What are the solar system’s planets made of

1st Jan 2023
What are the solar system’s planets made of

What are the planets made of in our solar system, and is it possible to expect that one of them will become our new home if something happens to the Earth? Read on to find the answers to these intriguing questions.

How do planets form?

According to scientists, the solar system’s planets were formed by the rotation of gases and dust. Eventually, a core, gradually increasing in size, formed inside this ring. This is how gases and various solid particles got into the planet’s structure. The interaction of gases and iron resulted in various compounds. But did they come to this conclusion?

How do we know what planets are made of?

Our current technology gives us a variety of tools to examine planets from on Earth and in orbit. Let’s take a look at the main ways to discover the composition of a particular planet.


Spectroscopy is currently the most common method for determining what planets are made out of. The process uses tools with a grating that distributes the light coming from an object. This scattered light is called a spectrum. Each element (and elements’ combinations) has a unique fingerprint that astronomers can look for in the spectrum of a given object. The identification of these imprints makes it possible to determine the composition of objects. How does this happen?

Each print is a light absorption line that looks like a dark area. Because the wavelengths at which absorption lines appear are unique to each element, astronomers can measure the position of the lines to determine which elements are present in an object. The amount of light absorbed can also provide information on the proportion of all elements.

The more elements an object contains, the more complex its spectrum; besides, motion can affect the position of spectral lines, too. Fortunately, computing has advanced enough to enable researchers to distinguish between many different elements and compounds, even in a dense spectrum and identify shifted lines.

Meteorite analysis

These space guests visit the Earth with stunning regularity. Scientists have been studying asteroid and comet fragments since the 18th century and have been able to divide them into groups:

  • stone;
  • iron;
  • stony-iron.

The diverse chemical composition of meteorites is an excellent source of data on the structure and composition of space bodies. For example, a detailed study of the Black Beauty meteorite (NWA 7034), found in Morocco in 2011, led to the conclusion that it was ejected into space from the surface of the Cimmerian region on Mars about 5-10 million years ago. And in 2017, meteorites helped provide important data on the age of Jupiter. An analysis of the ratio of various isotopes of molybdenum and tungsten in 19 iron meteorites made it possible to determine that they are fragments of the earliest planetesimals located near the orbit of Jupiter. This information formed the basis of the hypothesis that Jupiter arose no later than 1 million years after the compression of a gas and dust cloud that formed our solar system.

And now, let’s take a better look at each planet’s composition.

What are the inner planets made out of?

Solar system planets are divided into inner and outer groups, the nominal boundary between which is the asteroid belt. The inner or terrestrial group includes the four planets closest to the Sun:

  • Mercury;
  • Venus;
  • Earth;
  • Mars.

The inner group of planets makes up the smallest part of our solar system. Consider that the distance from the Sun to Mars is less than the distance between the orbits of Saturn and Jupiter. The inner planets have a high density and consist of stones, metals (iron, nickel) and silicates.


It is the largest and densest of all planets in the inner solar system. Besides being our home planet, Earth is unique because it has:

  • a hydrosphere;
  • lots of oxygen in the atmosphere;
  • gravity;
  • magnetic field;
  • the largest satellite — the Moon;
  • an average temperature of 7 degrees Celsius, which ensures the survival of biological organisms.

The structure of the Earth includes inner and outer cores, presumably containing a molten iron-nickel alloy and various impurities, a mantle made of rocks, and an earth crust consisting of silicates and basalts. Above the Earth’s crust, covered with the hydrosphere, are the lower dense layers of the atmosphere.


Mercury is the closest planet to the Sun. Most of Mercury’s volume — about 61% — is composed of a huge iron-nickel, presumably liquid core, about the size of our moon. The core is surrounded by a silicate mantle about 500 kilometres thick. An analysis of data collected by an American robotic space probe, Messenger, showed that the thickness of Mercury’s crust is 26 ± 11 km. The surface also resembles the moon — it is stony, hard, and densely covered with craters.

Mercury has a very thin atmosphere, which is why it does not retain solar heat well. This is why this planet has strong temperature fluctuations. The minimum nighttime temperature can drop to -183.2 °C, and the daytime maximum can reach + 426.9 °C.


Venus consists of a central iron core and a rocky mantle, similar in composition to Earth’s. Its atmosphere is mainly carbon dioxide (96%) and nitrogen (3%), with a small admixture of other gases. Due to its high atmospheric density, Venus resembles a large thermos. The maximum temperature of Venus is higher than that of Mercury, even though it is located further from the Sun. The surface of Venus is a very hot and dry place. Most of it consists of low-hilled plains covered with old lava flows; there are several large lowlands and two large mountainous regions the size of Australia and South America.


The core of the red planet is made up of iron, nickel and sulfur. Surrounding the core is a rocky mantle 770 to 1170 miles thick, and above it, is a crust of iron, magnesium, aluminium, calcium, and potassium. The reason Mars looks reddish is the oxidation, or rusting, of iron in the rocks, regolith (Martian “soil”), and Martian dust. This dust rises into the atmosphere, and from a distance, the planet appears red.

Mars has a thin atmosphere composed mostly of carbon dioxide, nitrogen, and argon. The temperature on the surface can reach as high as 20 degrees Celsius and as low as -153 degrees. It can also be very windy out there, and it sometimes takes months for the dust to settle after a dust storm.

And yet, despite such harsh conditions, Mars is considered the only planet hypothetically suitable for human life. It even has water, though mostly in the ice form. Due to this planet’s extremely rarefied atmosphere, it cannot exist on the surface in liquid form for long.

What are outer planets made of?

The outer part of the solar system is made up of four giant planets with satellites:

  • Jupiter;
  • Saturn;
  • Neptune;
  • Uranus.

All of them have a low density, a solid core and a gaseous atmosphere. Due to their large distance from the Sun, there is reason to believe that these planets’ cores, in addition to stone and iron, also contain ice. Because of this, they are also called gas or ice giants. So, what are gas giant planets made of?


This giant is 2.5 times heavier than all the planets in the solar system. Jupiter’s major components are hydrogen and helium, but it also contains ammonia, methane, and water in very small amounts. The core contains stones and metallic hydrogen.


It has the lowest density of all the planets and is similar in composition to Jupiter since its structure is also dominated by helium and hydrogen. Saturn’s core is made up of metals such as iron and nickel, surrounded by rocky material and other compounds that have solidified under intense pressure and heat.


The coldest planet in the solar system is made up of ice, methane and ammonia above a small stony centre. Similar to Jupiter and Saturn, Uranus’ atmosphere is hydrogen and helium, but it also contains methane, which gives this planet its blue colour.


Together with Uranus, scientists classify Neptune as an ice giant since its bowels are made of ice and stone, while hydrogen, helium, water, ammonia, methane ice, and traces of nitrogen are present in its atmosphere. By the way, we have dedicated a separate article to Neptune, and we suggest you give it a closer look.

What are the rings of planets made of?

All four giant planets have a common component of satellite system that is named rings. These are flat formations that revolve around the planet at its equator. The researchers managed to obtain information not only about the structure of these rings but also about their composition:

  • Jupiter’s rings were formed from dust particles kicked up by micrometeorite impacts on Jupiter’s small inner moons and later captured into this planet’s orbit. If the impacts on the moons were larger, the raised dust would be pulled by gravity to the surface of the moons.
  • The rings of Uranus are made up of ice blocks, big and small. Compared to other planets’ rings, Uranus’ rings are thin, narrow, and so dark that they reflect about as much light as charcoal.
  • Neptune’s rings are likely composed of ice particles coated with dark carbon material or silicates. The proportion of this dust can range from 20 to 70%.
  • Saturn’s rings contain ice and dusty rocks. They are thought to be pieces of comets, asteroids, or shattered moons that disintegrated before reaching the planet, torn apart by Saturn’s powerful gravity.

There are many theories about how and why rings formed around the outer planets. Although the rings themselves are considered as old as the solar system (4.5 billion years), the particles that make up them are quite young. Most of the particles are bright, which means that they have not had time to collect dust yet. This suggests that they are somehow recycled. Some scientists believe that these particles merge into moons and decay again and again.

What are the dwarf planets made of?

We covered what are the 8 Solar system planets made out of. But there are also dwarf planets. According to the International Astronomical Union classification, these celestial bodies have the following characteristics:

  • orbit around the Sun;
  • sufficient mass to maintain a spherical shape under the force of gravity;
  • is not a satellite of other planets;
  • cannot clear the area of its orbit from other objects.

There are 5 officially recognized dwarf planets: the largest asteroid Ceres and trans-Neptunian objects Pluto, Eris, Makemake, and Haumea. However, it is possible that at least 40 other known objects in the solar system belong to this category. Let’s find out what are 5 main dwarf planets made of:

  • Ceres — water ice, as well as stone, clay minerals, and carbonates.
  • Pluto — ice and stone.
  • Haumea is covered with water ice mixed with hydrogen cyanide, kaolinite, potassium cyanide, and carbonaceous minerals.
  • Makemake has a heterogeneous surface covered with methane snow mixed with organic substances of unknown origin — tholins, ethane, and nitrogen ice.
  • Eris is also covered with methane snow mixed with nitrogen, ethylene, and ethane ice.

A dwarf planet’s composition largely depends on the planet’s distance from the Sun. Closer planets, like Ceres, may have traces of liquid water in addition to rocks and ice. But more distant objects, as a rule, are almost completely icy.

Final thoughts

Of course, our knowledge when it comes to what planets are made of is still very scarce. We have studied the Earth reasonably well, but even our home planet can sometimes be unpredictable. In any case, an expedition to other planets will definitely take place, and our first destination will be Mars. This may probably happen already in this decade. So far, there is neither a technical possibility nor any urgent need for people to visit other planets — in this matter, we can rely on probes.

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