Dark spots have been observed on Neptune for more than 30 years. In the ice giant, these planetary vortices appear and disappear much like they do on Earth, and their nature is unknown apart from what can be observed in its atmosphere. To delve deeper into this cosmic mystery, an international consortium is publishing today in the journal Nature Astronomy the analysis of the phenomenon using a ground-based telescope, the first to capture and analyze the Great Dark Spot.
Thanks to the Very Large Telescope (VLT), the group led by Patrick Irwin, a professor at the University of Oxford in the UK, was able to identify aerosols (any solid or liquid particle that disrupts the sun’s light) as the cause of the darkening of the nebula formation by comparison to the usual bluish background of Neptune’s atmosphere. Irwin’s team writes in the study that they were able to analyze the sunlight reflected from the planet at different wavelengths, allowing them to determine the height of the spot, or how dark it is compared to the rest of the planet. The atmosphere. And all this with the help of the European Southern Observatory’s MUSE instrument, which stands on a hill in the Atacama Desert in Chile, where the VLT is also located.
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Studies of Neptune’s uppermost atmosphere indicate the presence of haze, methane ice clouds and, at greater depths, hydrogen sulfide. “Below the hydrogen sulfide clouds, the models also suggest the presence of clouds of ammonium hydrosulfide or water, but the lack of observations at such depths has not yet confirmed the presence of the latter,” explains co-author Daniel Toledo. For the National Institute of Aerospace Technology (INTA) physicist, the most important part of his work is understanding that Neptune’s dark spot is caused by changing the nature of aerosols deep in the planet’s interior, and not by a gap between stormy clouds in this height.
Divided into colors and wavelengths, Neptune provides a wealth of valuable information for astronomers.ESO/P. Irwin et al.
The Voyager 2 spacecraft in 1989 and the Hubble telescope in 1996 obtained snapshots of various large intermittent spots on Neptune during their space voyages. Photographs useful in determining the size and shape of the phenomena, “essentially an external description of the vortices,” Toledo clarifies. However, to determine its composition, scientists needed the VLT’s MUSE instrument, which, thanks to spectrographic techniques, can perform an analysis of the ‘full spectrum of the eddy at many wavelengths’. What is surprising about the spot is that it “disappears above a certain wavelength, at 700 nanometers,” says the physicist, describing the three-dimensional model of the results of his research.
“Thanks to the variation in the absorption of methane gas with wavelength, we can determine from what depth we are observing the light reflected from the atmosphere,” explains the INTA scientist. This indicates that the observed phenomenon occurs in the upper parts of the frozen planet’s atmosphere at pressure levels of 4 to 5 bar, which is below the condensation level of the methane clouds observed in the classic photographs of Neptune. Toledo draws a terrestrial analogy: “The same thing happens on earth with ultraviolet light, which is largely absorbed by ozone in the stratosphere. So if we look at the Earth from outside its atmosphere, the reflected light in the ultraviolet range is due to interactions between sunlight and the atmosphere at altitudes above the ozone layer.
In visible light, Neptune appears blue due to small amounts of methane gas in its atmosphere. Webb’s NIRCam instrument instead observed Neptune at near-infrared wavelengths, so Neptune doesn’t look as blue! pic.twitter.com/aZZa8B8x4f
— NASA Webb Telescope (@NASAWebb) September 21, 2022
Though aware of the limitations of the study, which focuses on the planet’s outer layer, Toledo celebrates “the knowledge that the dark spot is the result of an atmospheric phenomenon occurring at depths beyond our knowledge due to the lack of.” very limited knowledge is very limited.” direct observations. The work itself clarifies that what is causing the motion within the Great Spot remains unknown, although scientists suspect “it could be related to the photolysis of certain gases” in the giant.
Researchers Irwin and Toledo point out that they were able to get an image from Earth with so much information about the seventh planet in the solar system. However, the co-investigator emphasizes that the future of research will require space probes to be able to push the limits of current models: “The next step would be logical to have a mission specifically for these planets.” [Urano o Neptuno], since the ice giants are the only planets in the solar system that have not been given a mission of their own. Toledo assures that sending probes will be “top priority” for NASA in the years to come, as these natural satellites can provide insights into the origin of the solar system or, given their resemblance to the exoplanets, can aid in space exploration are you studying in the milky way.
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