Venus is hotter than Mercury, even though Mercury is closer to the Sun. That one fact trips up a surprising number of quiz teams, and it is a good way into the whole solar system, because nearly every planet has a detail like it. The order is Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. What follows is a walk outward from the Sun, one thing to remember per stop, with the reference numbers at the end. For more space questions, see our science trivia.
Walking outward from the Sun
Mercury. The smallest planet and the fastest: a year here lasts only 88 days. It has no moons and almost no atmosphere to hold heat, so it is not the hottest planet despite its position.
Venus. Its thick carbon dioxide atmosphere traps heat, pushing the surface to around 465°C. It also spins backward compared with most planets, so the Sun rises in the west, and a single day on Venus is longer than its year.
Earth. The largest of the four rocky planets, with one moon and a year of 365.25 days. The distance from here to the Sun, about 150 million km, is the unit astronomers call 1 AU.
Mars. Roughly half of Earth’s diameter, with two small moons and a year of 687 days.
The asteroid belt. Between Mars and Jupiter. It is the natural dividing line: four small rocky planets inside it, four giants outside.
Jupiter. About 11 times Earth’s diameter and more massive than all the other planets put together. It has at least 95 known moons, which makes it the runner-up in the moon count.
Saturn. Saturn holds the moon record: 274 confirmed as of 2025, after astronomers confirmed 128 new ones that year. Its rings are the brightest, but not unique, since Jupiter, Uranus and Neptune have faint rings too. Saturn is also so light for its size that it is less dense than water, a favorite tiebreaker fact.
Uranus. It rolls around the Sun on its side, its axis tilted about 98 degrees. A year here is 84 Earth years.
Neptune. The farthest planet, 30 AU out, with a 165-year orbit and 16 known moons.
The numbers in one place
| # | Planet | Type | Diameter | Average distance from Sun | Year | Known moons (as of 2025) |
|---|---|---|---|---|---|---|
| 1 | Mercury | Rocky | 4,879 km | 0.39 AU | 88 days | 0 |
| 2 | Venus | Rocky | 12,104 km | 0.72 AU | 225 days | 0 |
| 3 | Earth | Rocky | 12,756 km | 1 AU | 365.25 days | 1 |
| 4 | Mars | Rocky | 6,792 km | 1.52 AU | 687 days | 2 |
| 5 | Jupiter | Gas giant | 142,984 km | 5.2 AU | 11.9 years | 95+ |
| 6 | Saturn | Gas giant | 120,536 km | 9.5 AU | 29.5 years | 274 |
| 7 | Uranus | Ice giant | 51,118 km | 19.2 AU | 84 years | 28+ |
| 8 | Neptune | Ice giant | 49,528 km | 30.1 AU | 165 years | 16 |
Moon counts change as telescopes confirm new ones; “+” means more are known or awaiting confirmation. Figures follow NASA’s planetary fact sheets.
A sentence to hold the order
The most widely taught one is “My Very Educated Mother Just Served Us Nachos.” Each first letter is a planet, in order.
Why there are eight, not nine
In 2006 the International Astronomical Union gave “planet” its first formal definition: a body that orbits the Sun, is round under its own gravity, and has cleared its orbit of other objects. Pluto meets the first two, but it shares its orbit with many other icy bodies in the Kuiper Belt, so it became a dwarf planet, alongside Ceres and Eris. It is not even the farthest object in the solar system; many dwarf planets and comets orbit farther out.