Astronomy 101: The Solar System
The solar system is our neighborhood in space. It contains the Sun, planets, dwarf planets, comets, moons, and asteroids. Planetary Scientists are the ones studying solar system bodies.
But, what is it made of?
The Sun contains 99.8 % of all the mass in the solar system. Then comes the inner solar system, composed by Mercury, Venus, Earth, and Mars (the “terrestrial” planets). Earth, Venus, and Mars have substantial atmospheres, while Mercury appears to have a very thin one.
Beyond Mars, there’s the Asteroid Belt, which is a collection of rocky objects of various sizes. Further, lies the outer solar system. Dominated by four giant planets: Jupiter, Saturn, Uranus, and Neptune (the “gas giants”). Orbiting the Sun at large distances they contain about 99 percent of the rest of the solar system’s mass. These planets consist mostly of very “small” rocky cores deep within massive spheres made of liquid metallic hydrogen, and some helium, covered by cloudy atmospheres. Uranus and Neptune are sometimes described as “ice giants” because they also contain significant amounts of supercold forms of oxygen, carbon, nitrogen, sulfur, and possibly even some water.
We also know a region beyond the gas giants called the Kuiper Belt. It extends from the orbit of Neptune out to a distance of well beyond 50 AU from the Sun (50 times the distance from Earth to the Sun). You can think of it as a very distant and much more extensive version of the Asteroid Belt. It’s populated with dwarf planets (like Pluto, Haumea, Makemake, and Eris) as well as many other smaller icy worlds.
Nearly all the major planets, some of the dwarf planets, and some asteroids have natural satellites called moons. The one we’re most familiar with is Earth’s Moon. Mars has two moons, called Phobos and Deimos, and Mercury and Venus have none. The gas giants swarm with moons. Jupiter’s four largest are Io, Europa, Ganymede, and Callisto, and they’re often referred to as the Galileans. Over the past few decades, at least sixty more have been discovered orbiting Jupiter. Saturn, Uranus, and Neptune also sport dozens of smaller icy worlds.
So now we have: 1 star, 8 main planets, 10 (and counting) dwarf planets, 146 (and counting) moons, and 4 ring systems. But it doesn't end here, there are countless comets, and hundreds of thousands of asteroids. Each gas giant planet has a set of rings. Saturn’s is the most extensive and beautiful.
All the planets of the solar system travel around the Sun following paths called orbits. Those paths are defined by Kepler’s Laws, which state that orbits are elliptical (slightly flattened circles), with the Sun at one focus of the ellipse. If you connect a line between the Sun and the object, Kepler’s Law states that this line sweeps out equal areas in equal amounts of time as the object goes around the Sun.
The Oort Cloud:
The entire solar system is surrounded by a shell of bits of ice and rock called the Oort Cloud. It stretches out to about a quarter of the way to the nearest star. Both the Kuiper Belt and the Oort Cloud are the origin of most of the comets we see. Space probes have yet to reach the area of the Oort cloud. Voyager 1, the fastest and farthest of the interplanetary space probes currently leaving the Solar System, will reach the Oort cloud in about 300 years and would take about 30,000 years to pass through it! However, around 2025, Voyager 1 will no longer have enough power to operate any of its scientific instruments, preventing any further exploration by Voyager 1. But we are on the quest of building more probes that could eventually reach interstellar space and send data to scientifically analyze. Not an easy task, but definitely worth trying! Do you agree?
Adapted from: Petersen, Carolyn Collins. Astronomy 101: From the Sun and Moon to Wormholes and Warp Drive, Key Theories, Discoveries, and Facts about the Universe (Adams 101) (pp. 21–22). Adams Media. Kindle Edition.
