Neptune’s summer temperature drops dramatically. What may have caused this?

According to a new study, the average atmospheric temperature of Neptune fell by 8 degrees Celsius (°C) during 2003-2020.

Findings of the study:

• The atmospheric temperature of the eighth planet of the solar system fell to -117°C from -109°C between 2003 and 2018, according to the analysis published in The Planetary Science Journal. 
• The period covers the first half of the summer on the planet that started in 2005. Each season on the Neptune lasts 40 years.
• The researchers relied on a fleet of ground-based telescopes – Chile’s Very Large Telescope and Gemini South telescope, Hawaii’s Subaru Telescope, Keck Telescope, and the Gemini North telescope as well as a space telescope named Spitzer Space Telescope to study Neptune. 
• The telescopes were equipped with thermal cameras with infrared eyes.
• The cameras calculate temperature by measuring the infrared light emitted from objects in the stratosphere — a layer of the planet’s atmosphere.
• The unexpected reversal of the trend in the polar region suggests some interesting atmospheric dynamics are at play.

Few theories for the factors driving Neptune’s fluctuating temperatures:

• Seasonal changes in Neptune’s atmospheric chemistry could have a role to play, they surmised.
• Alternatively, the solar cycle – variation in the Sun’s activity every 11 years – might also be involved.
• Previous studies also suggested that the solar cycle might affect Neptune’s visible brightness.

About Neptune:

• Dark, cold, and whipped by supersonic winds, ice giant Neptune is the eighth and most distant planet in our solar system.
• More than 30 times as far from the Sun as Earth, Neptune is the only planet in our solar system not visible to the naked eye and the first predicted by mathematics before its discovery. In 2011 Neptune completed its first 165-year orbit since its discovery in 1846.
• NASA's Voyager 2 is the only spacecraft to have visited Neptune up close. It flew past in 1989 on its way out of the solar system.
• Potential for Life
• Neptune's environment is not conducive to life as we know it.
• The temperatures, pressures, and materials that characterize this planet are most likely too extreme and volatile for organisms to adapt to.
• Size and Distance
• With a radius of 15,299.4 miles (24,622 kilometers), Neptune is about four times wider than Earth.
• If Earth were the size of a nickel, Neptune would be about as big as a baseball.
• Neptune is 30 astronomical units away from the Sun. One astronomical unit (abbreviated as AU), is the distance from the Sun to Earth. From this distance, it takes sunlight 4 hours to travel from the Sun to Neptune.
• Moons
• Neptune has 14 known moons.
• Neptune's largest moon Triton was discovered on October 10, 1846
• Structure
• Neptune is one of two ice giants in the outer solar system (the other is Uranus). Most (80% or more) of the planet's mass is made up of a hot dense fluid of "icy" materials – water, methane, and ammonia – above a small, rocky core.
• Of the giant planets, Neptune is the densest.