Dark spots have been observed on Neptune for more than 30 years. In the ice giant, these planetary-scale vortices appear and disappear, similar in extension to Earth, and their nature is unknown beyond what can be observed in its atmosphere. To deepen this cosmic mystery, an international consortium publishes today in the scientific magazine nature astronomy the analysis of the phenomenon from a terrestrial telescope, the first that has managed to capture and analyze the great dark spot.
Thanks to Very Large Telescope (VLT), the group led by Patrick Irwin, a professor at the University of Oxford in the United Kingdom, has been able to identify aerosols (any solid or liquid particle that interferes with sunlight) as the cause of the darkening of the nebular formation with respect to the common bluish background of the Neptune’s atmosphere. Irwin’s team writes in the study that they have been able to analyze the sunlight reflected by the planet at different wavelengths, thus being able to determine the height at which the spot is located or the nature of its darkening compared to the rest of the planet. the atmosphere. And all this with the help of the MUSE instrument of the European Southern Observatorylocated on a hill in the Atacama desert in Chile, where the VLT is located.
Study of Neptune’s outermost atmosphere points to the presence of hazes, methane ice clouds, and, at greater depths, hydrogen sulfide. “Below the hydrogen sulfide clouds, the models also indicate the presence of clouds of ammonium hydrosulfide or water, but in the absence of observations at such depths, the presence of the latter has not yet been confirmed,” explains the co-author. Daniel Toledo. For the physicist from the National Institute of Aerospace Technology (INTA), the most important part of his work is to understand that Neptune’s dark spot is produced by the change in the nature of the aerosols deep within the planet, not by a gap between the clouds stormy at those heights.
the probe Voyager 2 in 1989 and the telescope hubble in 1996 they achieved snapshots of different large intermittent spots on Neptune during their space journeys. Useful photographs to determine the size and shape of the phenomena, “basically an external description of the vortices,” Toledo clarifies. But to know its composition, scientists have required the VLT’s MUSE instrument, which is capable of performing an analysis of the “full spectrum of the vortex, at many wavelengths.” thanks to spectrographic techniques. Something that is surprising about the stain is that “from a certain wavelength, at 700 nanometers, it disappears”, the physicist details when describing the three-dimensional model of the results of his research.
“Thanks to the variation of the absorption of methane gas with the wavelength, we can establish from what depths we are observing the light reflected by the atmosphere”, explains the INTA scientist. This indicates that the phenomenon that is seen occurs in the upper parts of the atmosphere of the frozen planet, at pressure levels of 4-5 bars, which is below the level of condensation of the methane clouds observed in the classical ones. photographs of Neptune. Toledo draws an earthly simile: “On Earth the same thing happens with ultraviolet light, which is mostly absorbed in the stratosphere by ozone. Hence, if we look at the Earth from outside its atmosphere, the reflected light in the ultraviolet is due to interactions between sunlight and the atmosphere at heights 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 so blue! pic.twitter.com/aZZa8B8x4f
— NASA Webb Telescope (@NASAWebb) September 21, 2022
Despite being aware of the limitations of the study that focuses on the outer layer of the planet, Toledo celebrates “knowing that the dark spot is the result of an atmospheric phenomenon that is occurring at depths where our knowledge is very limited due to the lack of direct observations. The work itself clarifies that it remains unknown what causes the movement within the great spot, although scientists theorize that “it could be related to the photolysis of certain gases” in the giant.
Researchers Irwin and Toledo highlight being able to achieve from Earth an image with so much information of the seventh planet in the solar system. But the co-investigator stresses that the future of research will require space probes to be able to exceed the limits of current models: “The next step would logically be to have a mission dedicated to these planets [Urano o Neptuno], since the Ice Giants are the only planets in the Solar System that have not had a mission dedicated to them. Toledo assures that sending probes will be a “top priority” for NASA in the coming years, due to the knowledge that these natural satellites can offer about the origin of the Solar System or their help in space exploration, due to their similarity with the exoplanets that are They study in the Milky Way.
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