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Artist’s rendering of the atmosphere of Mars and the volatile evolution of NASA, or the MAVEN spacecraft orbiting Mars. Credit: NASA / GSFC
Mars it had a global magnetic field much earlier, and much later, in the history of the planet than scientists had previously known.
A planet’s global magnetic field arises from what scientists call a dynamo: a flow of molten metal within the planet’s core that produces an electric current. On Earth, the dynamo is what makes the compass needles point north. But the dynamo on Mars has been extinct for billions of years.
New findings from UBC researchers working with colleagues in the US USA And France, published on May 1, 2020, in Progress of science, It brings us closer to knowing the precise moment and duration of the dynamo on Mars.
“We discovered that the Martian dynamo operated 4.5 billion and 3.7 billion years ago. Dynamo time is a big part of a planet’s evolution, and what we find is very different from what we’ve thought so far, “said Anna Mittelholz, a postdoctoral fellow in the Department of Earth, Ocean and Ocean Sciences. UBC atmosphere, and first author of the study. “The dynamo tells us something about the thermal history of the planet, its evolution and how it got to where it is today, and is unique to each of the terrestrial planets: Earth, Mars , Venus and Mercury. “
Clues to a planet’s magnetic history lie in magnetized rocks above and below its surface. The rock is like a burner, especially volcanic rocks. They start out as lava, but as they cool and solidify in the presence of a magnetic field, the minerals within the rocks align with the global magnetic field. By dating these rocks, scientists can estimate whether a dynamo was active at the time the rock was placed.
Lucus Planum lava flow. Credit: NASA
Magnetism in certain rocks on the surface of Mars indicates that the Martian dynamo was active between 4.3 and 4.2 billion years ago, but the absence of magnetism in three large basins that formed 3.9 billion years ago has led to most scientists to believe that the dynamo was inactive because of that. hour.
The UBC researchers analyzed new satellite data and found clear evidence of a magnetic field from the Lucus Planum lava flow that formed less than 3.7 billion years ago, much later than the aforementioned basins.
The researchers also detected low-intensity magnetic fields over the Borealis basin in the planet’s northern hemisphere, which formed 4.5 billion years ago and is believed to be one of the oldest features on Mars.
“We have these two observations that point to a dynamo at the earliest known moment in the history of Mars, and a dynamo that was present half a billion years after many people thought it had already gone out,” said Catherine Johnson, professor. from the Department of Earth, Ocean and Atmospheric Sciences and Senior Scientist at the Planetary Science Institute in Tucson, Arizona, who also contributed to the study.
The researchers offer two possible explanations for the absence of magnetic fields over the watersheds: the dynamo may have stopped before the watersheds formed and then restarted before Lucus Planum was formed, or the impacts that the watersheds created simply displaced the portion bark containing minerals that can carry strong magnetism.
The new data for this study comes from MAVEN, the Mars Atmosphere satellite, and Volatile Evolution. Previous data on magnetism on Mars had been collected by the Mars Global Surveyor satellite that orbited the planet between 1999 and 2006, primarily 400 kilometers above the surface. MAVEN, launched in 2013, operates as close to ~ 135 kilometers from the surface and picks up weaker signals that MGS was unable to detect.
MAVEN’s ability to pick up signals with smaller characteristics at and near the surface helps researchers distinguish whether magnetism comes from them or from older rocks buried deeper in the planet’s crust.
These new ideas make researchers wonder what might be revealed if they get even closer. Mittelholz noted that this study focused on two particular characteristics, but craters remain across Mars with stories to tell. In the future, exploration could progress from satellites to drones or balloons, providing even more detailed data.
Reference: “Moment of the Martian dynamo: new constraints for a central field of 4.5 and 3.7 Ga ago” by A. Mittelholz, C. L. Johnson, J. M. Feinberg, B. Langlais and R. J. Phillips, May 1, 2020, Scientific advances.
DOI: 10.1126 / sciadv.aba0513
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