Planets are not unchanging rocks—they grow, evolve, and age. Their lifespan depends mainly on their host star. Planets start as tiny dust grains around young stars. These grains collide and stick, growing into rocky or gas giants. Astrophysicist Sean Raymond explains planets form through countless impacts, with gas giants gathering thick hydrogen and helium layers, while rocky planets like Earth face violent collisions. Planetary death is tricky to define. It could mean complete destruction, like being swallowed by their star or smashed to bits. Or, as planetary scientist Matthew Reinhold says, a planet can be "dead" if it loses its oceans, atmosphere, or tectonic activity. Earth’s life depends on the Sun. In about five billion years, the Sun will run out of hydrogen and turn into a red giant. This will boil away Earth’s oceans long before it swallows the planet. Earth’s total lifespan from birth to destruction is about 9.5 billion years. Most stars are smaller red dwarfs that burn slowly and live much longer. Planets around them can last far beyond Earth’s age. Reinhold’s models show that geological activity like plate tectonics, which controls climate, could last 30 to 90 billion years on such planets. This means many rocky planets may "die" internally long before their stars fade away.