Today in 1781 William Herschel discovered the planet Uranus. To this day, it’s still shrouded in mystery.
Uranus is the seventh planet from the Sun. It is a gaseous cyan-coloured ice giant. Most of the planet is made of water, ammonia, and methane in a supercritical phase of matter, which in astronomy is called 'ice' or volatiles. The planet's atmosphere has a complex layered cloud structure and has the lowest minimum temperature of 49 K (−224 °C; −371 °F) out of all the Solar System's planets. It has a marked axial tilt of 82.23° with a retrograde rotation period of 17 hours and 14 minutes. This means that in an 84-Earth-year orbital period around the Sun, its poles get around 42 years of continuous sunlight, followed by 42 years of continuous darkness.
Uranus has the third-largest diameter and fourth-largest mass among the Solar System's planets. Based on current models, inside its volatile mantle layer is a rocky core, and surrounding it is a thick hydrogen and helium atmosphere. Trace amounts of hydrocarbons (thought to be produced via hydrolysis) and carbon monoxide along with carbon dioxide (thought to have been originated from comets) have been detected in the upper atmosphere. There are many unexplained climate phenomena in Uranus's atmosphere, such as its peak wind speed of 900 km/h (560 mph),[22] variations in its polar cap, and its erratic cloud formation. The planet also has very low internal heat compared to other giant planets, the cause of which remains unclear.
Like the other giant planets, Uranus has a ring system, a magnetosphere, and 28 orbiting natural satellites. Its ring system is extremely dark, with only about 2% of the incoming light reflected. Uranus's satellite system contains 18 known regular moons, of which 13 are small inner moons. Further out are the larger five major moons of the planet: Miranda, Ariel, Umbriel, Titania, and Oberon. Orbiting at a much greater distance from Uranus are the nine known irregular moons. The planet's magnetosphere is highly asymmetric and has many charged particles, which may be the cause of the darkening of its rings and moons.
Like a lot of discoveries, other people did see it before, but Herschel realized what he was looking at.
Before its recognition as a planet, Uranus had been observed on numerous occasions, albeit generally misidentified as a star. The earliest possible known observation was by Hipparchus, who in 128 BC might have recorded it as a star for his star catalogue that was later incorporated into Ptolemy's Almagest.[26] The earliest definite sighting was in 1690, when John Flamsteed observed it at least six times, cataloguing it as 34 Tauri. The French astronomer Pierre Charles Le Monnier observed Uranus at least twelve times between 1750 and 1769,[27] including on four consecutive nights.
We’ve only taken one close look at it so far.
Launched in 1977, Voyager 2 made its closest approach to Uranus on 24 January 1986, coming within 81,500 km (50,600 mi) of the cloudtops, before continuing its journey to Neptune. The spacecraft studied the structure and chemical composition of Uranus's atmosphere,[101] including its unique weather, caused by its extreme axial tilt. It made the first detailed investigations of its five largest moons and discovered 10 new ones. Voyager 2 examined all nine of the system's known rings and discovered two more.[115][140][161] It also studied the magnetic field, its irregular structure, its tilt and its unique corkscrew magnetotail caused by Uranus's sideways orientation.[132]
There’s some hope we will return.
The 2023-2032 Planetary Science Decadal Survey — a report produced every 10 years by the U.S. scientific community to guide future NASA missions — recommends sending a spacecraft to Uranus as the highest priority. If commissioned, the Uranus Orbiter and Probe (UOP) mission will paint us a clear picture of where and how Uranus formed, and how it subsequently evolved. Because of the two ice giants' similarity, these insights would also likely apply to Neptune. The mission would also provide us with missing information necessary to understand the migration of the gas giants and the connected evolution of our solar system and early Earth.
In the best-case scenario, UOP could launch on a SpaceX Falcon Heavy rocket in 2031 or 2032 and reach Uranus 12 to 13 years later. There’s strong international interest in the mission too. The 2021 report of ESA’s Voyage 2050 Senior Committee recommends that the agency contributes to an ice giant mission led by an international partner, similar to how ESA provided the Huygens landing probe to Saturn’s moon Titan as part of Cassini
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