NASA releases latest map of electric currents around Mars, which accelerate atmospheric escape!

[Mobile software: Bo Ke Yuan] Five years after NASA's MAVEN spacecraft entered Mars orbit, the data obtained allowed the creation of a map of the current system in the Martian atmosphere. Robin Ramstad, an experimental physicist at the University of Colorado Boulder, said: These ocean currents play an important role in the atmospheric loss that has transformed Mars from a world that can support life to an uninhabitable desert. Scientists are currently working to use ocean currents to determine the precise amount of energy extracted from the solar wind and power the atmospheric escape.

Earth also has such an electric current system: we can even see them in the form of colorful light displays in the night sky near the polar regions, which are called auroras (Northern Lights and Southern Lights). The research results were published in the journal Nature Astronomy. Earth's auroras are closely related to electric currents generated by the interaction of Earth's magnetic field with the solar wind. These currents flow into the atmosphere along vertical magnetic field lines and are concentrated in the polar regions. However, studying the flow of electric currents thousands of miles above our heads only tells part of the story on Mars. The difference lies in the planets' respective magnetic fields, because while Earth's magnetism comes from the interior, Mars's magnetism does not.

Planetary magnetic field

Earth's magnetic field comes from its core, where molten, conductive iron flows beneath its crust, and is global, meaning it surrounds the entire planet. Since Mars is a rocky, terrestrial planet like Earth, one might expect the same magnetic paradigm to be at work there. However, Mars itself does not generate a magnetic field outside of relatively small patches of magnetized crust. Something must be going on on the Red Planet that is different than what is observed on Earth.

What happened on Mars?

The solar wind consists mostly of electrically charged electrons and protons, blowing continuously from the Sun at about a million miles per hour. It flows around and interacts with objects in the Solar System. The solar wind is also magnetized, and this magnetic field does not easily penetrate the upper atmospheres of unmagnetized planets such as Mars. Instead, the currents it induces in the Earth's ionosphere cause the magnetic field to pile up and strengthen, creating what is known as an induced magnetosphere. How the solar wind drives the induced magnetosphere on Mars has not been well understood until now.

When solar wind ions and electrons hit this stronger induced magnetic field near Mars, they are forced apart due to their opposite charges. Some ions flow in one direction and some electrons flow in the other, creating an electric current that travels from the day side of the planet to the night side. At the same time, solar X-rays and ultraviolet light are constantly ionizing some of the upper atmosphere on Mars, turning it into a combination of electrons and charged ions that can conduct electricity. The Martian atmosphere behaves a bit like a metal sphere with an electrical circuit turned off. Currents flow in the upper atmosphere, with the strongest layers lasting 120-200 kilometers (about 75-125 miles) above the planet's surface.

MAVEN and previous missions have seen localized signs of these layers of currents before, but never before have they been able to map the complete system of currents, from their generation in the solar wind to where the electricity is stored in the upper atmosphere. Directly detecting these currents in space is notoriously difficult, but fortunately, these currents distort the magnetic field in the solar wind, which is what MAVEN's sensitive magnetometer can detect. The team used MAVEN to map the average magnetic field structure around Mars in three dimensions and calculated the currents directly from their distortions of the magnetic field structure. With just one elegant operation, the strength and paths of the currents emerged from this magnetic field map.

The fate of the red planet

In the absence of a global magnetic field around Mars, electric currents induced in the solar wind can form a direct electrical connection with the Martian upper atmosphere. The electric currents convert the energy of the solar wind into magnetic and electric fields, accelerating charged atmospheric particles into space and driving atmospheric escape into space. The new research results reveal several unexpected features of MAVEN's goal of understanding atmospheric escape: the energy driving the escape appears to come from a much larger volume than is generally assumed. Atmospheric loss driven by the solar wind has been active for billions of years and has contributed to Mars' transformation from a warm and humid planet to a global cold desert.

Maven is continuing to explore how this process works and how much of Earth's atmosphere has been lost. This research was funded by the MAVEN mission, with Maven principal investigators working at the Laboratory for Atmospheric and Space Physics at the University of Colorado Boulder. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the MAVEN project. NASA is exploring the solar system and beyond, uncovering mysteries of worlds near and far, stars and the universe with powerful instruments in space and on ground-based missions.

Bo Ke Yuan | Research/From: NASA Goddard Space Flight Center

The study was published in the journal Nature Astronomy

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