Nasa makes ‘almost unbelievable’ discovery of Mars’s protective layer

An extremely rare solar event that left a void in space resulted in “almost unbelievable” expansion of the Martian atmosphere by thousands of kilometres, Nasa revealed in a new study.

In December last year, Nasa’s Maven mission observed the sudden “disappearance” of a stream of charged particles constantly coming off the Sun, known as the solar wind – an event so powerful that it created a void in its wake as it traveled through the solar system.

Measurements revealed that the number of charged particles making up the solar wind dropped drastically during this event.

Without the pressure of the solar wind, the Martian atmosphere and magnetosphere expanded by thousands of kilometres, according to Nasa’s observations, being presented at the American Geophysical Union Fall Meeting in San Francisco.

“When we first saw the data, and how dramatic the drop in the solar wind was, it was almost unbelievable. We formed a working group to study the event, and we have found this period to be rich with incredible findings,” study co-author Jasper Halekas from the University of Iowa said.

Previous studies have shown that Mars, just like other planets in the Solar System, is constantly immersed in charged particles streaming from the Sun which exert pressure on the Red Planet’s sphere of magnetism that comes from the planet’s rotation.

The solar wind striking Mars drives much of the escape of its atmosphere.

During the December 2022 event, the density of the solar wind dropped by a factor of 100, and caused the pressure exerted on Mars to decrease, leading to the planet’s magnetosphere more than tripling in size.

The event was caused by faster-moving solar wind overtaking slower-moving wind, sweeping and compressing the two regions together.

This compression left behind a rare void of extremely low-density solar wind in its wake, Nasa scientists noted.

Researchers say this dramatic solar event and the Martian magnetosphere’s subsequent transformation can help better understand the physics driving water and atmosphere loss on Mars.

“MAVEN was designed to observe these types of interactions between the Sun and the Martian atmosphere, and the spacecraft provided exceptional data during this truly anomalous solar event,” Shannon Curry, another author of the study from the University of California, Berkeley said.

Such dramatic disappearing solar wind events are extremely rare, produced at a time of increasing solar activity, researchers say.

With the Sun currently moving towards the peak of its 11-year activity cycle, the latest findings can help provide an even better understanding of extreme solar events, they say.

“We are really getting to see how Mars responds when the solar wind is effectively removed. It makes for a great outlier study on what Mars would be like if it were orbiting a less ‘windy’ star,” Dr Halekas added.