Parts of the Universe: The Solar System

The Solar System can best be thought of as being composed of the Sun and astronomical objects that are bound to it by way of gravity. All of these were formed due to a giant molecular cloud’s collapse some 4.6 billion years ago. Much of the mass of the objects that orbit the Sun is found in eight planets who are quite solitary. These planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.


The inner planets are Mercury, Venus, Earth, and Mars. Their composition consists mainly of rocky and dense structures, and they feature no ring systems and only few moons or none at all. Metals like nickel and iron form their cores, while their mantles and crusts are made out of refractory minerals. Most of the inner planets have atmospheres that are sophisticated enough to produce weather.


Mercury is known as the smallest and innermost planet in the entire Solar System. It orbits the Sun one time every 87.969 Earth days. This planet has the tiniest axial tilt, and it also features the highest eccentricity of all planets. Mercury has been observed as a planet as far back as at least the first millennium BC.

? Mercury Observation: Webpage that discusses how difficult it is to observe the planet Mercury due to its nearness to the Sun.

? Facts on Mercury: Webpage from the Smithsonian that presents the facts about the planet Mercury in bullet-style fashion.

? Mercury Revealed: Webpage on Mercury features lots of information on the planet, everything from its properties to its geology.


Venus is known as the second planet from the Sun, and it orbits the Sun every 224.7 Earth days. The planet is covered by a layer of sulfuric acid clouds that are reflective, and it is made up of mainly carbon dioxide. Though Venus used to have oceans just like on Earth in its younger days, those have evaporated as the planet’s surface temperatures increased. After the Moon, it is the second brightest object in the night sky.

? Venus Facts: The planet Venus is spotlighted, including explorations of the kind of atmosphere on this planet.

? Venus’ Atmosphere: Webpage that delves into the kind of atmosphere that Venus produces, which is one full of carbon dioxide.

? Venus Explored: A look at Venus features, in part, a write-up on the conditions of the surface of this planet.


Earth is the fifth-biggest of all planets in the Solar System. The third planet from the Sun, it is the only planet where life is known to exist. Salt water oceans cover 71 percent of the planet’s surface, and Earth’s interior features a solid mantle, an inner core made of solid iron, and a liquid outer core. It is the biggest of the terrestrial planets in the Solar System.

? Earth Explained: A look at Earth features information on its plate tectonics and its interior structure.

? Facts about the Earth: Webpage that features facts and statistics about the Earth, such as its crust’s properties.

? Introduction to Earth: An introduction to the planet Earth features statistics like its mass and its orbital days.


The fourth planet from the Sun, Mars is named after Mars, the Roman god of war. It has a reddish appearance due to the iron oxide on its surface, a surface that features a landscape dotted with deserts, valleys, volcanoes and ice caps that are similar to those on Earth. The planet can be viewed from the Earth with the naked eye. It is a planet so bright that its brightness is only outshined by the Moon, the Sun, and Venus.

? Mars Defined: Webpage from the University of Washington displays information about Mars like its atmospheric temperature and its surface characteristics.

? Characteristics of Mars: Exploration into the physical characteristics of Mars includes mention of its appearance as a planet.

? The Facts about Mars: A fact-sheet on Mars features information about water on the planet as well as comparisons to the Earth.


A region of the Solar System, the asteroid belt can be located in between the orbits of Jupiter and Mars. Minor planets as well as asteroids occupy the region of the asteroid belt. The asteroid belt came to be from the primordial solar nebula. The asteroid belt initially formed as a group of tiny precursors to planets (or planetesimal's), before turning into proto-planets, which are moon-sized, planetary embryos.

? Definition of Asteroid Belt: A kid-friendly webpage that provides an understandable explanation of the asteroid belts, perfect for kids.

? Facts on the Asteroid Belt: Webpage that features bullet-style facts about the belt, such as where it lies.

? Asteroid Belt Explored: From ThinkQuest comes a look at the asteroid belt, including what lies inside of the asteroid belt.


The outer planets are also known as the gas giants. Collectively, they compose 99 percent of all of the mass that is known to orbit the Sun. The composition of these gas giants is mainly of helium and hydrogen, but Neptune and Uranus contain more ice in their makeup. All outer planets have rings, but only Saturn’s are viewable from Earth.


Jupiter is the biggest planet of all in the Solar System, and it is the fifth planet from the Sun. Much of the planet is made up of hydrogen gas with just one-quarter being helium. There is speculation that the planet also contains a rocky core that is composed of heavier elements. It is one of the gas giants because of its large size and the fact that it is not made entirely or rock or other solid elements.

? Jupiter’s Moons: Webpage that delves into the exploration of Jupiter’s moons, including some observations that Galileo made about them.

? The Basics: Amazing Space website that provides the basic facts on Jupiter.

? Jupiter Rundown: A rundown of Jupiter that features information about its magnetic field, its rotation, and its interior.


Named after the Roman god Saturn, Saturn is the sixth planet from the Sun. Saturn’s interior is made of iron, silicon, oxygen, and nickel compounds. It is also surrounded by a layer made of metallic hydrogen, a middle layer of liquid helium and liquid hydrogen, and a gaseous, outer layer. The planet has nine rings, each of which consists of particles of ice with a tinier amount of dust and rocky debris.

? Data on Planet Saturn: Webpage that offers visitors information the basic data about the planet, like its orbital elements and the names of its satellites.

? Magnetosphere and Magnetic Field: A look at Saturn includes information about the planet and also about its magnetosphere and magnetic field.

? The Moons of Saturn: Webpage of NASA’s Jet Propulsion Lab that talks about Saturn and its many moons.


Uranus is known as the seventh planet from the Sun. Visible to a person’s naked eye, Uranus is somewhat classified as an ice giant instead of a gas giant. This is because it features more ice elements like water, methane, and ammonia, along with helium and hydrogen, than Saturn or Jupiter. As with other big planets, Uranus has a magnetosphere, a system of rings, and many moons.

? The Seventh Planet Uranus: Webpage that features information on Uranus, which includes facts about its mass and its satellites.

? Uranus Explored: The planet Uranus is explored by way of providing information on its surface gravity and density.

? Data on Uranus: Government webpage features information on Uranus like what its atmosphere is like.


The planet Neptune is 17 times greater in mass than Earth. It is a planet that orbits the Sun at a distance that is 30 times greater than the distance between the Sun and the Earth. Neptune is a gas giant, but it can also be termed an ice giant because of its composition: It features more ices like ammonia, methane, and water along with traditional gas giant elements like helium and hydrogen. Neptune’s interior is mainly made up of rock and ices.

? Neptune Stats: Webpage from the US Geological Survey provides stats about Neptune, such as its rotation period and density.

? Orbit: Webpage that features the answer to a question about the length of days that Pluto is inside of Neptune’s orbit.

? Facts about Neptune: Facts on Neptune include such stunner's as the unusual texture of its moons as well as its orbital period.


Comets are icy and small Solar System bodies. When they get close enough to the Sun, they display their familiar tails, which are really fuzzy and thin atmospheres that are called comas. An orbital class of minor planets by the name of centaurs features behavioral characteristics of both comets and asteroids. As a result, centaurs have somewhat blurred distinctions between comets and asteroids.

? Comets You can Observe: Webpage about comets that features details about recently discovered comets and ones that can be seen.

? All about Comets: Webpage on comets breaks them down, explaining to kids details about their composition and other facts.

? Comet Basics: Webpage from UCLA explains the basics of comets to children.

? Threat!: Science article that explores the gravity of the threat of comets to planet Earth.


The Trans-Neptunian Region is simply the area beyond the planet Neptune. As of this date, it is still largely unexplored. As far as scientists can tell, it seems to be composed of small worlds whose makeup is of ice and rock. Another term for the Trans-Neptunian Region is the outer Solar System.

? Trans-Neptunian Region Defined: Webpage that goes into detail on what exactly this region of the Solar System is.

? Herschel: Science article about the Herschel Space Observatory and its efforts to look deeper into the Trans-Neptunian Region.

? Solar System Facts: A look at this region of the universe, in part, on a webpage that features information on the Solar System.


The Kuiper Belt is a portion of the Solar System that goes beyond planets that extend from Neptune’s orbit to about 55 AU away from the Sun. even though it is similar to an asteroid belt, the Kuiper Belt is around 20 times larger. Most of its composition is based on small bodies that are the remnants of the Solar System’s formation. Objects in the Kuiper Belt are made mainly of water, ammonia, and methane.


Pluto is best thought of as the second-biggest dwarf planet in the Solar System. It is also the tenth-biggest body that directly orbits the Sun. Up to 2006, it was classified as a planet. Since then, however, it is now referred to as the biggest member of a separate population that is known as the Kuiper Belt.

? Pluto Article: Science article that explores whether Pluto is a dwarf planet or a member of the Kuiper Belt.


Charon is known as the biggest satellite of the dwarf planet called Pluto. The diameter of Charon is about 1207 kilometers. Charon is thought to have no atmosphere and a surface that is dominated by water ice, which is less volatile than methane or nitrogen. Charon was discovered in 1978 by the US Naval Observatory Flagstaff Station.

? Dwarf Planet Revealed: From NOVA comes a webpage that explores Pluto in-depth, featuring details about its rotation and other properties.


Haumea is known as a dwarf planet that is found in the Kuiper Belt. This dwarf planet is one-third the mass of Pluto. It has a severe elongation, which makes it very unique among dwarf planets. Haumea was first discovered in 2004 by a team out of Caltech at the Palomar Observatory, which is in the US.

? All about Haumea: The dwarf planet is examined in this write-up, which features information on its size and other characteristics.


Makemake is the third-biggest dwarf planet in the Solar System. The diameter of this dwarf planet is about three-quarters that of Pluto. It features a very low temperature. This means that its surface is covered with nitrogen ice, ethane, and methane.

? MakeMake Defined: A look at Makemake includes particulars about its location, composition, and when it was first seen.

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