Solar System - Definition, Examples, Facts & Quiz, FAQ, Trivia

In 2006, astronomers created a new definition for what counts as a planet. For an object to be a planet, it must:
1. Orbit the Sun
2. Be round due to its own gravity
3. Have "cleared the neighborhood" around its orbit

Pluto meets the first two requirements but not the third because it shares its orbit with many other objects in the Kuiper Belt. So it was reclassified as a dwarf planet.

Scientists are actively searching for signs of life in our Solar System and beyond. While we haven't found life yet, some places show promise:

• Mars: Had water in the past and has ice today
• Europa (Jupiter's moon): Has a subsurface ocean beneath its icy crust
• Enceladus (Saturn's moon): Has geysers spraying water into space

These environments might support microbial life. Beyond our Solar System, thousands of planets orbit other stars, some in the "habitable zone" where liquid water could exist.

Our Solar System formed about 4.6 billion years ago from a giant, rotating cloud of gas and dust called the solar nebula. As the cloud collapsed due to gravity:

1. Most material collected in the center to form the Sun
2. The remaining material formed a disk around the young Sun
3. Dust particles in the disk collided and stuck together, forming larger bodies
4. Near the Sun, only rocky material could withstand the heat, forming terrestrial planets
5. Farther out, cooler temperatures allowed ices to form, leading to gas giants

The Kuiper Belt is a doughnut-shaped region beyond Neptune's orbit filled with icy bodies and dwarf planets. It's similar to the asteroid belt but much larger (20 times wider and 20-200 times more massive).

Important facts about the Kuiper Belt:
• It's home to dwarf planets like Pluto, Haumea, and Makemake
• Contains short-period comets that orbit the Sun in less than 200 years
• Extends from about 30 to 55 astronomical units from the Sun
• The New Horizons spacecraft visited Pluto and a Kuiper Belt object called Arrokoth