Astronomy

Hubble celebrates a decade of tracking the outer planets

By ScientifiCult 9 December 2024

Hubble celebrates a decade of tracking the outer planets

From 2014 to 2024, the NASA/ESA Hubble Space Telescope has been studying the outer planets under a program called OPAL (Outer Planet Atmospheres Legacy) to obtain long-time baseline observations of Jupiter, Saturn, Uranus, and Neptune in order to understand their atmospheric dynamics and evolution. Hubble is the only telescope that can provide high spatial resolution and image stability for global studies of cloud coloration, activity, and atmospheric motion on a consistent time basis to help constrain the underlying mechanics of weather and climate systems.

All four of the outer planets have deep atmospheres and no solid surfaces. Their churning atmospheres have their own unique weather systems, some with colorful bands of multicolored clouds, and with mysterious, large storms that pop up or linger for many years. Each also has seasons lasting many years as they revolve around the Sun.

Following the complex behavior is akin to understanding Earth’s dynamic weather as followed over many years, as well as the Sun’s influence on the solar system’s weather. The four wonder-worlds also serve as proxies for understanding the weather and climate on similar planets orbiting other stars.

Planetary scientists realized that any one year of data from Hubble, while interesting in its own right, doesn’t tell you the full story on the outer planets. Hubble’s OPAL program has routinely visited the planets once a year when they are closest to the Earth, an alignment called opposition. This has yielded a huge archive of data that has led to a string of remarkable discoveries to share with planetary astronomers around the world.

Highlights of the OPAL team’s decade of discovery is provided below.

Jupiter

Jupiter’s bands of clouds present an ever-changing kaleidoscope of shapes and colors. There is always stormy weather on Jupiter: cyclones, anticyclones, wind shear, and the largest storm in the solar system, the Great Red Spot (GRS). Jupiter is covered with largely ammonia ice-crystal clouds on top of an atmosphere that’s tens of thousands of miles deep.

Hubble’s sharp images track clouds and measure the winds, storms, and vortices, in addition to monitoring the size, shape and behavior of the GRS. Hubble follows as the GRS continues shrinking in size, but is still large enough to swallow Earth. OPAL data recently measured how often mysterious dark ovals—visible only at ultraviolet wavelengths—appeared in the “polar hoods” of stratospheric haze. Unlike Earth, Jupiter is only inclined three degrees on its axis (Earth is 23.5 degrees). Seasonal changes might not be expected, except that Jupiter’s distance from the Sun varies by roughly 64 million kilometres over its 12-year-long orbit, and so OPAL closely monitors the atmosphere for seasonal effects. Another Hubble advantage is that ground-based observatories can’t continuously view Jupiter for two Jupiter rotations, because that adds up to 20 hours. During that time, an observatory on the ground would have gone into daytime and Jupiter would no longer be visible until the next evening.

A two-panel image labeled “Jupiter, January 5, 2024, HST WFC3/UVIS” showcases the wealth of information provided by the spectral filters on the Hubble’s Wide Field Camera 3 (WFC3) science instrument. At left, this Hubble image of Jupiter is created using three filters at wavelengths similar to the colors seen by the human eye: F395N is blue, F502N is green, F658N is red. At right, the wavelength bounds are widened beyond the visible range to extend just into the ultraviolet (UV) and infrared regimes: F343N is blue, F467M is green, FQ889N is red. Humans can’t perceive these extended wavelengths. The result is a vivid disk that shows UV-absorbing lofty hazes as orange (over the poles and in three large storms, including the Great Red Spot), and freshely-formed ice as white (compact storm plumes just north of the equator). These filters (and others not shown here) allow astronomers to study differences in cloud thickness, altitude, and chemical makeup. — Two views of Jupiter showcase the wealth of information provided by the spectral filters on the Hubble Space Telescope’s Wide Field Camera 3 (WFC3) science instrument. At left, the RGB composite is created using three filters at wavelengths similar to the colors seen by the human eye. At right, the wavelength bounds are widened beyond the visible range to extend just into the ultraviolet (UV) and infrared regimes. Humans cannot perceive these extended wavelengths, but some animals are able to detect infrared and ultraviolet light. The result is a vivid disk that shows UV-absorbing lofty hazes as orange (over the poles and in three large storms, including the Great Red Spot), and freshly-formed ice as white (compact storm plumes just north of the equator). Astronomers, including the OPAL team, use these filters (and others not shown here) to study differences in cloud thickness, altitude, and chemical makeup.
Credit: NASA, ESA, A. Simon (NASA/GSFC), M. Wong (UC Berkeley), J. DePasquale (STScI)

OPAL’s findings may also support ESA’s Jupiter Icy Moons Explorer, Juice, which was launched on 14 April 2023. Juice will make detailed observations of Jupiter and its three large ocean-bearing moons — Ganymede, Callisto and Europa — with a suite of remote sensing, geophysical and in situ instruments. The mission will characterise these moons as both planetary objects and possible habitats, explore Jupiter’s complex environment in depth, and study the wider Jupiter system as an archetype for gas giants across the Universe.

A nine-panel collage showing Hubble images of Jupiter taken under the OPAL (Outer Planet Atmospheres Legacy) program from 2015-2024, with approximately true color. OPAL tracks the Great Red Spot (GRS) and other notable changes in Jupiter’s banded cloud structure of zones and belts over time.Credit:
NASA, ESA, A. Simon (GSFC), M. Wong (UC Berkeley), J. DePasquale (STScI) — A nine-panel collage showing Hubble images of Jupiter taken under the OPAL (Outer Planet Atmospheres Legacy) program from 2015-2024, with approximately true color. OPAL tracks the Great Red Spot (GRS) and other notable changes in Jupiter’s banded cloud structure of zones and belts over time.
Credit:
NASA, ESA, A. Simon (GSFC), M. Wong (UC Berkeley), J. DePasquale (STScI)

Saturn

Saturn takes more than 29 years to orbit the Sun, and so OPAL has followed it for approximately one quarter of a Saturnian year (picking up in 2018, after the end of the Cassini mission). Because Saturn is tilted 26.7 degrees, it goes through more profound seasonal changes than Jupiter. Saturnian seasons last approximately seven years. This also means Hubble can view the spectacular ring system from an oblique angle of almost 30 degrees to see the rings tilted edge-on. Edge-on, the rings nearly vanish because they are relatively paper-thin. This will happen again in 2025.

OPAL has followed changes in colors of Saturn’s atmosphere. The varying color was first detected by the Cassini orbiter, but Hubble provides a longer baseline. Hubble revealed slight changes from year-to-year in color, possibly caused by cloud height and winds. The observed changes are subtle because OPAL has covered only a fraction of a Saturnian year. Major changes happen when Saturn progresses into the next season.

Saturn’s mysteriously dark ring spokes, which slice across the ring plane, are transient features that rotate along with the rings. Their ghostly appearance only persists for two or three rotations around Saturn. During active periods, freshly formed spokes continuously add to the pattern. They were first seen in 1981 by Voyager 2. Cassini also saw the spokes during its 13-year-long mission, which ended in 2017. Hubble shows that the frequency of spoke apparitions is seasonally driven, first appearing in OPAL data in 2021. Long-term monitoring shows that both the number and contrast of the spokes vary with Saturn’s seasons.

A six-panel collage titled “Saturn, August 22, 2024, HST WFC3/UVIS.” This “Warhol-esque” array of Saturn images depict real data from multiple filters mapped onto the RGB colors perceptible to the human eye. Each filter combination emphasizes subtle differences in cloud altitude or composition. Infrared spectra from the Cassini mission suggested that Saturn’s aerosol particles may have even more complex chemical diversity than on Jupiter. The OPAL (Outer Planet Atmospheres Legacy) program extends Cassini’s legacy by measuring how the subtle patterns in the clouds vary over time. — n array of Saturn images depict real data from multiple filters mapped onto the RGB colors perceptible to the human eye. Each filter combination emphasizes the subtle differences in cloud altitude or composition. Infrared spectra from the Cassini mission suggested that Saturn’s aerosol particles may have even more complex chemical diversity than on Jupiter.
Credit: NASA, ESA, A. Simon (NASA/GSFC), M. Wong (UC Berkeley), J. DePasquale (STScI)

Uranus

Uranus is tilted on its side so that its spin axis almost lies in the plane of the planet’s orbit. This results in the planet going through radical seasonal changes along its 84-year-long trek around the Sun. The consequence of the planet’s tilt means part of one hemisphere is completely without sunlight, for stretches of time lasting up to 42 years. OPAL has followed the northern pole now tipping toward the Sun.

With OPAL, Hubble first imaged Uranus after the spring equinox, when the Sun was last shining directly over the planet’s equator. Hubble resolved multiple storms with methane ice-crystal clouds appearing at mid-northern latitudes as summer approaches the north pole. Uranus’ north pole now has a thickened photochemical haze with several little storms near the edge of the boundary. Hubble has been tracking the size of the north polar cap and it continues to get brighter year after year. As the northern summer solstice approaches in 2028, the cap may grow brighter still, and will be aimed directly toward Earth, allowing good views of the rings and north pole. The ring system will then appear face-on.

Neptune

When Voyager 2 flew by Neptune 1989, astronomers were mystified by a great dark spot the size of the Atlantic Ocean looming in the atmosphere. Was it long-lived like Jupiter’s Great Red Spot? The question remained unanswered until Hubble was able to show in 1994 that such dark storms were transitory, cropping up and then disappearing over a duration of two to six years each. During the OPAL program, Hubble saw the end of one dark spot and the full life cycle of a second one – both of them migrating toward the equator before dissipating. The OPAL program ensures that astronomers won’t miss another one.

Hubble observations uncovered a link between Neptune’s shifting cloud abundance and the 11-year solar cycle. The connection between Neptune and solar activity is surprising to planetary scientists because Neptune is our solar system’s farthest major planet. It receives sunlight with about 0.1% of the intensity Earth receives. Yet Neptune’s global cloudy weather seems to be influenced by solar activity. Do the planet’s four seasons (each lasting approximately 40 years) also play a role? We may find out, if the OPAL program continues running on Hubble until the year 2179!

A montage of Hubble Space Telescope images of our solar system’s four giant outer planets: Jupiter, Saturn, Uranus, and Neptune, taken under the OPAL (Outer Planet Atmospheres Legacy) program over a duration of 10 years, from 2014 to 2024. — This is a montage of NASA/ESA Hubble Space Telescope views of our solar system’s four giant outer planets: Jupiter, Saturn, Uranus, and Neptune, each shown in enhanced color. The images were taken over nearly 10 years, from 2014 to 2024. This long baseline allows astronomers to track seasonal changes in each planet’s turbulent atmosphere, with the sharpness of the NASA planetary flyby probes of the 1980s. These images were taken under a program called OPAL (Outer Planet Atmospheres Legacy).
From upper-left toward center, the hazy white polar cap on the three teal-colored Uranus images appears more face-on as the planet approaches northern summer.
From center-right to far-center right, three images of the blue planet Neptune show the coming and going of clouds as the Sun’s radiation level changes. Several of Neptune’s mysterious dark spots have come and gone sequentially over OPAL’s decade of observations.
Seven views of yellow-brown Saturn stretch across the center of the mosaic in a triangle—one for each year of OPAL observations—showing the tilt of the angle of the ring plane relative to the view from Earth. Approximately every 15 years the relatively paper-thin rings (about one mile thick) can be seen edge-on. In 2018 they were near their maximum tilt toward Earth. Colorful changes in Saturn’s bands of clouds can be followed as the weather changes.
At bottom center, three images of Jupiter spanning nearly a decade, form a triangle. There are notable changes in Jupiter’s banded cloud structure of zones and belts. OPAL measured shrinking of the legendary Great Red Spot, while its rotation period speeds up.
Credit: NASA, ESA, A. Simon (NASA-GSFC), M. H. Wong (UC Berkeley), J. DePasquale (STScI)

Press release from ESA Hubble.

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Astronomy

Hubble’s observations of Jupiter’s Great Red Spot, collected between December 2023 to March 2024

By ScientifiCult 9 October 2024

Hubble’s new observations of Jupiter’s Great Red Spot, collected over 90 days between December 2023 to March 2024

Astronomers have observed Jupiter’s legendary Great Red Spot (GRS), an anticyclone large enough to swallow Earth, for at least 150 years. But there are always new surprises – especially when the NASA/ESA Hubble Space Telescope takes a close-up look at it.

Eight Hubble images showing Jupiter’s Great Red Spot. The GRS appears as a bright red oval in the middle of cream-coloured cloud bands. The images trace changes in the GRS’s size, shape, brightness, colour, and twisting, over a period of 90 days between December 2023 and March 2024. — Using Hubble Space Telescope data spanning approximately 90 days (between December 2023 and March 2024) when the giant planet Jupiter was approximately 740 million kilometres from the Sun, astronomers measured the Great Red Spot’s size, shape, brightness, colour, and vorticity over one full oscillation cycle. The data reveal that the Great Red Spot is not as stable as it might look. It was observed going through an oscillation in its elliptical shape, jiggling like a bowl of gelatin. The cause of the 90-day oscillation is unknown.
Credit: NASA, ESA, A. Simon (GSFC)

Hubble’s new observations of the famous red storm, collected over 90 days between December 2023 to March 2024, reveal that the GRS is not as stable as it might look. The recent data show the GRS jiggling like a bowl of gelatin. The combined Hubble images allowed astronomers to assemble a time-lapse movie of the squiggly behaviour of the GRS.

“While we knew its motion varies slightly in its longitude, we didn’t expect to see the size oscillate. As far as we know, it’s not been identified before,” said Amy Simon of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “This is really the first time we’ve had the proper imaging cadence of the GRS. With Hubble’s high resolution we can say that the GRS is definitively squeezing in and out at the same time as it moves faster and slower. That was very unexpected, and at present there are no hydrodynamic explanations.”

Hubble monitors Jupiter and the other outer solar system planets every year through the Outer Planet Atmospheres Legacy program (OPAL) led by Simon, but these observations were from a program dedicated to the GRS. Understanding the mechanisms of the largest storms in the solar system puts the theory of hurricanes on Earth into a broader cosmic context, which might be applied to better understanding the meteorology on planets around other stars.

Eight images of the giant planet Jupiter spanning approximately 90 days between December 2023 and March 2024. The planet appears striped, with brown and white horizontal bands of clouds. These stripes are called belts (sinking air) and bands (rising air). The polar regions appear more mottled. — Using Hubble Space Telescope data spanning approximately 90 days (between December 2023 and March 2024) when the giant planet Jupiter was approximately 740 million kilometres from the Sun, astronomers measured the Great Red Spot’s size, shape, brightness, colour, and vorticity over a full oscillation cycle. The data reveal that the Great Red Spot is not as stable as it might look. It was observed going through an oscillation in its elliptical shape, jiggling like a bowl of gelatin. The cause of the 90-day oscillation is unknown. The observation is part of the Outer Planet Atmospheres Legacy program (OPAL).
Credit: NASA, ESA, A. Simon (GSFC)

Simon’s team used Hubble to zoom in on the GRS for a detailed look at its size, shape, and any subtle colour changes.

“When we look closely, we see a lot of things are changing from day to day,” said Simon.

This includes ultraviolet-light observations showing that the distinct core of the storm gets brightest when the GRS is at its largest size in its oscillation cycle. This indicates less haze absorption in the upper atmosphere.

“As it accelerates and decelerates, the GRS is pushing against the windy jet streams to the north and south of it,” said co-investigator Mike Wong of the University of California at Berkeley. “It’s similar to a sandwich where the slices of bread are forced to bulge out when there’s too much filling in the middle.”

Wong contrasted this to Neptune, where dark spots can drift wildly in latitude without strong jet streams to hold them in place. Jupiter’s Great Red Spot has been held at a southern latitude, trapped between the jet streams, for the extent of Earth-bound telescopic observations.

The team has continued watching the GRS shrink since the OPAL program began 10 years ago. They predict it will keep shrinking before taking on a stable, less-elongated, shape.

“Right now it’s over-filling its latitude band relative to the wind field. Once it shrinks inside that band the winds will really be holding it in place,” said Simon.

The team predicts that the GRS will probably stabilise in size, but for now Hubble only observed it for one oscillation cycle.

“This is a great example of the power of Hubble’s exquisite imaging for monitoring of the atmospheres of the outer planets,” said co-investigator Patrick Irwin of the University of Oxford. “With these new observations we were able to study the dynamics and evolution of the GRS over three months, building on our understanding of the long-term properties of Jupiter obtained from the OPAL program over the past decade.”

The researchers hope that in the future other high-resolution images from Hubble might identify other Jovian parameters that indicate the underlying cause of the oscillation.

Press release from ESA Hubble

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Astronomy

Hubble watches spoke season on Saturn

By ScientifiCult 21 December 2023

Hubble watches spoke season on Saturn

Planet Saturn with bright white rings, multi-colored main sphere, and moons Mimas, Dione, and Enceladus. Spoke features on the left and right sides of the rings appear like faint grey smudges against the rings’ bright backdrop, about midway from the planet to the rings’ outer edge. Above the rings plane, the planet’s bands are shades of red, orange and yellow, with bright white nearer the equator. — This photo of Saturn was taken by the NASA/ESA Hubble Space Telescope on 22 October 2023, when the ringed planet was approximately 1365 million kilometres from Earth. Hubble’s ultra-sharp vision reveals a phenomenon called ring spokes.
Saturn’s spokes are transient features that rotate along with the rings. Their ghostly appearance only persists for two or three rotations around Saturn. During active periods, freshly-formed spokes continuously add to the pattern.
In 1981, NASA’s Voyager 2 first photographed the ring spokes. Hubble continues observing Saturn annually as the spokes come and go. This cycle has been captured by Hubble’s Outer Planets Atmospheres Legacy (OPAL) program that began nearly a decade ago to annually monitor weather changes on all four gas-giant outer planets.
Hubble’s crisp images show that the frequency of spoke apparitions is seasonally driven, first appearing in OPAL data in 2021 but only on the morning (left) side of the rings. Long-term monitoring shows that both the number and contrast of the spokes vary with Saturn’s seasons. Saturn is tilted on its axis like Earth and has seasons lasting approximately seven years.
This year, these ephemeral structures appear on both sides of the planet simultaneously as they spin around the giant world. Although they look small compared with Saturn, their length and width can stretch longer than Earth’s diameter!
The OPAL team notes that the leading theory is that spokes are tied to interactions between Saturn’s powerful magnetic field and the sun. Planetary scientists think that electrostatic forces generated from this interaction levitate dust or ice above the ring to form the spokes, though after several decades no theory perfectly predicts the spokes. Continued Hubble observations may eventually help solve the mystery.
Credit: Credit: NASA, ESA, STScI, A. Simon (NASA-GSFC)

This photo of Saturn was taken by the NASA/ESA Hubble Space Telescope on 22 October 2023, when the ringed planet was approximately 1365 million kilometres from Earth. Hubble’s ultra-sharp vision reveals a phenomenon called ring spokes.

Saturn’s spokes are transient features that rotate along with the rings. Their ghostly appearance only persists for two or three rotations around Saturn. During active periods, freshly-formed spokes continuously add to the pattern.

In 1981, NASA’s Voyager 2 first photographed the ring spokes. Hubble continues observing Saturn annually as the spokes come and go. This cycle has been captured by Hubble’s Outer Planets Atmospheres Legacy (OPAL) program that began nearly a decade ago to annually monitor weather changes on all four gas-giant outer planets.

Hubble’s crisp images show that the frequency of spoke apparitions is seasonally driven, first appearing in OPAL data in 2021 but only on the morning (left) side of the rings. Long-term monitoring shows that both the number and contrast of the spokes vary with Saturn’s seasons. Saturn is tilted on its axis like Earth and has seasons lasting approximately seven years.

This year, these ephemeral structures appear on both sides of the planet simultaneously as they spin around the giant world. Although they look small compared with Saturn, their length and width can stretch longer than Earth’s diameter!

The OPAL team notes that the leading theory is that spokes are tied to interactions between Saturn’s powerful magnetic field and the sun. Planetary scientists think that electrostatic forces generated from this interaction levitate dust or ice above the ring to form the spokes, though after several decades no theory perfectly predicts the spokes. Continued Hubble observations may eventually help solve the mystery. This image was created with Hubble data from proposal 16995 (A. Simon).

Press release from ESA Hubble.

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Hubble monitors changing weather and seasons on Jupiter and Uranus

By ScientifiCult 23 March 2023

Hubble monitors changing weather and seasons on Jupiter and Uranus

Ever since its launch in 1990, the NASA/ESA Hubble Space Telescope has been an interplanetary weather observer, keeping an eye on the ever-changing atmospheres of the largely gaseous outer planets. And it’s an unblinking eye that allows Hubble’s sharpness and sensitivity to monitor a kaleidoscope of complex activities over time. Today new images are shared of Jupiter and Uranus.

The outer planets beyond Mars do not have solid surfaces to affect weather as on Earth. And sunlight is much less able to drive atmospheric circulation. Nevertheless, these are ever-changing worlds. And Hubble – in its role as interplanetary meteorologist – is keeping track, as it does every year. Jupiter’s weather is driven from the inside out, as more heat percolates up from its interior than it receives from the Sun. This heat indirectly drives colour-change cycles in the clouds, like the cycle that’s currently highlighting a system of alternating cyclones and anticyclones. Uranus has seasons that pass by at a snail’s pace because it takes 84 years to complete one orbit about the Sun. But those seasons are extreme, because Uranus is tipped on its side. As summer approaches in the northern hemisphere, Hubble sees a growing polar cap of high-altitude photochemical haze that looks similar to the smog over cities on Earth.

Inaugurated in 2014, the Hubble Space Telescope’s Outer Planet Atmospheres Legacy (OPAL) programme has been providing us with yearly views of the giant planets. Here are some recent images.

Jupiter

Credit:
NASA, ESA, STScI, A. Simon (NASA-GSFC), M. H. Wong (UC Berkeley), J. DePasquale (STScI)

The forecast for Jupiter is for stormy weather at low northern latitudes. A prominent string of alternating storms is visible, forming a ‘vortex street’ as some planetary astronomers call it. This is a wave pattern of nested cyclones and anticyclones, locked together like the alternating gears of a machine moving clockwise and counterclockwise. If the storms get close enough to each other and merge together, they could build an even larger storm, potentially rivalling the current size of the Great Red Spot. The staggered pattern of cyclones and anticyclones prevents individual storms from merging. Activity is also seen interior to these storms; in the 1990s Hubble didn’t see any cyclones or anticyclones with built-in thunderstorms, but these storms have sprung up in the last decade. Strong colour differences indicate that Hubble is seeing different cloud heights and depths as well.

The orange moon Io photobombs this view of Jupiter’s multicoloured cloud tops, casting a shadow toward the planet’s western limb. Hubble’s resolution is so sharp that it can see Io’s mottled-orange appearance, the result of its numerous active volcanoes. These volcanoes were first discovered when the Voyager 1 spacecraft flew by in 1979. The moon’s molten interior is overlaid by a thin crust through which the volcanoes eject material. Sulphur takes on various hues at different temperatures, which is why Io’s surface is so colourful. This image was taken on 12 November 2022.

Jupiter’s legendary Great Red Spot takes centre stage in this view. Though this vortex is big enough to swallow Earth, it has actually shrunk to the smallest size it has ever been according to observation records dating back 150 years. Jupiter’s icy moon Ganymede can be seen transiting the giant planet at lower right. Slightly larger than the planet Mercury, Ganymede is the largest moon in the Solar System. It is a cratered world and has a mainly water-ice surface with apparent glacial flows driven by internal heat. This image was taken on 6 January 2023.

Jupiter and its large ocean-bearing moons (Ganymede, Callisto and Europa) are the target of ESA’s Jupiter Icy Moons Explorer (Juice). Preparations are currently underway to ready Juice for liftoff from Europe’s Spaceport in French Guiana on 13 April 2023 [1].

Jupiter (November 2022 and January 2023). Credit:NASA, ESA, STScI, A. Simon (NASA-GSFC), M. H. Wong (UC Berkeley), J. DePasquale (STScI)

Uranus

Planetary oddball Uranus rolls around the Sun on its side as it follows its 84-year orbit, rather than spinning in a more ’vertical’ position as Earth does. Its weirdly tilted ‘horizontal’ rotation axis is angled just eight degrees off the plane of the planet’s orbit. One recent theory proposes that Uranus once had a massive moon that gravitationally destabilised it and then crashed into it. Other possibilities include giant impacts during the formation of the planets, or even giant planets exerting resonant torques on each other over time. The consequences of Uranus’s tilt are that for stretches of time lasting up to 42 years, parts of one hemisphere are completely without sunlight. When the Voyager 2 spacecraft visited during the 1980s, the planet’s south pole was pointed almost directly at the Sun. Hubble’s latest view shows the northern pole now tipping toward the Sun.

This is a Hubble view of Uranus taken in 2014, seven years after the northern spring equinox when the Sun was shining directly over the planet’s equator, and shows one of the first images from the OPAL programme. Multiple storms with methane ice-crystal clouds appear at mid-northern latitudes above the planet’s cyan-tinted lower atmosphere. Hubble imaged the ring system edge-on in 2007, but the rings are seen starting to open up seven years later in this view. At this time, the planet had multiple small storms and even some faint cloud bands.

As seen in 2022, Uranus’s north pole shows a thickened photochemical haze that looks similar to the smog over cities. Several little storms can be seen near the edge of the polar haze boundary. Hubble has been tracking the size and brightness of the north polar cap and it continues to get brighter year after year. Astronomers are disentangling multiple effects – from atmospheric circulation, particle properties, and chemical processes — that control how the atmospheric polar cap changes with the seasons. At the Uranian equinox in 2007, neither pole was particularly bright. As the northern summer solstice approaches in 2028 the cap may grow brighter still, and will be aimed directly toward Earth, allowing good views of the rings and the north pole; the ring system will then appear face-on. This image was taken on 10 November 2022.

Uranus (November 2014 and November 2022). Credit: NASA, ESA, STScI, A. Simon (NASA-GSFC), M. H. Wong (UC Berkeley), J. DePasquale (STScI)

Uranus (November 2014 and November 2022) compass image. Credit: NASA, ESA, STScI, A. Simon (NASA-GSFC), M. H. Wong (UC Berkeley), J. DePasquale (STScI)

Notes

[1] Ganymede is the main target of ESA’s Jupiter Icy Moons Explorer (Juice). As humanity’s next bold mission to the outer Solar System, Juice will complete numerous flybys around Ganymede, and eventually enter orbit around the moon. The mission will explore various key topics: Ganymede’s mysterious magnetic field, its hidden ocean, its complex core, its ice content and shell, its interactions with its local environment and that of Jupiter, its past and present activity, and whether or not the moon could be a habitable environment.

More information

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

The HST observations featured in this release include those from program 16790, 13937 , and 16995 (A. Simon).

Press release from ESA Hubble about the telescope observing the changing weather and seasons on Jupiter and Uranus.

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Hubble Sees Summertime on Saturn

By ScientifiCult 26 July 2020

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.

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