The giant vortex, which is wider than the Atlantic Ocean, was traveling south toward certain doom by atmospheric forces at the equator when it suddenly made a U-turn and began drifting back northward.
Hubble's Wide Field Camera 3 captured this visible-light image on Jan. That spot then vanished a few months later.
The smaller feature may have been a piece of the giant storm that broke off as the larger vortex approached the equator. Hubble uncovered the giant storm in September in Neptune's northern hemisphere. The feature is roughly 4, miles across. The estimated width of the smaller spot is 3, miles.
The large storm is the fourth transient dark spot Hubble has observed since NASA's Voyager 2 spacecraft first imaged two dark features in Neptune's southern hemisphere in as Voyager flew by the distant planet. Those storms had disappeared by the time Hubble looked at Neptune in Bright, high-altitude clouds accompany the new northern dark spot. Atmospheric gases that flow up over the spot cool to form the methane-ice crystal clouds.
The new spot might be a hole in Neptune's methane cloud tops, giving astronomers a peek at lower levels of the atmosphere. The distant, blue-green planet Neptune has again surprised astronomers with the emergence of a new great dark spot in the cloudy planet's northern hemisphere.
Only last June, Hubble images revealed that a great dark spot in the southern hemisphere - discovered by the Voyager 2 spacecraft during its flyby - had mysteriously disappeared. The new dark spot is a near mirror-image of the previous feature first mapped by Voyager 2. A dark storm on Neptune abruptly switched directions and started moving away from almost certain death, puzzling astronomers.
Usually, these dark spots on Neptune live for a few years before either vanishing or fading away. However, the storm mysteriously stopped moving south and made a sharp u-turn, drifting back northwards. The Great Red Spot has been observed since at least and could be up to years old.
Thin jet streams on Jupiter keep the Great Red Spot from breaking apart and from changing latitude; it rotates around Jupiter but doesn't move north or south. But Neptunian winds operate in much wider bands around the planet, so storms like the Great Dark Spot slowly drift across latitudes. These storms typically hover between westward equatorial wind jets and eastward-blowing currents in the higher latitudes before strong winds pull them apart. Planetary scientists hope to next study changes in the shape of the vortex and wind speed in storms that form dark spots.
More frequent observations using Hubble will help paint a clearer picture of how storm systems on Neptune evolve, he said. Materials provided by American Geophysical Union. Note: Content may be edited for style and length. Science News. Journal Reference : A.
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