Astronomers have discovered a confusing trend in Neptune’s atmosphere: Ever since the planet’s southern hemisphere summer began nearly two decades ago, atmospheric temperatures in this region have plummeted, and scientists are not sure why.
Neptune is the most distant planet in solar systemabout 30 times further away from sun than the earth is. Like all other planets orbiting the sun, Neptune has four different seasons: spring, summer, autumn and winter. But because Neptune takes about 165 years to orbit the sun, each of these seasons lasts about 40 years. Neptune’s southern hemisphere has experienced summer since 2005, the period when it leans towards the sun.
In a new study, researchers compiled infrared images of Neptune taken from a series of terrestrial and space-based telescopes between 2003 and 2020. The team initially expected the temperature of Neptune’s southern hemisphere to rise as it entered summer. However, the images revealed that atmospheric temperatures in the southern hemisphere had dropped by 14.4 degrees Fahrenheit (8 degrees Celsius) between 2003 and 2018.
“This change was unexpected,” said lead author Michael Roman, an astronomer at the University of Leicester in the United Kingdom. said in a statement. “As we observed Neptune during its early southern summer, we expected temperatures to slowly become warmer, not colder.”
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Furthermore, temperatures around Neptune’s South Pole rose by 19.8 F (11 C) between 2018 and 2020 in the last two years of the study. The scientists were amazed at the rapid and intense temperature changes and can not explain why this hotspot counteracts the overall trend. in the southern hemisphere.
“Our data covers less than half of a Neptune season,” co-author Glenn Orton, a planetary scientist at NASA’s Jet Propulsion Laboratory in California, said in the statement, “so no one expected to see big and rapid changes.”
This is not the first time that Neptune’s atmospheric temperatures have confused scientists. In 1989, NASA’s Voyager 2 probe passed Uranus and Neptune on its way out of the solar system and found that Neptune was hotter than its nearest neighbor despite being further away from the sun. Researchers have since discovered that this is likely due to gravitational differences between the two planets, Live Science previously reported.
Scientists do not yet know what causes the newly discovered temperature fluctuations in Neptune’s atmosphere, but they did offer some potential explanations.
One possible cause is a change in atmospheric chemistry. Neptune’s atmosphere consists mainly of hydrogen, as well as helium and methane. The methane gives Neptune and neighbor Uranus their blue color. However, Neptune’s striking nuances are more intense than Uranus, which probably means that another unidentified chemical lurks in Neptune’s atmosphere, according to NASA. This mysterious connection or changes in the abundance of other elements may, according to the statement, be responsible for these temperature changes.
Extreme weather can also affect temperatures. Neptune has the strongest winds in the solar system; they can reach 1,200 mph (1,931 km / h), according to NASA. These winds push gusts of frozen methane through the planet’s atmosphere, potentially affecting temperature. Neptune also has frequent and massive storms. In 1989, Voyager 2 discovered a massive storm near the planet’s south pole. At its greatest, the storm, known as the Great Dark Spot, was larger than Earth and disappeared in 1994.
The temperature changes may also be due to the solar cycle, the researchers said. Every 11 years, the sun’s magnetic field reverses and changes the level of solar radiation that scientists can measure by counting sunspots. There is a loose correlation between the temperature changes and the number of sunspots on the sun over time, but according to the new study, the relationship between the two is not strong enough to definitively support this idea.
Continued surveillance with ground-based telescopes and future surveys using NASA’s new James Webb Space Telescope could shed light on this phenomenon, the statement said. But so far, it’s still a mystery.
“I think Neptune itself is very exciting for many of us because we still know so little about it,” Roman said in the statement. “It all points to a more complicated picture of Neptune’s atmosphere and how it changes over time.”
The study was published April 11 in The Planetary Science Journal.
Originally published on Live Science.