The Rest of the Solar System

As we have already seen… Most of the solar systems mass is contained in the sun. Most of the remaining mass is contained in the 8 planets. The rest of the solar system consists of… dwarf (minor) planets (5) natural satellites, or moons (over 100) asteroids (possibly millions) comets (millions, maybe more)

Overview of the Solar System Sun at centre 4 terrestrial planets within 1.5 A.U. of sun Asteroid belt between Mars and Jupiter 4 gas giant planets Kuiper Belt beyond Neptune (30-50 A.U.) Oort cloud, part of Kuiper belt (theorized up to 50 000 A.U.)

Dwarf Planets In order for a body to be considered a planet, it must orbit the sun directly be large enough to form a sphere (roughly) have cleared its region of other objects (by capturing, absorbing, or colliding with them) Any body that satisfied the first 2 of these conditions only is considered a dwarf planet.

Dwarf Planets The largest of the DPs is Eris, with a very elliptical orbit (38-98 A.U.). Pluto (29-49 A.U.) is the most well known, and is also a trans-Neptunian object (TNO, any object beyond Neptune’s orbit  Kuiper belt). The Trans-Neptunian Dwarf Planets

Dwarf Planets The only other DP is Ceres, in the asteroid belt. It is also unique in that its orbit is only 8% elliptical (as opposed to the 16% to 44% for the other DPs)

Natural Satellites (Moons) 6 of the 8 planets have natural satellites 3 of the 5 DPs are known to have satellites Some asteroids even have moons! The largest, Jupiter’s Ganymede, is comparable in size to Mercury

Where do the moons come from? All moons come from the material in the original nebula that formed the sun and other planets. They either… formed at the same time and place as the (larger) planets and began orbiting became captured while passing nearby Formed after a collision with its planet (likely how our Moon was formed)

Asteroids Satisfy only condition 1 of being a planet Are found throughout the solar system Range in size from 100 m in diameter to a few 100 km in diameter, though few are larger than 100 km) Composition varies, but they are all rocky in nature. Some asteroids have been found to contain amino acids, other organic materials, and even water!

Asteroids There are many asteroids near Earth’s orbit When an asteroid comes close enough to Earth that it is inevitable that it is going to collide, it becomes a meteoroid. When a meteoroid enters Earth’s atmosphere and starts to burn up it becomes a meteor (aka: shooting star) Most meteors burn up completely in the atmosphere. Those that don’t become meteorites once they hit the ground. These can leave large craters.

Comets Tend to be similar in size to asteroids Unlike asteroids, comets likely formed in the Kuiper belt from frozen gases such as methane and ammonia around a core of rock or dust Orbital periods vary from 76 years (Halley’s comet) to possibly as much as millions of years!

Comets As a comet approaches, its frozen gases sublimate More dense material, like dust, will trail the comet’s direction of motion, forming a faint tail. Sublimated gases will be blown by solar wind away from the sun, forming a more visible tail.

Anatomy of a Comet