Neptune Cloud Cover Over Three Decades

This sequence of Hubble Space Telescope images chronicles the waxing and waning of the amount of cloud cover on Neptune. This long set of observations shows that the number of clouds grows increasingly following a peak in the solar cycle – where the Sun's level of activity rhythmically rises and falls over an 11-year period.

The chemical changes are caused by photochemistry, which happens high in Neptune's upper atmosphere and takes time to form clouds.

In 1989, NASA's Voyager 2 spacecraft provided the first close-up images of linear, bright clouds, reminiscent of cirrus clouds on Earth, seen high in Neptune's atmosphere. They form above most of the methane in Neptune's atmosphere and reflect all colors of sunlight, which makes them white. Hubble picks up where the brief Voyager flyby left off by continually keeping an eye on the planet yearly.

About the colours

These images were acquired by the WFPC2 and WFC3 instruments on the Hubble Space Telescope. The color results from assigning a blue hue to a monochromatic (grayscale) image.

About the data

The HST observations include those from several programs throughout three decades of observations including: 5221 , 5329 , 5831 , 6219 , 6650 , 7324 , 8634 , 9393 , 10170 , 10534 , 11156 , 11630 , 12675 , 13937 , 14044 , 14334 , 14756 , 15262 , 15502 , 16057 , 16084 , 16454