Birth of Planets
What did the solar system form from?
A rotating cloud of gas and dust called the solar nebula
What type of planets formed closer to the Sun?
Terrestrial (rocky) planets
What is the first stage in a star’s life?
A protostar
What causes craters on planets and moons?
Impacts from meteoroids or asteroids
What is the closest star to Earth?
The Sun
What force caused the solar nebula to collapse?
Gravity
Why did gas giants form farther from the Sun?
It was cold enough for gases and ices to condense
What gas do stars fuse to make energy?
Hydrogen
What causes a planet’s surface to change over time?
Erosion, volcanism, and tectonic activity
What is a galaxy?
A group of billions of stars, gas, and dust held by gravity
What was left at the center of the collapsing nebula?
The Sun
What keeps planets in orbit around the Sun?
The Sun’s gravitational pull
What is the balance between gravity pulling in and pressure pushing out in a star called?
Hydrostatic equilibrium
Why does Earth have fewer craters than the Moon?
Weather, erosion, and plate movement erase them
Which planet has the strongest magnetic field?
Jupiter
What are the small solid particles that stick together during planet formation called?
Planetesimals
What separates the inner and outer planets?
The asteroid belt
What happens when a massive star runs out of fuel?
It explodes in a supernova
How do scientists learn about other planets’ history?
By studying surface features, samples, and space probe data
What is a light-year?
The distance light travels in one year
What is the process called when small bodies collide and merge to form larger planets?
Accretion
What are leftover building blocks from the early solar system called?
Asteroids and comets
What are the two possible remnants of a massive star after a supernova?
Neutron star or black hole
What is planetary differentiation?
When heavier materials sink and lighter ones rise inside a planet
What do astronomers call the point where nothing can escape a black hole?
The event horizon