Observations from the Very Large Telescope in Chile suggest Neptune’s blemish is caused by dark particles deep within its atmosphere
By Chen Ly
24 August 2023
Images of Neptune split into different wavelengths of light captured by the Very Large Telescope. In the rightmost image all colours are combined, with the dark spot to the upper right
ESO/P. Irwin et al.
A strange dark spot on Neptune has been observed from Earth for the first time, offering fresh clues into how these marks form.
In 1989, NASA’s Voyager 2 space probe detected a shadowy region on Neptune, which was dubbed the “Great Dark Spot”. Since then, observations by the Hubble Space Telescope have revealed that these marks are quite common and tend to disappear after a few years.
The origin and nature of the spots have remained elusive, as observations have been restricted to those taken by Hubble, which primarily captures ultraviolet and visible light.
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Now, Patrick Irwin at the University of Oxford and his colleagues have witnessed one of these dark spots for the first time with a ground-based telescope and over a much wider spectrum of light.
After a new dark spot appeared on Neptune in 2018, seen by Hubble, the team decided to see whether the Very Large Telescope in Chile also picked it up.
Its Multi Unit Spectroscopic Explorer instrument split the light from the planet into different wavelengths including the longer, redder part of the spectrum, which allowed the team to see the spot from Earth and examine it in greater detail than before.