What objects make up the solar system?
The sun, the planets and their moons, and a variety of smaller objects
What is a planet?
A round object that orbits the sun and has cleared out the region of the solar system along its orbit
What are some smaller objects found in the solar system?
Asteroids and comets
Which two planets have no natural satellites?
Mercury and Venus
Why did gas giants form?
They were further from the sun, so ice formed and added mass. Their gravitational pull was strong enough to hold light gases like hydrogen and helium.
What are the eight planets?
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune
What does AU stand for?
Astronomical Unit
How did the planets form according to scientists?
Rock, ice, and gas pulled together due to gravity to form planetesimals which collided with each other to form all other solar system objects
Why are the inner planets small and rocky?
Their proximity to the sun made them warm, so ice didn't form. They have low mass, so their gravity was too weak to hold light gases like hydrogen and helium
How much of the mass of the solar system is contained within the sun?
About 99.85%
How old do scientists think the solar system is?
4.6 billion years old
What happened to the spinning disk of material that scientists theorize formed the solar system?
Temperature and pressure became so high that hydrogen atoms pressed together to form helium which gave off energy
How is a dwarf planet different from a planet?
It has not cleared the area of its orbit
What is the distance of one AU?
The average distance between Earth and the sun; about 150,000,000 kilometers
Why do scientists use AU to measure distances in the solar system?
Distances are so large that they can't be easily measured in meters or kilometers
How do scientists think the solar system formed?
A cloud of hydrogen, helium, rock, ice, and other materials pulled together by gravity
Which two planets have more than sixty moons?
Jupiter and Saturn
How does the size of our sun compare to the size of other stars?
It is midsized; there are stars that have volumes a thousand times greater than the sun
What is the center of our solar system?
The sun