Mars Kept Its Magnetic Field Much Longer Than Previously Thought

Artist rendering of the MAVEN satellite. NASA

Mars hasn’t got a magnetic field but it did have in the past, Now new research suggests that it had one earlier – and much later – than previously thought. A fact that might have played an important role in the Red Planet's possible habitability in the distant past.

On terrestrial planets, strong magnetic fields arise from an effect called a dynamo: Molten metal in the planet’s core creates an electrical current that induces a magnetic field. This is how it works for Earth, and how it worked for Mars billions of years ago, until it ended.

Scientists can track this ancient magnetism by looking at volcanic rocks, whose minerals were aligned with the magnetic field before the lava cooled down and solidified. Previous observations of Mars reported magnetic fields from rocks that settled between 4.3 and 4.2 billion year, but no signature had been found in three locations that formed 3.9 billion years ago, leading scientists to think the dynamo was extinct by that time.

Now reported in Science Advances, two more locations with a magnetic signature have been identified. Evidence of the magnetic field comes from the Lucus Planum lava flow, which is believed to have formed 3.7 billion years ago. Low-intensity magnetic fields have also been found over the Borealis Basin, one of the oldest features on Mars believed to have formed 4.5 billion years ago, at the very dawn of the planet’s formation.

Lucus Planum lava flows on Mars. NASA

"We find that the Martian dynamo operated at 4.5 billion and 3.7 billion years ago. Dynamo timing is a big part of a planet's evolution, and what we find is very different from what we have thought so far," lead author Dr Anna Mittelholz, from the University of British Columbia, said in a statement.

"The dynamo tells us something about the planet's thermal history, its evolution, and how it got to where it is today, and it is unique for each of the terrestrial planets—Earth, Mars, Venus, and Mercury."

Our original understanding of the Mars dynamo comes from data collected by the Mars Global Surveyor, which orbited the planet at an altitude of 400 kilometers (250 miles) between 1999 and 2006. The new data used in this study is from the Mars Atmosphere and Volatile Evolution (MAVEN) satellite. It orbits much closer to the Red Planet's surface at 135 kilometers (85 miles) and can detect weaker magnetism coming from smaller features.

Future exploration might go further, characterizing the magnetic field of Mars in even more detail.

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