"When most people think of tides, they picture ocean movements caused by the Moon passing overhead," explained Dr. Brynna Downey. "But tides affect solid surfaces too, just in a less noticeable way. That gravitational interaction is what we call tidal dissipation." Downey, a postdoctoral researcher in SwRI's Solar System Science and Exploration Division in Boulder, Colorado, is the lead author of a study on this phenomenon published in Science Advances.
Scientists typically measure tidal dissipation on the Moon by bouncing laser signals off mirrors placed on its surface, allowing them to track minute movements. Since this approach isn't feasible for Titan, researchers instead analyzed how its spin axis deviates from the expected alignment, revealing clues about its tidal friction.
"Tidal dissipation influences a satellite's orbital and rotational evolution, as well as its ability to sustain subsurface oceans," said Downey. "Now that we have an estimate for the strength of tides on Titan, we can better understand how quickly its orbit is evolving. Our findings indicate that its orbit is changing at a geologically rapid pace."
Collaborating with Dr. Francis Nimmo from the University of California, Santa Cruz, Downey explored how friction within Titan's interior alters its spin pole orientation. By linking this angle to a tidal friction parameter, they reconstructed aspects of Titan's orbital history. Downey hopes that as upcoming missions explore moons like Europa and Ganymede, this method can be applied elsewhere.
A satellite's orbital progression typically trends toward circularity due to internal friction. Given the rate at which Titan's orbit is shifting, it should have become fully circular within approximately 350 million years. However, its current elliptical orbit suggests that a significant event disrupted its path within that time frame.
"An impact event or even the loss of an ancient moon could have altered Titan's orbit, but our findings don't specify the exact cause," Downey said. "What we do know is that something perturbed Titan's orbit within the last 350 million years-relatively recent in solar system history. We are observing it in the interval between that event and its eventual return to a circular orbit."
Research Report:Titan's spin state as a constraint on tidal dissipation
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