press release
August 24, 2023
Using ESO’s Very Large Telescope (VLT), astronomers have observed a large dark spot in Neptune’s atmosphere, next to which lies an unexpectedly small bright spot. This was the first time that such a dark spot on the planet had been observed with a telescope on Earth. These occasional appearances in the blue background of Neptune’s atmosphere remain a mystery to researchers, and the new results provide further clues about their properties and origin.
Great spots are common features in the atmospheres of giant planets. The most famous is Jupiter’s Great Red Spot. In 1989, NASA’s Voyager 2 probe discovered a dark spot for the first time. Neptunewho disappeared again a few years later.”Since the first discovery of a dark spot, I have always wondered what these ephemeral and elusive dark apparitions correspond to.says Patrick Irwin, a professor at the University of Oxford in the United Kingdom and a senior researcher at Natural astronomy study published.
Irwin and his team used data from the ESO’s VLTto rule out the possibility that the dark spots were caused by cloud “loosening.” The new observations instead suggest that the dark spots are likely the result of air particles darkening below the visible haze layer as ice and haze mix in Neptune’s atmosphere.
It was not easy to reach this conclusion, because the dark spots are not permanent features of Neptune’s atmosphere and astronomers have not yet been able to study them sufficiently. The opportunity to do so arose after the NASA/ESA Space Telescope Hubble several dark points in Neptune’s atmosphere, including one in the planet’s northern hemisphere that was first noticed in 2018. Irwin and his team immediately set to work studying this location from the ground with an instrument ideal for such demanding observations.
With the multi-unit spectroscopic explorer (MUSE) of the VLT, the researchers were able to decompose the sunlight reflected by Neptune and its sunspot into individual colours or wavelengths and obtain a 3D spectrum (1). This meant they could examine the stain in more detail than before.”I am delighted that not only were we able to make the first discovery of a dark spot from the ground, but we were also able to record a reflection spectrum of such a phenomenon for the very first time.said Irwin.
Because different wavelengths sample different depths in Neptune’s atmosphere, astronomers were able to use the spectrum to better determine how high the dark spot was in the planet’s atmosphere. The spectrum also provided information about the chemical composition of different layers of the atmosphere, giving the team clues about why the spot appeared dark.
The observations also produced a surprising result.”We have discovered a rare, deep, bright type of cloud that has never been identified before, even from space.“, says study co-author Michael Wong, a researcher at the University of California, Berkeley, US. This rare type of cloud appeared as a bright spot right next to the larger, main dark spot. The VLT data show that the new “deep, bright cloud” is at the same level in the atmosphere as the main dark spot. This means that it is a completely new type of phenomenon compared to the small, high-altitude “companion clouds” of methane ice observed previously.
Thanks to ESO’s VLT, astronomers can now study features like these dots from Earth.”This surprisingly expands humanity’s ability to observe the cosmos. At first, we could only discover these places by sending a spacecraft like Voyager there. Then, with Hubble, we gained the ability to detect them remotely. Finally, technology has advanced to the point where we can detect them from the ground.” Wong concludes, before adding jokingly: “This could put me out of work as a Hubble observer!“
Endnotes
(1) MUSE is a 3D spectrograph that allows astronomers to observe an entire astronomical object such as Neptune in one go. At each pixel, the instrument measures the intensity of light as a function of its color or wavelength. The resulting data form a 3D array in which each pixel in the image has a full spectrum of light. In total, MUSE measures more than 3,500 colors. The instrument is designed to take advantage of adaptive optics which corrects for turbulence in Earth’s atmosphere, resulting in sharper images than would otherwise be possible. Without this combination of technical requirements, it would not have been possible to examine a dark spot on Neptune from the ground.
More information
This research was presented in a paper titled “Cloud structure of dark spots and storms in Neptune’s atmosphere” published in Nature Astronomy (doi: 10.1038/s41550-023-02047-0 ).
The team is composed of Patrick G. J. Irwin (University of Oxford, UK (Oxford)), Jack Dobinson (Oxford), Arjuna James (Oxford), Michael H. Wong (University of California, USA (Berkeley)), Leigh N. Fletcher (University of Leicester, UK (Leicester)), Michael T. Roman (Leicester), Nicholas A. Teanby (University of Bristol, UK), Daniel Toledo (Instituto Nacional de Técnica Aeroespacial, Spain), Glenn S. Orton (Jet Propulsion Laboratory, USA), Santiago Pérez-Hoyos (University of the Basque Country, Spain (UPV/EHU)), Agustin Sánchez Lavega (UPV/EHU), Lawrence Sromovsky (University of Wisconsin, USA), Amy Simon (Solar System Exploration Division, NASA Goddard Space Flight Center, USA), Raúl Morales-Juberias (University of New Mexico, USA), Imke de Pater (Berkeley) and Statia L. Cook (Columbia University, USA).
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The translations of ESO press releases into English are a service of the ESO Science Outreach Network (ESON), an international astronomy outreach network in which scientists and science communicators from all ESO Member Countries (and some other countries) are represented. It is the German node of the network. House of Astronomy in Heidelberg.
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Contact details
Patrick Irwin
Department of Physics, University of Oxford
Oxford, United Kingdom
Tel.: +44 1865 272083
E-mail: patrick.irwin@physics.ox.ac.uk
Michael H. Wong
Center for Integrative Planetary Science, University of California, Berkeley
Berkeley, California, United States
Tel: +1 510 224 3411
E-mail: mikewong@astro.berkeley.edu
Barbara Ferreira
ESO Media Manager
Garching near Munich, Germany
Tel: +49 89 3200 6670
Mobile: +49 151 241 664 00
E-mail: press@eso.org
Markus Nielbock (press contact Germany)
ESO Science Outreach Network and House of Astronomy
Heidelberg, Germany
Tel: +49 6221 528-134
E-mail: eson-germany@eso.org
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This is a translation of ESO press release eso2314.