The Sun, the eight planets and their moons, and countless asteroids, comets, and other small, icy objects comprise our Solar System.
The Solar System formed 4.5 billion years ago from leftover materials from the collapse of a cloud of interstellar material. The four inner planets, Mercury, Venus, Earth and Mars, were rocky, but the outer planets remained gaseous.
Planets
The Sun, the largest and brightest object in our solar system, is surrounded by an assortment of smaller objects known as planets. The closest planet to the Sun is Mercury, which is a fairly small, rocky planet. Next is Venus, then Earth and Mars. Beyond these is the asteroid belt, which contains millions of rocky space rocks that were left over from the formation of our planets about 4.5 billion years ago.
Then there are the gas giants, which are much larger than Earth but not so big as to be called planets. These include Jupiter, Saturn and Uranus.
There are also the moons of our solar system. Most of these are natural satellites, like those of Earth and Venus, but there are many other planetary moons that were formed by discs of dust and gas in the early days of our Solar System.
Most astronomers think that the moons are formed by gas and dust in orbit around planets, but some of them may have come from interstellar space. One of these is called ‘Oumuamua and it was thought to be composed of nitrogen ice.
Another is named Triton and it has a thin atmosphere of gases produced through volcanic activity on its surface.
What makes these moons special is that they are not just floating in space, but that they actually have their own atmospheres and are home to life! It is even possible for them to have oceans underneath the surface.
Moreover, they are made of rock that is very similar to the original rock that was formed by the explosions of volcanoes in our solar system! So, these are just some of the most interesting facts about our planets and their moons!
In addition, there are countless comets that have been observed in the distant parts of our solar system. These comets are a great way to study the outer regions of our Solar System and they help to reveal the enduring mysteries of our universe.
Moons
There are a total of 181 known moons orbiting planets and dwarf planets in our solar system. These are divided into three categories, based on size: Earth, Venus and Mercury do not have moons; Jupiter and Saturn have dozens of moons; and the ice giants Uranus and Neptune each have more than a dozen.
The most common type of moons are spherical. Some, such as our own Earth’s Moon, are made of rock. Others are icy, including the moons of Mars and Pluto. A small number of asteroids, too, have companion moons.
When we hear the word “moon,” most people imagine a large spherical object, like our own Earth’s Moon. However, the two moons of Mars, Phobos and Deimos, are not spherical at all. They are lumpy and dark, with nearly circular orbits that take them close to the plane of the planet’s equator.
Because they are so close, the two moons of Mars exert very strong gravity on each other. This causes the moons to whirl around each other in very short distances, a process that will eventually break them apart or crash into Mars.
Many of the comets in our solar system are long-period. These comets have periods of 200 years or more. They are thought to originate in the Oort cloud, an area of the Solar System where the Sun’s ionization creates a huge concentration of comet-like objects.
The short-period comets, on the other hand, are periodic. These comets are thought to originate in the Kuiper belt, an area of the Solar System outside Neptune’s orbit.
While it’s hard to get an accurate picture of the moons of Jupiter, astronomers are getting better at tracking them with space telescopes and new technology. They’ve discovered a few, such as S/2008 S4, and plan to continue observing them in the future.
Another recent discovery is the large moon of Io, a satellite of Jupiter. Io is the most volcanically active world in the Solar System, with mountains averaging over 1,000 feet tall and hundreds of eruptions occurring on its surface. It also has a few smaller, brighter moons. Io’s other moon, Ganymede, is one of the largest of its kind in the Solar System.
Asteroids
Our solar system contains many different kinds of objects, including eight planets and several moons. These objects are also joined by minor planets, dwarf planets, and comets.
The asteroid belt is a region of the Solar System that contains millions of asteroids, ranging in size from rocks as small as dust particles to giant ones that are hundreds of kilometers across. Astronomers estimate that there are 1.1 to 1.9 million asteroids larger than 1 km (0.6 mi) in diameter in this belt, and millions more smaller ones.
Asteroids vary in their composition, which is related to how far they formed from the Sun. Some were made from clay and silicate rocks, while others had metals in them. Some of the older asteroids were heated to high temperatures after they formed, causing them to melt. They then sank to their center and forced basaltic lava to the surface.
Most asteroids are spherical, but some are irregularly shaped. This is because they are pockmarked with craters and retain primitive material from the early days of the Solar System.
There are three broad types of asteroids: C-types, S-types, and M-types. C-types are dark, rocky bodies rich in carbonaceous materials, and they were the most common asteroids when our Solar System formed.
S-types are lighter, and they contain silicate and stony materials, as well as nickel-iron. They are more reflective than C-types and they occupy the outer parts of the asteroid belt, but they are rarer. M-types are metallic and occupy the inner belt.
Some asteroids, like Bennu, are essentially rubble piles made of smaller asteroids that are loosely bound together gravitationally. These are called “families.”
Other asteroids have a differentiated interior, like Ceres and Vesta. These are believed to have been remnants of protoplanets that survived the violent collisions of other asteroids and were reformed into planets.
Asteroids also differ in their shape, and some are elongated while others are flattened. The largest asteroids, Ceres and Vesta, are spherical with craters around their center. Other asteroids, such as Pallas and Hygiea, are not spherical at all.
Comets
The Solar System is a vast system of eight major planets, five dwarf planets, hundreds of moons, and a large number of asteroids, comets, and other small celestial bodies. Its origin and evolution is the subject of research for astronomers.
The Sun, a yellow star of moderate mass located in the middle of the Solar System, is its heart and center. Its magnetic field drives the solar wind, which is a stream of charged particles that extends outward from the Sun. This wind also interacts with the interstellar medium, which is a dense gas and dust cloud that surrounds the Milky Way galaxy. The heliopause is the boundary created when solar wind particles collide with interstellar gas.
Besides the planets, moons, and asteroids, the Solar System includes a variety of other objects that have left their mark on Earth’s history. Among them are the comets that have passed through our skies.
Comets are frozen remnants of the Sun’s formation in the outer regions of the solar nebula, the cloud of gas and dust that collapsed to form the stars. They contain ices, rock and dust that range in size from a few miles to tens of miles wide.
When they approach the Sun, comets heat up and spew gases and dust into a glowing head that can be several times larger than a planet. The dust and gases in the comet’s head then form a tail that stretches away from the Sun for millions of kilometers.
Scientists are still learning a great deal about the Solar System from comets and asteroids. Many of these objects have been studied by space probes and landers launched by Earth. They have also been observed by telescopes onboard aircraft, rovers on the Moon, and meteorites.
There are two different types of comets in the Solar System. Short-period comets originate in the Kuiper belt, a ring of icy bodies that orbit beyond Neptune. Long-period comets, on the other hand, originate in the Oort Cloud, a spherical shell of icy debris that is thought to reach halfway to the nearest star. These comets trace out very eccentric elliptical orbits.