In the realm of the ice giants, Uranus's inner moons appear to be about half water ice and half rock. Titan, the second largest in the solar system, is the only moon with a thick atmosphere.
These shepherd moons help keep the rings in line. The chunks of ice and rock in Saturn's rings (and the particles in the rings of the other outer planets) are not considered moons, yet embedded in Saturn's rings are distinct moons or moonlets.
Both have subsurface oceans and Titan also has surface seas of lakes of ethane and methane. Saturn has two ocean moons – Enceladus and Titan. Saturn, Uranus and Neptune also have some irregular moons, which orbit far from their respective planets. Many of Jupiter's outer moons have highly elliptical orbits and orbit backwards (opposite to the spin of the planet). Jupiter's menagerie of moons includes the largest in the solar system (Ganymede), an ocean moon (Europa) and a volcanic moon (Io). Or the planet's gravity might break Phobos apart, creating a thin ring around Mars. Phobos is slowly drawing closer to Mars and could crash into the planet in 40 or 50 million years. While both have nearly circular orbits and travel close to the plane of the planet's equator, they are lumpy and dark. The two moons of Mars, Phobos and Deimos, are different. Usually the term moon brings to mind a spherical object, like Earth's Moon. Twelve American astronauts landed on the Moon during NASA's Apollo program from 1969 to 1972, studying the Moon and bringing back rock samples. Debris from the early Earth and the impacting body accumulated to form the Moon approximately 4.5 billion years ago (the age of the oldest collected lunar rocks). Moons of the Inner Solar SystemĮarth's Moon probably formed when a large body about the size of Mars collided with Earth, ejecting a lot of material from our planet into orbit. Other Uranian moon names were chosen from Alexander Pope's poetry ( Belinda and Ariel). Uranus' moons are named for characters in William Shakespeare's plays with destinations such as Ophelia and Puck in orbit. Newer moons discovered at Saturn, for example, are named for Norse mythology such as Bergelmir, a giant. Most moons in our solar system are named for mythological characters from a wide variety of cultures. The most significant moons get an official name. For example, S/2009 S1 was the first satellite discovered at Saturn in 2009. How Moons Get Their NamesĮvery moon discovered in the modern era gets a number first. As these planets grew in the early solar system, they were able to capture smaller objects with their large gravitational fields. In the outer solar system, the gas giants Jupiter and Saturn and the ice giants Uranus and Neptune have dozens of moons. Of the terrestrial (rocky) planets of the inner solar system, neither Mercury nor Venus have any moons at all, Earth has one and Mars has its two small moons. There are hundreds of moons in our solar system – even asteroids have been found to have small companion moons. Most planetary moons probably formed out the discs of gas and dust circulating around planets in the early solar system. They are generally solid bodies, and few have atmospheres. Moons – also called natural satellites – come in many shapes, sizes and types.
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