NASA - National Aeronautics and Space Administration

The North Polar Ice Cap on Mars

If Santa Claus were a Martian, he'd be in for one bumpy ride.

That's the opinion of navigators and engineers controlling the flight of NASA's 2001 Mars Odyssey spacecraft as it presently flies four times daily above the north polar region of Mars.

"If he were flying above the North Pole of Mars, my advice to Santa would be 'Hang tight onto your reins,'" said Odyssey navigator John C. Smith. "You could be in for a rough ride."

During aerobraking maneuvers that are lowering the spacecraft's orbit around Mars, the Odyssey team discovered something unexpected. There is a somewhat unpredictable disturbance in the atmosphere above the north pole. This disturbance is making the job a real adventure, Smith said.

Fasten Your Seatbelt

This cold, low density region called the "polar vortex" forms each winter in the atmosphere above the planet's latitudes 70 degrees north and higher. The area between the polar vortex and the rest of the atmosphere is called the "transition zone." In this zone, strong winds swirl around the pole. The zone itself weaves in and out in the typical fashion of Earth's jet stream. It is an area where sometimes surprising shifts in the atmospheric density can become "fasten-your-seatbelt" territory for Odyssey.

Martian North Polar Cap on September 12, 1998

"When we're in the transition zone, the atmosphere is very unpredictable," said Smith.

Scientists and engineers have long known that Mars' atmosphere "breathes." It moves up and down - growing or decreasing in density with the effects of dust storms, winds, and other influences. But scientists and navigators are just getting to know up-close the moving polar vortex and its shifty transition zone. Excerpt from NASA's Mars Exploration Program