The search for life on Mars has brought scientists face to face with new information that the Red Planet was likely habitable until recently. A new paper presents evidence that Mars was likely teeming with life billions of years ago. Scientists have tried to find signs of life on the neighboring planet, and if it existed, when did it disappear?

Researchers at Harvard’s Paleomagnetics Laboratory in the Department of Earth and Planetary Sciences worked to understand the “when” part. In their paper published in Nature Communications, they argue that Mars’ vital magnetic field could have survived until about 3.9 billion years ago. This is hundreds of millions of years younger than previous estimates of 4.1 billion years.

Sarah Steele, a student at the Griffin Graduate School of Arts and Sciences, led the study and used simulation and computer modeling to estimate the age of the Martian “dynamo,” or the overall magnetic field produced by convection in the iron core of the planet.

Lead author Roger Fu, John L. Loeb Associate Professor of Natural Sciences, and his team say the magnetic field capable of deflecting harmful cosmic rays has existed for much longer than current estimates claim.

The team simulated the cooling and magnetization cycles of Martian craters that are only weakly magnetic. Scientists believe they formed after the dynamo shut down. They say these basins initially formed amid hot rocks when no other strong magnetic fields were present.

However, Steele and the team say this early shutdown of the magnetic field is not necessary for the craters to form. Instead, they say the craters formed when the north and south poles changed places in Mars’ dynamo. This is why, they say, these large impact basins have only weak magnetic signals today.

The Earth’s magnetic poles also reverse every few hundred thousand years. “We’re essentially showing that there may never have been a good reason to assume that the Mars dynamo stopped prematurely,” Steele said.

“We’re trying to answer primary and important questions about how everything got to be the way it is, and even why the entire solar system is the way it is,” Steele said.

“Planetary magnetic fields are our best probe to answer many of these questions and one of the only ways we have to learn about the deep innards and early histories of the planets.”