Hubble Reveals Dynamic Atmospheres of Uranus and Neptune

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Hubble Reveals Dynamic Atmospheres of Uranus and Neptune
NASA | GSFC | STScI | HubbleSite | 2019 Feb 07

Credits: NASA, ESA, A. Simon (GSFC), and M.H. Wong and A. Hsu (UC Berkeley) Uranus (left) and Neptune (right)

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During its routine yearly monitoring of the weather on our solar system's outer planets, NASA's Hubble Space Telescope has uncovered a new mysterious dark storm on Neptune (right) and provided a fresh look at a long-lived storm circling around the north polar region on Uranus (left).

Like Earth, Uranus and Neptune have seasons, which likely drive some of the features in their atmospheres. But their seasons are much longer than on Earth, spanning decades rather than months. ...

Both planets are classified as ice giant planets. They have no solid surface but rather mantles of hydrogen and helium surrounding a water-rich interior, itself perhaps wrapped around a rocky core. Atmospheric methane absorbs red light but allows blue-green light to be scattered back into space, giving each planet a cyan hue.

The new Neptune and Uranus images are from the Outer Planet Atmospheres Legacy (OPAL) program, a long-term Hubble project, led by Amy Simon of NASA's Goddard Space Flight Center in Greenbelt, Maryland, that annually captures global maps of our solar system's outer planets when they are closest to Earth in their orbits. OPAL's key goals are to study long-term seasonal changes, as well as capture comparatively transitory events, such as the appearance of Neptune's dark spot. These dark storms may be so fleeting that in the past some of them may have appeared and faded during multi-year gaps in Hubble's observations of Neptune. The OPAL program ensures that astronomers won't miss another one. ...

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Hubble Captures Birth of Giant Storm on Neptune
American Geophysical Union | 2019 Mar 25

This composite picture shows images of storms on Neptune from the Hubble Space Telescope (left) and the Voyager 2 spacecraft (right). The Hubble Wide Field Camera 3 image of Neptune, taken in Sept. and Nov. 2018, shows a new dark storm (top center). In the Voyager image, a storm known as the Great Dark Spot (GDS) is seen at the center. It is about 13,000 km by 6,600 km in size — as large along its longer dimension as the Earth. The white clouds seen hovering in the vicinity of the storms are higher in altitude than the dark material. Credit: NASA/ESA/GSFC/JPL

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Images taken by the Hubble Space Telescope document the formation of a Great Dark Spot on Neptune for the first time, report researchers in a new study.

Like Jupiter’s Great Red Spot, Neptune’s Great Dark Spots are storms that form from areas of high atmospheric pressure. In contrast, storms on Earth form around areas of low pressure.

Scientists have seen a total of six dark spots on Neptune over the years. Voyager 2 identified two storms in 1989. Since Hubble launched in 1990, it has viewed four more of these storms.

In the new study, planetary scientists analyzed Hubble’s photos of the ice giant taken over the past several years and chronicled the growth of a new Great Dark Spot that became visible in 2018.

By studying companion clouds that showed up two years before the new Great Dark Spot, the researchers conclude dark spots originate much deeper in Neptune’s atmosphere than previously thought.

The Hubble images also helped the researchers pinpoint how often Neptune gets dark spots and how long they last. The new findings give scientists insights on the inner workings of the poorly-understood ice giant planets but also have implications for studying exoplanets of similar size and composition. ...

Formation of a New Great Dark Spot on Neptune in 2018 ~ A. A. Simon, M. H. Wong, A. I. Hsu

• Geophysical Research Letters (online 25 Mar 2019) DOI: 10.1029/2019GL081961