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Why do some planets have moons and others don’t? -Siddharth, 6 years old, Texas
On Earth, you can look up at night and see the moon shining from hundreds of thousands of miles away. But if you go to Venus, that won’t be the case. Not every planet has a moon, so why do some planets have several moons, while others have none?
I am a physics teacher Which followed existing theories describing why some planets have moons and others don’t.
First, the moon is called a natural satellite. Astronomers point out Satellites as objects in space Which revolve around larger objects. Since the moon is not man-made, it is a natural satellite.
Currently, there are two main theories about why some planets have moons. Moons are captured by gravity if they are within what is called a planet The radius of the hill fieldOr it was formed with the solar system.
Radius of Hill sphere
Objects exercise a Gravity force Gravity On other nearby objects. The larger the object, the greater the force of attraction.
This force of gravity is the reason we all stay on Earth instead of floating away.
The solar system is dominated by a great force of gravity, which keeps all the planets in their orbits. The Sun is the most massive body in our solar system, which means it has the greatest gravitational influence on objects such as planets.
In order for a satellite to orbit a planet, it must be close enough so that the planet can exert enough force to keep it in orbit. The minimum distance that a planet must keep a satellite in its orbit is called Radius of Hill sphere.
The radius of a Hill sphere depends on the mass of the larger object and the smaller object. The Moon orbiting the Earth is a good example of how the radius of a Hill sphere works. The Earth orbits the Sun, but the Moon is close enough to the Earth that Earth’s gravity captures it. The Moon orbits the Earth, not the Sun, because it is within the radius of Earth’s Hill sphere.
Nicole Granucci
Small planets like Mercury have small spherical radii, because they cannot exert a large gravitational force. Any potential moons would likely be pulled down by the Sun instead.
Many scientists are still curious to know whether these planets had small moons in the past. Back during the formation of the solar system, they Maybe he had moons Which was destroyed as a result of its collision with other space objects.
Mars has two moons, Phobos and Deimos. Scientists are still debating whether these objects came from asteroids that passed close to the radius of Mars’ Hale sphere and were captured by the planet, or if they formed at the same time as the solar system. More evidence supports the first theoryBecause Mars is close to the asteroid belt.
Jupiter, Saturn, Uranus, and Neptune all have larger spherical radii, because they are much larger than Earth, Mars, Mercury, and Venus, and are farther from the Sun. They can pull their own gravity Attract and retain more natural satellites such as moons In orbit. For example, Jupiter has 95 moonswhile Saturn has 146.
Moons form in the solar system
Another theory suggests that some moons formed at the same time as their solar system.
Solar systems begin with a large disk of gas orbiting the Sun. As gas rotates around the sun, it… It condenses in the planets and moons that orbit around them. Then the planets and moons all rotate in the same direction.
But it is likely that only a few moons in our solar system were created this way. Scientists expect so Jupiter and Saturn The inner moons formed during the formation of our solar system Because they are so big. The rest of the moons in our solar system, including the outer moons of Jupiter and Saturn, are likely gravitationally captured by their planets.
Earth’s moon is special because it likely formed in a different way. Scientists believe that long ago, a large object the size of Mars collided with Earth. During this collision, a large piece It flew from Earth to its orbit And it became the moon.
Scientists believe that the moon formed in this way because they found a type of rock called basalt in the soil on the moon’s surface. Moon basalt It looks the same Like basalt inside the earth.
Ultimately, the question of why some planets have moons is still widely debated, but factors such as the planet’s size, gravitational pull, the radius of the Hill field, and how its solar system formed may play a role.
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