University of Iowa physicists have detailed interactions between magnetic field lines of the sun and Mars that may help explain how Mars turned from a warm, hospitable planet into a dry, cold, and hostile environment.

Using orbital observations and evidence obtained from NASA rovers on the red planet’s surface, scientists know that billions of years ago Mars was much wetter and warmer, with a thicker atmosphere. A big, unanswered question is how the planet evolved into today’s cold desert with a very thin atmosphere.

In a new study, the Iowa physicists propose that one reason may be because of a phenomenon known as an interplanetary magnetic field rotation. The rotation occurs when the powerful jet of energized particles flung out from the sun, called the solar wind, interacts with Mars’ magnetotail, a long, trailing magnetic field.

These interactions can cause magnetic reconnection, where magnetic field lines rapidly break and reconnect, releasing energy and accelerating charged particles.

On Earth, magnetic reconnection events can cause geomagnetic storms and auroras. On Mars, which lacks a global magnetic field, “these reconnection events could play a key role in how the Martian atmosphere escapes into space over time — something that may help explain how Mars lost much of its atmosphere and became the cold, dry planet we see today,” says Yuanzheng Wen, a graduate student in the UI Department of Physics and Astronomy and the study’s corresponding author.

The magnetic reconnection events were captured thanks to two spacecraft. Tianwen-1, China’s Mars orbiter, recorded the solar wind disturbance. NASA’s MAVEN spacecraft, positioned in Mars’ magnetotail, detected the magnetic reconnection event minutes later. 

The twin spacecraft allowed researchers to “establish a cause-and-effect relationship that was previously impossible to confirm using just one spacecraft,” says Wen, who studies under Jasper Halekas, professor in the Department of Physics and Astronomy.

The study, “Multipoint Observations of Magnetic Reconnection in the Martian Magnetotail Triggered by an Interplanetary Magnetic Field Rotation,” was published online April 1 in The Astrophysical Journal Letters.

Han-Wen Shen, a postdoctoral research scholar in the Department of Physics and Astronomy at Iowa, is a co-author on the study. Other co-authors include Abigail Azari, from the University of Alberta; David Brain and Yaxue Dong, from the University of Colorado-Boulder; David Mitchell and James McFadden, from the University of California-Berkeley; Christian Mazelle, from the Institut de Recherche en Astrophysique et Planetologie, in Toulouse, France; and Jared Espley, from NASA Goddard Space Flight Center.

NASA funded the research.