The Unprecedented Solar Event at Mars Witnessed By MAVEN

Thursday - December 14 2023, 02:38 UTC - 11 months ago

In December 2022, NASA's MAVEN mission observed the 'disappearance' of a stream of charged particles off the Sun, known as the solar wind. This provided an opportunity for scientists to understand Mars' behavior better, and the observations of the event revealed a transformation in the Martian atmosphere due to the rare void of low-density solar wind in its wake.

In December 2022, NASA’s MAVEN (Mars Atmosphere and Volatile EvolutioN) mission observed the dramatic and unexpected “disappearance” of a stream of charged particles constantly emanating off the Sun, known as the solar wind. This was caused by a special type of solar event that was so powerful, it created a void in its wake as it traveled through the solar system. Due to this event, MAVEN’s measurements at Mars showed that the number of particles making up the solar wind dropped significantly. Without the pressure of the solar wind, the Martian atmosphere and magnetosphere expanded by thousands of kilometers. MAVEN is the only asset currently at Mars able to simultaneously observe both the Sun’s activity and the response of the Martian atmosphere to these solar influences.

"When we first saw the data, and how dramatic the drop in the solar wind was, it was almost unbelievable," said Jasper Halekas, professor at the University of Iowa and the lead author on a new study on the event. "We formed a working group to study the event, and we have found this time period to be rich with incredible findings." .

Mars, like all the planets in our solar system, is constantly immersed in the solar wind. The solar wind exerts pressure on the Martian magnetosphere and ionosphere, and drives much of the escape of the atmosphere. The solar event in December 2022 was caused by faster-moving solar wind that overtook slower moving solar wind, which acted like a broom, sweeping and compressing the two regions together. This interaction, called a stream interaction region, left behind a rare void of extremely low-density solar wind in its wake, which was observed by MAVEN. This “disappearance” of the solar wind led to some incredible interactions within Mars’ magnetosphere and ionosphere.

As the density of the solar wind dropped by a factor of 100, it caused the pressure to decrease and the magnetosphere and ionosphere of the planet were able to expand by thousands of kilometers­—more than tripled the typical size—and dramatically changed in character. The Sun’s magnetic field that typically is embedded within the Martian ionosphere was pushed outwards, which transformed the ionosphere from a magnetized to unmagnetized state. At the same time, the layer between the solar wind and the magnetosphere became unusually electromagnetically quiet. MAVEN’s observations of this dramatic event and subsequent transformation and expansion of the whole system is important to better understand the physics that drive atmospheric and water loss at Mars.

"We are really getting to see how Mars responds when the solar wind is effectively removed," said Halekas. "This event was an unprecedented opportunity to understand the behavior of the Martian atmosphere and its interaction with the Sun at a fundamental level." .