7. Uranus | The one with an exceptional tilt |

Uranus is the seventh planet from the Sun and is extremely windy and cold. Uranus has the Third largest planetary radius in diameter and the Fourth largest planetary mass in our Solar System.

It is one of the epitomes for Ice Giant Planets and is surrounded by 27 small moons and 13 faint rings. It has a unique tilt angle of nearly 90-degrees from the plane of its orbit which appears to spin on its side as a rolling ball orbiting around the Sun.

It is similar in composition to Neptune, and has bulk chemical compositions which differ from that of the larger Gas Giants Planets. It was discovered in 1781 by astronomer William Herschel. But Uranus was accepted as a planet after two years from its discovery only after close observation by astronomer Johann Elert Bobe.

Formation and Structure

Gravity pulled swirling gas and dust in to become this ice giant Uranus. It is one of the two Ice Giant Planets of our Solar System. Most of Uranus; to be specific its mass is made up of: 80 percent or more of hot dense fluid of Icy materials namely Water, Methane and Ammonia over a small rocky core. Core heats up to 4,982 degrees Celsius (9,000 degrees Fahrenheit).

It is blueish-green in colour acquired due to Methane gas present in the atmosphere. Sunlight passes through the atmosphere and is reflected back out by Uranus’s cloud tops. Methane gas absorbs the red portion of the light, resulting in a blue-green colour.

Distance and Size

It is 9.8 Astronomical units away from the Sun. Sunlight takes about 2 hours and 40 minutes to reach the surface of the planet Uranus. To be more specific: Uranus is 2.9 billion kilometres (1.8 billion miles) from the Sun.

It’s mass is about 14.5 times larger than our Earth. It has a radius of 25,362 kilometres (15,759.2 miles) which is 4 times wider than our home planet Earth. For example if earth’s size is of a Tennis Ball then Uranus size is of a Football.

Orbit and Rotation

It is one of the two known planets that rotate in the opposite direction than most of the planets, that is from east to west. (The second opposite rotating planet known is Venus).

It’s equator is nearly at right angle to its orbit making it the only planet in our solar system to have a tilt of 97.77 degrees. Researchers believe that the tilt of the planet is possibly the result of a collision with an Earth-sized object in days of yore.

Seasons on the planet are at peak or extreme levels due to its eccentric tilt. 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.

The planet makes a complete orbit around the Sun (a year in Uranian time) in about 84 Earth years (30,687 Earth days). One day on Uranus takes about 17 hours (the time it takes for Uranus to rotate or spin once).

Northern HemisphereYearSouthern Hemisphere
Winter solstice1902, 1986Summer solstice
Vernal equinox1923, 2007Autumnal equinox
Summer solstice1944, 2028Winter solstice
Autumnal equinox1965, 2049Vernal equinox

Surface and Rings

As an ice giant, the planet is mostly made of swirling fluids as Uranus doesn’t have a real land surface. The extreme pressures and temperatures would easily destroy anything that is metal or any components for that matter. Spacecraft’s cannot land on Uranus due to its lack of surface land but be able to fly through its atmosphere unscathed either.

Uranus consists of two sets of rings. The inner system of nine rings consists mostly of narrow, dark grey rings. There are two outer rings: the innermost one is reddish like dusty rings elsewhere in the solar system, and the outer ring is blue like Saturn’s E ring. Larger rings of the planet are surrounded by belts of fine dust and in increasing order of distance from the planet, the rings are called Zeta, 6, 5, 4, Alpha, Beta, Eta, Gamma, Delta, Lambda, Epsilon, Nu and Mu.

To check on the ring system of Saturn, go through our Saturn post.

Uranus’s mass is roughly 14.5 times that of Earth, making it the least massive of the giant planets. Its diameter is slightly larger than Neptune’s at roughly four times that of Earth. A resulting density of 1.27 g/cm3 makes Uranus the second least dense planet, after Saturn.

Atmosphere

Uranus’ atmosphere is mostly made of Helium and Hydrogen, consisting small amount of Methane and very few traces of Water and Ammonia. Due to the presence of Methane, the planets gets its signature blue colour. Its planetary atmospheric minimum temperature is about -224.2 degree Celsius which makes it one of the coldest planet than Neptune only in few regions.

Winds on the planet are retrograde at the equator, blowing in the reverse direction of the planet’s rotation which can reach speeds up to 900 Kilometres per hour (560 Miles per hour). Due to Uranus’ rotation, the winds shift to a prograde direction near its poles.

Few discrete clouds; A great Dark Spot with a small dark spot was observed by Voyager 2 during its flyby in 1986. Recent observations reveal that Uranus exhibits dynamic clouds as it approaches equinox, including rapidly changing bright features.

Magnetosphere

Magnetic fields are mostly in alignment with a planet’s rotation but Uranus has an irregular, unusual shaped magnetosphere where magnetic field is tipped over. Magnetic axis is tilted about 60 degrees from the planet’s axis of rotation, and is also offset from the centre of the planet by one-third of the planet’s radius.

The magnetic field lines of the planet are twisted due to its sideways rotation into a long corkscrew shape. Hence the magnetosphere tail behind Uranus opposite the Sun extends into space for millions of miles. Like on Earth, Jupiter and Saturn; Auroras on Uranus are not in line with the poles due to the lopsided magnetic field.

Uranus’s magnetosphere contains charged particles: mainly protons and electrons, with a small amount of H2+ ions. Many of these particles probably derive from the thermosphere. The ion and electron energies can be as high as 4 and 1.2 megaelectronvolts, respectively. The density of low-energy (below 1 kiloelectronvolt) ions in the inner magnetosphere is about 2 cm−3.

Moons

Uranus has 27 known moons. Its moons are uniquely named from the characters from the works of William Shakespeare and Alexander Pope while most of the satellites orbiting other planets are named from Greek or Roman mythology.

The composition of the outer moons of the planet remains unknown, but they are likely captured asteroids but all of Uranus’ inner moons appear to be roughly half water ice and half rock.

Expectancy of Life Forms

The extreme levels of temperatures, pressures and materials that characterize Uranus are too volatile for organisms to adopt to. Also due to the atmospheric composition of the planet it’s highly impossible for expectancy of any form of life forms.

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