The universe is a gigantic place; Earth only makes up a tiny part of it. When we gaze at the stars, a mysterious vastness gazes back at us, waiting to be discovered. Let us not go too far; today, we are only discussing the solar system.
The solar system is made up of the Sun, the planets, and their satellites, in addition to comets and asteroids. A star, radiating heat and energy, the Sun is the largest object in the solar system, making up 99.85% of its mass. It is the center of the solar system, around which eight planets orbit: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Except for Earth, all planets were named according to Roman and Greek mythology.
Mercury travels fast in the sky; that is why it was named after the god of travel and commerce in Roman mythology. Venus shines the brightest in the sky; it was, thus, named after the goddess of love and beauty. Earth is the only planet that takes its name from Old English; Earth simply meaning “the ground”. Due to its “fiery” color, Mars carries the name of the god of war. Jupiter is the largest planet in the solar system, so it takes its name from the King of Gods in the Roman mythology. Meanwhile, Saturn is the Roman god of agriculture, Uranus is the name of the earliest god, while Neptune’s blue color is the reason it is named after the sea god.
Pluto is intentionally not included in this list simply because it is no longer considered a planet. In 2006, the International Astronomical Union (IAU) added criteria to define a planet, according to which, for an object to be considered a planet, it has to rotate around the Sun, be round or nearly round, and have gravitational dominance. Gravitational dominance means that the planet has to be the largest object in its orbit and has to eject other large objects from its space. Pluto failed to fulfill the last criterion, and therefore, it is now considered a “dwarf planet”.
In the solar system, in addition to the planets, there are also satellites of these planets; by definition, a satellite is an object that rotates around another object. As such, Earth is a satellite because it orbits the Sun, the Moon is a satellite because it orbits the Earth, and so on. Most planets in the solar system have satellites except for Venus and Mercury.
The Sun, the planets, and their satellites make up a large part of the solar system, but other objects are not of lesser significance. Comets are icy objects that contain dust, carbon dioxide, ammonia, and ice; they are believed to be leftovers. After the solar system was formed, the remains of the gases and dust made the comets.
Asteroids, on the other hand, are rocky objects that are too small to be considered planets; sometimes, they are called “minor planets”. Meanwhile, meteoroids are any small object that orbits the Sun; sometimes, they are the outcome of a comet coming near to the Sun, losing gas and dust, or they could be small asteroids. When they reach the Earth’s atmosphere, the heat and force of the impact create a visible phenomenon known as a meteor, colloquially known as a shooting star, which is basically a meteoroid burning as it enters the atmosphere.
The Sun is 1,391,000 kilometers across; the solar system is part of the Milky Way, a galaxy that contains more than 200 billion stars. As the universe is very large, astronomers do not know for sure the exact number of galaxies in the universe. However, they have come up with an estimate of a hundred billion galaxies by counting the galaxies in a certain region and multiplying the number up to estimate the number for the whole universe.
The whole solar system is a tiny part of the universe, the secrets of which human beings are still just scratching the surface of. Despite all what we know today, there is endless information that we are still unaware of; the universe is a huge place and human beings have only been able to visit the Moon. In 2030, NASA plans to send humans to Mars for the first time; hopefully, bit by bit, science will light up the dark areas of the vastness that gazes at us from the sky.
References
bbc.com
coolcosmos.ipac.caltech.edu
nasa.gov
physics.org
smartconversion.com
solarviews.com
space.com
starchild.gsfc.nasa.gov
sun.org
universetoday.com
This article was first published in print in SCIplanet, Winter 2017 issue.