Clouds on Neptune come and go, but why this is is a mystery to this day. Astronomers have now discovered that eleven solar cycles have something to do with it.
Approximately every eleven years, the polarity of the Sun’s magnetic field reverses. This is accompanied by intense solar flares and an increase in the number of sunspots. When activity peaks, the magnetic field collapses and the poles flip. Then the sun stops again to finally start a new cycle.
too far from the sun
The effect on Neptune’s clouds is amazing, because the planet is so far from the sun. Only 0.1% of the sunlight that reaches Earth reaches Neptune. However, the planet’s clouds are affected by solar activity, not by the four seasons, each of which lasts about 40 Neptune years.
discovery That didn’t happen overnight: Hubble, NASA’s famed space telescope, has been observing Neptune for at least thirty years. In addition, data from the WM Keck Observatory in Hawaii and observations from the Lick Observatory in California were used.
The clouds disappeared
As a result, astronomers saw the clouds suddenly recede in 2019. “I was amazed how quickly the clouds on Neptune dissipated,” said Emke de Pater, professor emeritus at UC Berkeley. “We’ve seen cloud activity collapse in months.” And these clouds just don’t come back. “So far, four years later, the latest images from last June show that the clouds have not reached their old levels,” said researcher Irandi Chavez. “This was very interesting and unexpected, especially because earlier periods when there were few clouds on Neptune were less intense and lasted much shorter.”
wild again
Images from Hubble and others reveal interesting cloud patterns depending on the season and solar cycle. When the weather is bad on the sun, more ultraviolet radiation flows into the solar system. The researchers found that two years after the peak of the solar cycle, the number of clouds on Neptune is increasing. There is also a correlation between the number of clouds and the brightness of the ice giant due to the reflection of sunlight from the planet.
Thirty years of clouds on Neptune. Images: NASA, ESA, Irandi Chávez (UC Berkeley) and Emke de Pater (UC Berkeley)
“These impressive data provide the strongest evidence yet that cloud thickness on Neptune is related to the solar cycle,” de Pater said. “Our findings support the theory that ultraviolet radiation from the Sun, if strong enough, can initiate photochemical reactions that cause clouds to form on this planet.”
postpone
Because the solar cycle lasts eleven years, it took some time for scientists to pinpoint the relationship of the clouds on Neptune. They tracked 2.5 cycles of cloud activity over a 29 year period. During this period, the planet brightened in 2002 and dimmed again in 2007. It brightened again in 2015 and darkened in 2020, when the amount of cloud cover decreased.
Neptune’s brightness, caused by the sun, appears to fade and fade at the same rate as planetary clouds, albeit with some delay: the zenith of the solar cycle comes two years earlier than the zenith of the sun, the clouds over Neptune. That’s because photochemical reactions occur in Neptune’s upper atmosphere and clouds take time to form.
There is still much to be learned
“It’s great that we can use telescopes on Earth to study world climates billions of kilometers away,” said astronomer Carlos Alvarez at the Keck Observatory. “Technological advances and better observability have allowed us to make better models of Neptune’s atmosphere. They are critical to understanding the relationship between the climate of the ice giants and the solar cycle.”
Clouds on Neptune in relation to the solar cycle. Images: NASA, ESA, LASP, Erandi Chavez (UC Berkeley) and Imke de Pater (UC Berkeley)
But astronomers still don’t understand everything. For example, increasing the sun’s ultraviolet radiation can produce more clouds, but it can also make them darker, thereby reducing Neptune’s brightness. Storms on Neptune also affect cloud cover, but are unrelated to photogenic clouds. So correlation studies can be carried out with the solar cycle. Also, more observations of Neptune are needed to see how long the cloudlessness lasts.
Neptune versus the outer planets
“We’ve seen more clouds in the latest Keck images, which were taken around the same time that the James Webb telescope observed the planet. These clouds are mainly observed in northern latitudes and at high altitudes, as expected after observing an increase in UV rays in the last two years, said De Pater.
Data collected from Hubble, James Webb and ground observatories will provide a wealth of new information about the dynamics of this planet’s future existence. In this way, not only do we get a better understanding of Neptune, but we can also get more distant exoplanets, because there are lots of Neptune-like planets out there.
2023-08-19 15:56:13
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