Our Solar System is a collection of planets, moons and dwarf planets that orbit the Sun. The planets range in size from the rocky Earth to the gaseous Jupiter.
The Solar System also contains a large number of comets, asteroids and other small objects that fall into the system from outer space. Many of these small bodies can impact the planets or moons of the inner Solar System.
Earth
The Solar System is a collection of eight known planets, many asteroids and their satellites, and billions of comets. This assemblage also includes vast reaches of highly tenuous gas and dust, referred to as the interplanetary medium.
The Sun is the central object in the Solar System, shedding most of its heat and light to space and shielding Earth from most harmful cosmic radiation. The resulting solar wind flows around the Sun, often at very high speeds. This plasma-rich solar wind can cause a lot of disturbances on Earth.
Our solar system is a collection of 8 (formerly 9) planets and many asteroids, some with their own moons. In addition, it includes two reservoirs of several billion comets and icy bodies called the Oort cloud and the Kuiper belt.
These objects are a mix of solid and liquid materials, including ices and rock, as well as gaseous compounds with varying compositions. The largest planets, Jupiter and Saturn, are considered gas giants, while Uranus and Neptune are ice giants.
The smallest planets, Mercury, Venus and Mars, are terrestrial. The fourth planet from the Sun, Pluto, has a rocky surface but is frozen. Astronomers are still hunting for a possible ninth planet, dubbed “Planet Nine” after mathematical evidence was found in January 2016. The planet is likely to be about 10 times the mass of Earth and 5,000 times the mass of Pluto.
Mars
Mars is the third planet from Earth and is sometimes referred to as the “red planet.” It has a reddish orange color because it is covered in iron oxides.
Mars’ surface has a wide variety of features, including craters and valleys that are similar to those on the Moon. It also has deserts and polar ice caps, like those on Earth.
There are a number of large canyon systems on the Martian surface, such as Valles Marineris which is up to 8 kilometers deep and 4,500 km long. The Tharsis Rise is the largest volcanic and tectonic feature on Mars.
It has a thick crust that appears to be divided into two parts, the southern highlands that are heavily cratered and the smooth northern lowlands. The southern highlands are thought to be 3.5 billion years old, while the northern lowlands were resurfaced about 1 billion years ago.
Mars has a thin atmosphere, but it is thought to have once had water on the surface. Evidence for surface water is found in canyons, dry lakebeds and river networks. These were formed by liquid water that once flowed across the Martian surface.
Venus
Venus is the second planet in our solar system and is sometimes referred to as the “twin” of Earth. It is a silicate rocky world with a thick atmosphere of carbon dioxide and sulfuric acid that traps heat, resulting in a runaway greenhouse effect.
Its surface is covered by clouds that completely obscure our view of the planet, and the visibility of features at visible wavelengths is limited to a few kilometers. This has prevented scientists from uncovering the geological nature of the surface, but new radar instruments have made it possible to map Venus’s surface.
Most of the Venusian surface is flat, but there are also several large depressions and two large highland areas. The Ishtar Terra region in the northern hemisphere and the Aphrodite Terra region along the equator have elevations that range from about 0.3 to 1.3 km above the planet’s surface.
There are thousands of volcanoes and volcanic features on the surface, including lava flows that extend hundreds of kilometers across Venus. Among them are more than 100,000 small shield volcanoes, and hundreds of large volcanoes with long, winding lava flows that can be up to 3,000 miles (5,000 km) wide.
Venus has had a history of intense volcanism. These eruptions are thought to have caused the formation of the planet’s surface features, including wrinkle ridges, fractures, and scarps. The sluggish winds of the planet’s atmosphere have also sculpted the surface in subtle ways, such as by creating mountains, rifts, and patterns of fractures that are called tessera.
Jupiter
Jupiter is the largest and most massive of our Solar System’s gaseous planets. The planet combines hydrogen and helium with small amounts of methane and ammonia. The hydrogen is compressed to form a liquid that gives the planet its magnetic field.
Jupiter has a number of features, including the Great Red Spot, which is a high-pressure storm that extends south of its equator. This spot is about 24,000 km in diameter and is big enough to hold two Earths.
Its atmosphere is also a colorful mix of gases that stretch into stripes over its surface. The winds that cause these clouds are powerful. They can be 100 m/s (300 km/h) or more.
One thing that distinguishes Jupiter from its fellow gaseous giants is its ring system. Its rings consist of an inner torus of particles called the halo, a bright main ring, and an outer gossamer ring that looks like dust.
Juno’s data have revealed that Jupiter’s belts and zones undergo a transition around 40 miles (65 kilometers) beneath its water clouds. The belts become more intense in microwave light, while the zones turn darker. Scientists think this reflects how these cloud systems are affected by the planet’s rotational forces.
Saturn
Saturn is the largest of our gas planets and is known for its beautiful rings. These are made up of bits of ice, dust and rock that orbit independently around the planet.
It’s a “gas giant” like Jupiter, but unlike Jupiter it doesn’t have a solid surface. Instead, its surface is made up of swirling gases mainly of hydrogen and helium.
At the center of Saturn is a dense core of metals like iron and nickel surrounded by rocky material and other compounds that were solidified at high pressure and temperature. This rocky core is enveloped by liquid metallic hydrogen, which also forms a molecular layer above it.
The atmosphere on Saturn is primarily made up of hydrogen with small amounts of helium and trace amounts of water, methane and ammonia. At its core, it’s a hot planet with a temperature of 12,000 Kelvin (11,700 degrees Celsius).
As viewed from Earth, Saturn looks hazy and yellow-brown. The haze comes from a complex of cloud layers that vary over time.
Storms on Saturn are much stronger than those on Earth, producing winds that can reach 1,800 kilometres per hour (1,000 miles per hour) in its equatorial regions. This is considered to be one of the Solar System’s fastest winds.
Uranus
Uranus, one of the outer planets in our solar system, has a distinctive bluish-green appearance. It has an atmosphere of mostly hydrogen and helium, but with traces of methane.
Its icy core contains a slush of partially frozen water, ammonia, and methane (which is much heavier than water) that accounts for about 9-13 Earth masses. This core is separated from a dense liquid layer of water and ammonia in its interior by a thin, rocky crust.
The outer atmosphere is mainly composed of hydrogen and helium, with traces of methane that absorb red light. Uranus’s atmosphere has a very low density, about 1.27 g/cm3, making it the second least dense planet in the solar system after Saturn.
This makes the planet surprisingly quiet, despite its winds at speeds that are among the fastest in our solar system (about twice as fast as Jupiter’s). Although the atmosphere looks like a haze of clouds, it is actually arranged into latitudinal bands similar to those on Saturn and Jupiter.
Uranus has 27 known moons, of which the largest are Oberon and Titania, discovered by Herschel in 1781, and Miranda, found by Voyager 2 in 1986. The inner moons are half water ice and half rock, while the outer moons are primarily captured asteroids.
Neptune
Neptune, the smallest of the ice giant planets, is a world of gases and liquid that is very distant from our solar system. Neptune completes one rotation in 16 hours and is 900 times fainter than the Sun.
Its outer atmosphere is made up of hydrogen and helium, with large amounts of methane gas that absorbs red light to produce a deep blue color. Like Uranus, Neptune also has a layer of high clouds that drift in its upper atmosphere.
When Voyager 2 flew by Neptune in 1989, it discovered that the atmosphere was extremely dynamic. The skies were dotted with long, bright cirrus clouds that circled the planet rapidly, sometimes moving across the globe in just 16 hours!
Another strange feature was the Great Dark Spot, a storm that is much like the Great Red Spot on Jupiter but with several different characteristics. These spots are anticyclonic, meaning they rotate in a different direction than the rest of the planet’s weather.
Neptune also has five known rings – named Galle, Le Verrier, Lassell, Arago and Adams – that begin near the planet and move outward in a spiral pattern. The rings are thought to be relatively young and short-lived.
Solar systems in space consist of the Sun, planets, dwarf planets, moons and asteroids. They are a complex and diverse assemblage, each with unique properties.
The Sun is the centre of the solar system and a primary source of energy for most of the other bodies in the solar system. It has more than 99 percent of the mass of our solar system, and influences all of the planets’ motion through its gravitational pull.
Asteroids
Asteroids are rocky and airless bodies that orbit our Sun but are too small to be called planets. They are a leftover of the humungous cloud of dust and gases that formed our solar system billions of years ago.
Most asteroids live in a doughnut-shaped ring of space between the orbits of Mars and Jupiter, but sometimes changes in gravitational flows and other forces in space cause them to get dislodged from this belt and move away from the Sun. They are called Trojans and are often located in gravitationally stable points between the Sun and Jupiter, such as Lagrange points.
Astronomers study asteroids by using radar measurements and telescopic observations. Their brightness and distance tell astronomers about their size, and their spectral properties can reveal their surface composition. Spectral analysis also helps astronomers figure out how long an asteroid has been on its current orbit.
Comets
Comets are icy balls of rock, ice and dust left over from the formation of our solar system 4.6 billion years ago. They orbit the Sun in highly elliptical orbits that can take hundreds of thousands of years to complete, according to NASA.
Scientists believe that most comets originate from two regions way out in the Solar System: the Kuiper Belt and the Oort Cloud. The Oort Cloud is about a light-year away from the Sun, while the Kuiper Belt lies beyond the orbit of Neptune.
When they pass stars outside our solar system, these comets begin the long trek inward towards the Sun. When they reach this point, the ice in their nucleus heats up and turns into gas. This release of gas can create jets that carry dust and a long tail.
Planets
Planets are celestial bodies in our solar system that orbit the Sun and have enough mass to sustain a self-gravity balance. In 2006, the International Astronomical Union redefined a planet to include the Kuiper belt and Pluto.
The four outer planets — Jupiter, Saturn, Uranus and Neptune–are called gas giants because they’re mostly composed of gases like hydrogen and helium rather than solid matter such as rocks.
In addition to the eight known inner planets and planetary moons, the solar system is also inhabited by many asteroids, comets, and other small bodies. The majority of these smaller objects orbit between Mars and Jupiter in an asteroid belt, but others are scattered throughout the solar system. Meteorites, or pieces of space rock that have fallen to Earth, can provide a glimpse into the origins of our solar system and help scientists better understand the composition of the interplanetary medium.
Moons
Many of the planets in the Solar System have their own natural satellites called Moons. They come in all shapes and sizes, and some even have atmospheres.
Most planetary moons are thought to have formed from discs of gas and dust that surrounded planets in the early years of the Solar System. However, some are “captured” objects that formed elsewhere and fell into orbit around larger worlds.
Jupiter’s inner moon Io is wracked by intense volcanism, while Saturn’s largest moon Titan is a primitive world that exhibits a primordial atmosphere denser than Earth’s. Another interesting moon is Enceladus, which erupts watery geysers into the rings of Saturn.
Scientists have recently discovered dozens of new moons surrounding giant planets, like Jupiter and Saturn. These tiny moons are fragments of once-larger satellites that broke apart when they collided with asteroids or other moons.
Sun
Our solar system is the gravitationally bound system of the Sun and objects that orbit it. It formed 4.6 billion years ago when a cloud of gas and dust collapsed under its own gravity.
Our Sun is a hot star that has a temperature of 27 million degrees Fahrenheit (15 million degrees Celsius). This heat is essential to sustain nuclear fusion, which produces the energy and heat that power our planets and solar systems in space.
The Sun’s core is about 100 kilometers (62 miles) across and is made of hydrogen, helium, and oxygen. It also contains other elements like lithium and magnesium.
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