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Hubble Sees Summertime on Saturn

Saturn is truly the lord of the rings in this latest snapshot from NASA’s Hubble Space Telescope, taken on July 4, 2020, when the opulent giant world was 839 million miles from Earth. This new Saturn image was taken during summer in the planet’s northern hemisphere.

Saturn summertime Hubble summer
NASA’s Hubble Space Telescope captured this image of Saturn on July 4, 2020. Two of Saturn’s icy moons are clearly visible in this exposure: Mimas at right, and Enceladus at bottom. This image is taken as part of the Outer Planets Atmospheres Legacy (OPAL) project. OPAL is helping scientists understand the atmospheric dynamics and evolution of our solar system’s gas giant planets. In Saturn’s case, astronomers continue tracking shifting weather patterns and storms.
Credits: NASA, ESA, A. Simon (Goddard Space Flight Center), M.H. Wong (University of California, Berkeley), and the OPAL Team

 

Hubble found a number of small atmospheric storms. These are transient features that appear to come and go with each yearly Hubble observation. The banding in the northern hemisphere remains pronounced as seen in Hubble’s 2019 observations, with several bands slightly changing color from year to year. The ringed planet’s atmosphere is mostly hydrogen and helium with traces of ammonia, methane, water vapor, and hydrocarbons that give it a yellowish-brown color.

Hubble photographed a slight reddish haze over the northern hemisphere in this color composite. This may be due to heating from increased sunlight, which could either change the atmospheric circulation or perhaps remove ices from aerosols in the atmosphere. Another theory is that the increased sunlight in the summer months is changing the amounts of photochemical haze produced. “It’s amazing that even over a few years, we’re seeing seasonal changes on Saturn,” said lead investigator Amy Simon of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Conversely, the just-now-visible south pole has a blue hue, reflecting changes in Saturn’s winter hemisphere.

Hubble’s sharp view resolves the finely etched concentric ring structure. The rings are mostly made of pieces of ice, with sizes ranging from tiny grains to giant boulders. Just how and when the rings formed remains one of our solar system’s biggest mysteries. Conventional wisdom is that they are as old as the planet, over 4 billion years. But because the rings are so bright – like freshly fallen snow – a competing theory is that they may have formed during the age of the dinosaurs. Many astronomers agree that there is no satisfactory theory that explains how rings could have formed within just the past few hundred million years. “However, NASA’s Cassini spacecraft measurements of tiny grains raining into Saturn’s atmosphere suggest the rings can only last for 300 million more years, which is one of the arguments for a young age of the ring system,” said team member Michael Wong of the University of California, Berkeley.

Two of Saturn’s icy moons are clearly visible in this exposure: Mimas at right, and Enceladus at bottom.

This image is taken as part of the Outer Planets Atmospheres Legacy (OPAL) project. OPAL is helping scientists understand the atmospheric dynamics and evolution of our solar system’s gas giant planets. In Saturn’s case, astronomers continue tracking shifting weather patterns and storms.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

 

 

Press release from NASA, on Hubble capturing summertime data from Saturn.

The most extensive system of haze layers ever observed in the solar system have been discovered and characterised on the planet Saturn

High-resolution images obtained by the Cassini spacecraft were used for this purpose by the Planetary Science Group at the University of the Basque Country

Saturn hexagon
High-resolution images of Saturn’s Hexagon obtained by the Cassini spacecraft. Credits: UPV/EHU

 

A rich variety of meteorological phenomena take place in the extensive hydrogen atmosphere of the planet Saturn, a world about ten times the size of the Earth. They help us to better understand those that operate in a similar way in the Earth’s atmosphere.  Featuring among them due to its uniqueness is the well-known “hexagon”, an amazing wave structure that surrounds the planet’s polar region and whose shape looks as if it had been drawn by a geometrician.

Discovered in 1980 by NASA’s Voyager 1 and 2 spacecraft, it has been observed without interruption since then, despite the planet’s long, strong cycle of seasons. A fast, narrow jet stream flows inside this gigantic planetary wave where winds reach maximum speeds of about 400 km/h. Yet, strangely enough, the wave itself remains almost static; in other words, it barely shifts with respect to the planet’s rotation. All these properties mean that the “hexagon” is a highly attractive phenomenon for meteorologists and planet atmosphere researchers.

Cassini, which was in orbit around the planet between 2004 and 2017, took a vast quantity of images from a whole range of distances from the planet and viewing angles. In June 2015 its main camera obtained very high-resolution images of the planet’s limb which are capable of solving details of between 1 and 2 km; they captured the hazes located above the clouds that shape the hexagonal wave. In addition, it used many colour filters, from ultraviolet to near infrared, thus enabling the composition of these hazes to be studied. To complete this study, images produced by the Hubble Space Telescope taken 15 days later and showing the hexagon not on the limb but seen from above were also used. “The Cassini images have enabled us to discover that, just as if a sandwich had been formed, the hexagon has a multi-layered system of at least seven mists that extend from the summit of its clouds to an altitude of more than 300 km above them,” said Professor Agustín Sánchez-Lavega, who led the study.  “Other cold worlds, such as Saturn’s satellite Titan or the dwarf planet Pluto, also have layers of hazes, but not in such numbers nor as regularly spaced out”.

The vertical extent of each haze layer is between approximately 7 and 18 km thick, and according to the spectral analysis, they contain minute particles with radii of the order of 1 micron. Their chemical composition is exotic for us, because, owing to the low temperatures in Saturn’s atmosphere ranging between 120° C and 180° C below zero, they could comprise hydrocarbon ice crystallites, such as acetylene, propyne, propane, diacetylene or even butane in the case of the highest clouds.

Another aspect studied by the team is the regularity in the vertical distribution of the hazes. The hypothesis put forward is that the hazes are organised by the vertical propagation of gravity waves that produce oscillations in the density and temperature of the atmosphere, a well-known phenomenon on the Earth and on other planets. The researchers raise the possibility that it could be the very dynamics of the hexagon itself and its powerful jet stream that may be responsible for the formation of these gravity waves. On the Earth, too, waves of this type produced by the undulating jet stream travelling at speeds of 100 km/h from West to East in the mid-latitudes have been observed. The phenomenon could be similar on both planets, even though the peculiarities of Saturn mean that it is the only case in the solar system. This is an aspect that remains subject to future research.

Saturn's hexagon
Santiago Pérez-Hoyos, Agustín Sánchez-Lavega, Teresa del Río-Gaztelurrutia and Ricardo Hueso. Credits: UPV/EHU

About the authors at the UPV/EHU  

Agustín Sánchez-Lavega is professor of physics at the UPV/EHU-University of the Basque Country, head of the GCP-Planetary Science Group and holder of the 2016 Euskadi Award for Research.  Teresa del Río-Gaztelurrutia and Ricardo Hueso are tenured lecturers, and Santiago Pérez-Hoyos is a permanent research doctor; they all belong to the GCP.

bibliographic reference

 

Press release on Saturn’s hexagon from the University of the Basque Country.