Mars’ atmosphere, once so thick that it was no thicker than Earth’s today, is leaking into space. About 0.25 pounds (0.11 kg) of the Martian atmosphere is pushed every second by the persistent solar wind, a fast stream of charged particles regularly ejected from the Sun, stretching across the Solar System and even reaching the outskirts of Pluto.

But for two rare days last December, some of that wind disappeared. Its sudden and dramatic disappearance caused the atmosphere on the solar side of Mars to nearly quadruple its normal size, from the normal 497 miles (800 km) to more than 1,864 miles (3,000 km). The unusual event was recorded by a NASA orbiter called MAVEN (short for Mars Atmosphere and Volatile Evolution), which observed both the Martian atmosphere and its response to behavior. Sun Since 2014. MAVEN data showed other aspects of the Martian system, including a teardrop-shaped magnetosphere, a mainshock, and a similarly expanding ionosphere.

“We’ve really gone beyond that,” said Jasper Halekas, a professor of physics and astronomy at the University of Iowa and a member of the MAVEN team, at this week’s AGU conference on Monday, Dec. 11. California and online. “This is something we haven’t seen before with MAVEN on Mars.”

The unusual event, the first in MAVEN’s nearly decade-long career, occurred when a fast-moving region of the solar wind caught up with a slower one, trapping the latter’s material and leaving behind a rarefied region. The dying storm reached Mars on December 25, 2022, giving scientists an exciting front-row seat to watching the planet’s atmosphere bulge as it might if it orbited a less “windy” star.

“This was a Christmas present for us,” said Halekas, who is conducting the new investigation into the incident. “Nature created this perfect science experiment.”

Using MAVEN data on unexpected dynamics on Mars, Halekas and colleagues examined how extreme solar events (and their absence) affect the planet’s atmosphere; This is valuable for understanding the evolution of the planet. The findings also have implications for our understanding of terrestrial planets outside our solar system and how they interact with their host stars, the team said Monday.

“We can look at what’s going on in the physics, how the dynamics work, and really get a feel for those details,” said MAVEN team member Skylar Shaver of the Laboratory for Atmospheric and Space Physics in Boulder.

Two days after the near-empty storm passed over Mars, the atmosphere around the Red Planet had returned to its original state, but not before bouncing a little like a wobbly saucer of jelly. A similar storm hit Earth in 1999, when our planet’s atmosphere expanded to five times its normal size. But orbiting spacecraft are not as well positioned as MAVEN is currently to study such events, New Atlas reported.