Uranus
The ice giant that is shrouded in mystery has fascinated explorers for decades
All About Space's latest report on the ice giant
The seventh planet from the Sun, Uranus became the first planet to be found with the aid of a telescope on 13 March 1781 by British astronomer William Herschel. On that fateful night, he described observing a “nebulous star or perhaps a comet”. Little did he know that he had just discovered Uranus – named after the the Greek god of the sky – a name proposed by Johann Elert Bode in 1783.
Over 230 years later, Uranus still remains to be a puzzle. What is known is that Uranus is located about 2.9 billion kilometres (1.8 billion miles) from the Sun, about 19-times the distance from Earth to the Sun, meaning that one orbit of the Sun takes 84 Earth years. The planet is enormous, with a diameter of 50,724 kilometres (31,518 miles) – fourtimes wider than the Earth.
Uranus has a compositional mass that is 80 per cent a fluid mixture of water, ammonia (NH3) and methane (CH4) ices. It is the methane in the outer atmosphere that gives it its blue-green colour, but the thick cloud coverage does not allow our instruments to peer down any further, and is one reason why Uranus remains an enigma.
What astronomers strongly suggest is that below the planet’s cloud tops is a main atmosphere which contains mostly hydrogen and helium by composition and has traces of methane and other volatiles. Below that is the fluid icy mantle, which makes up most of its composition by mass, but it is also theorised that the pressure and temperatures are enough to make it ‘rain diamonds’ at that depth. Finally at the centre is the silicate iron-nickel core, thought to be between half to just over three-times the mass of the Earth.
Although there has only been one mission to visit the ice giant close up – Voyager 2 in 1986 – the planet has long been studied by ground and space-based telescopes such as Hubble and the Keck Observatory in Hawaii, United States. Observations throughout the years have revealed more subtle, yet surprising details about the planet. These include the planet’s thin rings, which confirmed that Saturn is not an outlier and rings can form around any planet. Astronomers have also been able to deduce that Uranus’ planetary rotational tilt is off by a notable 97.77 degrees, which implies there was a collision in its early age that knocked it over.
Similar to the larger gas giants, Jupiter and Saturn, storms have been observed brewing in the cloud tops of Uranus. In November 2014 the planet was extremely active; storms raged on Uranus that were even observed by amateur astronomers. These observations caused another dilemma in regards to Uranus. As there seems to be no internal heat source and it’s a huge distance from the Sun’s heat, astronomers question what’s going on inside Uranus to make such storms arise. “The colours and morphology of this cloud complex suggest that the storm may be tied to a vortex in the deeper atmosphere similar to two large cloud complexes seen during the equinox," said Larry Sromovsky, a planetary scientist at the University of Wisconsin, Madison, United States at the time of its discovery.