First detection of a built-in wobble on another planet – Mars

Clouds on Mars [image credit: NASA]

Regarding the Earth’s equivalent Chandler wobble, Wikipedia says: ‘Since the Chandler wobble should die down in a matter of decades or centuries, there must be influences that continually re-excite it.’ Presumably the same will apply to Mars, but as relevant observations are all fairly recent no conclusion can be reached at present.
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Spacecraft find that Mars oscillates 10 centimeters off its axis of rotation, says Eos.

In a first for a solar system body other than Earth, scientists have detected the Chandler wobble on Mars, a repeated movement of the poles on the surface of the planet away from its average axis of rotation.

The Chandler wobble arises when a rotating body isn’t a perfect sphere. This imbalance affects its spin.

The result is a wiggle resembling that of a swaying top as it loses speed, rather than the smooth spin of a perfectly balanced globe.

Measurements over nearly 2 decades by spacecraft orbiting Mars uncovered that on the surface, the planet’s poles wander up to 10 centimeters from the average axis of rotation, with a repeated cycle of about 207 days.

The new findings by Konopliv et al provide new insights into the interior of Mars.

The amount of time it takes for the pole to complete one cycle of the wobble reflects how much Mars’s mantle can deform, providing hints about its material properties and thermal state.

“[The Chandler wobble] is a very small signal, typically,” said Alex Konopliv, an aerospace engineer at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “You need many years and high-quality data to detect it,” he said.

A previous study, for example, didn’t have enough data points to differentiate the Chandler wobble from seasonal effects. Konopliv is the lead author of the new research, which was published in AGU’s Geophysical Research Letters.

The Chandler wobble is one of several off-center motions exhibited by Earth as it rotates on its axis. Earth’s Chandler wobble varies from 3 to 6 meters at the poles and has a pattern that repeats approximately every 433 days.

Although such motion should naturally dampen over time, on Earth it persists because of ocean bottom and atmospheric pressure fluctuations.

In the new study, researchers were able to confirm the movement on Mars by calculating gravitational effects on the orbits of two NASA spacecraft circling the Red Planet: Mars Odyssey and the Mars Reconnaissance Orbiter.

The large quantity of data, collected over 18 years and not available during earlier analyses, ensured that the identified wobble was intrinsic to the planet’s shape and interior, rather than outside factors like seasonal melting of polar ice caps.

Full article here.

via Tallbloke’s Talkshop

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January 8, 2021 at 03:21AM

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