Evidence indicates that Mars may have hosted life billions of years ago.
Mars is now cold, dry, and without its protective magnetic field. Scientists study the planet as a scene that helps them find out if Mars was once able to support life and, if so, when that might have been.
The researchers at Harvard’s Paleomagnetics Lab in the Department of Earth and Planetary Sciences have focused on discovering when certain events happened on the red planet.
Their new paper in Nature Communications shows that Mars’ magnetic field, which could have supported life, might have lasted until about 3.9 billion years ago.
This is later than the estimated 4.1 billion years, suggesting it could have survived hundreds of millions of years longer than scientists thought.
Calculating magnetic field
A student from the Griffin Graduate School of Arts and Sciences, Sarah Steele, led a study using simulation and computer modeling to estimate the age of Mars’s global magnetic field, or “dynamo. “
Together with senior author Roger Fu, the John L. Loeb Associate Professor of the Natural Sciences, the team has doubled down on a theory they first argued last year that the Martian dynamo, capable of deflecting harmful cosmic rays, was around longer than prevailing estimates claim.
They argued that the Martian dynamo, which protects against harmful cosmic rays, lasted longer than earlier estimates suggested.
The researchers developed ideas by conducting experiments that mimic how large craters on Mars cool down and become magnetized.
Known to be only weakly magnetic, these well-studied impact basins have led researchers to assume they formed after the dynamo shut down.
This timeline was hypothesized using basic principles of paleomagnetics, or the study of a planet’s prehistoric magnetic field.
Scientists know ferromagnetic minerals in rock align themselves with surrounding magnetic fields when the rock is hot, but these small fields become “locked in” once the rock has cooled.
This effectively turns the minerals into fossilized magnetic fields, which can be studied billions of years later.
3.9 billion years
Looking at basins on Mars with weak magnetic fields, scientists surmised they initially formed amid hot rock during a period in which no other strong magnetic fields were present — after the planet’s dynamo had gone away.
However, according to Steele, the Harvard team says this early shutdown isn’t necessary to explain those largely de-magnetized craters.
Rather, they argue that the craters were formed while the dynamo of Mars was experiencing a polarity reversal — north and south poles switching places — which, through computer simulation, can explain why these large impact basins only have weak magnetic signals today.
Magnetic pole flips also happen on Earth every few hundred thousand years.
“We are basically showing that there may not have ever been a good reason to assume Mars’ dynamo shut down early,” Steele said.
Their results build on previous work that first upended existing Martian habitability timelines.
They used a famed Martian meteorite, Allan Hills 84001, and a powerful quantum diamond microscope in Fu’s lab to infer a longer-persisting magnetic field until 3.9 billion years ago by studying different magnetic populations in thin slices of the rock.
Steele says poking holes in a long-held theory is a little nerve-wracking but that they’ve been “spoiled rotten” by a community of planetary researchers who are open to new interpretations and possibilities.
“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 said.
“Planetary magnetic fields are our best probe to answer a lot of those questions, and one of the only ways we have to learn about the deep interiors and early histories of planets.”
