Meet the small worlds of our solar system
Dwarf planets, asteroids, comets and meteors, explained in plain English with facts from NASA, ESA, JAXA and other space agencies.
- 45plain-English guides in five categories
- 150quiz questions, each with a source
- 5constellations to light up
Five ways into the small bodies
Nine guides in each.
Dwarf planets
What the IAU definition says, Pluto, Ceres, Eris, Haumea, Makemake, and what spacecraft have shown us up close.
9 guidesAsteroids and the asteroid belt
Types of asteroids, the main belt, Vesta, near-Earth asteroids, sample-return missions and planetary defense explained without alarm.
9 guidesComets
Comet anatomy and tails, the Kuiper Belt and Oort Cloud, famous comets, and how to see one with your eyes or binoculars.
9 guidesMeteors, meteorites and impacts
Meteors and meteor showers, meteorites you can hold, impact craters, and historic events such as Tunguska and Chelyabinsk.
9 guidesExploration and how we know
Missions, telescopes, how small bodies are found and named, how to read an orbit, and how anyone can take part in the science.
9 guidesStart with these six guides
What Is a Dwarf Planet? The IAU Definition Explained
The three tests behind the label, the extra rule about moons, and how dwarf planets compare with planets, asteroids and satellites.
Why Pluto Is a Dwarf Planet
Pluto is not too small to be a planet. It failed one specific test. Here is the 2006 vote, the rule behind it and the arguments that continue.
What Are Asteroids? Types, Sizes and Where They Live
A plain-language guide to asteroids, from the 530 km giant Vesta to rocks under 10 m, with the main compositional classes and the zones where they gather.
What Is a Comet? Anatomy of a Dirty Snowball
The parts of a comet, from the frozen nucleus to the coma and two tails, and how close-up visits changed the old snowball picture.
Meteor, Meteoroid or Meteorite? The Difference Explained
A plain guide to the three words, with the extra terms fireball, bolide and micrometeorite placed where they belong.
Spin the wheel
One question per spin, with an explanation and a source.
The wheel picks a topic, and you answer a multiple-choice question about it. There are no prizes and no bets, only facts. Try one spin here. On any guide, a full round of 6 spins opens the rest of the article and lights that guide's star on your Star map.
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How we write
Every guide comes from pages we opened and read, mostly from space agencies, observatories and museums. We say where a number comes from and when we checked it, because many values in this field change with new measurements.
- Sources are agency and research pages, not Wikipedia.
- Counts and rankings carry a date.
- No ads, no tracking scripts and no invented experts.
- Mistakes are fixed in public on the corrections page.
- The method is on the methodology page.