What are the Planets?
Planets are celestial bodies that orbit stars, and there are eight planets in our solar system. Our planetary system is made up of the sun and 8 planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Planets have a gravitational force that traps gases and can create a surface on them. Planets go around stars in a circular pattern called an ellipse.
The name "planet" comes from ancient Greek meaning wanderer. This is because of how their orbits move around the Earth makes them look like they are wandering across the sky.
How Did We Know about the Planets?
The history of learning about the planets has been an incredible journey. It started with Aristarchus, who was the first person to measure the earth's distance from the sun.
He noticed that, when he looked at the moon, it was always at a different angle each time. This allowed him to calculate the earth's distance from other planets in our solar system. He hypothesized that this could be used to calculate other distances in our solar system as well. But his theory was not accepted by other astronomers until centuries later when Galileo used it to show that there were mountains on Jupiter’s moon, Callisto.
Different Types of Planet Systems
There are three main types: terrestrial, gas giants, and ice giants.
Terrestrial planets: These planets have a solid surface such as Mercury and Earth.
Gas Giants: These planets don’t have a surface and the gas engulfs the whole planet, like Jupiter and Saturn.
Ice Giants: These planets include Uranus and Neptune. They are typically covered in ice but also possess atmospheres consisting mostly of hydrogen and helium.
The Earth's Celestial Neighbors
The Earth's celestial neighbors are all the objects in space that are near or close to the earth.
The Earth's celestial neighbors are not limited to planets and other astronomical objects; they can also be other satellites, asteroids, meteoroids, and comets.
The Earth has only one moon, but it has many other celestial neighbors. The Earth's nearest neighbor is the Moon. The Moon orbits around the Earth and is about a quarter, in size, of the world we live on. We experience a Full Moon when our natural satellite is at its brightest in our sky, and a New Moon when it appears to be completely dark.
What is a Solar System?
The solar system is our planetary system. It contains the sun and all the objects that orbit it and may or may not be in the same plane. These objects include planets, dwarf planets, moons, asteroids, and comets.
Planets are spherical bodies that orbit a star (or sometimes another planet). They are composed mostly of rock and other solids with some gas and liquids forming them. They can also have rocky or icy surfaces but they cannot be made up of all gas like a star.
Asteroids are small rocky bodies that move around the sun in orbits between Mars and Jupiter while comets move in orbits around the sun but usually outside of Neptune's orbit.
The Sun and its Satellites
The Sun is the star of our solar system. It’s quite large and bright, which makes it easy to see with the naked eye. It is an object made up of hot gases, mostly hydrogen and helium, giving off energy in the form of light and heat.
But how did this giant mass of gas come to be? The Sun was formed from a huge cloud of gas that collapsed under its own weight. This cloud was mainly composed of hydrogen gas, but some heavier elements were also present - these created the iron core at the middle of the sun, while hydrogen eventually became its outer layers.
Mercury, Venus, Earth, and Mars
Mercury is the closest planet to the sun. It's also the smallest planet in our solar system. Mercury is so close to the sun that it takes only 88 days to orbit it. In contrast, Earth takes 365 days to orbit around the sun.
Venus is Earth's twin sister, but it’s a little bit different from Earth because Venus has a thick layer of clouds covering its surface and Venus doesn't have any moon.
Mars is the fourth planet from the Sun and its circumference is about 25% less than Earth, making it seem like a smaller, colder world. It’s also called the Red Planet because of iron oxide on its surface. Four NASA spacecraft have visited Mars since 1965, including two orbiters and two rovers. The most recent rover, Curiosity, landed there on August 6, 2012.
Jupiter, Saturn, Uranus, and Neptune
Jupiter is a gas giant and the largest planet in our solar system. It is so big that it could contain 1,300 Earths. Jupiter’s atmosphere is made mostly of hydrogen and helium. The temperature at the top of the atmosphere is -145 degrees Celsius, but this quickly becomes much hotter as you descend into the atmosphere.
Saturn is a gas giant that has been extensively studied by humans for decades, but still, there are many mysteries about its composition and how it formed. Saturn has a large ring system made up of chunks of ice and rock which may have been leftover from when Saturn was a young planet. The rings were first observed by Galileo Galilei in 1610 with his telescope, who originally thought they were two small moons orbiting around Saturn before he realized they were the remnants of an asteroid.
The planet Uranus is the third largest planet in our solar system and orbits the sun once every 84 years. Uranus has at least 27 moons that we know of and it's also home to a ring system. Astronomers believe this planet may have formed from a collision with another planetary body. Scientists currently believe geologic activity on Uranus is localized to its core, which could lead to instability in other areas such as its rings and atmosphere.
The vast, blue planet Neptune is the eighth and most distant planet in our solar system. It is so far away that it takes 165 years for sunlight to reach earth from Neptune's orbit! Even with its slow orbit, Neptune's atmosphere appears much clearer than Uranus'. There are three possible explanations for this. First, Neptune has a more circular orbit than Uranus, which means it spends less time near the sun and therefore stays cleaner. Second, Uranus is much heavier than Neptune, which means more of the planet's atmosphere is broken up by the planet's own gravity. Third, Neptune has a lower density than Uranus, which means less of its atmosphere is above the cloud layer.