Neptune’s clouds suddenly disappeared!

Those over 40 may remember the first close-up images of the planet Neptune provided by NASA during the summer of 1989, when the Voyager 2 probe reached Neptune’s north pole at a distance of about 4,950 kilometers. These images showed that the ice giant’s atmosphere was much more active than previously thought, and data collected by the probe showed that Neptune was emitting slightly more energy than it was receiving from the Sun.

We can clearly see Jupiter’s equivalent of the Great Red Spot, but here it is darker against a blue background resulting from Neptune having so much methane in its atmosphere. White clouds were also clearly visible in the upper atmosphere. All this data puzzled planetary scientists, as they wondered whether it might be the source of Neptune’s internal energy that made it hotter than the Sun, and how our star’s light might also contribute to the active and complex chemistry associated with it. Could The existence of linear and luminous clouds, reminiscent of cirrus clouds on Earth.

a large faint star barely 1/30th the diameter of a full moon

Located about 4.5 billion kilometers from the Sun, Neptune receives only 0.1% of the radiation measured on Earth. An observer in orbit, for example on Neptune’s satellite Triton, would see the Sun as a large faint star barely 1/30 of the way.^I The diameter of the full moon.

To better understand Neptune’s mysteries, since Voyager 2’s flyby, planetary scientists have periodically monitored its atmosphere first with the Hubble telescope and then with instruments from the WM Keck Observatory in Hawaii, using adaptive optics. possible to make. ,

Planetary scientists, such as the renowned Imke de Pater, Astronomy and Emeritus Professor of Terrestrial and Planetary Sciences at the University of California at Berkeley (and author of a famous treatise on planetary science), are therefore studying modifications of Neptune’s activity, and in 2019 I got a surprise. Within a few months, much of the ice giant cloud had disappeared, and much of it remains today.

Today in the famous newspaper Icarus these 30 years of observation and review of this mysterious disappearance has been published. The article in question can be found in open access on arXiv.

Cloud cover is controlled by the sunspot cycle

Data collected during the monitoring program now strongly suggest that the disappearance of Neptune’s clouds is cyclical and controlled by the 11-year solar cycle known from sunspots. This cycle is governed by the mechanisms behind our star’s magnetic field on the Sun and by the physics of the solar plasma in a turbulent magnetic field. There is an entanglement of field lines in relation to the differential rotation of the inner layers of the Sun, which concentrates energy which is eventually released.

The publication also includes a statement from NASA Icarus And we can read Emke de Pater’s declarations thus: I was amazed at how quickly the clouds on Neptune disappeared. We’ve basically seen a decline in cloud activity over the course of a few months. ,

, Even now, four years later, the most recent images we took last June still show that the clouds have not returned to their previous levels. This is extremely exciting and unexpected, especially since Neptune’s previous periods of low cloud activity were not so dramatic and prolonged. “, says Erandi Chávez, stationed at the Center for Astrophysics – Harvard-Smithsonian (CFA) in Cambridge, Massachusetts (USA), who led the writing of the articleIcarus When she was an astronomy student at UC Berkeley.

The press release continues with re-clarifications from Imke de Pater regarding comments made since 1994: ” These remarkable data give us the strongest evidence yet that Neptune’s clouds are related to the Sun’s cycle. Our findings support the theory that UV rays from the Sun, when strong enough, can trigger a photochemical reaction that forms Neptune’s clouds. ,

However, there is a two-year lag between the peak of solar radiation and the number of clouds observed on Neptune, which can be explained by the time taken by the energy injected by solar radiation into Neptune’s atmosphere to generate the amount of chemical reactions required. Could To make clouds.

Researchers will continue to study Neptune’s clouds with combined data from Hubble, the James Webb Space Telescope, Keck Observatory and Lick Observatory. Theoretical analysis of these data will also help us understand Neptune-like exoplanets in the future.