SPACE, EXPLAINED SIMPLY
Our cosmic home: the Sun, planets, moons, asteroids and comets.
01
At the centre of the Solar System is the Sun, orbited by eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. The system also includes hundreds of moons, dwarf planets, asteroids, comets, and many smaller bodies.
The Sun’s gravity keeps these objects in orbit. The Solar System extends far beyond Neptune, into distant regions of icy objects that can sometimes send comets inward.
02
In 2006, the International Astronomical Union adopted a definition of a planet. A planet must orbit the Sun, be nearly round through its own gravity, and have cleared its orbital neighbourhood of other large objects.
Pluto meets the first two criteria but shares its region with many Kuiper Belt objects, so it is classified as a dwarf planet. That does not make it uninteresting: New Horizons revealed a complex and varied world.
03
Spacecraft return images and measurements of magnetic fields, atmospheres, surfaces, and composition. Some missions return samples to Earth, while telescopes study planets and small bodies from afar.
NASA has sent missions to every planet and to asteroids, comets, and other small worlds. The most reliable picture emerges when different instruments and measurements agree.