Since its launch in 1990, the NASA/ESA Hubble Space Telescope has been an interplanetary weather observer, monitoring the ever-changing atmospheres of the largely gaseous outer planets. And it’s an unblinking eye that allows Hubble’s sharpness and sensitivity to track a kaleidoscope of complex activity over time. New images of Jupiter and Uranus are being shared today.
The outer planets beyond Mars do not have solid surfaces to influence the weather as they do on Earth. And sunlight is much less able to stimulate atmospheric circulation. Yet these are ever-changing worlds. And Hubble – in its role as an interplanetary meteorologist – is keeping track, as it does every year. Jupiter’s weather is driven from within, as more heat seeps from its interior than it receives from the sun. This heat indirectly drives color change cycles in the clouds, such as the one currently highlighting a system of alternating cyclones and anticyclones. Uranus has seasons that go by at a snail’s pace because it takes 84 years to complete one orbit around the sun. But those seasons are extreme, because Uranus is on its side. As summer approaches in the Northern Hemisphere, Hubble sees a growing polar cap of high-altitude photochemical haze similar to the smog above Earth’s cities.
Inaugurated in 2014, the Hubble Space Telescope’s Outer Planet Atmospheres Legacy (OPAL) program provides us with images of the giant planets every year. Here are some recent images.
Jupiter
[LEFT] – The forecast for Jupiter is for stormy weather at low northern latitudes. A prominent series of alternating storms is visible forming a “vortex strait,” 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 together and merge, they could create an even bigger storm, potentially matching the current size of the Great Red Spot. The staggered pattern of cyclones and anticyclones prevents individual storms from merging. There is also activity in these storms; in the 1990s, Hubble saw no cyclones or anticyclones with built-in thunderstorms, but these storms have formed over the past decade. Strong color differences indicate that Hubble also observes different cloud heights and depths.
The orange moon Io bombards this view of Jupiter’s multicolored cloud tops, casting a shadow toward the planet’s western edge. 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 molten interior of the moon is covered with a thin crust through which the volcanoes eject material. Sulfur takes on different hues at different temperatures, which is why Io’s surface is so colorful. This photo was taken on November 12, 2022.
[RIGHT] – Jupiter’s legendary Great Red Spot is central to this view. While this vortex is large enough to swallow the Earth, it has actually shrunk to the smallest size it has ever been according to observations going back 150 years. Jupiter’s icy moon Ganymede can be seen near the giant planet’s 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 surface of mostly water ice with apparent ice currents driven by internal heat.
This image was taken on January 6, 2023. This image is smaller because Jupiter was 80,000 miles away from Earth when the image was taken.
Jupiter’s legendary Great Red Spot is central to this view. While this vortex is large enough to swallow the Earth, it has actually shrunk to the smallest size it has ever been according to observations going back 150 years. Jupiter’s icy moon Ganymede can be seen near the giant planet’s 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 surface of mostly water ice with apparent ice currents driven by internal heat. This photo was taken on January 6, 2023.
Uranus
Planetary oddball Uranus rolls on its side around the sun as it follows its 84-year orbit, rather than orbiting in a more “vertical” position like Earth. Its oddly tilted “horizontal” axis of rotation is at an angle of only eight degrees to the plane of the planet’s orbit. A recent theory states that Uranus once had a huge moon that gravity destabilized it and then crashed into it. Other possibilities include giant impacts during the formation of the planets, or even giant planets exerting resonant couples on each other over time. The consequences of Uranus’s tilt are that for a period of up to 42 years, parts of a hemisphere are completely without sunlight. When the Voyager 2 spacecraft visited in the 1980s, the planet’s south pole was pointed almost directly at the sun. Hubble’s most recent view shows that the north pole is now tilting toward the sun.
[LEFT] – This is a Hubble view of Uranus taken in 2014, seven years after the northern vernal equinox when the sun was directly above the planet’s equator, and shows one of the first images from the OPAL program. Multiple storms with methane ice crystal clouds appear in northern latitudes above the planet’s cyan-hued lower atmosphere. Hubble photographed the ring system from the side in 2007, but the rings begin to open up in this image seven years later. At that time, the planet had several small storms and even some faint cloud bands.
[RIGHT] – As seen in 2022, the north pole of Uranus shows a thickened photochemical haze similar to the smog over cities. Several small storms can be seen near the edge of the polar nebula boundary. Hubble has been tracking the size and brightness of the north polar cap, and it’s getting brighter year by year. Astronomers are disentangling multiple effects – from atmospheric circulation, particle properties and chemical processes – that determine how the atmospheric polar cap changes with the seasons. During the 2007 Uranian equinox, neither pole was particularly bright. As the northern summer solstice approaches in 2028, the hood may brighten even more and point directly at Earth, allowing a good view of the rings and the north pole; the ring system then appears face-on. This photo was taken on November 10, 2022.
This is a Hubble view of Uranus taken in 2014, seven years after the northern vernal equinox when the sun was shining directly above the planet’s equator, and shows one of the first images from the OPAL program. Multiple storms with methane ice crystal clouds appear in northern latitudes above the planet’s cyan-hued lower atmosphere. Hubble photographed the ring system from the side in 2007, but the rings begin to open up in this image seven years later. At that time, the planet had several small storms and even some faint cloud bands.
As seen in 2022, Uranus’ north pole shows a thickened photochemical haze similar to the smog over cities. Several small storms can be seen near the edge of the polar nebula boundary. Hubble has been tracking the size and brightness of the north polar cap, and it’s getting brighter year by year. Astronomers are disentangling multiple effects – from atmospheric circulation, particle properties and chemical processes – that determine how the atmospheric polar cap changes with the seasons. During the 2007 Uranian equinox, neither pole was particularly bright. As the northern summer solstice approaches in 2028, the hood may brighten even more and point directly at Earth, allowing a good view of the rings and the north pole; the ring system then appears face-on. This photo was taken on November 10, 2022.
