Our Solar System
Our solar system is consists of one star called The Sun and nine planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto). Our Solar System is also includes the satellites of the planets, numerous comets, asteroids and meteoroids, and the interplanetary medium. The Sun is the richest source of electromagnetic energy (mostly in the form of heat and light) in the solar system. The Sun’s nearest known stellar neighbor is a red dwarf star called Proxima Centauri, at a distance of 4.3 light years away. The whole solar system, together with the local stars visible on a clear night, orbits the center of our home galaxy, a spiral disk of 200 billion stars we call the Milky Way. The Milky Way has two small galaxies orbiting it nearby, which are visible from the southern hemisphere. They are called the Large Magellanic Cloud and the Small Magellanic Cloud. The nearest large galaxy is the Andromeda Galaxy. It is a spiral galaxy like the Milky Way but is 4 times as massive and is 2 million light years away. Our galaxy, one of billions of galaxies known, is traveling through intergalactic space.
The planets, most of the satellites of the planets and the asteroids revolve around the Sun in the same direction, in nearly circular orbits. When looking down from above the Sun’s North Pole, the planets orbit in a counter-clockwise direction. The planets orbit the Sun in or near the same plane, called the ecliptic. Pluto is a special case in that its orbit is the most highly inclined (18 degrees) and the most highly elliptical of all the planets. Because of this, for part of its orbit, Pluto is closer to the Sun than is Neptune. The axis of rotation for most of the planets is nearly perpendicular to the ecliptic. The exceptions are Uranus and Pluto, which are tipped on their sides.
Composition of the Solar System
The Sun contains 99.85% of all the matter in the Solar System. The planets, which condensed out of the same disk of material that formed the Sun, contain only 0.135% of the mass of the solar system. Jupiter contains more than twice the matter of all the other planets combined. Satellites of the planets, comets, asteroids, meteoroids, and the interplanetary medium constitute the remaining 0.015%. The following table is a list of the mass distribution within our Solar System.
Sun: 99.85%
- Planets: 0.135%
- Comets: 0.01%
- Satellites: 0.00005%
- Minor Planets: 0.0000002%
- Meteoroids: 0.0000001%
- Interplanetary Medium: 0.0000001%
Interplanetary Space:
Nearly all the solar system by volume appears to be an empty void. Far from being nothingness, this vacuum of “space” comprises the interplanetary medium. It includes various forms of energy and at least two material components: interplanetary dust and interplanetary gas. Interplanetary dust consists of microscopic solid particles. Interplanetary gas is a tenuous flow of gas and charged particles, mostly protons and electrons — plasma — which stream from the Sun, called the solar wind.
The solar wind can be measured by spacecraft, and it has a large effect on comet tails. It also has a measurable effect on the motion of spacecraft. The speed of the solar wind is about 400 kilometers (250 miles) per second in the vicinity of Earth’s orbit. The point at which the solar wind meets the interstellar medium, which is the “solar” wind from other stars, is called the heliopause. It is a boundary theorized to be roughly circular or teardrop-shaped, marking the edge of the Sun’s influence perhaps 100 AU from the Sun. The space within the boundary of the heliopause, containing the Sun and solar system, is referred to as the heliosphere.
The solar magnetic field extends outward into interplanetary space; it can be measured on Earth and by spacecraft. The solar magnetic field is the dominating magnetic field throughout the interplanetary regions of the solar system, except in the immediate environment of planets which have their own magnetic fields.
The Terrestrial Planets
The terrestrial planets are the four innermost planets in the solar system, Mercury, Venus, Earth and Mars. They are called terrestrial because they have a compact, rocky surface like the Earth’s. The planets, Venus, Earth, and Mars have significant atmospheres while Mercury has almost none. The following diagram shows the approximate distance of the terrestrial planets to the Sun.
The Jovian Planets
Jupiter, Saturn, Uranus, and Neptune are known as the Jovian (Jupiter-like) planets, because they are all gigantic compared with Earth, and they have a gaseous nature like Jupiter. The Jovian planets are also referred to as the gas giants, although some or all of them might have small solid cores. The following diagram shows the approximate distance of the Jovian planets to the Sun.
Dwarf Planets
There are 5 officially recognized dwarf planets in our solar system, they are Ceres, Pluto, Haumea, Makemake and Eris. With the exception of Ceres, which is located in the asteroid belt, the other dwarf planets are found in the outer solar system. There are another 6 objects in our solar system that are almost certainly dwarf planets and there may as many as 10,000. Of the dwarf planets only 2 have been visited by space probes, in 2015 NASA’s Dawn and New Horizons missions reached Ceres and Pluto respectively. Dwarf planets share many of the same characteristics as planets though there is one significant difference. The International Astronomical Union’s definition of a dwarf planet is a celestial body that is in orbit around the Sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, has not cleared the neighborhood around its orbit, and it is not a satellite. The key difference is that a planet has cleared other objects in the area of its orbit while a dwarf planet has not. The largest dwarf planet in the solar system is Pluto followed by Eris, Makemake, Haumea, with the smallest being Ceres. The order of the dwarf planets from closest to Sun outwards is Ceres, Pluto, Haumea, Makemake, with Eris being the furthest from the Sun.
Pluto (The first Dwarf Planet)
Pluto was discovered in 1930 by astronomer Clyde Tombaugh. However, it was not until the year 2015 that we finally got a close-up look at the dwarf planet. After a nine-year journey, NASA’s New Horizons spacecraft flew by Pluto, taking pictures and collecting data.
We now know that the surface of the dwarf planet is a tannish-red color. Scientists also observed a large bright area shaped like a heart and dark regions near the equator. There are high mountains made out of water ice. These mountains are covered by layers of frozen gases. While a few craters were seen, there was not nearly as many as expected. This means that something must be changing the surface of Pluto. Scientists do not yet know what could be causing these changes.
From the data collected by the spacecraft, scientists also learned that Pluto has a rocky core surrounded by a thick mantle of ice. Some scientists wonder if there might be a thin liquid ocean beneath the frozen surface.
Data from the experiments on-board New Horizons determined Pluto’s diameter to be 2,372 kilometers. It has an atmosphere of gases that expands when Pluto is nearer to the Sun. When Pluto is at its greatest distance from the Sun, the atmosphere freezes and falls to the surface.
It takes 6.39 Earth days for Pluto to make one spin on its axis. It takes Pluto 248 Earth years to make one orbit around the Sun. Pluto is about 40 times farther from the Sun than Earth. Pluto has five known moons: Charon, Nix, Hydra, Kerberos, and Styx.
