) The appearance of a massive white cap on Uranus may seem alarming, but as scientists of planetary science are learning, an extended summer on the remote icy giant looks like this.  The ice giants Uranus and Neptune have a water-rich interior, which is coated with hydrogen, helium and a pinch of methane. The latter gives this outer planet its characteristic cyan complexion. Unlike Earth, Neptune and Uranus only last a few months. Experience decades of seasons that lead to strange and intense atmospheric phenomena.
New images from the Outer Planet Atmospheres Legacy (OPAL) program show a developing atmospheric event on both ice giants, namely an expanded white cap Uranus & # 39; north pole and a new dark vortex on Neptune: OPAL, a long-term side project of the Hubble Program, is an annual effort to map these two planets as their orbits bring them closest to Earth. The new data, collected in the fall of 2018, provide important new insights into the seasonal fluctuations of Neptune and Uranus.
"The annual observations help us to understand the frequency of storms and their longevity," said Amy Simon, a NASA-Goddard Space Flight Center researcher who heads the OPAL mission, to Gizmodo. "That's important because these planets are quite far from the sun. This will help to limit the shape of their formation and more about the internal heat and structure of these planets. Most extrasolar planets found have this size of planet, albeit at all possible distances from their parent stars.
The large white cap over Uranus' North Pole is particularly dramatic. The probable cause of this function is the planet's unique inclination, which causes sunlight to shine directly into the North Pole region during the summer for a long time. It is just high summer at the North Pole of Uranus, resulting in a long white cap.
"The image of Uranus in November 2018 appears at a time ten years after the midnight point, when the northern hemisphere emerged in the spring sunlight after decades of polar winter," said Leigh Fletcher, an astronomer at the University of Leicester Gizmodo. "In 2007, there did not seem to be anything like this pole cap over the spring post. Over time, however, a reflective band – whitish against Uranus & # 39; blue tones – began to show around the North Pole. And now, ten years later, this band has evolved into a thick polar cap made of aerosols that hides the deeper polar region in front of the eyes. "
Fletcher said it was a" spectacular example of seasonal change "of this ice giant, with" the aerosol cap developing with spring to summer. "The exact causes of these aerosol changes remain a mystery, with possibilities such as heating temperatures, unusual chemistry, some large-scale atmospheric circulation patterns, or a combination of all these factors.
"Fortunately, we are not too far from answering as the James Webb Space Telescope is able to diagnose the temperatures and chemistry responsible for these reflectivity changes that Hubble has monitored," added Fletcher ,
Patrick Irwin, a planet scientist at Oxford University, said the phenomenon was not a storm, as NASA described it in its release. Rather, "at least in our models, it is mainly due to lowering the methane abundance above the main cloud cover, possibly leading to a slight increase in turbidity turbidity," he told Gizmodo.
Simon thought the advanced Polar feature was cool, but "more interesting for me is the bright storm just below it," she told Gizmodo. "This particular storm had flared up and was visible in small groundscopes shortly before these observations, showing how fast these can change."
) Looking at the new Neptune image, it seems as if a dark vortex has re-erected its ugly but intriguing head. The new anti-cyclone storm seen above The top center image is about 11,000 kilometers (6,800 miles) wide and is now the fourth dark vortex Hubble has seen since 1993. Two of these storms were observed by the Voyager 2 probe during the system's flyby in 1989. In summary, these observations confirm the transient and recurrent nature of these storms: a polar vortex observed in 2016 has largely faded.
"The dark spot of Neptune is much larger than the one we saw few," said Simon. "This is also the first time that we have been able to see the region before a storm of this size has formed, so this will help us to model the model." Educational process. "
The causes of this dark spot are a mystery, but because they can only be seen at the blueest wavelengths," my money is in a kind of coloration of the clouds, "said Irwin.
These distant glacial giants, often overshadowed by their larger cousins, Jupiter and Saturn, prove themselves fascinating. We now look forward to next year's OPAL observations with great anticipation.