The Solar System

17 articles

The Sun, eight planets, moons, asteroids and comets moving together in a system 4.6 billion years old.

Comets: origin, structure and fate

Barely heated or altered in 4.6 billion years, comets are the closest thing we have to the raw material the planets were built from — and Rosetta's in-situ data revised a good deal of what was believed about them.

3 min read2

The Solar System

How the Solar System was born

It all began with a collapsing cloud of gas and dust 4.57 billion years ago. The hardest question is not how planets formed, but why the Sun holds 99.86% of the mass yet only 1% of the angular momentum.

6 min read2

The Solar System

The eight planets of the Solar System

The Solar System has eight planets — a number settled only in 2006, when the IAU set three criteria and Pluto failed the third.

6 min read0

The Solar System

Why planets spin on their axes

Nothing set the planets spinning by hand. Their rotation is the sum of billions of off-centre impacts in the protoplanetary disk — and sometimes one collision was enough to flip everything over.

4 min read1

The Solar System

The Sun: the reactor that holds a system together

The Sun holds 99.86% of the Solar System's mass and fuses 600 million tonnes of hydrogen every second. All light, weather and life on Earth trace back to it.

3 min read5

The Solar System

Kepler's three laws: the rules planets move by

Orbits are ellipses, not circles; planets move faster when near and slower when far; and one formula ties period to distance for everything orbiting the Sun.

6 min read1

The Solar System

Why Pluto is no longer a planet

Pluto lost nothing — the definition changed. It began with the 2005 discovery of Eris, more massive than Pluto, forcing astronomers to choose between many more planets or one fewer.

5 min read0

The Solar System

Jupiter: the fastest-spinning planet and its invisible brake

Eleven times wider than Earth, yet it turns once every 9 hours 55 minutes. Why Jupiter spins so fast — and what slowed it down.

4 min read0

The Solar System

Mercury: a rock baked and frozen at once

The smallest planet and the closest to the Sun, where a day outlasts a year and the day-night temperature gap reaches 600°C.

1 min read2

The Solar System

Magnetism and gravity: two invisible forces, two mechanisms

Both act at a distance, both propagate as fields, both weaken with range. But one arises from mass and the other only from moving charge — and that difference decides whether a planet keeps its atmosphere.

3 min read1

The Solar System

Venus: a lesson in runaway greenhouse

Earth's twin in size, yet 464°C at the surface under 92 times our pressure - Venus shows how far a climate can slide.

2 min read0

The Solar System

Earth: the only living world we know

Liquid water, an oxygen-rich atmosphere, a protective magnetosphere and plate tectonics - four rare conditions on one world.

1 min read4