Formation of the Solar System

What characteristic do terrestrial planets have in common?

Which of the following is a characteristic of asteroids?

What is the primary location of comets in our solar system?

What suggests a high degree of order in our solar system?

What is the suggested explanation for the formation of our solar system?

What has evolved over time in the solar system?

What is the age of the solar system, according to planetary scientists?

What is a characteristic of the planets' orbits in our solar system?

What is the direction of the planets' orbits around the Sun?

Which of the following planets does not rotate on its axis in the same direction as the Sun's rotation?

What is the direction of most moons' orbits around their parent planet?

What is a characteristic of our planetary system?

Which of the following is not a characteristic of the planets in our solar system?

What is an exception to the alignment of the planets' orbits with the Sun's equator?

The Age of the Solar System

The solar system is approximately 4.6 billion years old, based on the ages of the oldest meteorites and Earth and lunar rocks.

Key Features of the Solar System

The planets are relatively isolated in space, with no bunching together.
The orbits of the planets are nearly circular, with exceptions being Mercury and Pluto.
The orbits of the planets all lie in nearly the same plane, with a few degrees of variation.
The direction of planetary orbits and the Sun's rotation are the same, with a counterclockwise motion as viewed from above Earth's north pole.

Planetary Rotation and Moon Orbits

Most planets rotate on their axis in the same direction as the Sun's rotation.
Three planets (Venus, Uranus, and Pluto) do not share this property.
Most known moons revolve about their parent planet in the same direction as the planet's rotation, except for Neptune's moon Triton.

Planetary Differentiation

The solar system is highly differentiated, with terrestrial planets having high densities, moderate atmospheres, slow rotation rates, and few or no moons.
Jovian planets have low densities, thick atmospheres, rapid rotation rates, and many moons.

Asteroids and Comets

Asteroids are very old, exhibiting a range of properties not characteristic of terrestrial or jovian planets or their moons.
Asteroids share similar bulk orbital properties with the planets but appear to be made of primitive, unevolved material.
Comets are primitive, icy fragments that do not necessarily orbit in the ecliptic plane, primarily residing in the Kuiper Belt and the Oort Cloud.

Learn about the origins of our planetary system, from the age of the solar system to the nine known facts that shape our understanding of its architecture.