Our solar system is a collection of planets and other space material orbiting a star, the Sun. The Sun is the centre of the system, and planetary objects in the order Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto form its outer rim.
The four inner planets, Mercury, Venus, Earth and Mars are rocky, while the gas and water giants, Jupiter, Saturn, Uranus and Neptune are mostly made of gases.
Planets
There are eight planets in our solar system, along with many asteroids and a large number of comets. They orbit the Sun, an average star in our galaxy.
Until recently, scientists believed that only the four inner planets were rocky (terrestrial). However, new evidence shows that our Solar System also includes icy bodies like Pluto and Charon.
These ice bodies are called Kuiper belt objects, and they orbit around Neptune in a broad band of space that extends from 30 to 55 times the distance between Earth and the Sun. Astronomers have discovered hundreds of these objects since the late 20th century.
The outer planets (Jupiter, Saturn, Uranus, and Neptune) have massive atmospheres made of hydrogen and helium. Some of them, such as Jupiter and Saturn, are called gas giants; others, such as Uranus and Neptune, are known as ice giants.
Scientists now believe that all eight planets were formed in the early days of our solar system from smaller planetessimals, which collided with each other. These small worlds grew and evolved for millions of years.
They then gradually accreted together to form the rocky cores of the terrestrial planets. These rocky cores eventually filled up with water and other materials.
Some of the outer planets, including Neptune, have rings and moons; some, such as Pluto, have no rings at all. The orbits of the outer planets are so distant from each other that they can’t be seen with a simple telescope.
Moons
Moons are celestial bodies that orbit around the planets of our solar system. They are generally solid objects, although a few of them may have atmospheres and even oceans underneath their surfaces.
They can come in a variety of shapes and sizes, from smooth worlds like Earth’s moon to rocky ones such as Mars’s Phobos or Saturn’s Enceladus. Some, like Jupiter’s Io and Europa, have a surface that is mostly made of solid water ice.
Some moons, including Earth’s Moon, have been “caught” by bigger worlds and placed into orbit. This type of moon is called a natural satellite.
There are more than 240 known moons in the solar system, most of which are found around planets or dwarf planets like Pluto. The remaining small moons, often called shepherd moons, are found around smaller asteroids in the outer Solar System.
The largest moon in the solar system is Ganymede, which is about as big as Mercury and about a fifth the size of the planet Saturn. Beneath Ganymede’s icy crust, a large iron core radiates a magnetic field that creates glowing clouds of gas called auroras.
It’s also believed that some of the larger moons in the solar system, such as Earth’s Moon and the four Galilean moons of Jupiter (Io, Europa, Ganymede and Callisto), were formed from the dust and gas disks circling the planets during their formation.
Another possible source of planetary-mass moons is impact-induced accretion from the hot debris of impactors such as comets and asteroids. This process requires extremely grazing incidence and low relative velocity.
Asteroids
The solar system space contains a wide variety of asteroids, from the largest ones to small, near-Earth objects. The majority of these objects are C-type asteroids, which are made of carbonaceous materials. Some asteroids, called chondrites, are made of metals like nickel and iron.
The International Astronomical Union has established a number of classifications for asteroids based on their composition. These classifications are meant to help astronomers distinguish asteroids from each other, as well as from other types of objects in the solar system space, such as comets and Centaurs.
In addition to spectral classifications, asteroids are also classified based on their location in the solar system. The asteroid belt is the most common region for asteroids, but there are many other places where they can be found.
While most asteroids have been discovered by the use of large telescopes, many are still unknown. Telescopic observations can give astronomers information about the size of asteroids, their rotation periods and their surface compositions.
Some asteroid surfaces are covered with craters that were formed by impacts with other asteroids. These craters can range in size from the diameter of an asteroid to several kilometers in diameter. The asteroid Mathilde, shown in figure 6, is a good example of an asteroid that has been heavily disrupted by impacts.
In addition to impacts, asteroids can also undergo rotational disruption events. These disruption events can reveal information about an asteroid’s internal structure and material properties. These properties can be used to determine a model that predicts the failure modes of asteroids under different conditions. These models are important in understanding the origin of active asteroids and predicting their behavior over time.
Meteors
A meteor is a streak of light in the sky caused by an object that travels at the speed of sound through Earth’s atmosphere. Meteors come in all shapes and sizes, from large chunks of rock to tiny sand grains.
The majority of meteors are fragments of larger asteroids that formed when the planets in our solar system were young. These are called asteroid meteorites and are found throughout the inner asteroid belt, between Mars and Jupiter.
These meteorites can tell us a lot about how the solar system formed. They show how different parts of the original mini-planets changed in their early lives.
They can also tell us about the rocky composition of Earth and other planets. Many meteorites are stony, or made of silicate rocks.
But there are many other types of meteorites, too. Some are breccias, or broken pieces of rocks cemented together by a finer material. Others are composed of igneous (solidified) silicate and metal clasts, or chunks of old rock.
A small fraction of meteors hit Earth’s atmosphere and then fall back out again. These are known as Earth-grazing fireballs and occur infrequently.
Another type of meteor is called a “meteor shower.” These meteors are clusters of smaller objects that Earth passes through while traveling through space.
One of the most striking types of meteor is called a “superbolide,” or fireball. It can reach a brightness of -17 or brighter. It has the potential to cause a great deal of damage.
Other types of meteors are called micrometeoroids. These are smaller than asteroids, and can range from the size of boulders to the size of tiny sand grains. They can be found in a number of different orbits around the sun, including among the rocky planets and gas giants.
Comets
Comets are large balls of ice, rock, dust and gases that contain frozen leftovers from the early Solar System. These frozen materials are about 4,600 million years old.
The icy material that makes up the comet was originally thrown away by the Sun when the Sun was very young, but some of it remains in orbits around the Sun tens of thousands of times the Earth’s distance from the sun (up to 50,000 times the distance between Earth and the Sun). Every once in a while, these objects get perturbed into the inner part of the Solar System by the actions of passing stars or gravity from giant planets.
Most of these icy remnants are now orbiting the Sun in the Kuiper belt and Oort cloud, regions just beyond Neptune that contain dark comets that have been pushed into irregular orbits by gravity. These KBOs may be short-period comets that take less than 200 years to complete one orbit or long-period comets that have eccentric osculating orbits with periods ranging from several hundred years to thousands or even millions of years.
These comets are usually brighter than asteroids and can be seen from the Earth with binoculars. Some of them are also very small, ranging from a few miles to tens of miles across.
As they approach the Sun, these comets heat up and spew gases and dust into a glowing head that can be as big as a planet. This head is called the coma, and it extends hundreds of millions of miles from the comet. The coma and tail are then dispersed into the solar wind, a stream of energetic particles created by the Sun’s radiation pressure. There are two types of tails: a plasma tail made up of ions and a dust tail. The plasma tail points generally away from the Sun while the dust tail is more curved and does not point directly at the Sun.