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Despite both being rocky and terrestrial planets, Mars and Earth’s magnetic fields are poles apart. Whilst the flow of conducting molten iron in Earth’s core gives rise to electric currents that in turn generate the global magnetic field around our planet, Mars does not have the same ability to produce such a field on its own. Instead, induced electric currents in the Martian ionosphere generate the planet’s magnetosphere.
New data gathered by NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft has enabled scientists to map this system of electric currents around the planet for the first time. Not only does this highlight the differences between the systems of Earth and Mars, but it can also explain how charged particles escape to space from the Martian atmosphere.
“These currents play a fundamental role in the atmospheric loss that transformed Mars from a world that could have supported life into an inhospitable desert,” Robin Ramstad, experimental physicist of the University of Colorado, explained in a statement. “We are now currently working on using the currents to determine the precise amount of energy that is drawn from the solar wind and powers atmospheric escape.”
In order to understand the currents' effect, scientists needed to figure out how these currents form in the first place. In the absence of a protective atmosphere, solar X-rays and ultraviolet radiation can tear apart atoms in Mars’ upper atmosphere, creating electrically charged ions and electrons.
At the same time, magnetized solar wind is blown constantly from the Sun at around a million miles per hour. When the solar wind’s magnetic field interacts with the charged ions and electrons in the Martian upper atmosphere, an electric current is induced. These moving charges thus generate their own magnetic field – the Martian induced magnetosphere.
“Mars’ atmosphere behaves a bit like a metal sphere closing an electric circuit,” Ramstad explained. “The currents flow in the upper atmosphere, with the strongest current layers persisting at 120-200 kilometers (about 75-125 miles) above the planet’s surface.”
Before this study, published in Nature Astronomy, these currents had been infamously difficult to directly detect. However, fortunately for the researchers, the induced current actually gives rise to a feedback effect on the magnetic field of the solar wind, causing it to drape around the planet. Using MAVEN’s sensitive magnetometer, these distortions could be calculated and related back to the electric currents that were responsible for them.
“With a single elegant operation, the strength and paths of the currents pop out of this map of the magnetic field,” Ramstad said.
Having now generated this map, researchers hope to understand in greater depth the current’s involvement in driving the atmospheric loss of the planet, as well as its influence on the movement of charged particles around it.
