A storm the size of China on the face of Neptune is dying, and researchers who have been studying the dark vortex since it was first spotted in 2015 have no clue why. The vortex is packed with hydrogen sulfide - aka the chemical that makes farts or rotten eggs smell very bad - which it swept from deep within the planet's atmosphere. In all, only five of these dark spots have ever been documented on Neptune, the farthest planet from the Sun, with the most recent one appearing in 2015 (dubbed SDS-2015, meaning "southern dark spot discovered in 2015").
The images taken by the Hubble Space Telescope, which can be seen in a video uploaded by the official NASA Goddard account, showed that the storm is definitely shrinking. They appear and disappear and have only been captured a few times, thanks to Hubble and its unique ability to see these features in UV light. "The particles themselves are still highly reflective; they are just slightly darker than the particles in the surrounding atmosphere", Tollefson explained.
The storm has been raging on Neptune, the eighth planet in our solar system. The Hubble Space Telescope first detected the storm in June 2015, with astronomers likening its clouds to the pancake-shaped ones in the children's book Cloudy With a Chance of Meatballs. But because Hubble is used for so many different observational purposes, it was only able to look at Neptune every few years, always missing the "death" of these other storms.
"We thought that once the vortex got too close to the equator, it would break up and perhaps create a spectacular outburst of cloud activity".
"We have no evidence of how these vortices are formed or how fast they rotate", said study co-author Agustín Sánchez-Lavega in a Nasa statement.
Astronomers theorise that the vortices arise from an instability caused by the sheared eastward and westward winds, and they have created models to predict the movement of SDS-2015. Instead, the storm seems like it's just fading into nothing as it moves toward Neptune's south pole and not the planet's equator as expected, NASA said. Since 2015, it drifted southward where the researchers believe wind shear may have contributed to its fizzle. "The vortex should be free to change traffic lanes and cruise anywhere in between the jets".
Hubble and the Voyager are the only machines that have observed Neptune's vortices. Several years later, the Hubble Space Telescope started monitoring the weather conditions on the planet and arrived at some fascinating findings, which could provide the groundwork for more profound climate studies in space.
The anticyclones form between these jets, pulling up darker material from below the clouds.