A mysterious ‘wobble’ is moving Mars’ poles around

Like a teetering top, Mars refuses to rotate on a straight axis.

Mars and its two moons, Phobos and Deimos
(Image: © NASA/ JPL)

The Red Planet is wiggling and wobbling as it spins, research in the journalGeophysical Research Letters confirms, and astronomers have no idea why.

Like a toy top that teeters as it loses speed, the poles of Mars are wandering ever-so-slightly away from the planet’s axis of rotation, moving about 4 inches (10 centimeters) off-center every 200 days or so, researchers reported in a study published Oct. 13, 2020. That makes Mars only the second known planet in the universe to exhibit this phenomenon — known as the Chandler wobble— with Earth being the first, according to the American Geophysical Union’s (AGU) news blog, Eos.org.

This wobble — named for astronomer Seth Carlo Chandler, who discovered the phenomenon more than a century ago — is an effect seen in planets that aren’t perfectly round, science writer Jack Lee wrote at Eos. On Earth, the wobble is much more pronounced: Our planet’s poles wander roughly 30 feet (9 m) from its axis of rotation, wobbling in a circular pattern that repeats every 433 days or so.

This wonky wobble has negligible effect on our planet, according to Eos, but still presents a puzzle. Scientists have calculated that the wobble should naturally die down within a century of its origin, but our planet’s current wobble has been going strong for much longer than that. Something — perhaps a combination of pressure changes in the atmosphere and oceans, one 2001 study proposed — seems to be perpetually reigniting the wobble, though the exact mechanism is still unknown.

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