The Aurora is one of the most mysterious phenomena that can be seen on Earth.
However, auroras have not only been observed on Earth, but also on other planets in the solar system, such as Jupiter and Saturn.
However, the aurora could not be captured on Neptune, which is more than 40 times farther from the Sun than Earth .
Meanwhile, a new study from Northumbria University in the UK has finally observed the aurora above Neptune for the first time in history .
Are Neptune’s auroras different from those on Earth?
When we hear the word “aurora ,” we immediately conjure up images of the fantastical curtains of light seen at the North and South Poles of the Earth.
This phenomenon occurs when high-energy particles from the sun are captured by the Earth’s magnetic field, collide with the upper atmosphere, and emit light .
In fact, auroras have been observed not only on Earth, but also on giant gas planets such as Jupiter, Saturn, and Uranus.
However, Neptune , located at the very edge of the solar system , had no auroras spotted for many years and remained a mystery.
When NASA ‘s Voyager 2 flew by Neptune in 1989 , it saw signs that might have been auroras, but they were not conclusive evidence.
One reason for this is that Neptune’s magnetic field is extremely complex and tilted at 47 degrees to its axis of rotation.
For this reason, Neptune’s auroras do not appear at the polar regions like they do on Earth.
They appear not at the poles but at mid-latitudes, around South America on Earth .
Furthermore, a molecular ion called the trihydrogen cation (H3+) , which is key to observing the aurora , can be easily observed on Jupiter and Saturn, but for some reason it has not been found on Neptune for over 30 years, which has puzzled astronomers.
The reasons behind this were sudden changes in atmospheric temperature in the upper atmosphere and the limitations of observation technology.
Neptune’s aurora has finally been captured!
The research team used the near-infrared spectrometer on NASA ‘s James Webb Space Telescope (JWST) to observe Neptune in June 2023.
The observations were carried out in two separate phases, taking data from different longitudes on the planet (172 degrees apart), covering almost the entire surface visible from Earth.
The near-infrared spectrometer can capture the wavelength range from 2.87 to 5.27 micrometers with high resolution, which includes the emission line characteristic of the trihydrogen cation (H3+).
The observations not only clearly detected the spectrum of H3+, but also revealed that infrared auroras exist locally in the mid-latitudes of the Southern Hemisphere .
The glow of this H3+ star is about 1.7 times stronger than the surrounding atmosphere, and is thought to be caused by particles raining down into the atmosphere along magnetic fields, similar to the auroras seen on other planets .
What was even more surprising was that the temperature of Neptune’s surface atmosphere had dropped from about 750 K (about 480 degrees Celsius) in 1989 to 358 K (about 85 degrees Celsius) .
This study also showed that this temperature difference was the main reason why H3+ had not been detected on Neptune until now .
At low temperatures the emission becomes very weak, making it difficult to detect with conventional ground-based telescopes as it is lost in the bright reflections of the clouds.
The researchers also suggested that this significant drop in temperature cannot be explained solely by long-term variations such as seasons and solar activity cycles, and may involve unknown short-term changes in Neptune.
This achievement was made possible in part by the James Webb Space Telescope (JWST), one of the world’s most advanced observational instruments.
The JWST has the ambitious mission of not only unlocking the mysteries of our solar system, but also exploring distant star systems, the structure and origin of the universe, and the meaning of our existence.
The JWST’s continued efforts may reveal unknown facets of the universe.