The Solar System and Its Formation

Many of these objects are in the ______ belt between the orbits of Mars and Jupiter (1.5–4.5 AU), and the Kuiper belt just outside Neptune's orbit (30–50 AU).[d] Six of the major planets, the six largest possible dwarf planets, and many of the smaller bodies are orbited by natural satellites, commonly called "moons" after Earth's Moon.Two natural satellites, Jupiter's moon Ganymede and Saturn's moon Titan, are larger than Mercury, the smallest terrestrial planet, though they are less massive.The Solar System is constantly flooded by the Sun's charged particles, the Solar wind, forming the heliosphere.Pushed against by the surrounding interstellar medium of the Local Cloud, the Solar wind starts slowing at 75 to 90 AU (the termination shock), before being halted, resulting in the heliopause, the boundary of the Solar System to interstellar space.The outermost region of the Solar System is the Oort cloud, the source for long-period comets, extending from 2,000 AU to the edge of the Solar System's sphere of gravitational influence at up to 200,000 AU (3.2 ly).The closest star to the Solar System, Proxima Centauri, is 4.25 ly away.The Solar System orbits the Galactic Center of the Milky Way galaxy, as part of its Orion Spur, at a distance of 26,000 ly.Formation and evolution The Solar System formed 4.568 billion years ago from the gravitational collapse of a region within a large molecular cloud.[e] This initial cloud was likely several light-years across and probably birthed several stars.As is typical of molecular clouds, this one consisted mostly of hydrogen, with some helium, and small amounts of heavier elements fused by previous generations of stars.As the pre-solar nebula collapsed, conservation of angular momentum caused it to rotate faster.The center, where most of the mass collected, became increasingly hotter than the surrounding disc.As the contracting nebula rotated faster, it began to flatten into a protoplanetary disc with a diameter of roughly 200 AU (30 billion km; 19 billion mi) and a hot, dense protostar at the center.The planets formed by accretion from this disc, in which dust and gas gravitationally attracted each other, coalescing to form ever larger bodies.Hundreds of protoplanets may have existed in the early Solar System, but they either merged or were destroyed or ejected, leaving the planets, dwarf planets, and leftover minor bodies.Due to their higher boiling points, only metals and silicates could exist in solid form in the warm inner Solar System close to the Sun (within the frost line).They would eventually form the rocky planets of Mercury, Venus, Earth, and Mars.Because metallic elements...

The Solar System is constantly flooded by the Sun's charged particles, the Solar wind, forming the heliosphere.Pushed against by the surrounding interstellar medium of the Local Cloud, the Solar wind starts slowing at 75 to 90 AU (the termination shock), before being halted, resulting in the heliopause, the boundary of the Solar System to interstellar space.The outermost region of the Solar System is the Oort cloud, the source for long-period comets, extending from 2,000 AU to the edge of the Solar System's sphere of gravitational influence at up to 200,000 AU (3.2 ly).The closest star to the Solar System, Proxima Centauri, is 4.25 ly away.The Solar System orbits the Galactic Center of the Milky Way galaxy, as part of its Orion Spur, at a distance of 26,000 ly.Formation and evolution The Solar System formed 4.568 billion years ago from the gravitational collapse of a region within a large molecular cloud.[e] This initial cloud was likely several light-years across and probably birthed several stars.As is typical of molecular clouds, this one consisted mostly of hydrogen, with some helium, and small amounts of heavier elements fused by previous generations of stars.As the pre-solar ______ collapsed, conservation of angular momentum caused it to rotate faster.The center, where most of the mass collected, became increasingly hotter than the surrounding disc.As the contracting ______ rotated faster, it began to flatten into a protoplanetary disc with a diameter of roughly 200 AU (30 billion km; 19 billion mi) and a hot, dense protostar at the center.The planets formed by accretion from this disc, in which dust and gas gravitationally attracted each other, coalescing to form ever larger bodies.Hundreds of protoplanets may have existed in the early Solar System, but they either merged or were destroyed or ejected, leaving the planets, dwarf planets, and leftover minor bodies.Due to their higher boiling points, only metals and silicates could exist in solid form in the warm inner Solar System close to the Sun (within the frost line).They would eventually form the rocky planets of Mercury, Venus, Earth, and Mars.Because metallic elements...

The center, where most of the mass collected, became increasingly hotter than the surrounding disc.As the contracting nebula rotated faster, it began to flatten into a protoplanetary disc with a diameter of roughly 200 AU (30 billion km; 19 billion mi) and a hot, dense ______ at the center.

The planets formed by ______ from this disc, in which dust and gas gravitationally attracted each other, coalescing to form ever larger bodies.Hundreds of protoplanets may have existed in the early Solar System, but they either merged or were destroyed or ejected, leaving the planets, dwarf planets, and leftover minor bodies.Due to their higher boiling points, only metals and silicates could exist in solid form in the warm inner Solar System close to the Sun (within the frost line).They would eventually form the rocky planets of Mercury, Venus, Earth, and Mars.Because metallic elements...

They would eventually form the rocky planets of Mercury, Venus, Earth, and Mars.Because metallic elements...