Neptune’s Vanishing Cloud Mystery: Astronomers Discover a Solar Connection

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The Mystery of Neptune’s Disappearing Clouds: A Solar Connection Uncovered

Hubble Space Telescope’s observations have recorded the growing and shrinking of cloud cover on Neptune, revealing a pattern that aligns with the Sun’s 11-year cycle of activity. The formation of these clouds is affected by photochemistry occurring in Neptune’s upper atmosphere.

In 1989, NASA’s Voyager 2 spacecraft shared the first close-up images of bright linear clouds in Neptune’s atmosphere, similar to Earth’s cirrus clouds. Formed above Neptune’s methane, these clouds reflect all sunlight colors, appearing white.

Although distant from the Sun, Neptune’s weather, including cloud cover, is influenced by the Sun. Despite its distance of 3 billion miles from Neptune, the Sun’s radiation still impacts the planet with 1% of the starlight that Earth receives.

Over 30 years of observations from Hubble and Keck telescopes have made the Sun’s influence on Neptune’s clouds increasingly evident. The pattern of cloud growth and shrinkage mirrors the Sun’s 11-year cycle of magnetic field changes, sunspots, and violent outbursts.

![Recent observations from the Hubble Space Telescope show that Neptune’s clouds are almost completely disappearing! Credit: NASA’s Goddard Space Flight Center]

Solar Cycle Tied to Neptune’s Changing Clouds

Astronomers found a connection between Neptune’s fluctuating cloud coverage and the 11-year solar cycle. The discovery comes from three decades of data gathered by the Hubble Space Telescope, the W. M. Keck Observatory, and the Lick Observatory.

Despite receiving only 0.1% of the sunlight that Earth does, Neptune’s global weather seems to be affected by solar activity rather than the planet’s 40-year-long seasons.

Currently, cloud coverage on Neptune is unusually thin, except at the south pole. A UC Berkeley-led team noticed a decrease in clouds at the planet’s mid-latitudes beginning in 2019.

Imke de Pater, emeritus professor of astronomy at UC Berkeley, expressed surprise at how rapidly the clouds vanished.

Monitoring Neptune’s Cloud Fluctuations

Four years after the observations began, Erandi Chavez, a graduate student at the Center for Astrophysics | Harvard-Smithsonian, reported that clouds have not returned to previous levels.

To track Neptune’s changes, images were analyzed from Keck, Hubble, and Lick observatories taken from 1994 to 2022. The Twilight Zone program and Hubble’s Outer Planet Atmospheres Legacy (OPAL) program have also contributed to these observations.

The images showed a link between Neptune’s cloud cover changes and the Sun’s 11-year magnetic field cycle, with increasing sunspots and solar flare activity.

Impact of Solar Activity

More intense UV radiation accompanies stormy weather on the Sun. Researchers found that clouds increase on Neptune two years after the solar cycle’s peak, correlating with the ice giant’s brightness reflecting sunlight.

This data supports the idea that the Sun’s strong UV rays trigger a reaction producing Neptune’s clouds.

The solar cycle’s connection to Neptune’s weather was established by examining 29 years of observations. During this time, Neptune’s brightness fluctuated in sync with the presence of clouds, but with a two-year lag due to the time taken for chemical changes to form clouds.

Further Insights into Neptune’s Weather

Carlos Alvarez, staff astronomer at Keck Observatory, expressed the excitement of studying Neptune’s climate from Earth and the importance of constraining atmospheric models.

However, more studies are needed to understand the complex relationship between UV sunlight, clouds, and Neptune’s brightness, and to observe how long the current low-cloud activity lasts.

Continued tracking is underway, with more clouds observed in recent images, especially at northern latitudes.

Combining data from various observatories, including the new James Webb Space Telescope, may further explore the physics and chemistry of Neptune’s appearance, possibly shedding light on Neptune-like exoplanets.

The findings were published in the journal Icarus on June 9, 2023.

Reference details are provided, followed by a note on the collaboration between NASA and ESA in managing and conducting the Hubble Space Telescope’s science operations.

Frequently Asked Questions (FAQs) about fokus keyword Neptune’s clouds

What is the connection between Neptune’s clouds and the solar cycle?

Astronomers have discovered a link between Neptune’s varying cloud abundance and the Sun’s 11-year solar cycle. The waxing and waning of the Sun’s entangled magnetic fields drive solar activity, and this influence is evident in Neptune’s clouds. Following a peak in the solar cycle, the clouds on Neptune tend to grow in number.

How were the observations of Neptune’s clouds made?

The observations were made using the Hubble Space Telescope, the W. M. Keck Observatory in Hawaii, and the Lick Observatory in California over three decades. Recent initiatives like the Twilight Zone program and Hubble’s Outer Planet Atmospheres Legacy (OPAL) program have also contributed to the data.

What makes the connection between the solar cycle and Neptune’s clouds surprising?

The link is surprising because Neptune is the farthest major planet in our solar system and receives sunlight with only about 0.1% of the intensity that Earth receives. Despite this, Neptune’s global cloudy weather appears to be driven by solar activity rather than the planet’s own four seasons.

What are the implications of the connection between Neptune’s clouds and solar activity?

The correlation between Neptune’s clouds and the Sun’s cycle might help deepen astronomers’ understanding of not only Neptune but also exoplanets, as many of the planets beyond our solar system may have Neptune-like qualities. The connection also helps to constrain Neptune’s atmospheric models, crucial to understanding the correlation between the ice giant’s climate and the solar cycle.

Who led the study on Neptune’s cloud activity?

The study was led by Erandi Chavez, who was an undergraduate astronomy student at UC Berkeley at the time, along with Imke de Pater, emeritus professor of astronomy at UC Berkeley.

What changes in Neptune’s brightness were observed?

During the 29-year span of Neptunian observations, the planet’s reflectivity increased in 2002 and then dimmed in 2007. It became bright again in 2015, then darkened in 2020 to the lowest level ever observed, coinciding with the disappearance of most of the clouds.

Where can the findings of the study be found?

The findings were published in the journal Icarus, in a paper titled “Evolution of Neptune at near-infrared wavelengths from 1994 through 2022.”