Neptune’s Clouds Have Almost Disappeared – And It’s Because of the Sun

Neptune, the eighth and farthest planet from the sun, is a mysterious and fascinating world. It has a thick atmosphere made mostly of hydrogen, helium, and methane, and it is the coldest planet in the solar system, with an average temperature of -200°C. It also has a powerful storm system, with winds reaching up to 2,100 km/h, and a giant dark spot that comes and goes. But perhaps the most striking feature of Neptune is its beautiful blue colour, which is caused by the reflection of sunlight on its clouds.

But what if we told you that those clouds have almost disappeared in the past four years? And that this phenomenon is related to the activity of the sun, which changes every 11 years? This is the surprising discovery that astronomers have made using two of the most powerful telescopes in the world: the W. M. Keck Observatory and the Hubble Space Telescope. In this article, we will explain how they observed Neptune’s clouds, what they found out, and why it matters for our understanding of the weather and climate of distant planets.

How Did They Observe Neptune’s Clouds?

Neptune is very far away from Earth, about 4.5 billion kilometers. This means that it is very difficult to observe it with high resolution and detail. To overcome this challenge, astronomers used two different methods: spectroscopy and imaging.

Spectroscopy is the study of how light interacts with matter. By analyzing the spectrum of light that comes from Neptune, astronomers can infer what elements and molecules are present in its atmosphere, and how they vary over time. For example, methane absorbs red light and reflects blue light, which gives Neptune its color.

Imaging is the process of taking pictures of an object using a camera or a telescope. By comparing images of Neptune taken at different times, astronomers can see how its clouds change in shape, size, and location. For example, they can track the movement of the dark spot, which is a huge storm that rotates around Neptune.

The astronomers used both methods to observe Neptune’s clouds from 2015 to 2019. They used the W. M. Keck Observatory, which is located on Mauna Kea in Hawaii, and has two 10-meter telescopes that can capture infrared light. They also used the Hubble Space Telescope, which orbits around Earth and has a 2.4-meter telescope that can capture visible light. By combining data from both sources, they were able to get a comprehensive view of Neptune’s cloud cover.

What Did They Find Out?

The results of their observations were astonishing. They found out that Neptune’s cloud cover has dramatically decreased since 2019, except near the south pole. In fact, they estimated that only about 10% of Neptune’s surface was covered by clouds in 2019, compared to about 30% in 2015.

What could cause this phenomenon? The astronomers think that it has something to do with the solar cycle, which is the periodic change in the sun’s activity and radiation. The solar cycle lasts about 11 years, and it affects the amount of ultraviolet (UV) light that reaches Neptune.

UV light is important for cloud formation on Neptune, because it breaks down methane molecules into smaller fragments, such as ethane and acetylene. These fragments then condense into tiny particles that form clouds in Neptune’s atmosphere.

The solar cycle has two phases: solar maximum and solar minimum. Solar maximum is when the sun is more active and emits more UV light. Solar minimum is when the sun is less active and emits less UV light.

The astronomers noticed that Neptune’s cloud cover was higher during solar maximum (around 2015) and lower during solar minimum (around 2019). They also noticed that this pattern was reversed near the south pole, where there was more cloud cover during solar minimum and less during solar maximum.

They think that this difference is due to the tilt of Neptune’s axis, which is about 29 degrees. This means that different parts of Neptune receive different amounts of sunlight throughout its year, which lasts about 165 Earth years. The south pole was facing the sun during solar minimum (around 2019), while the rest of Neptune was facing away from it.

Why Does It Matter?

This discovery is important for several reasons. First, it shows that Neptune’s weather and climate are influenced by external factors, such as the sun’s activity and radiation. This means that we need to take these factors into account when we study other planets with similar atmospheres, such as Uranus or exoplanets.

Second, it shows that Neptune’s weather and climate are dynamic and complex, and that they can change dramatically over time. This means that we need to monitor Neptune’s clouds continuously and with high resolution, to understand how they evolve and what they tell us about the planet’s interior and history.

Third, it shows that Neptune’s weather and climate are beautiful and fascinating, and that they can surprise us with unexpected phenomena. This means that we need to appreciate Neptune’s clouds as a natural wonder and a source of inspiration, and that we need to share our knowledge and curiosity with the public and the next generation of astronomers.

Conclusion

Neptune’s clouds have almost disappeared since 2019, and it’s because of the sun. This is the amazing discovery that astronomers have made using the W. M. Keck Observatory and the Hubble Space Telescope. They found out that Neptune’s cloud cover is related to the solar cycle, which is the periodic change in the sun’s activity and radiation. They also found out that this pattern is reversed near the south pole, where there is more cloud cover during solar minimum and less during solar maximum.

This discovery has important implications for our understanding of the weather and climate of distant planets, and for our appreciation of Neptune’s beauty and mystery. It also raises new questions and challenges for future research, such as how Neptune’s clouds affect its temperature, pressure, and wind, and how they compare to those of other planets.

Neptune’s clouds are a window into a world that is far away from us, but also close to our hearts. They are a reminder that we live in a solar system that is full of wonders and surprises, and that we have the tools and the passion to explore them. As Carl Sagan once said: “Somewhere, something incredible is waiting to be known.”