Researchers Create Map of Electric Currents in Magnetosphere of Mars

Using five years of magnetic field data obtained by NASA’s MAVEN (Mars Atmosphere and Volatile EvolutioN) spacecraft, a team of scientists has created the first-ever map of the electric current systems in the Martian induced magnetosphere. Their results appear in the journal Nature Astronomy.

Earth’s magnetism comes from its core, where molten, electrically conducting iron flows beneath the crust. Its magnetic field is global, meaning it surrounds the entire planet.

Since Mars is a rocky planet like Earth, one might assume that the same kind of magnetic paradigm functions there, too. However, the Red Planet doesn’t generate a magnetic field on its own, outside of relatively small patches of magnetized crust.

Something different from what we observe on Earth is happening on Mars.

The solar wind blows constantly from the Sun and interacts with the objects in the Solar System.

It is also magnetized and this magnetic field cannot easily penetrate the upper atmosphere of non-magnetized planets like Mars.

Instead, currents that it induces in the planet’s ionosphere cause a pile-up and strengthening of the magnetic field, creating a so-called induced magnetosphere. How the solar wind powers this induced magnetosphere at Mars has not been well understood until now.

As solar wind ions and electrons smash into this stronger induced magnetic field near Mars, they are forced to flow apart due to their opposite electric charge. Some ions flow in one direction, some electrons in the other direction, forming electric currents that drape around from the dayside to the nightside of the planet.

At the same time, solar X-rays and ultraviolet radiation constantly ionize some of the upper atmosphere on Mars, turning it into a combination of electrons and electrically charged ions that can conduct electricity.

“Mars’ atmosphere behaves a bit like a metal sphere closing an electric circuit,” said Dr. Robin Ramstad, a physicist in the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder.

“The currents flow in the upper atmosphere, with the strongest current layers persisting at 120-200 km (75-125 miles) above the planet’s surface.”

Both MAVEN and previous missions have seen localized hints of these current layers before, but they have never before been able to map the complete circuit, from its generation in the solar wind, to where the electrical energy is deposited in the upper atmosphere.

Directly detecting these currents in space is infamously difficult.

Fortunately, the currents distort the magnetic fields in the solar wind, detectable by MAVEN’s sensitive magnetometer.

Dr. Ramstad and colleagues from the University of Colorado, Boulder, NASA’s Goddard Space Flight Center, and the University of Iowa used MAVEN data to map out the average magnetic field structure around Mars in 3D and calculated the currents directly from their distortions of the magnetic field structure.

“With a single elegant operation, the strength and paths of the currents pop out of this map of the magnetic field,” Dr. Ramstad said.

“We find unexpected features, in particular: coupling of the ionosphere and the bow shock, asymmetries between the north-south electric hemispheres and a twist in the near-Mars current system,” the researchers said.

“The current flow pattern in the induced magnetosphere of Mars indicates a system driven by a magnetospheric convective electric field, powered by the solar wind interaction.”