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SKEPTOID BLOG:

Solar System: Pale Blue Uranus

by Dani Johnson

April 13, 2013

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Donate Uranus is a spectacular planet in our Solar System that scientists still don't know much about. It is the seventh planet from our sun and it shares the title of Ice Giant with only Neptune. We've only had one space probe visit the planet, and that was more than 25 years ago but it still hands us surprises every now and then. I'm truly excited to learn as much as I can about this cold gas giant.

There are four gas giants in our Solar System, Jupiter, Saturn, Uranus and Neptune. Uranus' atmosphere, although similar to Jupiter's and Saturn's in its primary composition of hydrogen and helium, contains more "ices" such as water, ammonia, and methane, along with traces of hydrocarbons. (1) The atmosphere of hydrogen, helium and methane most likely sits atop an icy mantle of ammonia, water and methane. The traces of methane in the atmosphere are absorbing the red light which is at least one reason we see the pale blue-green color of the planet. The icy mantle probably sits atop a molten rocky core. The icy mantle isn't exactly the same kind of ice that we know of here on Earth. It is mostly a very dense and hot liquid but some parts of it might have a slushy or icy composition that is most likely a result of the high pressure inside the planet.

Much like Venus, Uranus rotates east to west. Uranus' rotation axis is tilted so that it is almost horizontal, giving the appearance that the planet is rolling on its side like a bowling ball. This unique rotation means that for a quarter of its 84 year orbit each pole is facing the sun which plunges the other side into a long, dark and cold winter. The planet's rotation was probably thrown off kilter by a rogue planet that barreled into it at some point, more than likely also taking out a chunk of the planet's core causing it to become a much colder planet. Uranus is the coldest planet in our Solar System, the temperatures in the cloud tops average about 49K (-371.47F). Like Neptune, Uranus boasts an irregular magnetic field. Most planet's magnetic field lines up with the rotation, but Uranus' field is 60 degrees off-center. Uranus also has rings just like the other gas giants of our Solar System, but the rings are faint and very hard to see in visible light.

It was German astronomer Johann Bode who suggested the planet be named after the Greek god of the sky, Uranus. Other proposed names include Minerva (Roman goddess of Wisdom), Hypercronius (Meaning "above Saturn"), Herschel and even Georgium Sidus (Latin for "The Georgian Planet"). The German-born British astronomer William Herschel discovered Uranus while studying the constellation Gemini in March of 1781. He thought it was a comet, so he reported it as one and it wasn't until a few months later that other astronomers and mathematicians deduced that it was the seventh planet from our Sun. Uranus is the first planet that was discovered using a telescope, making it the first planetary discovery of the modern age.

Voyager 2 is the only space probe to visit Uranus and it saw a very calm and cloudless planet in 1986. The Hubble Space Telescope and Keck Observatory in Hawaii have since taken pictures that reveal the dynamic cloud structures exhibited during the planet's Equinox, when the planet is fully illuminated by the Sun. Images have been taken that show Uranus has a dark spot like Neptune, but it has since disappeared.

Uranus' rings were the first to be discovered after Saturn's, which is significant because it was our first clue that Saturn's rings were not unique in the sense that another planet couldn't boast a set. We now know that all of our Solar System's gas giant have a set of rings, but Saturn has the most extensive collection. Uranus has 13 rings, divided into 10 dark inner rings and 2 brightly colored outer rings. Uranus' rings are different because they're full of boulder-sized rocks rather than dust particles.

Uranus has 27 moons that are thought to be asteroids that got trapped in the planet's gravitational field. Instead of being named after Greek and Roman gods, the moons of Uranus are named after characters in the works of both Shakespeare and Alexander Pope. Between Cordelia, Ophelia and Miranda is a swarm of eight small satellites crowded together so tightly that astronomers don't yet understand how the little moons have managed to avoid crashing into each other. (2)

"Sweet Moon," William Shakespeare wrote in "A Midsummer Night's Dream," "I thank thee for thy sunny beams; I thank thee, Moon, for shining now so bright." Centuries later, the moons of Uranus pay homage to the famous playwright.

Image Credit:


NASA/JPL/STScI

A recent Hubble Space Telescope view reveals Uranus surrounded by its four major rings and by 10 of its 17 known satellites. This false-color image was generated by Erich Karkoschka using data taken on August 8, 1998, with Hubble's Near Infrared Camera and Multi-Object Spectrometer. Hubble recently found about 20 clouds—nearly as many clouds on Uranus as the previous total in the history of modern observations.


The Wide Field/Planetary Camera 2 was developed by the Jet Propulsion Laboratory and managed by the Goddard Space Flight Center for NASA's Office of Space Science.


This image and other images and data received from the Hubble Space Telescope are posted on the World Wide Web on the Space Telescope Science Institute home page at URL http://oposite.stsci.edu/.


Image Credit:


NASA/JPL/STScI


These two pictures of Uranus -- one in true color (left) and the other in false color -- were compiled from images returned Jan. 17, 1986, by the narrow-angle camera of Voyager 2. The spacecraft was 9.1 million kilometers (5.7 million miles) from the planet, several days from closest approach. The picture at left has been processed to show Uranus as human eyes would see it from the vantage point of the spacecraft. The picture is a composite of images taken through blue, green and orange filters. The darker shadings at the upper right of the disk correspond to the day-night boundary on the planet. Beyond this boundary lies the hidden northern hemisphere of Uranus, which currently remains in total darkness as the planet rotates. The blue-green color results from the absorption of red light by methane gas in Uranus' deep, cold and remarkably clear atmosphere. The picture at right uses false color and extreme contrast enhancement to bring out subtle details in the polar region of Uranus. Images obtained through ultraviolet, violet and orange filters were respectively converted to the same blue, green and red colors used to produce the picture at left. The very slight contrasts visible in true color are greatly exaggerated here. In this false-color picture, Uranus reveals a dark polar hood surrounded by a series of progressively lighter concentric bands. One possible explanation is that a brownish haze or smog, concentrated over the pole, is arranged into bands by zonal motions of the upper atmosphere. The bright orange and yellow strip at the lower edge of the planet's limb is an artifact of the image enhancement. In fact, the limb is dark and uniform in color around the planet. The Voyager project is managed for NASA by the Jet Propulsion Laboratory.
Image Credit:


NASA/JPL


The infrared image allows astronomers to probe the structure of Uranus' atmosphere, which consists of mostly hydrogen with traces of methane. The red around the planet's edge represents a very thin haze at a high altitude. The haze is so thin that it can only be seen by looking at the edges of the disk, and is similar to looking at the edge of a soap bubble. The yellow near the bottom of Uranus is another hazy layer. The deepest layer, the blue near the top of Uranus, shows a clearer atmosphere.


Image processing has been used to brighten the rings around Uranus so that astronomers can study their structure. In reality, the rings are as dark as black lava or charcoal.


This false color picture was assembled from several exposures taken July 3, 1995 by the Wide Field Planetary Camera-2.


The Wide Field/Planetary Camera 2 was developed by the Jet Propulsion Laboratory and managed by the Goddard Space Flight Center for NASA's Office of Space Science.


This image and other images and data received from the Hubble Space Telescope are posted on the World Wide Web on the Space Telescope Science Institute home page at URL http://oposite.stsci.edu/.

Image Credit:

NASA/JPL/STScI

Sources:

http://solarsystem.nasa.gov/planets/profile.cfm?Object=Uranus&Display=OverviewLong

http://web.archive.org/web/20060210222142/http:/vesuvius.jsc.nasa.gov/er/seh/hersc.html

http://www.space.com/45-uranus-seventh-planet-in-earths-solar-system-was-first-discovered-planet.html

http://www.universetoday.com/18855/uranus/

http://www.space.com/45-uranus-seventh-planet-in-earths-solar-system-was-first-discovered-planet.html

http://www.space.com/18706-uranus-composition.html

http://www.universetoday.com/18855/uranus/

http://solarsystem.nasa.gov//multimedia/display.cfm?IM_ID=422

by Dani Johnson

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