Biggest Satellites of our Solar System

1. Ganymede

Ganymede is a satellite of Jupiter and the largest moon in the Solar System. It is larger than Mercury and Pluto, If Ganymede orbited the sun instead of orbiting Jupiter, it would easily be classified as a planet. Ganymede's discovery is credited to Galileo Galilei, who was the first to observe it on January 7, 1610.

Earth, Moon (on the top), Ganymede

 Astronomers using the Hubble Space Telescope found evidence of thin oxygen atmosphere on Ganymede in 1996. The atmosphere is far too thin to support life as we know it. Ganymede is composed of approximately equal amounts of silicate rock and water ice. Ganymede orbits Jupiter at a distance of 1,070,400 km, third among the Galilean satellites and completes a revolution every seven days and three hours.

2.Titan

Titan is a satellite of Saturn and the second largest moon in our solar system. It is the only natural satellite known to have a dense atmosphere. Titan has a diameter roughly 50% larger than Earth's moon and is 80% more massive. Titan was discovered on March 25, 1655, by the Dutch astronomer/physicist Christiaan Huygens. Titan orbits Saturn once every 15 days and 22 hours.

Earth, Moon (on the top), Titan

Titan has a lot of conditions that make it similar to Earth. It is the only moon in the solar system with clouds and a dense, planet-like atmosphere. The atmosphere of Titan is largely composed of nitrogen; minor components lead to the formation of methane and ethane clouds and nitrogen-rich organic smog. The climate—including wind and rain—creates surface features similar to those of Earth, such as dunes, rivers, lakes and seas (probably of liquid methane and ethane), and deltas, and is dominated by seasonal weather patterns as on Earth. It is surrounded by an orange haze that kept its surface a mystery for Earth´s scientists.
Titan is called 'Space Oasis' because of its Natural diversities and change of seasons.

3. Callisto

Callisto is a satellite of Jupiter and  third-largest moon in the Solar System.  It was discovered in 1610 by Galileo Galilei. Callisto has about 99% the diameter of the planet Mercury but only about a third of its mass. Callisto's surface is the darkest of the Galileans, but it is twice as bright as our own Moon.
Callisto is the most heavily cratered object in the solar system. It is thought to be a long dead world, with hardly any geologic activity on its surface. Callisto is very different from other rocky moons in the Solar System. There are no mountains on Callisto. With a surface age of about 4 billion years, Callisto has the oldest landscape in the solar system.

4. Lo

Lo is a satellite of Jupiter and  forth-largest moon in the Solar System. Io is the most volcanically active body in the solar system. It contains above 400 active volcanoes. Lo is a bit larger than the Earth's moon. Its surface is also dotted with more than 100 mountains and some of these peaks are taller than Earth's Mount Everest. 

It was discovered on 8 January 1610 by Galileo Galilei. The discovery of the four Galilean satellites eventually led to the understanding that planets in our solar system orbit the sun, instead of our solar system revolving around Earth. Galilean satellite means the four moons of Jupiter which was also discovered by Galileo Galilei. 

5. Moon

Moon is the only natural satellite of  Earth and nearest large celestial body from Earth. It is the fifth largest satellite in the Solar System. The Moon is the second densest satellite after Lo. From Earth it is the brightest object in the sky after the Sun, although its surface is actually very dark.
The Moon is the only celestial body other than Earth on which humans have set foot. In past civilizations the Moon was regarded as a deity.