A combined team of researchers from the Jet Propulsion Laboratory, California Institute of Technology and the Royal Observatory of Belgium, has found evidence that Mars has a Chandler wobble. In their paper published in the journal Geophysical Research Letters, the group describes their study of decades of data from Mars probes and what it showed them.

Approximately a century ago, astronomer Seth Carlo Chandler discovered that imperfectly round objects (such as planets) sometimes spin off their axis for periods of time. The phenomenon has come to be known as the Chandler wobble, and has been documented for planet Earth, which veers from its axis for distances up to 30 feet in a pattern that repeats approximately every 433 days. Researchers have suggested that other planets likely have a Chandler wobble, but until now, it has never been observed because measuring it on the planet scale requires precise measurements over many years. In this new effort, the researchers obtained the right kind of data from space probes that orbited Mars over many years: The Mars Reconnaissance Orbiter, the Mars Global Surveyor and Mars Odyssey.