Clues revealed about hidden interior of Uranus

November 14, 2014
By enhancing contrast and teasing out previously hidden information in images taken by the Voyager-2 spacecraft, LPL scientist Erich Karkoschka discovered that Uranus' southern hemisphere is anything but bland. Credit: Erich Karkoschka

( —Long believed to be one of the blandest regions of any of the giant gas planets, the southern hemisphere of Uranus indicates a flurry of previously unknown atmospheric phenomena, hinting at an unusual feature in the interior of the planet.

By re-analyzing images that NASA's Voyager-2 spacecraft took 28 years ago, University of Arizona astronomer Erich Karkoschka has teased out hidden features in Uranus' atmosphere that reveal an unexpected, strange rotation pattern and point to the possible existence of an unusual feature inside the planet's interior. The findings shed light on the interior structures of , not only of Uranus, a planet for which observational data are sparse, but also those of the many extrasolar that are being discovered.

When Voyager-2 flew by Uranus in January 1986 and sent the first close-up images back to Earth, it revealed a giant, pale blue icy ball that lacked the stunningly detailed, colorful bands and swirls of Jupiter, Saturn and Neptune. No more than eight faint features could be tracked, all located in the southern hemisphere. Only one of the eight features was located in the southern half of the southern hemisphere. Images taken with the Hubble Space Telescope and the largest telescopes on Earth did not reveal any feature there. The southern half of Uranus' southern hemisphere seemed to be the blandest region in the outer solar system.

The animation below, provided by Karkoschka, shows Uranus as Voyager-2 saw it during its fly-by in 1986, superimposed with the new look of the giant gas planet as a result of this study.

By teasing out subtle differences from the information contained in Voyager's images, Karkoschka discovered previously unseen features in Uranus' atmosphere, revealing that Uranus' southern hemisphere rotates unlike any region observed on the giant gas planets before. Karkoschka presented his findings at the meeting of the Division for Planetary Science of the American Astronomical Association in Tucson.

"Some of these features probably are convective clouds caused by updraft and condensation," said Karkoschka, a senior staff scientist at the UA's Lunar and Planetary Laboratory. "Some of the brighter features look like clouds that extend over hundreds of kilometers."

Uranus as photographed by Voyager-2 in 1986. Credit: NASA

"What we're really looking at when we observe the giant planets are their thick atmospheres," Karkoschka explained. "Cloud features tracking winds move mostly east or west at a speed depending on the latitude. Once we know the wind speed or rotational period at each latitude, we know the circulation of the planet's atmosphere."

In 1665, Giovanni Cassini performed the first rotational measurement of a giant planet when he tracked the Great Red Spot on Jupiter. Over the last three and a half centuries, astronomers have pinned down essentially the complete circulation of Jupiter and Saturn and about 75 percent for Uranus and Neptune. Karkoschka's new work fills in the remaining 25 percent for Uranus.

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A gas giant's observable atmosphere extends less than one percent of the planet's radius. Knowledge is limited about the more than 99 percent beneath it. In the absence of a visible surface, scientists rely on atmospheric features to determine the rotation periods of gas giants. The picture is complicated by atmospheric circulation patterns that vary with latitude and may or may not be in sync with the planet's core rotation rate.

"All previous observations of the giant planets indicated that these planets rotate in a regular way, meaning the rotational rates in their respective southern and northern latitudes are about the same," Karkoschka said. "My analysis suggests rotational rates in the high latitudes of Uranus are highly asymmetrical, with some southern latitudes possibly rotating as much as 15 percent faster than their northern counterparts."

Karkoschka found several sharp kinks in the rotational profile, defying all previous observations and theoretical considerations.

"The unusual rotation of high southern latitudes of Uranus is probably due to an unusual feature in the interior of Uranus," he said. "While the nature of the feature and its interaction with the atmosphere are not yet known, the fact that I found this unusual rotation offers new possibilities to learn about the interior of a giant planet."

Astronomers have tried to find clues about the interior of the giant planets, but little is known so far. Signals at radio wavelengths have indicated the rotation of the magnetic field of the giant planets, which likely reflects the rotation of the deep interior core. However, these data do not reveal much about the interior structure. Additional clues have come from measurements of the ' gravitational fields, but data are extremely sparse. Karkoschka's detailed rotational measurements of Uranus may help determine the interior structure of Uranus fairly accurately by eliminating some of the proposed models of the planet's interior.

This image shows Uranus with its rings and satellites such as moons indicated. Credit: Erich Karkoschka

"Most of the more than a thousand planets discovered around other stars are similar in size to Uranus," Karkoschka said. "They are too far for us to be able to measure their rotational profiles for the foreseeable future, but with an improved knowledge about Uranus, we might be better able to draw conclusions about their interior structure."

Uranus is an oddball in the solar system. Its rotational axis is tilted by almost 90 degrees, like a spinning top lying on its side. One lap around the sun takes about 85 years. Uranus' spring equinox in 2007 marked the beginning of a 43-year long period of darkness for the south pole and its surroundings, hidden from Earth's view. It seemed that the southern half of Uranus southern hemisphere was destined to stay a bland spot in the solar system—a region of unknown winds for decades to come.

Karkoschka did not want to wait that long. He experimented with different processing techniques and developed pattern recognition software until previously unseen features popped out. The largest improvement came when he stacked 1,600 images on top of one another to account for various possibilities of the rotation of Uranus. In the end, dozens of features became visible where only a single one was known before. The features were scattered all over the southern half of Uranus' so that its detailed circulation pattern finally became known. All these features, except the one previously known, are of very low contrast and become visible when the contrast is enhanced 300 times.

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This animation shows the differential rotation of previously unseen atmospheric features in Uranus's southern hemisphere. Credit: Erich Karkoschka

Karkoschka's work illustrates the scientific value that can be gleaned from data that have been around for a long time, available to anyone with Internet access. He had similar success when he investigated 13-year-old Voyager images of Uranus' surroundings and discovered the satellite Perdita.

"The computer memory necessary to process 1,600 images was not available at the time Voyager took these images," Karkoschka said. "As computers and calibration methods get better, we can now do this kind of work, at a tiny fraction of the cost necessary to send a spacecraft to a planet."

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Nov 14, 2014
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4.5 / 5 (12) Nov 14, 2014
I saw the title of this article and thought --the editor was asleep and the author just slipped this jem on by.

"Clues revealed about hidden interior of Uranus"

3.9 / 5 (7) Nov 14, 2014
And I'm still on my one-man mission to change the pronounciation to
4.2 / 5 (5) Nov 14, 2014
And I'm still on my one-man mission to change the pronounciation to

You can call your anus whatever you want. Don't tell me what to call mine.
1 / 5 (2) Nov 14, 2014
I want to see the rings around Uranus.
3.4 / 5 (5) Nov 14, 2014
I think it long past time to probe Uranus. Seriously, why no lander to this most unusual world yet?
3.7 / 5 (3) Nov 15, 2014
I saw the title of this article and thought --the editor was asleep and the author just slipped this jem on by.

"Clues revealed about hidden interior of Uranus"


I thought that was funny too! Bloody creative lol
5 / 5 (4) Nov 16, 2014

Space is eternal and infinity place which is nothing!

expanding movement / energy from Sun go through expanding planets and pushing expanding nucleus of atoms away from expanding Sun!


google: Etimespace

Could you translate into Human Readable, THX :)
5 / 5 (5) Nov 16, 2014
Definitely these two Voyager thingies were worth the investement.
It's amazing how they are still offering new insight into the solar system and the cosmos.
5 / 5 (2) Nov 17, 2014
I think it long past time to probe Uranus. Seriously, why no lander to this most unusual world yet?

They can't. Afaik, it's not even solid.
not rated yet Nov 18, 2014
I think it long past time to probe Uranus. Seriously, why no lander to this most unusual world yet?

Cuz Uranus is a gassy giant.
Da Schneib
not rated yet Nov 20, 2014
Actually it's "UR-ann-us."

I think it long past time to probe Uranus. Seriously, why no lander to this most unusual world yet?
They can't. Afaik, it's not even solid.
It's 13 or so Earths of ices, which means water, ammonia, methane, and CO₂ in astronomy, and an Earth or two of hydrogen and helium, and an Earth or two of rocks. It might have a diamond core or a diamond coating around the core, according to some recent high-pressure experiments at Lawrence Livermore.

By the time anything we can make today got a few thousand miles below the cloud tops it would be junk. So we could drop some sort of spacecraft in and then get data until it fell too far and was crushed and melted. Nobody's currently up for spending a couple billion bux on a thing that's going to last an hour or so and then melt.

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