Unit 15: The Solar System
The Sun, the eight planets, and the debris left over from their formation, all moving under the same law of gravity.
6 topics · 18 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
The Sun: Structure and Energy Source
- How it worksHow does nuclear fusion in the Sun's core convert hydrogen into helium and release the energy that reaches Earth?
- How it worksWalk me through energy traveling from the Sun's fusing core out through the radiative and convective zones to the surface.
- Common mistakeWhy isn't the Sun on fire the way a burning log is?
Your turn1 of 2
The Sun converts about 4 million metric tons of mass into energy every second through nuclear fusion, following Einstein's E equals mc squared. Over 87 seconds, about how many million metric tons of mass does the Sun convert into energy?The Inner Rocky Planets
- How it worksHow did the young Sun's heat blow away light gases nearby, leaving only heavier rock and metal to build the inner planets?
- Going furtherWhat happens to a planet's surface temperature when a thick atmosphere like Venus's traps heat through a runaway greenhouse effect?
- Ties togetherHow does each inner planet's distance from the Sun explain its wildly different surface temperature?
Your turn1 of 2
The intensity of sunlight reaching a planet falls off with the square of its distance from the Sun. Mercury orbits at about 0.4 AU and Mars orbits at about 1.539 AU. About how many times more intense is sunlight at Mercury than at Mars, using 1 over distance squared?The Outer Gas and Ice Giants
- How it worksHow did the cold temperatures of the outer solar system let these planets hold onto gases the inner planets lost?
- Going furtherWhat happens to the ring systems and moon counts of the outer planets compared to the four small inner planets?
- Ties togetherHow does the difference between a gas giant and an ice giant come down to which compounds were common at that distance from the Sun?
Your turn1 of 2
Jupiter and Saturn are made mostly of hydrogen and helium gas, while Uranus and Neptune are built mostly around frozen water, ammonia, and methane. Why are Jupiter and Saturn made mostly of gas while Uranus and Neptune are made mostly of icy compounds?How the Solar System Formed
- How it worksHow does a spinning, collapsing cloud of gas and dust flatten into a disk that goes on to build planets?
- How it worksWalk me through dust grains colliding and sticking together until they build up into full-sized planets.
- Ties togetherHow does the solar nebula's flattened disk shape explain why the planets all orbit in nearly the same plane?
Your turn1 of 2
Nearly every planet in the solar system orbits the Sun in almost the same flat plane and spins in the same general direction. How does a spinning, collapsing cloud of gas and dust flatten into a disk that goes on to build planets?Asteroids, Comets, and Meteors
- How it worksHow does solar radiation vaporizing a comet's ice and dust push material away into a tail that always points away from the Sun?
- Common mistakeWhy isn't a shooting star an actual star burning up in the atmosphere?
- Ties togetherHow does an asteroid belt made of leftover rocky debris differ from a comet made mostly of ice from the outer solar system?
Your turn1 of 2
A comet's glowing tail grows longer as it nears the Sun and shrinks away again as it heads back into the outer solar system. How does solar radiation vaporizing a comet's ice and dust push material away into a tail that always points away from the Sun?Kepler's Laws of Planetary Motion
- How it worksHow does Kepler's law of equal areas force a planet to speed up as its elliptical orbit brings it closer to the Sun?
- Worked exampleFind a planet's orbital period using Kepler's third law if its average distance from the Sun is 4 AU.
- Common mistakeWhy isn't a planet's orbit a perfect circle with the Sun sitting exactly at the center?
Your turn1 of 2
Using Kepler's third law, a planet's orbital period in years squared equals its average distance from the Sun in astronomical units cubed. If a planet orbits at an average distance of 8 AU, about how many years does one orbit take?