Uranus’ Atmosphere, Rings and, Moons

Uranus is the seventh planet from the Sun. It’s an icy gaseous planet, discovered in 1781, mistaken by a comet and finally two years later accepted as a planet. After decades of observations and only one close visit by a spacecraft, Uranus still shared one new fact about its atmosphere.

Uranus image taken by Voyager 2 on Jan. 14, 1986.

Uranus in visual light. This is image was taken by the spacecraft Voyager 2 on January 14th, 1986 from a distance of approximately 7.8 million miles (12.7 million km).

William Herschel, British astronomer.

Sir William Herschel, a German-born British astronomer, he discovered the planet Uranus, hypothesized that nebulae are composed of stars, and developed a theory of stellar evolution. He was knighted in 1816.

 

It was discovered in 1781 by astronomer William Herschel who originally thought it was either a comet or a star. Two years later, in part to observations by astronomer Johann Elert Bode the object was recognized as a planet. Herschel tried to name his discovery Georgium Sidus after King George III but instead, the planed became Uranus, the Greek god of the sky, suggested by Bode.

Compared to Other Planets

Uranus is 1.8 billion miles from the Sun; taking sunlight 2 hours and 40 minutes to reach Uranus. One day equals 17 hours, 14 minutes and, one year is the same as 84 Earth years. Uranus is four times wider than Earth with a radius of 15,759.2 miles (25,362 Km). If Earth was the size of a nickel, Uranus would be about as big as a softball. Most interestingly Uranus is the only planet turned more than 90 degrees on its axis.

Its equator sits at an angle or 97.77 degrees -possibly the result of a collision with an Earth-sized object long ago. Like its neighbor Neptune, Uranus likely formed closer to the Sun and moved to the outer solar system about 4 billion years ago.

An infrared composite image of the two hemispheres of Uranus. The images were obtained on July 11 and 12, 2004. The North pole is at 4 o’clock.

The unique 97.77-degree tilt causes the most extreme seasons in the solar system. For nearly a quarter of each Uranian year, the Sun shines directly over each pole, plunging the other half of the planet into a 21-year-long, dark winter. Wind speeds can reach up to 560 miles per hour (900 kilometers per hour. Uranus’ winds are retrograde at the equator -blowing in the reverse direction of the planet’s rotation but, closer to the poles, winds shift to a prograde direction, flowing with Uranus’ rotation.

Uranus is also one of just two planets that rotate in the opposite direction. Venus is the other one, both rotate from east to west or clockwise on their axis.

Uranus is an ice giant just like Neptune. Uranus’ core is very small -smaller than Earth, and its surrounded by a very thick layer called the Mantle, composed of water, ammonia, and methane. Outer solar system planetary scientists refer to these three elements as “ice” but the Mantle is not cold at all. It is very dense and under a lot of pressure, near the core, the mantle heats up to 9,000 degrees Fahrenheit (4,982 degrees Celsius).

Atmosphere

Uranus atmosphere is comprised of hydrogen and helium, with only 2% methane. However, the methane gives Uranus its signature aquamarine color. Methane is really good at absorbing red light which means the light it reflects is mostly green and blue. In a recent global research team that includes Glenn Orton of NASA’s Jet Propulsion Laboratory in Pasadena, California, scientists studied infrared light from Uranus using the Gemini North telescope on Hawaii’s Mauna Kea. They discovered that Uranus’ cloud tops were composed of hydrogen sulfide -the same smell as rotten eggs.

Rings

The scheme of Uranus's ring-moon system.

The scheme of Uranus’s ring-moon system. Solid lines denote rings; dashed lines denote orbits of moons. Click image to expand.

Uranus’ rings were discovered by accident in 1977. There are 13 rings known and are very faint and narrow. The innermost ring is reddish and the outer ring is blue with most of the rings being grey-ish.

Uranus inner rings

This false-color view of the inner rings of Uranus was made from images taken by Voyager 2 on Jan. 21, 1986. Click image to expand.

This false-color view of the inner rings of Uranus was made from images taken by Voyager 2 on Jan. 21, 1986, from a distance of 4.17 million kilometers (2.59 million miles). Nine known rings are visible here; the somewhat fainter, pastel lines seen between them are contributed by the computer enhancement. Two images each in the green, clear and violet filters were added together and averaged to find the proper color differences between the rings. The image shows the brightest ring, Epsilon (ε), further right in neutral color, with the fainter eight other rings showing color differences between them. Moving down, toward Uranus, we see the delta (δ), gamma (γ) and eta (η) ring in shades of blue and green; the beta (β) and alpha (α) rings in somewhat lighter tones; and then a final set of three, known simply as the 4, 5 and 6 rings, in faint off-white tones.

Voyager 2

On August 20, 1977, Voyager 2  launched from Cape Canaveral, Florida. Voyager 2 targeted Jupiter, Saturn, Uranus, and Neptune. It returned spectacular photos of the entire Jovian system. Like its sister spacecraft, Voyager 1, it also was designed to find and study the edge of our solar system beyond the orbits of the planets. Voyager 2 reached Uranus on January 24, 1986.  It remains the only spacecraft to have flown by Uranus. Voyager 2 spacecraft discovered 10 new moons, two new rings, and a strangely tilted magnetic field stronger than that of Saturn. A gravity assist at Uranus propelled the spacecraft toward its next destination, Neptune.

Moons

Uranus has 27 known moons. They are unique in being named for characters from the works of William Shakespeare and Alexander Pope.

Resources for Educators:

  1. Solar System Exploration: Uranus
  2. Kid-Friendly Uranus
  3. What Uranus Cloud Tops Have in Common with Rotten Eggs
  4. Read the latest news about Uranus in NASA.org