Planetary Geology 101

The Solar System

Formation of the Solar System

• The stages of solar system formation start with a protostar embedded in a gas cloud, then to an early star with a circumstellar disk, to a star surrounded by small "planetesimals" that are starting to clump together to a solar system like ours today.

Formation of the Solar System

www.jwst.nasa.gov/birth.html Credit: Shu et al. 1987

protostar circumstellar disk

planetesimals home

Structure(from the inside out)

• Central star

• Inner “terrestrial” planets

• Asteroid belt

• Outer “gas giant” planets

• Outer “ice giant” planets

• (Dwarf planets)

• Trans-Neptunian objects (Kuiper belt, scattered disk, Oort Cloud)

• Miscellaneous

The Sun

• “Yellow dwarf”, 1.4 million km in diameter

• Fuses 620 million tonnes/sec of H

• 8.3 light-minutes away

The Sun

Mercury

• Innermost planet, 4,880 km in diameter

• Very dense, with its own magnetic field

• Enigmatically large iron core

• Recent evidence for volcanism

Mercury

Venus

• Regarded as Earth’s “Evil Twin”

• Surface T: 460°C, P: 92 Bar

• Subject to runaway greenhouse effect

• Extensive resurfacing due to volcanism

Venus

Mars

• Diameter: ~6800 km (= Earth’s core)

• Same surface area of all Earth’s continents

• Deserts, ice caps, canyons, giant volcanoes

• Upper hemisphere may be giant impact basin

Mars

Asteroid Belt

• Small bodies: asteroids/minor planets

• >50% mass: Ceres, Vesta, Pallas, Hygiea

• Protoplanets that orbited too fast to acrete

• Mainly loosely-bound piles of rubble

Asteroid Belt

Jupiter

• Largest body after the Sun (D: ~143,000 km)

• Primarily H, He, with putative rocky core

• High-energy storms in its atmosphere

• At least 63 moons

Jupiter

Saturn

• Second-largest planet, diameter ~121,000 km

• Prominent set of rings

• 53 officially-named moons

• Hosts largest moon in the system, Titan

Saturn

Uranus

• Larger of the two “ice giants”, D ~51,000 km

• Gas atmosphere + contains H20, NH3, CH4

• Axis of rotation inclined almost 90

Neptune

• Second “ice giant”, D ~49,000 km

• Same composition as Uranus (H20, NH3, CH4)

• Tenuous ring system, 13 known moons

Dwarf Planets

• Currently 5: Ceres, Pluto, Haumea, Makemake, Eris

• Most occur beyond Neptune (except Ceres)

• Best known is Pluto (former planet)

Trans-Neptunian Objects (TNOs)

• Composed of 3 regions: Kuiper Belt, scattered disk, and Oort Cloud

Trans-Neptunian Objects (TNOs)

• Composed of 3 regions: Kuiper Belt, scattered disk, and Oort Cloud