The Solar System formed 4. 6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud. The vast majority of the system’s mass is in the Sun, with the majority of the remaining mass contained in Jupiter. The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being primarily composed of rock and metal. The four outer planets are giant planets, being substantially more massive than the terrestrials. The two largest, Jupiter and Saturn, are gas giants, being composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are ice giants, being composed mostly of substances with relatively high melting points compared with hydrogen and helium, called volatiles, such as water, ammonia and methane. All eight planets have almost circular orbits that lie within a nearly flat disc called the ecliptic.
"From what we know about cloud formation on Titan, we can say that such methane clouds in this area and in this time of year are not physically possible. The convective methane clouds that can develop in this area and during this period of time would contain huge droplets and must be at a very high altitude--much higher than the 6 miles that modeling tells us the new features are located," Dr. Rodriguez explained in the September 24, 2018 JPL Press Release. But there is an important difference. On our own planet, lakes and seas are flowing with water, while Titan's lakes and seas are filled primarily with methane and ethane, that slosh around within these liquid reservoirs. In this never-before-seen cycle, the hydrocarbon molecules evaporate and condense into clouds that send an exotic "rain of terror" back down to this strange moon-world's carbon-slashed surface. But small moons like Methone are usually geologically inactive and bereft of an atmosphere. Therefore, they are usually unable to smooth away the scars. Dr. Peter Thomas of Cornell University in Ithaca, New York, explained it this way in the May 17, 2013 New Scientist: "When we look at objects less than 200 kilometers in radius, they are all like potatoes. They have lumps, grooves, craters." This makes Methone's smooth surface a mystery. Dr. Thomas is a Cassini team member.