Saturn’s Rival to Jupiter’s Great Red Spot –A Storm as Wide As Earth


Similar to Venus, Saturn has a well developed vortex of swirling clouds at each pole imaged during the Cassini Mission. And, like Jupiter, Saturn has storms too, but they’re not as massive as the famous Red Spot, intense or large lived, but they’re still enormous. Staurn's hexagon-shaped storms at its poles is an enduring mystery.

Winds on Saturn reach their highest velocities are near the equator, where easterly blowing winds can reach speeds of 1,800 km/h, and drop off as you travel towards the poles.

One of Saturn's largest storms was the Great White Spot, observed by the Hubble Space Telescope in 1990. These storms seem to appear once every year on Saturn (once every 30 Earth years).

NASA’s Cassini spacecraft discovered static hexagonal storm circling around Saturn’s north pole, including a clearly defined eyewall – just like a typical tropical hurricane. Each side on the northern polar hexagon is approximately 13,800 km long, and the whole structure rotates once every 10 hours and 39 minutes -a day on Saturn.

After waiting years for the sun to illuminate Saturn's north pole again, cameras aboard NASA's Cassini spacecraft captured the most detailed images yet of the intriguing hexagon four times the size of Earth crowning the planet.

Because Saturn does not have land masses or oceans on its surface to complicate weather the way Earth does, its conditions should give scientists a more elementary model to study the physics of circulation patterns and atmosphere, said Kevin Baines, an atmospheric scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif., who has studied the hexagon with Cassini's visual and infrared mapping spectrometer.

The new images of the hexagon, whose shape is the path of a jet stream flowing around the north pole, reveal concentric circles, curlicues, walls and streamers not seen in previous images.

The last visible-light images of the entire hexagon were captured by NASA's Voyager spacecraft nearly 30 years ago, the last time spring began on Saturn.

After the sunlight faded, darkness shrouded the north pole for 15 years. Much to the delight and bafflement of Cassini scientists, the location and shape of the hexagon in the latest images match up with what they saw in the Voyager pictures.

"The longevity of the hexagon makes this something special, given that weather on Earth lasts on the order of weeks," said Kunio Sayanagi, a Cassini imaging team associate at the California Institute of Technology. "It's a mystery on par with the strange weather conditions that give rise to the long-lived Great Red Spot of Jupiter."

The hexagon was originally discovered in images taken by the Voyager spacecraft in the early 1980s. It encircles Saturn at about 77 degrees north latitude and has been estimated to have a diameter wider than two Earths. The jet stream is believed to whip along the hexagon at around 100 meters per second (220 miles per hour).

Early hexagon images from Voyager and ground-based telescopes suffered from poor viewing perspectives. Cassini, which has been orbiting Saturn since 2004, has a better angle for viewing the north pole. But the long darkness of Saturnian winter hid the hexagon from Cassini's visible-light cameras for years. Infrared instruments, however, were able to obtain images by using heat patterns. Those images showed the hexagon is nearly stationary and extends deep into the atmosphere. They also discovered a hotspot and cyclone in the same region.

Scientists are still trying to figure out what causes the hexagon, where it gets and expels its energy and how it has stayed viable for so long. They plan to search the new images for clues, taking an especially close look at the newly identified waves that radiate from the corners of the hexagon — where the jet takes its hardest turns — and the multi-walled structure that extends to the top of Saturn's cloud layer in each of the hexagon's six sides. Scientists are also particularly intrigued by a large dark spot that appeared in a different position in a previous infrared image from Cassini. In the latest images, the spot appears in the 2 o'clock position.

A massive blizzard was observed raging on Saturn this past May— a storm so large and fierce NASA astronomers and amateur skywatchers could see it from Earth. NASA's Cassini spacecraft currently orbiting Saturn has a mission control window to the otherworldly tempest and is recording the most detailed data yet of storms on the ringed planet.

The Cassini data showed a large, turbulent storm, dredging up a lot of material from the deep atmosphere and covering an area at least five times larger than the biggest blizzard that hit Earth so far this year — the "Snowmageddon" storm that blanketed the Washington, D.C. area in snow in February.

Cassini's radio and plasma wave instrument and imaging cameras have been tracking thunder and lightning storms on Saturn for years in a region around Saturn's mid-latitudes that is nicknamed "storm alley."

But, gathering data on storms requires a tricky balancing act, since storms on Saturn can come and go on a time scale of weeks, while Cassini's imaging and spectrometer observations have to be locked in place months in advance.

The radio and plasma wave instrument regularly picks up electrostatic discharges that are associated with the storms, so scientists have been sending periodic tips to amateurs, who can quickly go to their backyard telescopes and try to spy the bright convective storm clouds.

Amateur astronomers Anthony Wesley, Trevor Barry and Christopher Go received one of those notices in February, and were able to snap dozens of pictures over the next several weeks.

In fact, in late March, Wesley — who is based in Australia and was the first person spot the aftermath of an comet impact on Jupiter last summer — sent Cassini scientists an e-mail with a picture of the storm attached.

"I wanted to be sure that images like these were being seen by the Cassini team just in case this was something of interest to be imaged directly by Cassini or the Hubble Space Telescope," Wesley wrote.

Luckily, the composite infrared spectrometer happened to be targeting the latitude of the storms. The Cassini scientists had known there might be storms in that area, but were unsure when they might be active.

The Cassini spectrometer obtained data on March 25 and 26 that showed larger than expected amounts of phosphine, a gas typically found in Saturn's deep atmosphere, and an indicator that powerful currents were lifting material upward into the upper troposphere.

The spectrometer data also showed that the tropopause, which is the dividing line between the serene stratosphere and the lower churning troposphere, was about 1 degree Fahrenheit (minus 17.2 degrees Celsius) colder in the storm cell than in neighboring areas.

"A balloonist floating about 100 kilometers (62 miles) down from the bottom of Saturn's calm stratosphere would experience an ammonia-ice blizzard with the intensity of Snowmageddon," said Brigette Hesman, a composite infrared spectrometer team member and assistant research scientist at the University of Maryland.

"These blizzards appear to be powered by violent storms deeper down — perhaps another 100 to 200 kilometers (62 to 124 miles) down — where lightning has been observed and the clouds are made of water and ammonia," Hesman said.

The Daily Galaxy via NASA/Cassini


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