The Sun is only one of billions of stars in our galaxy, the Milky Way. This means there are many other solar systems out in space, each with their own planets and moons.
The eight planets in the Solar System and their hundreds of natural satellites (moons) are surrounded by countless asteroids, comets and other small bodies that orbit in a belt of rocky objects called the asteroid belt. Beyond the asteroid belt is a disk-shaped region known as the Kuiper belt. There is also a spherical cloud of icy objects, called the Oort cloud, that lies at the outer edge of our solar system.
The Sun is the dominant body in our solar system, constituting more than 99 percent of its mass. It is the source of an enormous amount of energy that powers life on Earth and beyond.
The Sun’s primary source of energy is nuclear fusion of hydrogen atoms in its core, which releases huge amounts of heat and light. The radiation released by this fusion is pumped outward through the Sun’s radiative zone, accounting for about 45 percent of the Sun’s radius.
In this zone, photons – particles of light – travel a fraction of a micron, and are absorbed by a gas molecule that is heated to re-emit another photon of the same wavelength. This process repeats itself over and over, releasing a lot of energy into space.
When this happens, some of the particles escape the sun’s gravity and become a type of high-speed, magnetic “bubble” called the solar wind, which blasts outward at 400 kilometers per second (249 miles per second). This magnetic bubble is known as the heliosphere, and it extends into interstellar space, where other planets and their moons reside.
As the Sun’s radiation is pushed outward, it creates an expanding atmosphere called the corona, which is primarily made of hot gases that are mostly hydrogen and helium. The outermost layer of the corona is called the chromosphere, which is red due to its high hydrogen content.
Astronomers are attempting to unlock the secrets of the Sun’s structure by examining its various layers and regions. These include the core, radiative zone, and convection zone. They also are studying the effects of the Sun’s magnetic field and its impact on Earth and its planets.
The Solar System is a collection of the planets and a variety of smaller objects that orbit the Sun. Our planets include Mercury, Venus, Earth and Mars, as well as the four gas giants Jupiter, Saturn, Uranus and Neptune.
The outer planets, also known as Jovian or “Jupiter-like” planets, are much larger than the terrestrial planets, and they’re mostly made of gases like hydrogen, helium and ammonia rather than of rock. However, some of them have solid cores, as astronomers believe is the case for Neptune and Pluto.
In theory, it’s possible to create a solar system with as many as ten Earth-sized planets in orbit around the Sun. But in practice, the number of planets that can fit into a solar system is limited by how much space they take up.
This is because a planet has to be stable in its orbit. Otherwise it could be pulled into a collision with another planet, which would cause it to break apart. This happened when a planet-sized object collided with the Earth about 4.5 billion years ago.
Scientists have discovered over five thousand planets outside the Solar System, called exoplanets. These include hot Jupiters, which are large planets that orbit close to their parent stars, and super-Earths, which have a mass in between that of Earth and Neptune.
During the formation of the Solar System, a hundred or more planets may have formed around the Sun, but they drifted in a chaotic state and had no stable orbits. The resulting clumps of rock and ice were left over from the early stages of the formation of the planets, and formed what we know today as our solar system.
There are thousands of rocky objects orbiting the Sun ranging in size from tiny dust like particles to the dwarf planet Ceres. This vast population is mainly made up of the asteroid belt, Kuiper belt and comets.
Asteroids are rocky leftovers from the formation of our solar system about 4.6 billion years ago, when the sun was formed. These celestial rocks formed through a process called accretion – smaller space rocks came together with others and became larger, eventually developing their own gravity.
They are a key part of the story of how the solar system was formed. Some of these rocky pieces were not able to form into planets because they were too small, and so were left behind to fall into the outer regions of the solar system.
These rocky bodies are scattered all over the solar system, but there is a main asteroid belt between Mars and Jupiter that holds about half of them. Most of these asteroids are irregularly shaped, but they are broadly similar to each other.
Most of these asteroids appear to be cratered, with their surfaces filled with rubble that has been swept away by the force of impacting another object. This is evident for the four largest asteroids, Ceres, Pallas, Vesta and Hygiea (see image), as well as for many of the medium-sized ones.
The main asteroid belt contains a huge concentration of asteroids that are large enough to be seen by the naked eye. However, astronomers have discovered that a significant proportion of the asteroid population in this belt is hidden from sight. The main reason is that most of these asteroids are dark. Luckily, NASA’s WISE spacecraft has been able to spot them using infrared light instead of visible.
The dwarf planets
The dwarf planets are a different class of celestial objects that orbit the Sun. These objects are smaller than the eight planets and are mostly located in the outer parts of the solar system. The International Astronomical Union (IAU) officially recognizes five of them: Pluto, Ceres, Haumea, Makemake and Eris. There are also several more objects that may be classified as dwarf planets.
Dwarf planets are smaller than the classic planets, but they are still worlds in their own right. Scientists can’t yet tell whether they are made of solid matter or if they have liquid water on their surfaces.
They are very cold, so life on them is unlikely. However, scientists are trying to find out if life could exist on any of them.
There are two main types of dwarf planets: those that orbit in the asteroid belt and those that orbit around Neptune. The first group is made of asteroids, while the second is made of Kuiper belt objects.
The asteroid belt is a narrow zone between the orbits of Mars and Jupiter. The Kuiper belt is a much wider zone that is dominated by icy bodies.
Before the 2006 resolution, Pluto was considered the ninth planet in our solar system. But it was demoted to the dwarf planet status because it satisfies only two of the three criteria: it has not cleared the neighborhood around its orbit, and other icy Kuiper belt bodies are within its orbital path.
In 2003, astronomers discovered a small body that is slightly larger than Pluto called Eris. It is also in the Kuiper belt, but it orbits much closer to the Sun than Pluto does. Observers were able to measure Eris’s mass and found that it is almost 30% more massive than Pluto. This is why astronomers think it may be one of the oldest objects in our solar system.
The Kuiper belt
The Kuiper belt is a huge region of space that is home to the majority of dwarf planets and icy objects. It contains more than 1 trillion comets and hundreds of thousands of icy objects that are 62 miles (100 kilometers) or larger in diameter.
The discovery of the Kuiper belt began in 1943 when Irish astronomer Kenneth Edgeworth suggested that the outer regions of the Solar System were occupied by a large number of comparatively small bodies. In 1951, Dutch astronomer Gerard Kuiper developed a stronger case that the Solar System must have an outer belt of objects beyond Neptune.
He showed that this region of space had a lot of small icy bodies, but they weren’t big enough to form a planet. He also explained why the ices inside these objects deflected near the Sun and vaporised.
Eventually, these icy objects collided with each other. Some of them formed new planets, while others became comets.
Today, the Kuiper belt is a very crowded place with more than 1 trillion comets and hundreds and thousands of icy objects that are 62-miles (100-kilometer) wide in diameter. These objects are all located between 42 and 48 times the distance of Earth from the sun.
One of the most imposing objects in the Kuiper belt is Sedna, which orbits the sun more than 10 times every 10,000 years. It’s so far out that the light from the Sun is reflected back into space, making it nearly impossible to detect.
Other large Kuiper Belt objects include Eris, Makemake, Haumea and Quaoar. These objects have orbits that are similar to Pluto’s. However, the mass of these objects is only about one-tenth the mass of Earth.
The solar system consists of eight planets and hundreds of smaller objects like asteroids and moons. They orbit the sun in paths shaped like circles.
The gases in the solar system shoot out a stream of charged particles called the solar wind. This creates a bubble-like region of interplanetary space known as the heliosphere. The edge of the heliosphere is called the heliopause.
The Sun is the center of our solar system and, as such, influences the motion of all other bodies in the solar system through its gravitational force. The Sun is a glowing, spinning ball of hot plasma containing primarily hydrogen and helium gas.
The solar energy that powers the sun is primarily produced by nuclear fusion reactions in its core, which converts 600 million tons of hydrogen atoms into 4 million tons of helium atoms every second. This fuel is gradually being withdrawn from the core over time, leading to the formation of a red giant star and the Sun’s eventual death.
The Moon is Earth’s natural satellite, orbiting us in a slightly eccentric orbit at a distance of 384,000 km (238,600 miles) from the Sun.
It has a crust, a thick, partially molten layer of minerals called olivine and pyroxene. Its mantle extends from the top of this molten layer to the bottom of its crust, most likely made of magnesium, iron, silicon, and oxygen atoms.
The Moon was subject to violent heating more than four billion years ago, which led to its differentiation and a more dense underlying mantle. This was followed by a second episode of heating from internal radioactivity that resulted in volcanic outpourings of lava.
The Solar System consists of 11 planets and a large number of small bodies, including asteroids. It also includes two huge reservoirs of comets: the Oort Cloud and the Kuiper Belt.
Several billion of these objects are believed to be circling the outer edge of the solar system, far beyond the orbits of Saturn and Neptune. They are mainly found in the Oort Cloud and the Kuiper belt, which is about 30 to 50 astronomical units (AU) from the Sun.
From space, Earth appears like a blue marble with white swirls of clouds and areas of brown, yellow, green and white. These colors are based on the color of water, which covers 71 percent of the planet’s surface.
The Solar System has eight planets and 210 known planetary satellites (moons).
Astronomers are trying to learn how these planets formed, how they’ve evolved over time and whether there are other Earth-like planets out there. This information is vital to astrobiology, the study of extraterrestrial life.
Using the radial velocity method, astronomers have found two exoplanets that orbit in a close ring around their star. The first is labeled L 98-59b, which has a mass of 1.01 times that of Venus and orbits its star in 2.3 days.
The Solar System (opens in new tab) is an assemblage of eight planets, more than 210 planetary satellites (moons), many asteroids, comets and other icy bodies, and vast reaches of highly tenuous gas and dust.
Astronomers have learned a lot about the rocky, airless worlds that make up the solar system over the past century. Most of that knowledge has been derived from observations of their orbits and their physical characteristics.
The asteroid belt, the doughnut-shaped ring of asteroids that stretches between the orbits of Mars and Jupiter, has more than a million known asteroids (or minor planets) and probably more. Most of the asteroids are separated on average by a few tens of millions of kilometers. But some mean-motion resonances, rather than dispersing asteroids, cause them to cluster near certain points on their orbits.
The Dwarf Planets
The Solar System is an assemblage of eight planets and more than 210 planetary satellites (moons). There are also many asteroids, comets, and icy bodies in the interplanetary medium.
In 2006, the International Astronomical Union (IAU) decided that a new class of objects should be added to the solar system – dwarf planets. There are currently five known dwarf planets in the Solar System: Ceres, Pluto-Charon, Haumea, Makemake, and Eris.
The Kuiper Belt
The Kuiper Belt is a chilly region of space beyond the gas giant Neptune. It holds trillions of icy bodies that are remnants from the early solar system.
In 1943, Kenneth Edgeworth suggested that comets and other large bodies might exist at this farthest point in the Solar System. In 1951, Gerard Kuiper made an even more detailed proposal.
The Kuiper belt is a disk-shaped region of space that extends from 30 to 55 astronomical units (AU) from the Sun. It is a vast, cold, and dark expanse.