The number of galaxies in the universe is largely unknown to humans. In fact, scientists speculate that there may be an infinite number of galaxies. Our galaxy, the Milky Way, is estimated to host about 100 billion planets most of which orbit a star. In the near past, astronomers have discovered hundreds of planets in our galaxy, some of whom exhibit some Earth-like characteristics. Our solar system comprises of the sun, eight planets and their moons, and several small solar system bodies.
Previously, Pluto was considered to be the ninth planet in the Solar System. However, in 2006, Pluto was demoted to the status of a "dwarf planet" due to more concrete, strict definitions of what a planet is. To be a planet, an object must not only orbit the Sun but also have sufficient mass to have a rounded shape induced by gravity. A potential planet must also be the most important object in its "neighborhood."
The planets in the Solar System are as follows:
Mercury is the closest planet to the sun. It is also the smallest planet in our solar system. Mercury completes a full revolution around the sun in 88 days. It is a rocky planet with an equatorial radius of 1,516 miles. Interestingly, Mercury does not have an atmosphere. This means that the temperature on Mercury can fluctuate from 840 °F during the day to minus 275 °F during the night!
Mercury's orbit is oval-shaped. On some occasions, Mercury can be viewed from Earth.
Venus is the second closest planet to the sun. Venus is also the hottest planet with a mean temperature of 863 °F. The atmosphere on Venus is dense and traps warm air within it. Venus is Earth's closest neighbor.
Venus has the longest revolution and rotation times of any planet in the solar system. Venus takes 224.7 Earth days to revolve around the sun. The rotation of Venus on its axis is so slow that it takes the equivalent of 243 Earth days to complete a single rotation, which means a single day on Venus is longer than a whole year on Venus.
Planet Earth is the only planet known to host life. It completes a revolution around the sun every 365.256 days. It is 92,955,820 miles away from the sun and is the third closest planet to the sun.
It is estimated that the formation of Earth began 4.54 billion years ago. Its total surface area is 196,940,000 square miles, 71% of which is covered by water while the remaining 29% is land. The Earth’s atmosphere protects life from uninhabitable space, shields us from harmful radiation, and controls the weather. Earth is the densest planet in the Solar System.
Mars, also known as the “red planet,” is the fourth planet in the solar system as well as the second smallest one. It has a solid surface just like the Earth, but its atmosphere is thin.
Mars is half the size of the Earth and is 143,000,000 miles from the sun. Mars is sometimes visible from the Earth in the evening due to its bright surface. Liquid water is not found on the surface of the planet due to the low atmospheric pressure. Researchers are examining the possibility that life once existed on Mars. Scientists believe that the ice caps on the poles of the planet are made up of water and that the ice on the south pole would fill the planet's surface to a depth of 36 ft if melted.
Jupiter is the fifth and largest planet in the solar system. Along with Saturn, Uranus, and Neptune, Jupiter is considered to be one of the Solar System's gas giants. Jupiter's mass is 2.5 times the total mass of the other planets combined. Jupiter is a gaseous planet meaning that it has no solid surface, although researchers believe that its core is solid. Jupiter is so large that 1,300 Earths would fit inside it.
Jupiter’s atmosphere is violent. Wind speed travels at an average speed of 340 mph, twice the speed of a category five hurricane on earth. The planet has three rings made of dust particles that are difficult to see. It takes 12 Earth years for Jupiter to make a revolution around the sun.
Saturn is the second-largest planet in the solar system after Jupiter. It is a gaseous planet just like Jupiter but has nine continuous rings and several ringlets made of rocks and ice. It is considered the most beautiful planet in the solar system and is composed of hydrogen and helium.
The diameter of Saturn is nine times that of the Earth. Its volume equals that of 763.5 Earths, and its surface is equal to 83 Earths. However, it weighs only one-eighth the mass of the Earth. Saturn has nearly 150 moons, 53 of whom have been named.
Uranus is the third-largest planet in the solar system. Its surface is composed of a frozen component and it is therefore considered an ice giant. However, its atmosphere is made up of hydrogen and helium alongside other “ices” such as methane, ammonia, and water.
Although it is not the furthest planet from the sun, it is the coldest with temperatures that reach −224 °C. Uranus is the only planet that does not radiate heat from its core. Uranus is around 2 billion miles from the sun.
Neptune is the furthest planet from the sun. It was first considered a fixed star by Galileo who used mathematical predictions to discover it rather than the regular method of making observations. It is nearly 2.8 billion miles from the sun and completes a revolution round the sun every 164.8 Earth years.
Neptune completed its first revolution in 2011 since it was discovered in 1846. It has 14 known moons with Triton being the largest. Its atmosphere consists of hydrogen and helium. It is the windiest planet in the solar system, hosting nine times the average wind speed of the Earth. Recently, NASA discovered that Neptune had flowing rivers and lakes of liquid methane.