Solar System Test Grade 4

The Solar System formed 4. 6┬ábillion 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.

Among the ringed gas giant planet Saturn's amazing collection of 62 diverse, bizarre, and beautiful moons and moonlets, sometimes one of them just seems to stand out in the crowd. Such a moon is little Methone. Looking like a shiny white egg in Space, and composed of very lightweight fluffy stuff, Methone is less dense than any other known moon or asteroid in our Solar System. In March 2013, astronomers announced at the 44th Lunar and Planetary Science Conference held in the Woodlands, Texas, that this strange little 5-kilometer-size moon is one of a batch of Space eggs in orbit around Saturn! Imagine, a frigid, distant shadow-region in the far suburbs of our Solar System, where a myriad of twirling icy objects--some large, some small--orbit our Sun in a mysterious, mesmerizing phantom-like ballet within this eerie and strange swath of darkness. Here, where our Sun is so far away that it hangs suspended in an alien sky of perpetual twilight, looking just like a particularly large star traveling through a sea of smaller stars, is the Kuiper Belt--a mysterious, distant deep-freeze that astronomers are only now first beginning to explore. Makemake is a denizen of this remote region, a dwarf planet that is one of the largest known objects inhabiting the Kuiper Belt, sporting a diameter that is about two-thirds the size of Pluto. In April 2016, a team of astronomers announced that, while peering into the outer limits of our Solar System, NASA's Hubble Space Telescope (HST) discovered a tiny, dark moon orbiting Makemake, which is the second brightest icy dwarf planet--after Pluto--in the Kuiper Belt. The existence of such powerful roaring winds kicking up violent and powerful dust storms suggests that the underlying sand can be set in motion, too, and that the giant dunes covering Titan's equatorial regions are still active and continually changing.