Our Solar System is an immense and amazing place. Between its eight planets, 176 moons, 5 dwarf planets (possibly hundreds more), 659,212 minor planets, and 3,296 known comets, it has w0nders to sate the most demanding of curiosities.
For example, the Solar System is made up of different regions, which are delineated based on their distance from the Sun, but also the types of planets and bodies that can be found within them.
In the Inner Solar System, we find the Inner Planets – Mercury, Venus, Earth, and Mars – which are so named because they orbit closest to the Sun. In addition to their proximity, these planets have a number of key differences that set them apart from planets elsewhere in the Solar System.
For starters, the inner planets are rocky and terrestrial, composed mostly of silicates and metals, whereas the outer planets are gas giants. The inner planets are also much more closely spaced than their outer Solar System counterpart. In fact, the radius of the entire region is less than the distance between the orbits of Jupiter and Saturn.
This region is also within the “frost line”, which is a little less than 5 AU (about 700 million km) from the Sun. This line represents the boundary in a system where conditions are warm enough that hydrogen compounds such as water, ammonia, and methane are able to take liquid form. Beyond the frost line, these compounds condense into ice grains.
Generally, inner planets are smaller and denser than their counterparts, and have few to no moons or rings circling them. The outer planets, meanwhile, often have dozens of satellites and rings composed of particles of ice and rock.
They are composed largely of refractory minerals, such as the silicates, which form their crusts and mantles, and metals – such as iron and nickel which form their cores. Three of the four inner planets (Venus, Earth and Mars) have atmospheres substantial enough to generate weather. All of them have impact craters and tectonic surface features as well, such as rift valleys and volcanoes.
Of the inner planets, Mercury is the closest to our Sun and the smallest of the terrestrial planets. This small planet looks very much like the Earth’s Moon and is even a similar grayish color, and it even has many deep craters and is covered by a thin layer of tiny particle silicates.
Its magnetic field is only about 1 percent that of Earth’s, and it’s very thin atmosphere means that it is during the day (up to 430°C) and freezing at night (as low as -187 °C) because the atmosphere can neither keep heat in or out. It has no moons of its own and, comprised mostly of iron and nickel, is one of the densest planets in the Solar System.
Venus, which is about the same size as Earth, has a thick toxic atmosphere that traps heat, making it the hottest planet in the solar system. This atmosphere is composed of various gases, including carbon dioxide, which transforms the planet into a raging storm. Much of its surface is marked with volcanoes and deep canyons — the biggest of which is over 6400 km (4,000 mi) long.
Only two spacecraft have ever penetrated Venus’s thick atmosphere, but it’s not just man-made objects that have trouble getting through. There are fewer crater impacts on Venus than other planets because all but the largest meteors can’t make it through the thick air. Venus is often called the morning star because, with the exception of Earth’s moon, it’s the brightest object in the sky. Like Mercury, it also has no moon of its own.
Earth is the third inner planet and the one we know best. Of the four terrestrial planets, Earth is the largest, and the only one that has liquid water, which is necessary for life as we know it. Earth’s atmosphere protects the planet from dangerous radiation and helps keep valuable sunlight in, which is also essential for life to survive.
Like the other terrestrial planets, Earth has a rocky surface with mountains and canyons, and a heavy metal core. Earth’s atmosphere contains water vapor, which helps to moderate daily temperatures. Like Mercury, the Earth has an internal magnetic field. And our moon, the only one we have, is comprised of a mixture of various rocks and minerals.
Mars is the fourth and final inner planet, and also known as the “Red Planet” due to the rust of iron-rich materials that form the planet’s surface. Mars also has some of the most interesting terrain features of any of the terrestrial planets. These include the largest mount in the Solar System – Olympus Mons, which rises some 21,229 m (69,649 ft) above the surface.
Much of the surface is very old and filled with craters, but there are geologically newer areas of the planet as well. At the Martian poles are polar ice caps that shrink in size during the Martian spring and summer. Mars is less dense than Earth and has a smaller magnetic field, which is indicative of a solid core, rather than a liquid one
Mars’ thin atmosphere has led some astronomers to believe that the surface water that once existed there might have actually taken liquid form, and has since leaked into space. The planet has two small moons called Phobos and Deimos. One of Mars’ best-known features is its network of canals and canyons that led many to believe there was even a civilization on this planet.
Beyond Mars are the four outer planets: Jupiter, Saturn, Uranus, and Neptune.
If you are looking for more information, check out this article from NASA on the planets of the Solar System and this article from Solstation about the inner planets.
Universe Today has numerous articles on the inner planets including the planets of the inner Solar System as well as a detailed breakdown of all the planets in the Solar System.
Astronomy Cast also has episodes on all of the inner planets including this one about Mercury.
Our Solar System is an immense and amazing place. Between its eight planets, 176 moons, 5 dwarf planets (possibly hundreds more), 659,212 minor planets, and 3,296 known comets, it has w0nders to sate the most demanding of curiosities.
For example, the Solar System is made up of different regions, which are delineated based on their distance from the Sun, but also the types of planets and bodies that can be found within them.
In the Inner Solar System, we find the Inner Planets – Mercury, Venus, Earth, and Mars – which are so named because they orbit closest to the Sun. In addition to their proximity, these planets have a number of key differences that set them apart from planets elsewhere in the Solar System.
For starters, the inner planets are rocky and terrestrial, composed mostly of silicates and metals, whereas the outer planets are gas giants. The inner planets are also much more closely spaced than their outer Solar System counterpart. In fact, the radius of the entire region is less than the distance between the orbits of Jupiter and Saturn.
This region is also within the “frost line”, which is a little less than 5 AU (about 700 million km) from the Sun. This line represents the boundary in a system where conditions are warm enough that hydrogen compounds such as water, ammonia, and methane are able to take liquid form. Beyond the frost line, these compounds condense into ice grains.
Generally, inner planets are smaller and denser than their counterparts, and have few to no moons or rings circling them. The outer planets, meanwhile, often have dozens of satellites and rings composed of particles of ice and rock.
They are composed largely of refractory minerals, such as the silicates, which form their crusts and mantles, and metals – such as iron and nickel which form their cores. Three of the four inner planets (Venus, Earth and Mars) have atmospheres substantial enough to generate weather. All of them have impact craters and tectonic surface features as well, such as rift valleys and volcanoes.
Of the inner planets, Mercury is the closest to our Sun and the smallest of the terrestrial planets. This small planet looks very much like the Earth’s Moon and is even a similar grayish color, and it even has many deep craters and is covered by a thin layer of tiny particle silicates.
Its magnetic field is only about 1 percent that of Earth’s, and it’s very thin atmosphere means that it is during the day (up to 430°C) and freezing at night (as low as -187 °C) because the atmosphere can neither keep heat in or out. It has no moons of its own and, comprised mostly of iron and nickel, is one of the densest planets in the Solar System.
Venus, which is about the same size as Earth, has a thick toxic atmosphere that traps heat, making it the hottest planet in the solar system. This atmosphere is composed of various gases, including carbon dioxide, which transforms the planet into a raging storm. Much of its surface is marked with volcanoes and deep canyons — the biggest of which is over 6400 km (4,000 mi) long.
Only two spacecraft have ever penetrated Venus’s thick atmosphere, but it’s not just man-made objects that have trouble getting through. There are fewer crater impacts on Venus than other planets because all but the largest meteors can’t make it through the thick air. Venus is often called the morning star because, with the exception of Earth’s moon, it’s the brightest object in the sky. Like Mercury, it also has no moon of its own.
Earth is the third inner planet and the one we know best. Of the four terrestrial planets, Earth is the largest, and the only one that has liquid water, which is necessary for life as we know it. Earth’s atmosphere protects the planet from dangerous radiation and helps keep valuable sunlight in, which is also essential for life to survive.
Like the other terrestrial planets, Earth has a rocky surface with mountains and canyons, and a heavy metal core. Earth’s atmosphere contains water vapor, which helps to moderate daily temperatures. Like Mercury, the Earth has an internal magnetic field. And our moon, the only one we have, is comprised of a mixture of various rocks and minerals.
Mars is the fourth and final inner planet, and also known as the “Red Planet” due to the rust of iron-rich materials that form the planet’s surface. Mars also has some of the most interesting terrain features of any of the terrestrial planets. These include the largest mount in the Solar System – Olympus Mons, which rises some 21,229 m (69,649 ft) above the surface.
Much of the surface is very old and filled with craters, but there are geologically newer areas of the planet as well. At the Martian poles are polar ice caps that shrink in size during the Martian spring and summer. Mars is less dense than Earth and has a smaller magnetic field, which is indicative of a solid core, rather than a liquid one
Mars’ thin atmosphere has led some astronomers to believe that the surface water that once existed there might have actually taken liquid form, and has since leaked into space. The planet has two small moons called Phobos and Deimos. One of Mars’ best-known features is its network of canals and canyons that led many to believe there was even a civilization on this planet.
Beyond Mars are the four outer planets: Jupiter, Saturn, Uranus, and Neptune.
If you are looking for more information, check out this article from NASA on the planets of the Solar System and this article from Solstation about the inner planets.
Universe Today has numerous articles on the inner planets including the planets of the inner Solar System as well as a detailed breakdown of all the planets in the Solar System.
Astronomy Cast also has episodes on all of the inner planets including this one about Mercury.
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