This image shows Neptune observed with the MUSE instrument on ESO's Very Large Telescope .
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A large dark spot has been observed for the first time in Neptune's atmosphere with a terrestrial telescope.
This detection was carried out by the MUSE spectrograph, one of the instruments of the Very Large Telescope (TGT) of the European Southern Observatory (ESO) installed in Chile.
These occasional structures against the blue background of Neptune's atmosphere are a mystery to astronomers, and the new data provide additional clues about their nature and origin, the organization notes in a press release.< /p>
A large dark spot was first detected in Neptune's northern hemisphere by the Voyager 2 probe in 1989. Since then, it has appeared and disappeared every few years.
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This image shows Neptune observed with the MUSE instrument on ESO's Very Large Telescope.
Several large spots have been detected in the atmospheres of giant planets. The best known is undoubtedly the Great Red Spot on Jupiter, considered to be the largest storm in the solar system. This 16,000 kilometer wide anticyclone has existed for more than 185 years.
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The Jupiter's Great Red Spot is 1.3 times the diameter of Earth.
The spot detected on Neptune, first identified by Voyager 2, is much less known. It would be an anticyclonic storm like that of Jupiter, but its interior would have relatively few clouds.
For this reason, a theory put forward so far by some Scientists believed the spot was caused by a clearing in the clouds.
Observations carried out in 2018 by the Hubble telescope noted the presence of several dark spots in Neptune's atmosphere, including one in the Neptune's atmosphere. northern hemisphere of the planet.
Since these dark spots are not permanent structures in Neptune's atmosphere, astronomers associated with TGT 'quickly turned in the direction of Neptune.
Thanks to the MUSE instrument, Professor Patrick Irwin and his colleagues at the University of Oxford in the United Kingdom were able to decompose the sunlight reflected by Neptune and its spot in its different colors (wavelengths) and obtain a 3D spectrum.
The team was thus able to analyze the stain in more detail than before.
I am absolutely delighted that I was able to not only detect a dark spot for the first time from the ground, but also to have recorded for the first time a reflection spectrum of such a spot.
A quote from Patrick Irwin, University of Oxford
The team of astronomers' analyzes show that these spots are probably the result of the darkening of air particles in an area of the atmosphere located below the main layer of haze, when the latter mixes to ice in the planet's atmosphere.
Additionally, the spectrum allowed astronomers to better determine how high the dark spot is in the planet's atmosphere. The spectrum also provided information on the chemical composition of different layers of the atmosphere, which allowed the team to understand why the spot appeared dark.
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The observations also made it possible to detect a very rare type of cloud taking the form of a bright spot right next to the large dark spot. We discovered a rare type of deep, bright cloud that had never been identified before, even from space, explains American astronomer Michael Wong, co-author of the study and researcher at the x27;University of California at Berkeley.
This bright cloud is at the same level in the atmosphere as the main dark spot. This is therefore a completely new type of cloud compared to the small high-altitude methane ice clouds previously observed, notes ESO.
According to Michael Wong, these observations show a stunning increase in humanity's ability to observe the cosmos.
At first, we could only detect these spots by sending a spacecraft there, like Voyager. Then we acquired the ability to distinguish them from a distance thanks to Hubble. Finally, technology has advanced to allow us to do this from the ground.
A quote from Michael Wong, University of California, Berkeley
The details of these observations are the subject of an article published in the journal Nature Astronomy (New window) (in English). /p>
In addition, another study (New window) published earlier in August shows that there is a link between the abundance of clouds present in Neptune's atmosphere and the 11-year solar cycle.
The discovery is based on three decades of observations of Neptune captured by NASA's Hubble Space Telescope and the W.M. Keck Observatory in Hawaii, as well as data from the Lick Observatory in California. /p>
At present, the cloud cover observed on Neptune is extremely low, with the exception of a few clouds hovering above the South Pole. The abundance of clouds normally seen in the icy giant's midlatitudes began to fade in 2019.
