PRAGUE, Czech Republic — The universe really is expanding — astronomers are proposing to rewrite the textbooks to say that our solar system has 12 planets rather than the nine memorized by generations ...

As the United States prepares to celebrate its 250th anniversary, the history of the solar system tells its own story of ...

When 'Oumuamua traversed our solar system in 2017 it was the first confirmed Interstellar Object (ISO) to do so. Then in 2019, Comet 2l/Borisov did the same thing. These are the only two confirmed ...

1. What is a planet? -- 2. Seven perfect planets made of aether -- 3. The Earth becomes a planet -- 4. Sixteen planets -- 5. Not everything that orbits the Sun is a planet -- 6. Uranus! -- 7. The ...

When I was a kid, there were nine planets. Now we know of thousands! But that includes exoplanets, alien worlds that orbit alien suns. Only eight planets call our solar system home. Or there might ...