Astronomers associate Neptune’s Clouds with solar activity

American astronomers have discovered a previously unknown connection between the state of cloud cover on Neptune and solar activity cycles. The more active the Sun, the brighter the clouds on the eighth planet.

Images of Neptune taken by the Hubble telescope between 1994 and 2020. Source: NASA, ESA, Erandi Chavez (UC Berkeley), Imke de Pater (UC Berkeley)

This discovery was made based on the results of observations of Neptune collected over the past three decades by the Hubble Space Telescope, as well as the Keck and Lick observatories. Computer analysis revealed a pattern between seasonal changes in Neptune’s cloud cover and the solar cycle — an eleven-year period during which the activity of our luminary reaches a maximum, and then gradually decreases to minimum values.

Thus, in 2002, the number of bright clouds on Neptune increased dramatically, but after only five years, the planet dimmed. Neptune became bright again in 2015, only to darken to the lowest level in the entire history of observations by 2020, when most of its clouds simply disappeared. All these changes in the brightness of the planet directly correlate with the maxima and minima of solar activity.

The relationship between the number of clouds on Neptune and solar activity. Source: NASA, ESA, LASP, Erandi Chavez (UC Berkeley), Imke de Pater (UC Berkeley)

According to the researchers, they were very surprised by the revealed pattern. The fact is that Neptune receives a thousand times less sunlight than Earth. Therefore, they assumed that the conditions of Neptune’s cloud cover were associated with the change of its seasons, which occur once every forty years. But it turned out that it was all about the Sun.

Apparently, the changes in the appearance of Neptune are caused by photochemical processes in the upper layers of the planet’s atmosphere, which occur due to the increased flow of ultraviolet radiation during solar storms. At the same time, there is a two-year delay between the peak of Solar Activity and the maximum number of clouds on the eighth planet. It is related to the fact that they take a certain time to form.

According to

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