Neptune's Disappearing Clouds Linked to the Solar Cycle

Astronomers have uncovered a link between Neptune's shifting cloud abundance and the 11-year solar cycle, in which the waxing and waning of the Sun's entangled magnetic fields drives solar activity.

This discovery is based on three decades of Neptune observations captured by NASA's Hubble Space Telescope and the W. M. Keck Observatory in Hawaii, as well as data from the Lick Observatory in California.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.