ago. 

This contrasts with older estimates that placed its demise around 4.1 billion years ago, suggesting the dynamo persisted for hundreds of millions of years longer than previously thought.

Modeling the Martian dynamo

Leading the study is Griffin Graduate School of Arts and Sciences student Sarah Steele, who, with the help of computer modeling and simulation, has worked to pinpoint the age of Mars’ dynamo. 

The Martian dynamo, driven by convection within the planet’s iron core much like Earth’s, could shield the surface from harmful cosmic rays, crucial for maintaining a habitable environment. 

Steele, along with senior author Roger Fu, a professor of natural sciences, is challenging prevailing theories that Mars’ magnetic field weakened early. Their research incorporates simulations of the cooling and magnetization processes in Mars’ surface craters. 

Previously studied impact basins on the planet are known for their weak magnetic fields, leading to the assumption they were formed after the planet’s dynamo had already ceased.

Magnetic fields preserved in rock 

Paleomagnetics, which involves studying ancient magnetic fields preserved in rock, provided the foundation for these assumptions. According to the experts, ferromagnetic minerals within rock align with magnetic fields when heated, and once the rock cools, this alignment is “frozen” in place. 

Such fossilized magnetic signatures can be examined billions of years later, revealing the state of the magnetic environment during the rock’s formation.

The weak magnetic signals observed in some Martian craters led researchers to theorize that these features formed in the absence of an active dynamo. 

However, Steele’s team proposes an alternative explanation: these basins may have formed during a polarity reversal, where the north and south magnetic poles switch places. 

These reversals occur periodically on Earth, and simulations indicate that they could account for the weak magnetic fields detected in Martian craters.

Habitable Mars: A shift in perspective 

According to Steele, this finding challenges long-held beliefs about when Mars’ dynamo ceased. 

“We are basically showing that there may not have ever been a good reason to assume Mars’s dynamo shut down early,” she said. This new interpretation builds on the team’s earlier work that first questioned the established Martian habitability timeline.

Their previous research involved examining a well-known Martian meteorite, Allan Hills 84001, using an advanced quantum diamond microscope in Fu’s lab. 

The analysis revealed varying magnetic properties within the rock that hinted at a magnetic field lasting until approximately 3.9 billion years ago.

Significance of planetary magnetic fields

Steele acknowledged that challenging a widely accepted theory can be daunting. However, she noted that the planetary research community has been supportive of fresh perspectives. 

“We are trying to answer primary, important questions about how everything got to be like it is, even why the entire solar system is the way that it is,” Steele explained. Magnetic fields play a key role in these explorations, as they offer insights into the deep interiors and the early history of planets.

The potential implications extend beyond Mars. Understanding the longevity and nature of magnetic fields on other planets helps scientists draw parallels and contrasts with Earth’s history. 

These insights also inform the search for habitability on planets beyond our solar system, suggesting that the presence and persistence of a magnetic field could be vital indicators of a world’s potential to host life.

When was Mars habitable?

The research by Steele and her team is a testament to how scientific thinking evolves with new data and innovative methodologies. 

By re-examining the nature and duration of Mars’ magnetic field, they open new paths for understanding the planet’s ability to support life billions of years ago. 

This deeper exploration of planetary history emphasizes the need for continuous investigation and creative approaches to age-old questions in planetary science.

The findings offer a renewed lens through which to view Mars’ ancient environment, ultimately bringing researchers a step closer to deciphering the planet’s mysterious past and its implications for life beyond Earth.

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