2023-08-24 17:00:03
Las big spots are common phenomena in the atmospheres of the giant planets, like the famous Great Red Spot of Jupiter, the most iconic. The first time a dark spot was discovered on Neptune was in 1989 thanks to observations from NASA’s Voyager 2. This stain disappeared a few years later.
“Since the first discovery of a dark spot, I have always wondered what these elusive short-lived dark phenomena are,” he says. Patrick Irwina professor at the University of Oxford in the United Kingdom and principal investigator of the study now published in Nature Astronomy.
Irwin and his team used data from the Very Large Telescope (VLT) that the European Southern Observatory (ESO) has in Chile to rule out the possibility that the dark spots were caused by a “clearing” in the clouds.
These dark spots are likely the result of air particles darkening as ice and clouds mix in the atmosphere.
Rather, the new observations indicate that these dark spots are likely the result of air particles They darken as ice and clouds mix in the atmosphere, and would be located in a layer below Neptune’s main visible haze layer.
Coming to this conclusion was not an easy task, since dark spots are not permanent features of Neptune’s atmosphere and the astronomical community has never been able to study them in sufficient detail until now.
Following the clue offered by Hubble
The opportunity arose after the Hubble Space Telescope (of NASA and ESA) discovered several dark spots in Neptune’s atmosphere, including one in the planet’s northern hemisphere first detected in 2018. Irwin and his team immediately jumped on to work, studying it from the ground with an ideal instrument for these challenging observations.
With the MUSE instrument it has been possible to divide the sunlight reflected by Neptune and its spot into its colors or wavelengths, and obtain a 3D spectrum
Using the Multi Unit Spectroscopic Explorer (MUSE) from the VLT, the team was able to split the sunlight reflected from Neptune and its spot into its colors, or wavelengths, and obtain a 3D spectrum. This implied that they could study the blob in more detail, something that had not been done so far.
“I am absolutely delighted to have been able to not only make the first detection of a dark spot from the ground, but also to have been able to record such a reflection spectrum for the first time,” says Irwin.
It is the first detection of a dark spot from the ground, and we have also recorded a reflection spectrum of these characteristics for the first time.
Patrick Irwin (Un. Oxford)
Since different wavelengths provide information about different depths in Neptune’s atmosphere, having a spectrum allowed us to better determine how high the dark spot is in the planet’s atmosphere. The spectrum also provided information on the chemical composition from the different layers of the atmosphere, which gave clues as to why the spot appeared dark.
A surprise result
The observations also offered a surprise result at long wavelengths. “In the process we discovered a rare type of deep glowing cloud that has never been identified before, even from space,” he says. Michael Wongco-author of the study and researcher at the University of California at Berkeley (USA).
Neptune’s dark spot, most prominent at shorter or blue wavelengths. The second image, at longer latitudes, also shows a small bright spot (apart from the shallower bright spots toward the lower left edge of the planet). /ESO/P. Irwin et al.
A rare type of cloud appeared as a bright spot right next to the main dark spot.
This rare type of cloud appeared as a bright spot right next to the main, larger dark spot. The VLT data shows that the new “deep bright cloud” was at the same level of the atmosphere as the main dark spot. This means that it is a completely new type of phenomenon compared to the small “companion” clouds of methane ice, previously observed at high altitude.
Now, with the help of the VLT and other large telescopes under construction, it will be possible for the astronomical community to study features like these spots from Earth.
“It’s amazing momentum in the humanity’s ability to observe the cosmos. At first, we could only detect these points by sending a spacecraft, like Voyager, there. We then had the ability to distinguish them remotely with Hubble. Technology has finally advanced to allow it to be done from the Earth’s surface,” Wong concludes, before jokingly adding: “This could put me out of a job as a Hubble observer!”
Reference:
Patrick G. J. Irwin et al. “Cloud structure of dark spots and storms in Neptune’s atmosphere”. Nature Astronomy2023
Rights: Creative Commons.
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