Neptune cloud cover over three decades

This sequence of NASA/ESA Hubble Space Telescope images chronicles the waxing and waning of the amount of cloud cover on Neptune. This nearly-30-year-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 Sun’s level of ultraviolet radiation is plotted in the vertical axis. The 11-year cycle is plotted along the bottom from 1994 to 2022. The Hubble observations along the top, clearly show a correlation between cloud abundance and solar peak of activity.

The theory is that the increased ultraviolet radiation from the Sun, during its peak of activity, causes chemical changes deep in Neptune’s atmosphere. After a couple years this eventually percolates into the upper atmosphere to form clouds.

The findings are published in the journal Icarus.

[Image description: This graphic shows a scientific plot in the form of a graph displaying changes in Neptune’s cloud cover compared to the 11-year-long repeating solar cycle of relative activity and inactivity on the Sun’s surface. The vertical axis plots the level of ultraviolet radiation coming from the Sun. The horizontal axis is a timeline from the years 1994 to 2022. Seven Hubble photos of Neptune taken in the years 1994, 1998, 2002, 2006, 2010, 2015, and 2020 are plotted above the graph. The planet is blue (due to methane absorption of red light in its atmosphere) and the high-altitude, cirrus-like clouds are white. A comparison of Neptune’s waxing and waning amount of cloud cover corresponds to peaks in the solar cycle. This graph clearly demonstrates the level of solar activity influences Neptune’s weather.]