Start here · Essential guide
A Tour of the Solar System
A plain walk from the Sun through the rocky planets, gas and ice giants, moons, asteroids and comets, and how all these worlds fit together as one system.
Space and Science
The Solar System
Planets, moons, comets and the Sun explained for curious readers.
Comets and Asteroids: Leftovers from the Early Solar System
How comets and asteroids differ in makeup, orbit and origin, where each family lives, and why scientists study these preserved remnants of planet building.
How the Moon Formed and Why It Matters to Earth
The leading ideas for how the Moon formed, especially the giant impact hypothesis, and how it shapes ocean tides, day length and the stability of Earth's tilt.
How the Sun Makes Its Energy
Inside the Sun's core, hydrogen fuses into helium and releases energy. See how that energy travels outward and reaches Earth as sunlight about eight minutes later.
Icy Moons and the Hunt for Hidden Oceans
Why several moons of Jupiter, Saturn and beyond may hold liquid water under their ice, what evidence points to it, and why scientists find these oceans so interesting.
Jupiter and Saturn: Life Inside the Gas Giants
What Jupiter and Saturn are made of, how their storms, rings and many moons work, and why life as we know it is very unlikely to exist inside gas giants.
Mars Then and Now: Climate Clues from the Red Planet
Evidence that Mars was once wetter, how its atmosphere thinned over billions of years, and what rovers and orbiters have learned about its climate history.
Why Pluto Is Called a Dwarf Planet
What the 2006 definition of a planet says, why Pluto fell into the new dwarf planet category, and what spacecraft have since revealed about this distant world.
Why Venus Is the Hottest Planet
Why Venus is hotter than even Mercury: its thick carbon dioxide atmosphere traps heat, and a runaway greenhouse effect may have dried out a once wetter world.
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