The Universe is a very big place, whereas we occupy a very small corner of it known as the Solar System. Our stomping grounds are not only a tiny fraction of the Universe we know, but is also a very small part of our Milky Way Galaxy.
Nevertheless, the solar system is still a big place and one which is filled with its fair share of mysteries. In fact, it was only in a relatively recent past that we began to understand its true extent.
With very few expectations, few people or civilizations before the era of modern astronomy recognized the Solar System for what it was. In fact, the vast majority of astronomical systems pointed out that the Earth was a stationary object and that all known celestial objects revolved around it. In addition, they viewed it as being fundamentally different from different stellar objects which they held to be divine in nature
During the 17th century, scientists like Galileo Galilei, Johannes Kepler, and Isaac Newton developed an understanding of physics which led to the gradual acceptance that the Earth revolves around the Sun. By the 19th century, three observations made by three separate astronomers determined the true nature of the Solar System and its place in the Universe.
Structure and composition.
At the core of the Solar System lies the Sun which is surrounded by four terrestrial planets, the Main Asteroid Belt, four gas giants, and a massive field of small bodies. The system is then surrounded by a spherical cloud of planetesimals, that is believed to extend to a distance of 10,000 AU from the Sun into the Interstellar Medium.
The Sun contains 99.86% of the system’s known mass and its gravity dominates the entire system. The planets are very close to the ecliptic, whereas comets and Kuiper Belt are frequently at greater angles to it. Most of the planets in the Solar System possess secondary systems of their own, orbited by planetary objects -“Natural Satellites”. In the case of four giant planets, there are also planetary rings- thin bands of tiny particles that orbit them in unison. Most of the largest natural satellites are in synchronous rotation, with one face permanently turned towards the planet.
Together, gases and ice are referred to as volatiles. The boundary in the Solar System beyond which these volatile substances could condense is known as the frost line. Within the Kuiper Belt, objects and planetesimals are composed mainly of these materials and rocks.
Inner Solar System.
In the Inner Solar System, we find the “Inner Planets”-Mercury, Venus, Earth, and Mars- which are so named because they orbit closest to the Sun. In addition to this proximity, the planets have a number of key differences that set them apart from planets elsewhere in the Solar System.
- Mercury is the smallest planet in the Solar System by surface area, volume, and equatorial diameter
- Venus is the brightest object in the sky after the Sun and the Moon and sometimes looks like a bright star in the morning or evening sun.
- Earth is the third planet from the Sun and the only astronomical object known to harbor life.
- Mars has dark slope streaks, dust devil tracks, sand dunes, fretted terrain, layers, gullies, and glaciers.
Outer Solar System.
The outer planets are huge planets swaddled in gas that have rings and plenty of moons. Despite their size, only two of them are visible without a telescope. Those include Jupiter and Saturn, Uranus, and Neptune were the first planets discovered since antiquity and showed astronomers that the Solar System was bigger than previously thought.
Jupiter has a dense core of uncertain composition, surrounded by a helium-rich layer of fluid metallic hydrogen.
Saturn is a gas giant made up mostly of hydrogen and helium. It is also known as ‘The Ringed Planet”.
Uranus is often dubbed an ice giant since at least 80% of its mass is a fluid mix of water, methane, and ammonia ice.
Our knowledge of the Solar System was also benefited immensely with the advent of robotic spacecraft, and robotic landers.
Universe, the whole cosmic system of matter and energy, of which the Earth, and therefore the human race, is a part. Humanity has traveled a long road since societies imagined the Earth, the Sun, and the Moon, as the main objects of creation, with the result of the Universe being formed almost as an afterthought.
Beginning in the mid-20th century, in what was known as “The Space Age”, manned and robotic spacecraft began exploring planets, asteroids, and comets in the Inner and Outer Solar System.
As our exploration of the Inner and Outer Solar System has improved and expanded, our conventions for categorizing planets have also changed. Our current model of the Solar System includes eight planets, four dwarf planets, and a growing number of Trans-Neptunian objects that yet have to be designated. It also contains and is surrounded by countless asteroids and planetesimals.
This is yet an incomplete picture of this vast Universe to be explored.