A large dark spot in Neptune’s atmosphere has been observed for the first time with a ground-based telescope.
This detection was carried out using the MUSE spectrograph, one of the instruments of the European Southern Observatory’s (ESO) Very Large Telescope (TGT) installed in Chile.
These occasional structures against the blue background of Neptune’s atmosphere are a mystery to astronomers, and the new data provides further clues about their nature and origin, the organization notes in a statement.
A large dark speck was first discovered in 1989 by the Voyager 2 probe in Neptune’s northern hemisphere. He has appeared and disappeared every few years since then.
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This image shows Neptune observed with the MUSE instrument on ESO’s Very Large Telescope.
Photo: ESO/P. Irwin et al.
Neptune 101
- The planet is the eighth and final planet in the solar system.
- It is 4,490 million kilometers from the Sun.
- It receives 900 times less light than Earth, so the average temperature on its surface is -213 ° C.
- Neptune has 13 satellites, two of which (Nereit and Triton) are visible from Earth.
- The planet has four rings of dark matter, making it difficult to observe.
Common stains
Several large spots have been discovered in the atmospheres of giant planets. The most famous is undoubtedly the Great Red Spot on Jupiter, which is considered the largest storm in the solar system. This 16,000 kilometer wide high pressure area has existed for more than 185 years.
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Jupiter’s Great Red Spot is 1.3 times the diameter of Earth.
Photo: NASA
The spot discovered on Neptune, first identified by Voyager 2, is much less well known. It would be an anticyclonic storm like Jupiter’s, but with relatively few clouds inside.
For this reason, some scientists have previously put forward the theory that the spot was caused by a clearing in the clouds.
New sightings
Observations conducted in 2018 with the Hubble Telescope revealed the presence of several dark spots in Neptune’s atmosphere, including one in the planet’s northern hemisphere.
Because these dark spots are not permanent features in Neptune’s atmosphere, astronomers associated with TGT quickly pointed them toward Neptune.
Using the MUSE instrument, Professor Patrick Irwin and his colleagues at the University of Oxford in the United Kingdom were able to separate the sunlight reflected from Neptune and its spot into its different colors (wavelengths) and obtain a 3D spectrum.
This allowed the team to analyze the stain in more detail than before.
I am very happy that I was not only able to see a dark spot from the ground for the first time, but also recorded a reflection spectrum of such a spot for the first time.
The astronomy team’s analyzes show that these patches are likely the result of air particles in a region of the atmosphere below the main haze layer darkening as it mixes with the ice in the planet’s atmosphere.
In addition, the spectrum allowed astronomers to better determine the height of the dark spot in the planet’s atmosphere. The spectrum also provided information about the chemical composition of different layers of the atmosphere, which helped the team understand why the spot appeared dark.
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An unknown type of cloud
The observations also made it possible to detect a very rare type of cloud in the form of a bright spot right next to the large dark spot. “We have discovered a rare type of deep, bright cloud that has never been identified before, even from space,” explains American astronomer Michael Wong, co-author of the study and researcher at the University of California, Berkeley.
This bright cloud is at the same height in the atmosphere as the main dark spot. This is a completely new type of cloud compared to the previously observed small methane ice clouds at high altitudes, notes the ESO.
A giant step
According to Michael Wong, these observations show a stunning increase in humanity’s ability to observe the cosmos.
At first we could only discover these places by sending a spacecraft like Voyager there. Then, thanks to Hubble, we acquired the ability to distinguish them from a distance. Finally, technology has advanced to the point where we can do this from the ground.
The details of these observations are the subject of an article published in the journal Nature Astronomy (new window).
Fewer clouds since 2019
In addition, another study (new window) published in early August shows that there is a connection between cloud abundance in Neptune’s atmosphere and the 11-year solar cycle.
The discovery is based on three decades of Neptune observations collected by NASA’s Hubble Space Telescope and WM Keck Observatory in Hawaii, as well as data from the Lick Observatory in California.
Currently, cloud cover observed on Neptune is extremely low, with the exception of a few clouds hovering over the South Pole. The abundance of clouds normally seen in the ice giant’s mid-latitudes began to dwindle in 2019.