Uranus & Moons
- Equatorial Diameter: 51,118 km
- Polar Diameter: 49,946 km
- Mass: 8.68 × 10^25 kg (15 Earths)
- Moons: 27 (Miranda, Titania, Ariel, Umbriel & Oberon)
- Rings: 13
- Orbit Distance: 2,870,658,186 km (19.19 AU)
- Orbit Period: 30,687 days (84.0 years)
- Effective Temperature: -216 °C
- Discovery Date: March 13th 1781
- Discovered By: William Herschel
- Uranus was officially discovered by Sir William Herschel in 1781. It is too dim to have been seen by the ancients. At first Herschel thought it was a comet, but several years later it was confirmed as a planet. Herschel tried to have his discovery named “George’s Star” after King George III. The name Uranus was suggested by astronomer Johann Bode. The name comes from the ancient Greek deity Ouranos.
- Uranus turns on its axis once every 17 hours, 14 minutes. The planet rotates in a retrograde direction, opposite to the way Earth and most other planets turn.
- Uranus makes one trip around the Sun every 84 Earth years. During some parts of its orbit one or the other of its poles point directly at the Sun and get about 42 years of direct sunlight. The rest of the time they are in darkness.
- Uranus is often referred to as an “ice giant” planet. Like the other gas giants, it has a hydrogen upper layer, which has helium mixed in. Below that is an icy “mantle, which surrounds a rock and ice core. The upper atmosphere is made of water, ammonia and the methane ice crystals that give the planet its pale blue colour.
- Uranus hits the coldest temperatures of any planet. With minimum atmospheric temperature of -224°C Uranus is nearly coldest planet in the solar system. While Neptune doesn’t get as cold as Uranus it is on average colder. The upper atmosphere of Uranus is covered by a methane haze which hides the storms that take place in the cloud decks.
- Uranus has two sets of very thin dark coloured rings. The ring particles are small, ranging from dust-sized particles to small boulders. There are eleven inner rings and two outer rings. They probably formed when one or more of Uranus’s moons were broken up in an impact. The first rings were discovered in 1977 with the two outer rings being discovered in Hubble Space Telescope images between 2003 and 2005.
- Uranus’ moons are named after characters created by William Shakespeare and Alexander Pope.
- These include Oberon, Titania and Miranda. All are frozen worlds with dark surfaces. Some are ice and rock mixtures. The most interesting Uranian moon is Miranda; it has ice canyons, terraces, and other strange-looking surface areas.
- Only one spacecraft has flown by Uranus. In 1986, the Voyager 2 spacecraft swept past the planet at a distance of 81,500 km. It returned the first close-up images of the planet, its moons, and rings. © Space Facts.com
1. Uranus is the coldest planet in the Solar System: Uranus is the seventh planet from the Sun, orbiting at a distance of 2.88 billion km. But it’s still much closer than Neptune, which averages a distance of 4.5 billion km from the Sun. However, this does not prevent Uranus from being colder than Neptune. Whereas the former experiences an average temperature of 72 K (-201 °C/-330 °F), reaching a low of 55 K (-218 °C/-360 °F). In contrast, the temperatures at the cloud tops on Uranus (which is defined as “surface temperature” for gas giants) averages 76 K (-197.2 °C/-323 °F), but can dip as low as 47 K (-226 °C/-375 °F). This is due to the fact that, unlike the other large planets in the Solar System, Uranus actually gives off less heat than it absorbs from the Sun. While the other large planets have tremendously hot cores, which radiate infrared radiation, Uranus’ core cooled down to the point that it no longer radiates much energy.
2. Uranus orbits the Sun on its side: All of the planets in the Solar System rotate on their axis, with a tilt that’s similar to the Sun. In many cases, planets have an axial tilt, where one of their poles will be inclined slightly towards the Sun. For example, the axis of the Earth’s rotation is tilted 23.5-degrees away from the Sun’s plane. Mars is similar, with a tilt of about 24 degrees, which results in seasonal changes on both planets. But the axial tilt of Uranus is a staggering 99 degrees! In other words, the planet is rotating on its side. All the planets look a bit like spinning top as they go around the Sun, but Uranus looks more like a ball rolling in a circular pattern. And this leads to another strange fact about Uranus…
3. A Season on Uranus lasts one long day – 42 years: A sidereal day on Uranus (that is, the time it takes for the planet to complete a single oration on its axis) is only about 17 hours long. But the tilt of Uranus is so pronounced that one pole or the other is usually pointed towards the Sun. This means that a day at the north pole of Uranus lasts half of a Uranian year – 84 Earth years. So, if you could stand on the north pole of Uranus, you would see the Sun rise in the sky and circle around for 42 years. By the end of this long, drawn-out “summer”, the Sun would finally dip down below the horizon. This would be followed by 42 years of darkness, otherwise known as a single “winter” season on Uranus.
4. Uranus is the second-least dense planet: The least dense planet in the Solar System is Saturn. In fact, with a mean density of 0.687 g/cm3, Saturn’s body is actually less dense than water (1 g/cm³). This means that the planet would float in a pool, provided it were roughly 60,000 km wide. With a mean density of 1.27 g/cm3, Uranus has the second-lowest density of any planet in the Solar System. This low density has an interesting side effect. Despite the fact that Uranus is 14.5 times as massive as the Earth, its significantly lower density means that you would only experience about 89% the force of gravity, assuming you could stand on Uranus’ cloud tops.
5. Uranus has rings: When it comes to ring systems, Saturn’s are the most famous. In addition to be colorful and far-reaching, they are also highly visible. One could spot them using nothing more than a backyard telescope. But in truth, all the gas and ice giants have their own ring systems, and Uranus’ is the second most dramatic set of rings in the Solar System. However, these rings are composed of extremely dark particles which vary in size from micrometers to a fraction of a meter – hence why they are not nearly as discernible as Saturn’s. Thirteen distinct rings are presently known, the brightest being the epsilon ring. And with the exception of two very narrow ones, these rings usually measure a few kilometers in width. The rings are probably quite young, and are not believed to have formed with Uranus. The matter in the rings may once have been part of a moon (or moons) that was shattered by high-speed impacts. From numerous pieces of debris that formed as a result of those impacts, only a few particles survived, in stable zones corresponding to the locations of the present rings.
6. The atmosphere of Uranus contains “ices”: Compared to Jupiter and Uranus, Neptune seems quite… normal. When one looks at the swirling clouds and eddies that stream across the surface of Jupiter and Saturn, the violent and turbulent nature of their atmospheres is made clear. Uranus, by contrast, appears as a light and uniform blue. But thanks to improved instruments that can examine planets through other wavelengths (i.e. infrared) and the flyby conducted by the Voyager 2 spacecraft, some significant things become apparent. For example, Uranus has powerful zonal winds within its atmosphere that can reach up to 250 m/s (900 km/h, 560 mph), and can generate anticyclonic storms like Jupiter’s Great Red Spot. It also has cloud patterns that differ between hemispheres, some of which last for mere hours while others can persist for years or decades. But perhaps most interesting is the presence of certain “ices” in Uranus’ atmosphere. The third-most-abundant component of Uranus’s atmosphere is methane (CH), which is what accounts for Uranus’ aquamarine color. There are also trace amounts of other hydrocarbons, such as ethane, acetylene, methylacetylene, and diacetelyne – all of which are believed to be the result of methane interacting with solar ultraviolent radiation (aka. photolysis). And last, there are confirmed traces of water, ammonia, carbon dioxide, carbon monoxide, and hydrogen sulfide within the layers of Uranus’ atmosphere. And due to the extreme cold, they are suspended in an icy state (hence the term “ice giant”).
7. Uranus has 27 moons: Like all of the giant planets, Uranus has its share of moons. [As of 2021], astronomers have confirmed the existence of 27 natural satellites (as of. But for the most part, these moons are small and irregular. If you were to add up all of their masses, they would still be less than the half the mass of Triton, Neptune’s largest moon. However, unlike Triton, Uranus’ larger moons are all believed to have formed from an accretion disk that surrounded the planet, rather than being captured objects. The largest moons of Uranus are, in order of size, Miranda,Ariel, Umbriel, Oberon, and Titania. These moons range in diameter and mass from 472 km and 6.7 × 1019 kg for Miranda to 1578 km and 3.5 × 1021 kg for Titania. Each of these moons is particularly dark, with low bond and geometric albedos. Ariel is the brightest while Umbriel is the darkest. Each one is comprised of roughly equal amounts of rock and ice, except for Miranda which is made primarily of ice, which may include ammonia and carbon dioxide, while the rocky material is believed to be composed of carbonaceous material. Their compositions are believed to be differentiated, with an icy mantle surrounding a rocky core. In the case of Titania and Oberon, it is believed that liquid water oceans may exist at the core/mantle boundary. The rest of Uranus’ moons, which are either situated within the orbit of Miranda or beyond Oberon, are all connected to Uranus’ ring system, which probably resulted from the fragmentation of one or several small inner moons. All of them are composed of ices contaminated with a dark material, which are most likely organic compounds darkened by exposure to UV radiation.
8. Uranus was the first planet discovered in the modern age: Most of the planets are visible to the unaided eye, and were known in ancient times. Uranus was the first planet discovered after the invention of the telescope. It was first recorded in 1690 by John Flamsteed, who thought it was a star in the constellation Tauri. But it wasn’t until Sir William Herschel made his observations in 1781 that astronomers finally realized it was a planet. Herschel originally wanted to call Uranus “George’s Star” after King George III of England. However, this was not a popular name outside of England. Eventually, the astronomical community officially settled on the name Uranus – the Latinized version of the Greek god of the sky, Ouranos – and the name stuck.
9. You can see Uranus with the unaided eye: You might be surprised to know that you can see Uranus without a telescope. At magnitude 5.3, Uranus is just within the brightness scale that a human eye can perceive. Unfortunately, you’d need to make sure that the night sky was extremely dark (i.e. no light pollution), and would have to know exactly where to look. Because of this, Uranus has actually been spotted many times in the past by ancient and pre-modern astronomers. But given its low luminosity compared to the other planets, it was generally mistaken for a star. In fact, when Flamsteed first observed it, he cataloged it as 34 Tauri, believing it to be a star in the Taurus constellation.
10. Uranus has only been visited once: Only one spacecraft in the history of spaceflight has ever made a close approach to Uranus. NASA’s Voyager 2 conducted its closest approach to Uranus on January 24th, 1986, passing within 81,000 km of the cloud tops of Uranus. It took thousands of photographs of the gas/ice giant and its moons before speeding off towards its next target: Neptune. No other spacecraft have ever been sent towards Uranus, and there are currently no plans to send any more. The possibility of sending the Cassini spacecraft from Saturn to Uranus was evaluated during a mission extension planning phase in 2009. However, this never came to fruition, as it would have taken about twenty years for Cassini to get to the Uranian system after departing Saturn. While several proposals are currently under consideration, none have been confirmed yet. © Universe Today.com
Moons of Uranus
Early moon discoveries The discovery of Uranus and its first two moons came from the same astronomer: Sir William Herschel. The English sky gazer found Oberon and Titania in 1787, just six years after discovering the planet itself. Close-up pictures two centuries later showed that Oberon is abot half ice and half rock, with craters peppering its surface. Titania has fault lines running across its surface, hinting at past or present seismic activity. English astronomer William Lassell spotted Umbriel, the darkest of Uranus' big moons, in 1851. In Voyager 2's quick fly-by, scientists were unable to figure out how the surface got so dark, or why there is a bright ring on Umbriel's surface that is 90 miles (140 kilometers) in diameter. Ariel, another find from Lassell in 1851, has the youngest and brightest known surface among the moons. This could be due to meteorite hits, as well as possible geologic activity — among its features are grabens, or valleys surrounded by faults. Voyager 2 detected a silicate rock and water ice composition on this moon, with hints of carbon dioxide. The last find before the space age was perhaps the most bizarre moon of all — Miranda. Found by Gerard P. Kuiper at the McDonald Observatory in 1948, the moon appears to be a jumble of disconnected features. It's unclear what made the mashed-up surface. Perhaps a huge meteorite blew the moon apart and it reassembled, or smaller meteorites melted the surface and caused slush to flow and freeze again.
Voyager 2's early discoveries When Voyager 2 skimmed closest to Uranus' system in January 1986, its view turned up 10 new satellites within a month. While most of NASA's pictures of these moons show them as distant dots, if not for the spacecraft the moons probably would have gone unseen for decades if not longer. Ophelia and Cordelia are sometimes called shepherd moons. They are close to Uranus' Epsilon ring, with their gravitational influence essentially keeping the ring from falling apart. No one knows how big Cordelia is, or what its composition might be. Ophelia is believed to be 12 miles (20 kilometers) in diameter. Voyager 2 captured a picture of Puck that showed a mottled, dark surface. Astronomers believe it is made of carbonaceous material, and assume that much of the rest of the moons are of the same material. A 2003 study of the moon suggested water ice is on its surface. Most of the other moons were so small and far away from the spacecraft that little is known about their composition and in some cases, their sizes. Belinda and Cressida have low reflectivity, indicating they are probably carbonaceous moons as Puck is. The other moons found right away were Portia, Rosalind, Juliet, Desdemona, and Bianca. A 2001 study using the Hubble Space Telescope suggested these satellites (called the "portia Group" in this study) all have similar compositions and orbits.
Discoveries after Voyager Since 1986, astronomers have turned up 12 new Uranus moons using the Voyager 2 data, as well as with newer observations with telescopes on or orbiting Earth. Perdita has the most tangled history. The University of Arizona's Erich Karkoschka found the moon in 1999 using public Voyager 2 images and comparing them to some taken by the Hubble Space Telescope. At first, the IAU designated it a moon, but then rescinded that when other astronomers couldn't find it. Perdita was made official again in 2003 when Hubble spotted it again. Caliban, found by a team at the Palomar Observatory in 1997, moves in an inclined opposite orbit to the rotation of Uranus. "These characteristics suggest that Caliban was an independent body that was captured by Uranus' gravity," NASA stated. The same team also found Sycorax, which appears red in telescopes and also has a retrograde orbit. Three more discoveries happened in 1999 using the Canada-France-Hawaii Telescope at the Mauna Kea Observatory: Setebos, Prospero, and Stephano. In 2001, a team at the Cerro Tololo Inter-American Observatory in Chile found Trinculo, Francisco, and Ferdinand. The latest finds took place in 2003. Hubble spotted Mab and Cupid, while and Margaret was found using the Subaru 8.2-meter reflector at the Mauna Kea Observatory.
Recent publications With no spacecraft visiting Uranus in the near future and its sheer distance from the Earth, the potential for observations of its moons is limited. That said, there have been several scientific examinations of the system in recent years, as well as proposals to send spacecraft there in the distant future. Some astronomers envision using small cubesats to reduce the cost of getting a spacecraft out that far, while still returning valuable science. A team also submitted a Uranus Pathfinder orbiter mission concept to the European Space Agency in 2010, and again in again in 2015, but neither concept was accepted for funding. With the realization from Cassini observations that so many of Saturn's moons may have subsurface oceans, some astronomers have suggested that Uranus' moons could be host to oceans as well. The possibilities for life may be more limited because the moon is that much more distant from the sun, but it is hard to say for sure without doing detailed examination of the moons. Some observations of the moons have been performed from Earth. In 2013, a group probed Miranda for evidence of volatiles such as ammonia hydrate, and could not exclude the possibility from their observations. A 2015 Icarus publication based on Uranus system observations suggested that several of Uranus' moons have a mix of water and carbon dioxide ice on their surfaces. Separately, a 2014 model of Miranda in the journal Geology suggested that its strange surface could at least in part have come by tidal heating, which created slow convection on the icy surface. "Miranda has a really bizarre, deformed surface," Noah Hammond, a planetary scientist at Brown University in Rhode Island, told Space.com. "It's a really beautiful and exotic moon." The thin rings that surround Uranus hint that the planet could have even more moons in orbit. "At the edges of the rings … it's almost like the amount of stuff is going up and down in a periodic fashion that looks kind of like a wave, with crests troughs," then-graduate student Robert Chancia, of the University of Idaho, told Space.com. "It seems consistent with something disturbing the rings there," he added. "Based on the amplitude of this wave pattern and that distance from the ring … and our attempts to find the moon in images, it basically points toward if they exist, they're pretty tiny," Chancia said. He estimated that the moons, if they exist, are likely smaller than 3 miles (5 kilometers) in radius. © Elizabeth Howett, Space.com. February 27, 2018© Additional reporting by Nola Taylor Redd, Space.com contributor.
10 Interesting Facts about Titania With a circumference of 4,956 km (271,104 miles), Titania is the biggest moon of the planet Uranus, and the 8th biggest solar system moon overall. Titania was discovered by William Herschel on January 11, 1787, on the same day that he also discovered Oberon, Uranus’s second biggest moon. Below are some more interesting facts about Titania: – Titania is named after a daughter of the TitansThe moon is named after Titania, who was a daughter of the Titans, the primordial Gods of Greek mythology. Despite its ancient origins, the name Titania was taken from ‘A Midsummer Night’s Dream’, a play by William Shakespeare in which the Queen of the Fairies was named Titania. However, Shakespeare took the name from a work by the Roman poet Ovid called Metamorphoses which contained references to over 250 myths. Interestingly, all bu a couple of Uranus’s moons are named after characters from William Shakespeare plays, including Miranda, Ariel, Umbriel, and Oberon.
– Seasons on Titania last for 42 yearsSince all of Uranus’s moons orbit the planet on their sides and almost exactly in the planet’s equatorial plane, each of Titania’s poles spend 42 years (50% of Uranus’s orbital period around the Sun) in perpetual sunlight, and 42 years in perpetual darkness. Thus, at each solstice, the Sun rises almost exactly at the zenith above each pole.
– Titania may have formed by accretionTitania’s high density suggests that it had either formed from a disc of dust and debris that was left over after Uranus had formed, or from the debris of the proposed collision that tilted Uranus onto its side. While the exact nature of the material from which Titania had formed is not known with any degree of certainty, the high density of Titania and other Uranian moons suggest that this material contained comparatively little water, unlike the material from which some of Saturn’s other moons had formed, which is reflected in their high percentage of water ice, and correspondingly lower density.
– Titania’s canyons are cracks in its crustWhile very little is known about the geological processes that take place on Titania, it is likely that the huge canyons in the moon’s icy crust are the result of the subsurface layers (possibly a frozen subsurface ocean) freezing shortly after the moon’s formation. If these layers did indeed freeze, it would have expanded by about 7%, while the outer layers contracted as it cooled. The opposing forces would have caused the surface to crack, resulting in the fissures that cover most of the observed parts of the moon.
– Titania has a carbon cycleSince Uranus and its moons orbit the Sun almost on their sides, the moons receive more solar radiation on their poles than their equators. In practice, this means that carbon dioxide that had collected on the polar regions get warmed by the Sun when a pole faces sunward; thus, when a polar region reaches a temperature of about 85–90K (-1880 C), the carbon dioxide sublimates, and migrates to the equatorial and opposite polar region. This process is reversed when the opposite pole faces the Sun, thereby maintaining a sort of carbon cycle, somewhat similar to the hydrological cycle on Earth.
– Titania has a carbon dioxide atmosphereThe observed presence of relatively large amounts of carbon dioxide on Titania suggests that the moon may maintain an atmosphere consisting almost entirely of carbon dioxide. During an occultation of the star HIP106829 by Titania in 2008, such an atmosphere was indeed confirmed, but it turned out to be extremely tenuous, and seasonal at that, with a maximum possible surface pressure of only 10–20 nanobars (1-2 millipascal).
– Titania has few impact cratersThe paucity of impact craters on Titania is thought to be the result of endogenic processes that have all but obliterated the original surface. However, while much about the moon’s evolution remains unknown, the process of resurfacing was almost certainly tectonic in nature, although much of Titania’s surface appears to be covered by ejecta, which is relatively smooth “blankets” of material that was excavated during major impact events such as the formation crater Gertrude, the largest known crater on the moon, which has a diameter of 326 km (202 miles).
– Titania has a nearly perfectly circular orbitTitania orbits Uranus in an almost perfectly circular orbit, at a distance of 436,000 km (271,000 miles), taking 8.7 days to complete an orbit at an average speed of 3.64 km/sec. Titania’s orbit has an eccentricity of only 0.0011, and is inclined relative to Uranus’s equator by only 0.340 degrees. The moon is also tidally locked to Uranus, meaning that its own rotation equals its orbital period.
– For 50 years, only William Hershel could see TitaniaAlthough Titania is rather dim at an apparent magnitude of +13.9, it is easy to find with a large aperture amateur telescope today. However, for nearly 50 years after its discovery, only its discoverer, William Herschel could see it, for reasons that are not entirely clear. While Herschel was a skilled observer, other equally skilled observers failed to observe Titania. One possible explanation is that Herschel’s instrument was simply outperforming all others in the world at the time, which is entirely plausible, because Herschel was as an accomplished a telescope maker as he was an observer.
– The largest canyon on Titania is 1,492 km longThe largest canyon on Titania, Messina Chasma, stretches across 1,492 km (927 miles) from the moons’ equator nearly to its south pole. Named after Messina, a location in Shakespeare’s play, Much Ado About Nothing, the feature consists of two normal faults that cut across numerous impact craters and other features, which suggests that this structure must have formed comparatively recently in the moon’s history. By way of comparison, the Grand Canyon in the USA is only 446 km (277 miles) long. © Peter Christoforou, July 11, 2017