Moons of Uranus: Facts About the Tilted Planet's SatellitesFor millennia, human beings stared up at the night sky and were held in awe by the Moon. To many ancient cultures, it represented a deity, and its cycles were accorded divine significance. By the time of Classical Antiquity and the Middle Ages, the Moon was considered to be a heavenly body that orbited Earth, much like the other known planets of the day Mercury, Venus, Mars, Jupiter, and Saturn. From this point onward, astronomers have come to understand that planets other than Earth can have their own moons — in some cases, several dozen or more. So just how many moons are there uranus moons how many 2017 the Solar System?
Moons of Uranus: Facts About the Tilted Planet's Satellites
For millennia, human beings stared up at the night sky and were held in awe by the Moon. To many ancient cultures, it represented a deity, and its cycles were accorded divine significance. By the time of Classical Antiquity and the Middle Ages, the Moon was considered to be a heavenly body that orbited Earth, much like the other known planets of the day Mercury, Venus, Mars, Jupiter, and Saturn.
From this point onward, astronomers have come to understand that planets other than Earth can have their own moons — in some cases, several dozen or more. So just how many moons are there in the Solar System? In truth, answering that question requires a bit of a clarification first. If we are talking about confirmed moons that orbit any of the planets of the Solar System i.
If, however, we open the floor to dwarf planets that have objects orbiting them, the number climbs to The moons, several minor planets and comets of the Solar System, shown to scale.
However, over minor-planet moons have also been observed in the Solar System as of Jan. This includes the 76 known objects in the asteroid belt with satellites, four Jupiter Trojans, 39 near-Earth objects two with two satellites each , 14 Mars-crossers, and 84 natural satellites of Trans-Neptunian Objects.
And some additional small bodies have been observed within the rings of Saturn. If we include all these, then we can say that the Solar System has known satellites.
The planets of the Inner Solar system — Mercury, Venus, Earth and Mars — are all terrestrial planets , which means that they are composed of silicate rock and minerals that are differentiated between a metallic core and a silicate mantle and crust. For a number of reasons, few satellites exist within this region of the Solar System. All told, only three natural satellites exist orbiting planetary bodies in the Inner Solar System — Earth and Mars.
While scientist theorize that there were moons around Mercury and Venus in the past, it is believed that these moons impacted on the surface a long time ago. The reason for this sparseness of satellites has a lot to do with the gravitational influence of the Sun.
Earth and Mars were able to retain satellites, but mainly because they are the outermost of the Inner planets. Earth has only the one natural satellite, which we are familiar with — the Moon. With a mean radius of km and a mass of 7. It is also the second densest moon in our Solar System after Io , with a mean density of 3. Several theories have been proposed for the formation of the Moon. The prevailing hypothesis today is that the Earth-Moon system formed as a result of an impact between the newly-formed proto-Earth and a Mars-sized object named Theia roughly 4.
This impact would have blasted material from both objects into orbit, where it eventually accreted to form the Moon. Mars, meanwhile, has two moons — Phobos and Deimos. Like our own Moon, both of the Martian moons are tidally locked to Mars, so they always present the same face to the planet. Compared to our Moon, they are rough and asteroid-like in appearance, and also much smaller. Phobos measures just Phobos and Deimos, photographed here by the Mars Reconnaissance Orbiter.
It is even smaller, measuring just Its orbit places it much farther away from Mars, at a distance of 23, km, which means that Deimos takes These three moons are the sum total of moons to be found within the Inner Solar System at least, by the conventional definition.
But looking further abroad, we see that this is really just the tip of the iceberg. To think we once believed that the Moon was the only one of its kind! Beyond the Asteroid Belt and Frost Line , things become quite different. In this region of the Solar System, every planet has a substantial system of Moons; in the case of Jupiter and Saturn, reaching perhaps even into the hundreds.
So far, a total of moons have been confirmed orbiting the Outer Planets , while several hundred more orbit minor bodies and asteroids. Due to its immense size, mass, and gravitational pull, Jupiter has the most satellites of any planet in the Solar System.
At present, the Jovian system includes 67 known moons, though it is estimated that it may have up to moons and moonlets the majority of which are yet to been confirmed and classified.
The four largest Jovian moons are known as the Galilean Moons named after their discoverer, Galileo Galilei. Io , the most volcanically active body in our Solar System; Europa , which is suspected of having a massive subsurface ocean; Ganymede , the largest moon in our Solar System; and Callisto , which is also thought to have a subsurface ocean and features some of the oldest surface material in the Solar System.
Illustration of Jupiter and the Galilean satellites. This groups includes the moons of Metis , Adrastea , Amalthea , and Thebe. Jupiter also has an array of Irregular Satellites, which are substantially smaller and have more distant and eccentric orbits than the others. Similar to Jupiter, it is estimated that Saturn has at least moons and moonlets, but only 53 of these moons have been given official names. Of these, 34 are less than 10 km in diameter and another 14 are between 10 and 50 km in diameter.
However, some of its inner and outer moons are rather large, ranging from to over km. The innermost moons and regular moons all have small orbital inclinations and eccentricities and prograde orbits. Meanwhile, the irregular moons in the outermost regions have orbital radii of millions of kilometers, orbital periods lasting several years, and move in retrograde orbits.
A collage of Saturn bottom left and some of its moons: Titan, Enceladus, Dione, Rhea and Helene. These moons are all composed primarily of water ice, and are believed to be differentiated into a rocky core and an icy mantle and crust.
Titan is also the only large moon to have its own atmosphere, which is cold, dense, and composed primarily of nitrogen with a small fraction of methane. Scientists have also noted the presence of polycyclic aromatic hydrocarbons in the upper atmosphere, as well as methane ice crystals. The surface of Titan, which is difficult to observe due to persistent atmospheric haze, shows only a few impact craters, evidence of cryo-volcanoes, and longitudinal dune fields that were apparently shaped by tidal winds.
Uranus has 27 known satellites, which are divided into the categories of larger moons, inner moons, and irregular moons similar to other gas giants. These moons range in diameter and mass from km and 6.
Each of these moons is particularly dark, with low bond and geometric albedos. Ariel is the brightest while Umbriel is the darkest. All of the large moons of Uranus are believed to have formed in the accretion disc, which existed around Uranus for some time after its formation, or resulted from the large impact suffered by Uranus early in its history.
Each one is comprised of roughly equal amounts of rock and ice, except for Miranda which is made primarily of ice. The ice component may include ammonia and carbon dioxide, while the rocky material is believed to be composed of carbonaceous material , including organic compounds similar to asteroids and comets.
Their compositions are believed to be differentiated, with an icy mantle surrounding a rocky core. These moons are divided into two groups — the regular and irregular moons — based on their orbit and proximity to Neptune. They generally follow inclined eccentric and often retrograde orbits far from Neptune. The only exception is Triton, which orbits close to the planet, following a circular orbit, though retrograde and inclined.
Global Color Mosaic of Triton, taken by Voyager 2 in In order of their distance from the planet, the irregular moons are Triton, Nereid , Halimede, Sao, Laomedeia, Neso and Psamathe — a group that includes both prograde and retrograde objects.
However, thanks to ongoing exploration and improvements made in our instrumentation, satellites are being discovered in orbit around minor bodies as well. As already noted, there are several dwarf planets, TNOs, and other bodies in the Solar System that also have their own moons.
These consist mainly of the natural satellites that have been confirmed orbiting Pluto , Eris , Haumea and Makemake. With five orbiting satellites, Pluto has the most confirmed moons though that may change with further observation.
The largest, and closest in orbit to Pluto, is Charon. Beyond Charon lies the four other circumbinary moons — Styx , Nix , Kerberos , and Hydra , respectively. A portrait from the final approach of the New Horizons spacecraft to the Pluto system on July 11th, The same team discovered Kerberos in The fifth and final satellite, Styx, was discovered by the New Horizons spacecraft in while capturing images of Pluto and Charon.
Charon, Styx and Kerberos are all massive enough to have collapsed into a spheroid shape under their own gravity. Nix and Hydra, meanwhile, are oblong in shape.
In addition, it is unusual in that each body is tidally locked to the other. Charon and Pluto always present the same face to each other; and from any position on either body, the other is always at the same position in the sky, or always obscured. This also means that the rotation period of each is equal to the time it takes the entire system to rotate around its common center of gravity.
In , observations by the Gemini Observatory of patches of ammonia hydrates and water crystals on the surface of Charon suggested the presence of active cryo-geysers. This would seem indicate that Pluto does have a subsurface ocean that is warm in temperature, and that the core is geologically active. The collision released material that consolidated into the moons around Pluto. Infrared observations indicate that its surface is almost entirely covered by pure crystalline water ice.
Because of this, Brown and his team have speculated that the moon is a fragment of Haumea that broke off during a collision. Both moons circle Haumea is highly eccentric orbits.
No estimates have been made yet as to their mass. Eris has one moon called Dysnomia , which is named after the daughter of Eris in Greek mythology, which was first observed on September 10th, — a few months after the discovery of Eris. The moon was spotted by a team using the Keck telescopes in Hawaii, who were busy carrying out observations of the four brightest TNOs Pluto, Makemake, Haumea, and Eris at the time.
The title for largest moon in the Solar System goes to Ganymede, which measures These two satellites, both of which orbit Jupiter, measure about 1 km 0. With every passing year, more satellites are being confirmed, and the vast majority of those we now know about were only discovered in the past few decades. As our exploration efforts continue, and our instruments improve, we may find that there are hundreds more lurking around out there!
We have written many interesting articles about the moons of the Solar System here at Universe Today. What are the Planets of the Solar System? We have recorded a whole series of podcasts about the Solar System at Astronomy Cast.