Structure & Composition
How many planets are in our solar system?
8
What is the solar system believed to have formed from?
A cloud of gas and dust called a nebula.
What force keeps planets orbiting the Sun?
Answer: Gravity.
What three things does life (as we know it) need most?
Liquid water, an energy source, and the right temperature range.
What is an asteroid?
A small, rocky object that orbits the Sun, mostly found in the asteroid belt.
Name the four rocky inner planets ?
Mercury, Venus, Earth, and Mars.
About how old is the solar system?
Answer: Around 4.6 billion years old.
What shape is a planet’s orbit?
An oval shape called an ellipse.
Why is Earth considered habitable?
It has liquid water, oxygen-rich air, and moderate temperatures.
What is a comet made of?
Answer: Ice, dust, and rock — often called “dirty snowballs.”
Name the 2 gas giants and the 2 ice giants?
Jupiter, Saturn (gas giants) and Uranus, Neptune (ice giants).
What process caused the Sun to form?
Answer: Gravity pulling gas together until nuclear fusion began.
Why does Earth have seasons?
Because Earth is tilted on its axis as it orbits the Sun.
What is the “habitable zone”?
The distance from a star where temperatures allow liquid water to exist.
Which planet has the most moons?
Answer: Jupiter.
What is the main difference between rocky planets and gas giants?
Answer: Rocky planets have solid surfaces; gas/ice giants are made mostly of gases and ices with no solid surface.
Why are inner planets rocky and outer planets giant?
Only heavy, solid materials stayed close to the Sun; lighter gases collected farther away.
Why does the Sun appear to rise and set?
Because Earth rotates once every 24 hours
What do living things need to survive?
Water, air, and the right temperature
What do robots sent to space do?
Take pictures and test rocks
What is a moon?
Answer: A natural object that orbits a planet.
What are planetesimals?
Small building‑blocks of rock and ice that combined to form planets.
What causes the length of a planet’s year?
The time it takes to orbit the Sun.
How is Earth different from Mars?
Earth has air and water; Mars is cold and dusty
Scientists use a ________ to see faraway planets.
Telescopes