We've always known Neptune was cool, but now we know it's way cooler, temperature wise.
A recent study published in Planetary Science Journal revealed how temperatures in Neptune's atmosphere have unexpectedly fluctuated over the past two decades, with the study being led by scientists at the University of Leicester in collaboration with scientists at NASA’s Jet Propulsion Laboratory. The researchers combined all existing thermal infrared images of Neptune gathered from multiple observatories over almost two decades. These include the European Southern Observatory's Very Large Telescope and Gemini South telescope in Chile, together with the Subaru Telescope, Keck Telescope, and the Gemini North telescope, all in Hawai'i, and spectra from NASA's Spitzer Space Telescope.
By analysing the data, the researchers were able to reveal a more complete picture of trends in Neptune's temperatures than ever before, which revealed that Neptune’s globally-averaged temperatures in Neptune's stratosphere -- the layer of the atmosphere just above its active weather layer -- have dropped by roughly 8 degrees Celsius (14 degrees Fahrenheit) between 2003 and 2018.
"This change was unexpected. Since we have been observing Neptune during its early southern summer, we would expect temperatures to be slowly growing warmer, not colder," said Dr Michael Roman, Postdoctoral Research Associate at the University of Leicester and lead author on the paper. “"Temperature variations may be related to seasonal changes in Neptune's atmospheric chemistry, which can alter how effectively the atmosphere cools. But random variability in weather patterns or even a response to the 11-year solar activity cycle may also have an effect."
While Voyager 2 has been the only spacecraft to visit Neptune, scientists have still been able to study the distant planet using ground- and space-based observation techniques, using data as recently as 2020.
Much like Earth, the planet Neptune has an axial tilt, meaning it experiences seasons, as well. But due to its vast distance from the Sun at 2.8 billion miles (4.5 billion kilometers), these seasons can last for as long as 40 years. What makes this study so intriguing is that scientists were not expecting such rapid temperature fluctuations to occur during only half of a season on Neptune.
The cause of these unexpected stratospheric temperature changes is currently unknown, and the results challenge scientists' understanding of Neptune's atmospheric variability.
As always, keep doing science & keep looking up!
Sources: Planetary Science Journal