Astronomers have detected an extraterrestrial cyclone at Neptune's south pole, which may improve our understanding of the violent weather conditions that rage across the distant planet.
It could also help us better understand Neptune's internal structure.
The team of astronomers made the discovery while studying clouds on other planets using the giant 10-metre Keck Telescopes on Mauna Kea, Hawaii.
The paper appears in the pre-press website arXiv.org and has accepted for publication in the journal Icarus.
"Ever since the 1989 Voyager 2 flyby of Neptune, scientists have known of a white spot racing around the planet's south pole," says Dr Mate Adamkovics, a research scientist at the University of California, Berkeley.
"But very high resolution images taken in July 2007, thanks to the adaptive optics on Keck, allowed us to see that the spot had divided into two, and then just two days later in another image from Keck showed they had recombined."
Adamkovics and collagues, led by Statia Luszcz-Cook, believe they're probably seeing methane clouds caught in a powerful cyclonic vortex of winds at Neptune's south pole.
"I've seen the same sort of thing at one of Saturn's poles, and we know that's caused by clouds caught in a giant hurricane like vortex," Adamkovics says.
"Neptune's clouds are behaving the same way. Although we can't see it, a vortex is likely to be at the heart of this activity.
"Although huge by Earth standards, being thousands of kilometres wide, extraterrestrial hurricanes are remarkably similar to the ones we see on Earth, including a well-formed eye in the middle and a surrounding ring of strong convection".
The clouds on Neptune are also consistent with clouds formed by the up welling and condensation of methane gas. In other words it rains methane on Neptune.
Adamkovics hopes the study will provide further incentive for a new mission to the outer gas giants Uranus and Neptune.
"That would be the only way to verify that the dynamics seen at Neptune's pole are analogous with what we see closer in on Saturn," he says.
"We still need to know more about the internal energy that's driving these weather patterns. It's not just heat from the Sun, and gravitational heating, those we know about fairly well.
"There's got to be some radiological heating as well. So by studying clouds on other planets like Neptune we can understand more about that planets internal structure."