Utilizing ESO’s Very Giant Telescope (VLT), astronomers have noticed a big darkish spot in Neptune’s ambiance, with an sudden smaller vivid spot adjoining to it. That is the primary time a darkish spot on the planet has ever been noticed with a telescope on Earth. These occasional options within the blue background of Neptune’s ambiance are a thriller to astronomers, and the brand new outcomes present additional clues as to their nature and origin.
Giant spots are frequent options within the atmospheres of big planets, probably the most well-known being Jupiter’s Nice Purple Spot. On Neptune, a darkish spot was first found by NASA’s Voyager 2 in 1989, earlier than disappearing just a few years later. “For the reason that first discovery of a darkish spot, I’ve at all times puzzled what these short-lived and elusive darkish options are,” says Patrick Irwin, Professor on the College of Oxford within the UK and lead investigator of the research printed right now in Nature Astronomy.
Irwin and his workforce used information from ESO’s VLT to rule out the chance that darkish spots are attributable to a ‘clearing’ within the clouds. The brand new observations point out as a substitute that darkish spots are doubtless the results of air particles darkening in a layer under the primary seen haze layer, as ices and hazes combine in Neptune’s ambiance.
Coming to this conclusion was no straightforward feat as a result of darkish spots aren’t everlasting options of Neptune’s ambiance and astronomers had by no means earlier than been in a position to research them in ample element. The chance got here after the NASA/ESA Hubble Area Telescope found a number of darkish spots in Neptune’s ambiance, together with one within the planet’s northern hemisphere first seen in 2018. Irwin and his workforce instantly set to work finding out it from the bottom — with an instrument that’s ideally suited to those difficult observations.
Utilizing the VLT’s Multi Unit Spectroscopic Explorer (MUSE), the researchers have been in a position to break up mirrored daylight from Neptune and its spot into its element colors, or wavelengths, and procure a 3D spectrum . This meant they might research the spot in additional element than was doable earlier than. “I am completely thrilled to have been in a position to not solely make the primary detection of a darkish spot from the bottom, but additionally file for the very first time a mirrored image spectrum of such a function,” says Irwin.
Since totally different wavelengths probe totally different depths in Neptune’s ambiance, having a spectrum enabled astronomers to raised decide the peak at which the darkish spot sits within the planet’s ambiance. The spectrum additionally offered info on the chemical composition of the totally different layers of the ambiance, which gave the workforce clues as to why the spot appeared darkish.
The observations additionally supplied up a shock consequence. “Within the course of we found a uncommon deep vivid cloud kind that had by no means been recognized earlier than, even from house,” says research co-author Michael Wong, a researcher on the College of California, Berkeley, USA. This uncommon cloud kind appeared as a vivid spot proper beside the bigger most important darkish spot, the VLT information displaying that the brand new ‘deep vivid cloud’ was on the identical degree within the ambiance as the primary darkish spot. This implies it’s a utterly new kind of function in comparison with the small ‘companion’ clouds of high-altitude methane ice which have been beforehand noticed.
With the assistance of ESO’s VLT, it’s now doable for astronomers to check options like these spots from Earth. “That is an astounding enhance in humanity’s means to watch the cosmos. At first, we might solely detect these spots by sending a spacecraft there, like Voyager. Then we gained the power to make them out remotely with Hubble. Lastly, expertise has superior to allow this from the bottom,” concludes Wong, earlier than including, jokingly: “This might put me out of labor as a Hubble observer!“
 MUSE is a 3D spectrograph that enables astronomers to watch the whole thing of an astronomical object, like Neptune, in a single go. At every pixel, the instrument measures the depth of sunshine as a operate of its color or wavelength. The ensuing information type a 3D set through which every pixel of the picture has a full spectrum of sunshine. In whole, MUSE measures over 3500 colors. The instrument is designed to make the most of adaptive optics, which corrects for the turbulence within the Earth’s ambiance, leading to sharper pictures than in any other case doable. With out this mixture of options, finding out a Neptune darkish spot from the bottom wouldn’t have been doable.