THE SOLAR SYSTEM
What is the solar system?
This question is a bit more complicated than you might think, but generally, the solar system is a region of space consisting of a star at the center which we call the Sun (derived from the Latin word Sol, hence the term solar system) and the numerous planets, moons, asteroids and comets that are gravitationally bound to it. It is only one among hundreds of billions of star systems within the Milky Way galaxy but, for the foreseeable future, humans leaving the solar system remains in the realm of science fiction. Luckily for us, it is a relatively big and complex region of space full of fascinating objects and phenomena.
THE FORMATION OF THE SOLAR SYSTEM
As with all others like it, the solar system formed from the gravitational collapse of a massive cloud of gas and dust, called a nebula. The high abundance of gold and uranium within the Sun, relative to other stars, suggests that the Sun’s formation originated from the remnants of a supernova, the explosive death of a high-mass star where these heavier elements were likely synthesized.
As the massive nebula gradually contracted under its own gravity over millions of years, matter started to coalesce into numerous dense cores scattered throughout. One of these would become our solar system. At the densest point of this region, an object would begin to form, hungrily swallowing up the gas and dust around it, growing and growing until its gravity was strong enough to cause it glow hot from the intense pressure. This was a protostar, our Sun in its infancy.
As the infant Sun consumed and grew, the surrounding material would have began to churn around it in all directions. The paths of trillions of rocks and boulders would have constantly crisscrossed and collided. Over time, these violent clashes would have developed a dominant flow, and the surrounding sphere of debris and dust would have flattened out into a disk with the shrouded infant Sun at the center. Within this cosmic vortex of gas and dust, the collisions would have accrued mergers upon mergers of rocks which would develop into the numerous planets, moons and asteroids that populate much of the solar system.
TAKING A TOUR OF THE SOLAR SYSTEM
We are privileged to live amongst such a diverse array of fascinating celestial objects.
Astronomers recognize the present-day solar system as having sorted itself into a number of distinct regions. Moving outward from the Sun, we have the four inner terrestrial planets, the asteroid belt, the four outer giant planets, beyond lies the icy Kuiper belt and the distant spherical Oort cloud. Despite this expansive diverse array of celestial objects, our solar system has maintained remarkable stability.
A common unit of measurement when discussing distances in the solar system is the astronomical unit (AU). This is the average distance between the Earth and Sun, which is about 150 million kilometers (93 million miles). So, if something is said to be 2 AU away, that means its distance is twice the distance between the Earth and Sun. If something is said to be 0.5 AU away, that means its distance is half the distance between the Earth and Sun.
Note: At the end of each planet’s section is a subsection on that planet’s natural satellites (aka moons), if it has any.
With all that said, let’s take a trip and explore our cosmic neighborhood!
The shining, celestial jewel at the center of the solar system.
The closest planet to the Sun.
Earth’s lead-melting twin sister.
The cradle of humanity.
The crimson planet.
The rocky, fragmented halo dividing the planets.
The king of the planets.
The ringed wonder.
The coldest planet.
The furthest planet from the Sun.
The icy, orbital outskirts of the solar system.
Frozen vagabonds that blaze through the night sky.
Wonderous worlds that brave the perilous reaches of the solar system.
WHERE DOES THE SOLAR SYSTEM END?
The outer bounds of the solar system are defined in different ways by different kinds of scientists, usually depending on the nature of the inquiries.
Some might say the main planets are the dominating force of the solar system beyond the Sun, therefore ending at the orbit of Neptune (~30 AU). Some may even include the Kuiper belt as it’s the last major population zone (~50 AU) which also contains the furthest planetary bodies. Many scientists would classify the solar system’s true limit to extend to the farthest reaches of the Oort cloud where the Sun’s gravity loses its dominance over the competing grasp of the stars (up to ~100,000 AU or 1.6 light years). However, there is very little known about this region or how far it actually spans. The scientific community’s “official” definition would draw the line at the heliosphere, a huge bubble of solar wind surrounding the solar system. The termination shock is where this solar wind slows abruptly as it begins interacting with the interstellar medium (~120 AU). Only two spacecraft, NASA’s twin Voyager probes, have ever reached beyond this point.
THE FATE OF THE SOLAR SYSTEM
The Sun is roughly halfway through its main sequence phase. Over time, the Sun will continue to steadily fuse the hydrogen in its core into helium. However, its fuel supply will eventually deplete. A shell of fusion hydrogen will form around the inert, helium-filled core.
The Sun’s core is not hot or dense enough to fuse helium as much. Without sufficient thermonuclear fusion, there is no longer the same outward pressure to counteract the inward gravity. The Sun will contract; the core will squeeze and heat up even more which will trigger the fusion of shell hydrogen faster than the previous fusion of core hydrogen. The increased energy from fusion will cause the outer layers of the Sun to expand. This is the beginning of the end.
It is expected that this expansion will reach over 200 times the Sun’s current radius, obliterating Mercury and Venus and possibly even reaching the Earth’s orbit. Whatever in the inner solar system isn’t vaporized, will be reduced to burning cinders. However, the intense radiation will render Earth completely uninhabitable long before it too is consumed. As the Sun expands, it will spread its energy over a larger surface area, which has an overall cooling effect on the star. This expansion and cooling will shift the sun’s visible light to a red color, becoming a red giant.
Planetary nebula
White dwarf