Images obtained by NASA’s Hubble Space Telescope on May 16 portray a dark vortex in Neptune’s atmosphere. This is the first time this phenomenon has been witnessed in the 21 century, as the previous sightings were in 1989 and 1994.
The dark spot seen in 1989 was known as the Great Dark Spot and it was almost as large as the earth.
Spotting a new planetary storm
Amateurs and astronomers from the W. M. Keck Observatory in Hawaii managed to see the first stages of the dark vortex back in July 2015. Although the clouds are able to be seen through telescopes, the vortex itself is only able to be seen through blue wavelengths, which only the Hubble is capable of. The announcement was made on May 17 in a Central Bureau for Astronomical Telegrams (CBAT) through a telegram sent by astronomical researcher Mike Wong, the leader of the team that analyzed the Hubble telescope’s data.
Bright clouds were witnessed on the atmosphere, which are known to form as high-pressure vortices become visible, specifically on Neptune. These clouds are made out of expelled frozen gas. Lead analyst Mike Wong stated that these dark vortices are like “huge, lens-shaped gaseous mountains.” He also commented that the companion clouds are very similar to earth’s orographic clouds, which tend to look like discs or “pancakes.”
A dark spot on Neptune’s atmosphere was first seen on September 2015, it seemed to form right next to the cluster of bright clouds. Further imaging procedures allowed for better quality maps to be released, which effectively indicated that a dark vortex was forming on Neptune’s surface. It is approximately 3,000 miles wide and its located in Neptune’s southern hemisphere.
One of the main features of Neptune’s dark vortices is that they last much less than similar events such as the storms in Jupiter, which can last decades. Neptune’s dark vortices last a couple of years and they habitually change their size, speed, shape and location.
Astronomers are not yet sure the exact reasons why dark vortices are formed and what factors affect their characteristics over time.
Researchers will keep studying the atmosphere of gas giants
The astronomers were part of NASA’s Outer Planet Atmospheres Legacy (OPAL), a project that tries to understand how the atmospheric phenomena of gas giants are formed and their implications on the whole planet. The team mostly analyzes images from the Hubble’s observations of Saturn, Jupiter, Uranus, and Neptune.
OPAL has registered the precise behavior of Jupiter’s gas bands rotations, which flows in opposite directions. OPAL is comprised of Mike Wong, Amy Simon, and Glenn Orton, who were able to find the latest dark vortex in Neptune’s atmosphere along collaborators from UC Berkeley, AURA, AMNH, Universidad del Pais Vasco, University of Wisconsin, and the University of Hawaii.
Joshua Tollefson, a doctorate student at Berkeley, received a NASA Earth and Space Science Fellowship to study Neptune’s atmosphere. He commented that planetary astronomers are looking forward into determining exactly how dark vortices originate, and what causes them to change their oscillations, speed, and stability, how they affect the environment and what causes them to eventually disappear. He claims that determining the mechanics behind the recently discovered dark vortex will provide important leads into understanding how the surrounding atmosphere behaves when submitted to these sorts of high-pressure anticyclonic storms.
Planetary great spots
Not much is known about Neptune’s dark vortices other than they’re anticyclonic storms, closely related to Jupiter’s Great Red Spot which has lasted for years. Although a report of this recent spot’s behavior has not been released, one can compare it to 1989’s Great Dark Spot, which had winds blowing at speeds of 1,500 per hour, the fastest to be ever registered in our Solar System. When astronomers tried to photograph the Great Dark Spot back in 1995 they found out that it had either disappeared or it was covered by the atmosphere.
Storms like the Great Dark Spot and the Great Red Spot are classified as anticyclonic, which means that they flow contrary to the Coriolis effect. To experience the Coriolis effect you could go and flush your toilet. You will notice that, if you’re in the U.S., for example, the water will always flow in a clockwise direction. On earth’s southern hemisphere, such as in Australia or Brazil, the water would flow in a counter-clockwise direction.
The Coriolis effect on earth is perceived due to our atmosphere being of low pressure. These planetary storms are formed in high-pressure systems, which are easily found in gas giants such as Jupiter, Saturn, and Neptune. The Great Red Spot on Jupiter is one of the most recognizable of this sort, as there is documentation that proves its sighting over the course of 300 years. Close to the Great Red Spot, there is a smaller white spot, which is roughly the same size as the earth.
Although Neptune is 72 times larger than earth, it is only 17 times heavier, which is due to its status as a gas giant. It is comprised of a thick gaseous atmosphere made out of hydrogen, helium and methane, a liquid surface and sometimes, a solid core. Even if the planet has a high reflectivity due to its composition, it is never able to be seen from earth with the naked eye.
Source: HubbleSite