Mysterious Neptune dark spot detected from Earth for the first time

Massive spots are frequent options within the atmospheres of large planets, probably the most well-known being Jupiter’s Nice Crimson Spot. On Neptune, a darkish spot was first found by NASA’s Voyager 2 in 1989, earlier than disappearing a couple of years later. “Because the first discovery of a darkish spot, I’ve all the time 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 revealed right this moment in Nature Astronomy.

Irwin and his workforce used knowledge from ESO’s VLT to rule out the likelihood that darkish spots are attributable to a ‘clearing’ within the clouds. The brand new observations point out as a substitute that darkish spots are probably the results of air particles darkening in a layer under the principle seen haze layer, as ices and hazes combine in Neptune’s ambiance.

Coming to this conclusion was no simple feat as a result of darkish spots aren’t everlasting options of Neptune’s ambiance and astronomers had by no means earlier than been capable of research them in adequate 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 observed in 2018. Irwin and his workforce instantly set to work learning 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 capable of break up mirrored daylight from Neptune and its spot into its element colors, or wavelengths, and acquire a 3D spectrum [1]. This meant they may research the spot in additional element than was doable earlier than. “I am completely thrilled to have been capable of 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 completely different wavelengths probe completely different depths in Neptune’s ambiance, having a spectrum enabled astronomers to higher decide the peak at which the darkish spot sits within the planet’s ambiance. The spectrum additionally supplied data on the chemical composition of the completely different layers of the ambiance, which gave the workforce clues as to why the spot appeared darkish.

The observations additionally provided up a shock consequence. “Within the course of we found a uncommon deep vibrant cloud kind that had by no means been recognized earlier than, even from area,” says research co-author Michael Wong, a researcher on the College of California, Berkeley, USA. This uncommon cloud kind appeared as a vibrant spot proper beside the bigger foremost darkish spot, the VLT knowledge exhibiting that the brand new ‘deep vibrant cloud’ was on the identical degree within the ambiance as the principle darkish spot. This implies it’s a fully new kind of function in comparison with the small ‘companion’ clouds of high-altitude methane ice which were 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 improve in humanity’s skill to look at the cosmos. At first, we might solely detect these spots by sending a spacecraft there, like Voyager. Then we gained the flexibility to make them out remotely with Hubble. Lastly, know-how 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!“

Observe

[1] MUSE is a 3D spectrograph that enables astronomers to look at 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 perform of its color or wavelength. The ensuing knowledge kind a 3D set through which every pixel of the picture has a full spectrum of sunshine. In complete, MUSE measures over 3500 colors. The instrument is designed to reap the benefits of adaptive optics, which corrects for the turbulence within the Earth’s ambiance, leading to sharper photos than in any other case doable. With out this mix of options, learning a Neptune darkish spot from the bottom wouldn’t have been doable.