Well, the UFOlogists won't like it, but UCLA scienstists have come up with an explanation for the giant white arrow observed on the surface of Titan, Saturn's largest moon - and it's not an 'X marks the spot' from aliens.
Using a global circulation model of Titan, assistant professor Jonathan Mitchell says that planetary-scale atmospheric waves can affect the moon's weather patterns and lead to a 'stenciling' effect that results in sharp and sometimes surprising cloud shapes.
"These atmospheric waves are somewhat like the natural, resonant vibration of a wine glass," he says. "Individual clouds might 'ring the bell,' so to speak, and once the ringing starts, the clouds have to respond to that vibration."
The resulting clouds can cause intense precipitation — sometimes more than 20 times Titan's average seasonal rainfall — and could be essential in shaping Titan's surface by erosion.
Mitchell and a colleague have described Titan's climate as "all-tropics", with the entire planet experiencing the sort of weather that's only found near the equator on Earth.
"Our new results demonstrate the power of this analogy, not only for general features of Titan's climate but also for individual storms," Mitchell said. "In future work, we plan to extend our analysis to other Titan observations and make predictions of what clouds might be observed during the upcoming season."
Titan has a thick nitrogen atmosphere and experiences clouds formed of methane, which falls as rain and is resupplied from surface sources.
Earth may once have been very similar, as its early atmosphere had large amounts of methane and very little oxygen.
Methane provided an important greenhouse warming effect that's probably what prevented the Earth from staying perpetually frozen.
"Therefore, by studying Titan's modern climate, we may gain new insights about the way the early Earth's climate was," says Mitchell.