Random Planet
Discover random planets for sci fi writing, classroom fun, or game worlds. Generate multiple picks and filter results by letters when needed.
Random Planet
How this random planet generator works
Press Generate and you get a planet. There are eight, so the Number box tops out at eight.
Mercury. Venus. Earth. Mars. Jupiter. Saturn. Uranus. Neptune.
Eight is a very recent number, and it is the only count in geography whose exact date of adoption you can look up.
There were nine planets until 2006
On 24 August 2006, at the closing session of the International Astronomical Union's General Assembly in Prague, the members voted on a definition of the word planet.
A planet, they decided, is a celestial body that:
- is in orbit around the Sun,
- has enough mass that its own gravity has pulled it into a nearly round shape, and
- has cleared the neighbourhood around its orbit.
Pluto satisfies the first two. It fails the third. It shares its region of space with a great many other icy bodies and has never swept them up.
Pluto was reclassified as a dwarf planet, along with Eris, the object whose discovery had forced the question in the first place. Textbooks were reprinted. Posters were replaced. The solar system lost a planet without anything moving.
The one sentence that removed Pluto
The third clause is doing all the work, and it was not in the draft.
An earlier proposal defined a planet by roundness and orbit alone. Under that version the solar system would have gained planets rather than lost one, and Ceres, the largest object in the asteroid belt, would have been readmitted.
The assembly added the neighbourhood-clearing requirement on the day of the vote. Pluto went out. Ceres stayed out.
Note what the clause actually measures. Not size, not composition, not roundness, not whether anybody has landed on it. It measures how lonely an object is. A planet is a body that has won its orbit.
By that standard, Earth is a planet because nothing else of consequence shares our lane. Not because we are large. Pluto is not a planet because its lane is crowded.
And in 1851 there were twenty-three
Everybody remembers 2006. Almost nobody remembers that the same thing happened before, more slowly and on a larger scale.
By 1851 the solar system had twenty-three planets: the eight we still recognise, plus fifteen bodies between Mars and Jupiter.
Astronomers had been finding them for fifty years. They had names, and symbols, and they were printed in the textbooks of the day exactly as Neptune was. Then hundreds more turned up, and it became obvious that what lay between Mars and Jupiter was not a series of small planets but a belt of rubble.
The word for the rubble, asteroid, was chosen by William Herschel in 1802, from a coinage by the Greek scholar Charles Burney. By the 1860s the distinction between planets and asteroids was settled.
Fifteen planets were quietly deleted, and nobody wrote an angry newspaper column about it, because the newspapers had not noticed they were there.
Ceres was a planet for fifty years
The first of them was found on the first day of the nineteenth century.
On 1 January 1801, Giuseppe Piazzi, at the observatory in Palermo, was correcting star positions when he noticed that one of his stars moved from night to night. He followed it until February, and then lost it.
Piazzi's object was announced as a new planet. It was called Ceres, and it filled a gap between Mars and Jupiter that astronomers had been expecting for decades.
Within four years, Pallas and Juno had been found in the same region. Vesta followed in 1807. Then hundreds more.
Ceres was demoted from planet to asteroid, then in 2006 promoted from asteroid to dwarf planet. It is the only dwarf planet inside Neptune's orbit, and the only one in the asteroid belt. It has been reclassified more times than any other object in the solar system.
Nobody marched for Ceres.
Nothing about Pluto changed
It is worth being clear about what the 2006 vote did and did not do.
Pluto is exactly where it was. Exactly as large. Exactly as cold. It still has Charon, a moon nearly half its own size, sharing its orbit. The New Horizons spacecraft flew past it in 2015 and photographed a world with mountains of water ice and a heart-shaped plain of frozen nitrogen.
What changed is the word. A category is a decision people make about how to sort things, and it can be remade when the things turn out to be arranged differently than anyone thought.
So there are eight planets. Not because the solar system contains eight important objects, but because eight of them have won their orbits, and in 2006 enough astronomers in one room agreed that winning your orbit is what the word should mean.
There are five recognised dwarf planets: Ceres, Pluto, Eris, Haumea and Makemake. There are almost certainly more.
Ways people actually use this
- Random assignment. Eight buckets, evenly weighted, which is fine as long as nobody mentions Jupiter.
- Teaching. Ask a class how many planets there are. Then ask how many there were in 1851.
- Quizzes. Show the planet, ask the order from the Sun. Show Uranus and Neptune and watch people hesitate.
- Settling arguments. Pluto is a dwarf planet. This is not a matter of opinion, but it remains a matter of feeling.
Getting more out of the filters
- With eight entries the filters are a toy, but a useful one. Contains the letter r and only Venus and Neptune escape.
- Starts with M gives you Mercury and Mars, the two rocky ones people confuse.
- Ends with s gives you Venus, Mars and Uranus.
- Set Number to eight and you have the entire solar system, or at least the part of it that has won its orbit.
Questions people ask
How many planets are there?
Eight, since 24 August 2006. Nine before that, and twenty-three in 1851.
Why is Pluto not a planet?
Because it has not cleared the neighbourhood around its orbit, which is the third condition in the definition the International Astronomical Union adopted in 2006. It meets the other two.
Was Ceres ever a planet?
Yes. It was discovered on 1 January 1801 by Giuseppe Piazzi and announced as a planet. It was reclassified as an asteroid once hundreds of similar bodies were found nearby, and reclassified again in 2006 as a dwarf planet.
What is a dwarf planet?
A body that orbits the Sun and is round under its own gravity, but has not cleared its orbital neighbourhood. Five are recognised: Ceres, Pluto, Eris, Haumea and Makemake.
Could the number change again?
It has changed twice already. Definitions follow discoveries, and there is a great deal of the outer solar system that nobody has looked at closely.
References
Skanda Aryal is a full stack engineer focused on accessible web experiences, with personal interests in time zones, travel, hiking, and geography. His enjoys playing with utilities tied to movement, schedules, places, and time based coordination. At Eon Tools, he reviews geography, transportation, times now, and date and time tools.