Like Earth, Uranus and Neptune also have seasonal and experienced weather patterns. However, unlike on Earth, the seasons on this planet last years and not months, and the weather patterns are on a scale unimaginable to Earth standards. A good example is the storms observed in the atmosphere of Neptune and Uranus, including the famous Dark Spot of Neptune.
During its annual routine monitoring of Uranus and Neptune, NASA's Hubble Space Telescope (HST), recently updated observations of the weather patterns of both planets have been provided. In addition to a new mysterious storm on Neptune Hubble gave a long-lasting storm around the North Pole of Uranus. These observations are part of Hubble's long-term mission to improve our understanding of outer planets.
The new images were taken as part of the Outer Planet Atmospheres Legacy (OPAL) program -term Hubble project, led by Amy Simon of the Goddard Space Flight Center of NASA. Each year, this program captures global maps of the outer planets of our solar system when they are closest to Earth. A key objective of OPAL is to study long-term seasonal changes and relatively transitory events, such as the appearance of dark spots.
It's not an easy task to discover, as these dark patches are fast and relatively short-lived, to the point where some may have appeared and disappeared during Hubbard Neptune's multi-year gaps , This is another objective of the OPAL program to ensure that astronomers do not miss another one.
This last dark spot with a diameter of about 11,000 km (6,800 mi) appears at the top center of the planet. Hubble first discovered it in September 2018, when Neptune's southern hemisphere experienced summer. This is in line with the seasonal changes on the planet, where warming in the southern hemisphere makes the weather in the north more dramatic.
Although it is not known exactly how these storms are forming, new research by Simon and the OPAL team suggests they are fast, take four to six years and then disappear within two years. Like the Great Red Spot of Jupiter, the dark vortex swirls in an anticyclonic direction and seem to hurl material from deeper levels in the ice giant's atmosphere.
In fact, the Hubble observations obtained since 2016 suggest that the eddies likely develop deeper in Neptune's atmosphere and only become visible when the top of the storm reaches higher altitudes. Meanwhile, they are accompanied by accompanying clouds, which are visible in the Hubble images as bright white spots to the right of the dark feature.
These clouds are made of methane ice, which freezes when the vortices cause the Airflow is deflected upwards the storm is deflected. The long, thin cloud to the left of the dark spot is a transitory feature that is not part of the storm system. The same applies to Uranus, who shows a huge bright cloud cap over the North Pole.
In the case of Uranus, scientists believe that this is a consequence of the unique orientation of Uranus, where the axis is tilted 90 ° from the equator of the Sun. As Uranus practically orbits on its side, the sun shines almost directly on the North Pole in summer in the northern hemisphere. At the moment, Uranus is approaching the middle of the summer season, making the polar cap region more prominent.
This polar cap can be the result of seasonal changes in atmospheric flow and is accompanied by a large, compact methane ice cloud near its edge. Also visible is a narrow band of clouds surrounding the planet north of the equator. This is another puzzle of Uranus and Neptune, which is why bands like this are limited to such narrow latitudes when the planet has such wide west-wafting windjets.
This is the fourth mysterious vortex mapped by Hubble since 1993 and the sixth since astronomers became aware of these phenomena for the first time. The first two dark spots were discovered by the spacecraft Voyager 2 (19459005) when it made its historic flyby of Neptune in 1989. To date, only the Hubble Space Telescope has been able to track these features for its sensitivity to blue light.
These images are part of a growing database of Hubble snapshots of Neptune and Uranus, tracking the weather behavior of the planet over time. Just as forecasters predict weather on Earth due to long-term trends, astronomers hope Hubble's long-term monitoring of the outer planets will help them solve the long-lasting secrets of their atmospheres.
The analysis of the weather on these worlds will also improve the understanding of the diversity of atmospheres in the solar system and their similarities. In the end, this could also make a big contribution to conveying our understanding of extrasolar planets and their atmospheres, and perhaps even determining whether they can support life or not.
Further Reading: Hubblesite