Mercury is the smallest planet and the closest to the Sun, an airless, cratered world of iron and rock that swings between scorching days and freezing nights.
At a glance
| radius | 2,440 km (0.383 × Earth) |
|---|---|
| distance from the Sun | 0.387 AU (57.9 million km) |
| sunlight takes | 3.22 minutes |
| one orbit | 88 days |
| orbit eccentricity | 0.21 |
| reflects | 14% of the sunlight it gets |
Read off the piece’s own catalogue, the same values it draws with.
About Mercury
Mercury looks at first glance like the Moon: grey, battered by impacts, with no air to speak of and no weather to wear its craters down. Underneath it is very different. An unusually large iron core fills most of its interior, which is why such a small planet is so dense, and it still generates a weak magnetic field. Without an atmosphere to hold heat, the sunlit side bakes while the night side cools far below freezing.
Even so close to the Sun, Mercury keeps ice. Radar from Earth and the MESSENGER spacecraft, which orbited the planet, found it in craters near the poles whose floors never see sunlight. Mercury also played a part in physics: the slow turning of its elongated orbit could not be fully explained by Newton’s gravity, and Einstein’s general relativity accounted for the difference exactly.
From Earth it is never far from the Sun in the sky, so it shows itself only low in the twilight, just after sunset or before sunrise. Its orbit is the most elongated of all the planets, carrying it noticeably closer to the Sun at one end than the other.
What you see in the piece
Mercury is drawn with its real surface map and lit only by sunlight, so its night side is truly dark. At the true scale of the Solar System it is a speck beside the Sun, and from any other star it cannot be seen at all.
Questions
How long is a year on Mercury?
Mercury goes round the Sun once every 88 days, the shortest year of any planet.
Does Mercury have an atmosphere?
Not in any real sense. Mercury has only a trace of gas around it, far too thin to hold heat or stop meteorites, so its surface is cratered and its temperatures swing wildly between day and night.