Mysterious dark swirl on Neptune seen from Earth for the first time: ScienceAlert

Since Voyager 2 has flown by Neptune in 1989Giant dark smudges appearing in the distant planet’s atmosphere presented a strange mystery.

Now, for the first time, we’ve spotted one with ground-based instruments with unprecedented precision, helping scientists figure out why the spots appear so dark and why they’re so different from spots on other planets.

“Since the first discovery of the dark spot, I have always wondered what these short-lived and elusive dark features are.” says astronomer Patrick Irwin from the University of Oxford in the United Kingdom.

“I am very happy that I was able to not only make the first detection of a dark spot on Earth, but also record a reflection spectrum of such a feature for the first time.”

dark neptune swirls She actually is Hurricane proof Storms, like Jupiter’s Great Red Spot, differ in several major and mysterious ways. For one thing, they are relatively short-lived, appearing and dissipating every few years.

Neptune as seen by MUSE for the Very Large Telescope. (iso/r. Irwin et al.)

It is also thought to be relatively cloud-free at its centres, compared to the storm vortexes of Saturn and Jupiter. The clouds we can detect are thin white clouds that appear around the edges, possibly as a result of gases congealing into methane ice crystals as they are lifted from lower altitudes.

But learning anything else has been difficult because of Neptune’s remoteness and the short-lived nature of the vortices. Since 1994, the Hubble Space Telescope has been the only instrument capable of observing and tracking it, which limits the range of wavelengths through which the planet can be seen.

However, when a large storm vortex emerged in 2018, Irwin and his team worked on another instrument: the Very Large Telescope’s Multi-Unit Spectroscopic Explorer (VLR).contemplation). MUSE was able to detect sunlight reflecting off Neptune, and split it into its component wavelengths to reconstruct a three-dimensional spectrum of the planet.

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Different wavelengths are associated with different heights in Neptune’s atmosphere, so the researchers were able to determine the height of the dark spot. And they found something surprising: It didn’t appear to be a “hole” in Neptune’s atmosphere.

Instead, the deeper color appears to be a result of darkening of molecules in the hydrogen sulfide layer below the upper layer of Neptune’s aerosol haze. The researchers believe this could be a result of local heating in the deep part of the anticyclonic vortex, which vaporizes the hydrogen sulfide ice to reveal a darker vortex core. The researcher’s observations are consistent with the particles in the aerosol layer above becoming smaller, which reduces the opacity.

And they found another surprise, too: a bright cloud accompanying the vortex. This was not one of the methane clouds that often accompany Neptune’s vortices, but rather a type of cloud that had never been seen before. Instead of sitting higher in the atmosphere, it appeared to be at the same height as the dark vortex.

What this is, and whether any of the mechanisms proposed by the team for the dimming of Neptune’s atmosphere are correct, will need further investigation. But with Neptune visible from Earth, we seem to be getting closer to the answers.

“This is an amazing increase in humanity’s ability to observe the universe.” says astronomer Michael Wong from the University of California, Berkeley.

“At first, we could only detect these spots by sending spacecraft there, like Voyager. Then we gained the ability to detect them at a distance using Hubble. Finally, technology has advanced to enable this from Earth.”

The research has been published with Nature Astronomy.

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