Planetary Moons: Titan, Ganymede and Europa
A natural satellite or moon is a body that revolves around a planet. Every planet except Mercury and Venus has at least one moon, and the giant planets have dozens. Examinations ask this topic through the number of moons of each planet, the largest moon in the solar system, and the special features of Titan, Ganymede and Europa, such as atmosphere, magnetic field and subsurface oceans. The facts are record-based, so a table of moons and their unique points makes this topic easy to score.
How many moons each planet has
Mercury and Venus have no moons. The Earth has one moon, and Mars has two small moons called Phobos and Deimos. Among the giant planets, Jupiter has about 95 confirmed moons, Saturn has the largest number, about 146, Uranus has about 28 and Neptune has about 16. The four largest moons of Jupiter, discovered by Galileo, are called the Galilean moons: Io, Europa, Ganymede and Callisto. The dwarf planet Pluto has a large moon called Charon.
Ganymede: the largest moon
Ganymede is a moon of Jupiter and is the largest moon in the solar system, even larger than the planet Mercury. It is the only moon known to have its own magnetic field. Ganymede is made of ice and rock and has a thin oxygen atmosphere. It is one of the four Galilean moons. The European Space Agency's JUICE mission is planned to study Ganymede along with the other icy moons of Jupiter. Because Ganymede is larger than Mercury but orbits Jupiter, it clearly shows that a moon can be bigger than a planet.
Titan: the moon with a thick atmosphere
Titan is the largest moon of Saturn and the second largest moon in the solar system, after Ganymede. Titan is the only moon known to have a dense atmosphere, which is rich in nitrogen like the Earth's atmosphere. It has lakes and rivers, but of liquid methane and ethane, not water. The Huygens probe, part of the Cassini mission, landed on Titan in 2005, the first landing on a moon in the outer solar system. Titan is often studied because its chemistry may resemble the early Earth.
Europa: the icy moon with an ocean
Europa is another moon of Jupiter and is one of the four Galilean moons, and the smallest of them. Its surface is made of ice, and beneath the icy crust scientists believe there is a large ocean of liquid water. For this reason Europa is considered one of the best places to search for life beyond the Earth. NASA's Europa Clipper mission has been sent to study whether Europa can support life. Other interesting moons are Io, the most volcanically active body in the solar system, and Enceladus, a moon of Saturn that shoots water geysers from its south pole.
Quick revision
Remember that Mercury and Venus have no moons, Earth has one, Mars has two, and Saturn has the most moons, followed by Jupiter. Ganymede, a moon of Jupiter, is the largest moon and the only one with a magnetic field. Titan, the largest moon of Saturn and the second largest overall, is the only moon with a thick nitrogen-rich atmosphere and has methane lakes; the Huygens probe landed there in 2005. Europa, a moon of Jupiter, has an icy surface and a probable subsurface ocean and is a leading candidate in the search for life. The Galilean moons are Io, Europa, Ganymede and Callisto.
How to prepare this topic
- Memorise the moon counts: Mercury and Venus none, Earth one, Mars two, Jupiter about 95, Saturn the most at about 146, Uranus about 28, Neptune about 16.
- Fix the records: Ganymede the largest moon, Titan the largest moon of Saturn and the only one with a thick atmosphere.
- Link each important moon with its planet and its one special feature, such as Europa's ocean or Io's volcanoes.
- Remember the Galilean moons in order and note that they were discovered by Galileo.
- Keep the mission names ready: Huygens for Titan, Europa Clipper for Europa and JUICE for Ganymede.
Common exam traps
- Saturn, not Jupiter, has the largest number of confirmed moons, although Jupiter is the largest planet.
- Ganymede is the largest moon and is larger than the planet Mercury; it is not a planet itself.
- Titan and Ganymede are often confused: Ganymede is the largest overall, while Titan is the largest of Saturn and the only moon with a thick atmosphere.
- Europa's ocean is below an icy crust, so it is not visible on the surface.
- Mercury and Venus have no moons at all, while Mars has two.
Frequently Asked Questions
Which is the largest moon in the solar system and around which planet does it orbit?
Ganymede is the largest moon in the solar system and orbits Jupiter. It is even larger than the planet Mercury and is the only moon known to have its own magnetic field. Ganymede is one of the four Galilean moons, the others being Io, Europa and Callisto.
What is special about Titan?
Titan is the largest moon of Saturn and the second largest moon in the solar system. It is the only moon known to have a dense atmosphere, which is rich in nitrogen. Titan has lakes and rivers of liquid methane and ethane rather than water. The Huygens probe, part of the Cassini mission, landed on Titan in 2005.
Why is Europa important in the search for life?
Europa is a moon of Jupiter with an icy surface, and scientists believe there is a large ocean of liquid water beneath its icy crust. Because liquid water is essential for life as we know it, Europa is considered one of the best places to search for life beyond the Earth. NASA's Europa Clipper mission has been sent to study it.
How many moons do the planets have?
Mercury and Venus have no moons. Earth has one moon and Mars has two, Phobos and Deimos. Jupiter has about 95 confirmed moons, Saturn has the largest number at about 146, Uranus has about 28 and Neptune has about 16. Pluto, a dwarf planet, has a large moon called Charon.
Which other moons are important for examinations?
Io, a moon of Jupiter, is the most volcanically active body in the solar system. Enceladus, a moon of Saturn, shoots water geysers from its south pole. Triton is the largest moon of Neptune and orbits in the opposite direction to its planet's rotation. Charon is the largest moon of Pluto.