Planetary geology facts for kids

Planetary geologist and NASA astronaut Harrison "Jack" Schmitt collecting lunar samples during the Apollo 17 mission in early-December 1972

Surface of Mars as photographed by the Viking 2 lander December 9, 1977.

ESA Huygens in situ image from Titan's surface—the only image from the surface of a body farther away than Mars

Same image with contrast enhanced

Planetary geology, alternatively known as astrogeology or exogeology, is the study of the geology of celestial bodies such as planets, moons, asteroids, comets, and meteorites. It combines the knowledge of geology with that of astronomy and planetary science. Planetary geologists study the composition, structure, processes, and history of these objects to understand their origin and evolution.

What do planetary geologists do?

Planetary geologists are like space detectives! They use all sorts of tools and techniques to study other worlds, including:

• Telescopes: To observe planets and moons from Earth.
• Spacecraft: To send probes and rovers to explore planets up close.
• Remote Sensing: Using cameras and other instruments on spacecraft to take pictures and collect data from afar.
• Sample Analysis: Studying rocks and soil samples brought back from other planets (like the Moon!).
• Computer Models: Creating simulations to understand how planets form and change.

Building blocks of planets

Just like Earth, other planets are made of rocks, minerals, and metals. But the amounts of these materials can be very different!

• Rocks: Solid materials made of different minerals. Common rocks on Earth and other planets include basalt (dark volcanic rock) and granite (light-colored rock).
• Minerals: Naturally occurring, solid substances with a specific chemical composition and crystal structure. Examples include quartz, feldspar, and olivine.
• Metals: Elements like iron, nickel, and aluminum that are good conductors of electricity and heat. Many planets have a core made mostly of iron.
• Ices: Frozen water, carbon dioxide, methane, or ammonia. Ices are common on planets and moons far from the Sun, where it's very cold.

Processes that shape planets

Planets are not static; they are constantly changing due to various geological processes. These processes include:

• Impact Cratering: When asteroids or comets crash into a planet or moon, they create impact craters. The number and size of craters can tell us how old a surface is. For example, the Moon is covered in craters because it doesn't have an atmosphere to burn up incoming space rocks.
• Volcanism: The eruption of molten rock (magma) onto the surface. Volcanoes can create mountains, plains, and other interesting features.
• Tectonics: The movement of a planet's crust. On Earth, plate tectonics causes earthquakes, volcanoes, and the formation of mountains. Other planets, like Mars and Venus, show evidence of past tectonic activity.
• Erosion: The wearing away of a planet's surface by wind, water, or ice. Earth has a lot of erosion because of its atmosphere and oceans. Mars also has evidence of past water erosion, like dried-up riverbeds.
• Sedimentation: The deposition of sediments (like sand, silt, and clay) by wind, water, or ice. Sedimentary rocks can form over time as these sediments are compacted and cemented together.

Exploring the planets

Let's take a quick tour of some of the planets and moons in our solar system and see what planetary geologists have discovered!

Mercury

• What we know: Mercury is the smallest planet in our solar system and the closest to the Sun. It has a heavily cratered surface, like the Moon, and a very thin atmosphere.
• Interesting fact: Mercury has huge cliffs called scarps that formed as the planet cooled and shrank.
• Missions: Mariner 10 (1974-1975), MESSENGER (2011-2015), BepiColombo (currently en route).

Venus

• What we know: Venus is similar in size to Earth, but it has a very thick atmosphere made mostly of carbon dioxide. This creates a runaway greenhouse effect, making Venus the hottest planet in our solar system.
• Interesting fact: Venus has thousands of volcanoes, but no evidence of plate tectonics.
• Missions: Venera program (1961-1984), Magellan (1990-1994), Venus Express (2006-2014).

Earth

• What we know: Earth is the only planet known to support life. It has a dynamic surface with plate tectonics, [[volcanoes, mountains, and oceans.
• Interesting fact: Earth's atmosphere is made mostly of nitrogen and oxygen, which is essential for life.
• Missions: Countless missions, including satellites, space stations, and rovers.

Mars

• What we know: Mars is a cold, desert planet with a thin atmosphere. It has evidence of past water, including dried-up riverbeds, lakes, and possibly even oceans.
• Interesting fact: Mars has the largest volcano in the solar system, Olympus Mons, and a giant canyon system called Valles Marineris.
• Missions: Viking program (1975-1980), Mars Pathfinder (1997), Mars Exploration Rovers (Spirit and Opportunity, 2004-2018), Curiosity rover (2012-present), Perseverance rover (2021-present).

Jupiter

• What we know: Jupiter is the largest planet in our solar system. It is a gas giant, meaning it is made mostly of hydrogen and helium.
• Interesting fact: Jupiter has a giant storm called the Great Red Spot that has been raging for at least 300 years!
• Missions: Pioneer program (1973-1974), Voyager program (1979), Galileo (1995-2003), Juno (2016-present).

Saturn

• What we know: Saturn is famous for its beautiful rings, which are made of ice and rock particles. It is also a gas giant, similar to Jupiter.
• Interesting fact: Saturn has many moons, including Titan, which has a thick atmosphere and liquid methane lakes.
• Missions: Pioneer 11 (1979), Voyager program (1980-1981), Cassini-Huygens (2004-2017).

Uranus

• What we know: Uranus is an ice giant, meaning it is made mostly of icy materials like water, methane, and ammonia. It is tilted on its side, so its poles point towards the Sun.
• Interesting fact: Uranus has faint rings and many moons.
• Missions: Voyager 2 (1986).

Neptune

• What we know: Neptune is another ice giant, similar to Uranus. It has strong winds and a dark spot, like Jupiter's Great Red Spot.
• Interesting fact: Neptune has a large moon called Triton, which orbits in the opposite direction of Neptune's rotation.
• Missions: Voyager 2 (1989).

Pluto

• What we know: Pluto is a dwarf planet located in the Kuiper Belt, a region beyond Neptune filled with icy objects. It has a heart-shaped glacier made of nitrogen ice.
• Interesting fact: Pluto has five moons, including Charon, which is almost half the size of Pluto.
• Missions: New Horizons (2015).

Why is planetary geology important?

Planetary geology helps us understand:

• The origin and evolution of the solar system: By studying other planets, we can learn how our solar system formed and how it has changed over time.
• The potential for life beyond Earth: By studying the conditions on other planets, we can assess whether they could support life.
• The future of Earth: By studying how other planets have changed, we can better understand the processes that could affect Earth in the future.

See also

In Spanish: Astrogeología para niños