4.3 Comparative planetology within our solar system
4 min read•july 22, 2024
Planets in our solar system fall into two main categories: terrestrial and Jovian. are smaller, rocky bodies closer to the Sun, while are massive farther out. Their differences stem from their formation and location.
A planet's distance from the Sun greatly affects its properties. Closer planets are hotter and struggle to keep light gases, while farther planets are colder and can hold onto more volatile elements. This influences their atmospheres, surface features, and potential for life.
Planetary Properties and Characteristics
Terrestrial vs Jovian planets
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Terrestrial planets (, , Earth, Mars)
Smaller in size and mass compared to Jovian planets
Higher average densities due to their rocky composition
Solid, rocky surfaces that allow for the formation of landforms and geological features
Thin or no atmospheres (except Venus) because of their lower gravity and proximity to the Sun
Slower rotation rates, which affect the length of their days and nights
Few or no moons orbiting them
Jovian planets (Jupiter, Saturn, , )
Larger in size and mass compared to terrestrial planets, often referred to as "gas giants"
Lower average densities because they are primarily composed of hydrogen and helium
No solid surfaces; composed mainly of gas and ice, with possible rocky cores
Thick, massive atmospheres that are dominated by hydrogen, helium, and other volatile compounds
Faster rotation rates, leading to strong zonal winds and banded appearance
Numerous moons and ring systems surrounding them, created by the planets' strong gravitational fields
Planetary characteristics and solar distance
Distance from the Sun
Affects the amount of solar radiation received by a planet
Closer planets (Mercury, Venus) receive more energy, leading to higher surface temperatures
Farther planets (Mars, Jupiter, Saturn, Uranus, Neptune) receive less energy, resulting in colder temperatures
Influences the state of matter and the potential for atmospheric retention
Closer to the Sun, lighter elements and compounds (hydrogen, helium) can escape more easily due to higher thermal energy
Farther from the Sun, even lighter elements can be retained in the atmosphere because of lower temperatures
Initial composition
Determined by the solar nebula's temperature gradient during planetary formation
Closer to the Sun, higher temperatures allowed only refractory elements (metals, silicates) to condense and form terrestrial planets
Farther from the Sun, lower temperatures allowed the condensation of volatiles (ices, gases) in addition to refractory elements, leading to the formation of Jovian planets
Affects the overall density and structure of a planet
Terrestrial planets formed from refractory materials, resulting in higher densities and rocky compositions
Jovian planets formed from a mix of refractory and volatile materials, leading to lower densities and gas-rich compositions
Atmospheres and Surface Processes
Planetary atmospheres in solar system
Terrestrial planets
Venus and Mars: primarily carbon dioxide (CO2), creating a strong greenhouse effect on Venus
Earth: nitrogen (N2), oxygen (O2), and trace gases that support life and moderate temperatures
Mercury: virtually no atmosphere due to its proximity to the Sun and low gravity
Jovian planets
Jupiter and Saturn: primarily hydrogen (H2) and helium (He), similar to the composition of the Sun
Uranus and Neptune: H2, He, and substantial amounts of methane (CH4) and other ices, giving them their blue-green appearance
Venus: super-rotating atmosphere that completes a full rotation in just 4 Earth days, creating strong winds and a runaway greenhouse effect
Earth: moderate greenhouse effect, weather systems, and atmospheric circulation cells that distribute heat and moisture
Mars: that allows for large temperature fluctuations, dust storms, and seasonal carbon dioxide at the poles
Jovian planets: strong zonal winds, storms (Jupiter's Great Red Spot, Neptune's Great Dark Spot), and banded appearance due to rapid rotation and convection
Geological processes on planets and moons
Observed on Earth, Venus, Mars, and Io (Jupiter's moon)
Responsible for shaping planetary surfaces and atmospheres through lava flows, ash deposits, and outgassing
Examples: Olympus Mons (largest known volcano in the solar system on Mars), Mauna Loa (Earth's largest active volcano), Ionian (powered by tidal heating)
Plate tectonics on Earth
Driven by mantle convection, which causes plates to move and interact
Creates features like mountains (Himalayas), rift valleys (East African Rift), and subduction zones (Mariana Trench)
Plays a crucial role in the carbon cycle and the recycling of surface materials
Possible tectonic activity on Venus and Mars
Venus: coronae (circular volcanic features) and tesserae (deformed highland regions) suggest past or present tectonic activity
Mars: Valles Marineris (largest canyon system) and Tharsis bulge (volcanic region) indicate possible tectonic processes in the past
Common feature on most terrestrial planets and moons, as they lack thick atmospheres to protect against impacts
Provides insights into the age and of a surface
Older surfaces have more craters because they have been exposed to impacts for a longer time
Younger surfaces have fewer craters due to resurfacing events (volcanism, ) that erase or bury older craters
Examples: Caloris Basin (largest impact basin on Mercury), Chicxulub crater (site of the dinosaur extinction event on Earth), Hellas Basin (one of the largest impact basins on Mars)