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Why Do All the Planets Orbit in the Same Direction?
If you’ve ever looked at a model of the solar system, you’ve probably noticed that all the planets orbit in the same direction. But why is it the case? The simple answer is because of the conservation of angular momentum. To understand it correctly, we need to travel back in time to the beginning of our solar system, approximately 4.5 billion years ago. Before we talk about “Why do all the planets orbit in the same direction,” let us first learn what an orbit is.
What is an Orbit?
An orbit is a path that an object in space follows around another object on a regular, repeated basis. A satellite is an example of a thing that is in orbit. Earth and the Moon are examples of natural satellites. But there are many satellites that humans built. The International Space Station (ISS) is one such example.
Why Do the Planets Orbit the Sun?
Well, it’s not because they got a Group Rate on First Class! On a serious note, paradoxically, the Sun’s gravity holds the planets in orbit around it, just as the Earth’s gravity keeps the Moon and satellites in orbit around it. So let us go into a bit of detail.
The Sun’s gravity is powerful compared to other objects, which keeps the planets in their orbits. A body’s mass determines its gravitational pull; the Sun, with its enormous mass and powerful gravity, causes the planets it orbits to circle it as it revolves. Therefore, gravity is the reason why the planets orbit the Sun.
The fact that the planets are traveling at a specific speed that allows them to orbit the Sun (rather than spiraling into it or whirling away into space) is not a coincidence or evidence of divine intervention. Instead, it dates back to when the Solar System was just a spinning, molecular cloud of gas and dust, as previously stated. Whatever was rotating slowly in the cloud of dust became part of the Sun. At the same time, anything that turned too quickly went into outer space. Everything else remained in orbit around the Sun, gradually becoming the planets, keeping their spin speed and path (encountering little resistance in the near-vacuum of space).
Do Planets Orbit Stars?
A “planet,” by definition, must revolve around a star, which in our case is the Sun. Besides our own solar system, there are trillions, if not more, solar systems in all of the universe. According to those who get to define the term ” planet, ” if it orbits no star at all, it is not a planet, according to those who get to define the term “planet.” A star is a celestial body that emits its light and is composed of a dense mass of gas held together by its gravity.
The International Astronomical Union (IAU) defined in August 2006 that, in the Solar System, a planet is a celestial body that:
- is in orbit around the Sun,
- has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and
- has “cleared the neighborhood” around its orbit.
If a big body orbits another star, you refer to it as an exoplanet. When a planet orbits no star at all, you refer to it as a “rogue planet.” If a planet is massive but does not fit all three of these characteristics, you refer to it as a “dwarf planet.” Pluto was earlier regarded as a planet but was later declassified as one. Pluto was declassified because it does not fit requirement #3 – Asteroids surround pluto. If asteroids surround you, you cannot be considered a “planet.” All “planets” revolve around our Sun.
How Many Planets Orbit the Sun in the Same Direction That Earth Does?
The solar system’s eight planets orbit the Sun in the opposite direction of the Sun’s spin, or counterclockwise when viewed from above the Sun’s north pole. Six of the planets rotate in the same direction around their axes. Venus and Uranus are the individual exceptions – planets orbiting with retrograde rotation. Researchers found that these discrepancies were caused by collisions later when both planets formed.
Except for Venus and Uranus, every planet in our solar system revolves clockwise, from west to east, as seen above the North Pole. All planets revolve around the Sun in the same direction the Earth does.
Why Do All the Planets Orbit in the Same Direction?
A large, revolving cloud of gas and dust, called the solar nebula, is widely believed to have generated the solar system. Even though it was only composed of dust and gas molecules, that cloud grew so large that it began to collapse and contract under the weight of its bulk.
As gravity condensed this cloud, angular momentum conservation caused a rise in rotational speed, flattening the cloud like a spinning disc. Angular momentum is a law of physics that states that things rotate faster as they shrink in size. That is precisely what happened to the very first solar system.
The Sun was formed by the gravitational attraction of most of the material. Asteroids, comets, moons, and planets form from planetesimals, once asteroid-sized particles that hit and stuck together within the disc.
The planets that originated within this disc of material all ended up orbiting the Sun in the same direction, almost precisely on the same plane, and with the same spin direction, which is consistent with the theory. It holds for all planets apart from Venus and Uranus, which were probably hit by other bodies, altering their spin.
Why Do Planets Spin?
Most scientists believe that planets similarly got their spin to stars when clumps of matter collided during the planets’ formation some 4.5 billion years ago. However, why do they all rotate in the same direction simultaneously?
This stability resulted from the fact that the entire solar system formed billions of years ago in a massive cloud of dust and gas. When our solar system was nothing more than a cloud of gas and dust, a shock wave from a nearby supernova likely collided with it and caused it to collapse. Instead, its gravitational forces dragged it into a flat, spinning disc as it collapsed. Our solar system formed from the same disc, and its momentum caused practically everything to spin in the same direction. (Notable exceptions are Uranus and Venus, whose unusual spins are likely the result of future collisions with asteroids.)
Our solar system’s giant gas planets (Jupiter, Saturn, Uranus, and Neptune) rotate more rapidly on their axes than the inner planets. According to the International Astronomical Union, they hold most of the system’s angular momentum. Only once a month does the Sun rotate. All planets orbit the Sun in the same general direction and almost on the same orbital plane, except Venus and Uranus.
Because of inertia, our planets have continued to revolve. Because no external force has been applied to halt them, spinning objects maintain their velocity and direction in space. That is why our planet, along with the other planets in our solar system, will continue to revolve.
Which Planets Rotate Clockwise?
In truth, there are two planets, Venus and Uranus, that revolve about their axes in the Sun’s direction from east to west. Venus spins from east to west on its axis. Uranus is tilted so far over that it appears to be rotating on its side.
But you might think that since all the planets’ origin was from the same cloud of gas and dust, they should all be spinning the same way. Venus and Uranus rotate in a reverse direction from the Sun, a phenomenon known as retrograde rotation.
Although there is no consensus among the scientific community why this happened, a long-held idea holds that Venus formerly rotated in the same direction as the other planets but was struck by a planet-sized object billions of years ago. The impact and its aftermath shifted the planetary axis in a new direction.
In 2011, computer simulations revealed that a series of more minor collisions, rather than a single enormous impact, may have caused Uranus’ rotation to change direction to a 98-degree angle. Furthermore, it might explain why all of the planet’s moons rotate at the same angle — something that would be highly implausible if there was only one massive impact.
Astronomers proposed an alternative theory in 2009, claiming that Uranus formerly had a big moon, the gravitational pull of which caused Uranus to lie on its side. The big Moon must have been pushed out of orbit by another planet present.
Scientists believe that Venus, our nearest neighbor, began revolving counter-clockwise, then slowed to practically a standstill before starting to rotate clockwise as it does now. But, for the time being, no one knows for sure what makes Venus and Uranus the exceptions in our Solar System’s family of planets.
The mysteries of the Universe are endless. Although science has discovered many of them, the great extent of the Universe is such that this feat is not easy to achieve. The sheer brilliance with which everything follows an order in the Universe is mind-blowing! Next time you look at the night sky, don’t fail to admire the colossal work going on up there.