Mysterious dark spot in Neptune's atmosphere

Astronomers have discovered a large and mysterious dark spot in Neptune's atmosphere .

Astronomers have discovered a large and mysterious dark spot in Neptune's atmosphere . The observation was made using the European Southern Observatory's Very Large Telescope in Chile.

Neptune is blue due to methane gas in its atmosphere.

Space-based observatories have spotted vortex-like storms that appear as dark spots in the planet's atmosphere before. But this is the first time an Earth-based telescope has seen a storm on Neptune. The study was published in the journal Nature Astronomy.

'Since I first discovered a dark spot, I have always wondered what these elusive, short-lived features are,' said Patrick Irwin, professor of planetary physics at the University of Oxford.

The gas giants in our Solar System, including Neptune, are known for dark spots that appear in their atmospheres. Neptune, an ice giant, has been plagued by storms for years. The storms appear to follow a pattern of appearing and disappearing over the course of two years.

That makes them difficult to study. Voyager 2, a NASA probe launched in the 1970s, also saw two dark storms on Neptune in 1989. The Great Dark Spot on Neptune, the nickname given to the largest storm Voyager 2 saw, was so large it could have contained Earth.

Neptune's storms behave differently than those on Earth. The dark spots are high-pressure systems that begin to stabilize and spin clockwise. Meanwhile, storms in Earth's Northern Hemisphere are low-pressure systems that spin counterclockwise. What Irwin and his team wanted to learn was how the massive storms on Neptune form.

Neptune is blue because of methane in its atmosphere. Neptune is a frozen world with an average temperature of minus 392 degrees Fahrenheit (minus 235 degrees Celsius) and howling winds that send methane clouds across the planet at 1,200 miles per hour (1,931 kilometers per hour).

It is the most distant planet in our Solar System, about 30 times farther from the Sun than Earth, a distance that makes noon on Neptune look like sunset on Earth.

The data collected helped astronomers determine that the dark spots were not caused by gaps in the clouds. Instead, the observations showed that the dark spots appeared when dark air particles gathered below Neptune's prominent atmosphere, where fog and ice mix.

'In the process, we discovered a rare type of cloud that had never been identified before, even from space ,' said study co-author Michael Wong, a planetary scientist at the University of California, Berkeley.

Astronomers said they were intrigued by this new feature, and the team hopes to learn more through future observations that can be made from Earth.