The innermost planet: cratered, with a huge iron core, almost no atmosphere and extreme swings between day and night.
Mercury is roughly two fifths as wide as Earth.
Mercury orbits on average about two fifths as far from the Sun as Earth does.
Mercury takes about 88 Earth days to go once round the Sun. That is about a whole season.
Mercury turns round once in about 59 Earth days; Earth takes about 24 hours. That is about two months.
On Mercury, sunrise comes round again every 6 months.
Mercury has roughly one eighteenth the mass of Earth.
Mercury has roughly one eighteenth the volume of Earth.
On Mercury you would weigh roughly two fifths of what you weigh on Earth.
Mercury runs from −173 to 427 °C. Earth runs from −89.2 to 56.7 °C.
Sidereal rotation: 58.65 days. Solar day (sunrise to sunrise): 175.9 days — the fast 87.97-day orbit means Mercury has to turn further to “catch up with” the Sun again.
| Across | 4,879 km |
|---|---|
| Distance from the Sun | 0.3871 AU on average, from 0.3075 to 0.4667 AU · sunlight takes 3 minutes 13 seconds at its average distance |
| Once round its orbit | 87.97 days |
| Sunrise to sunrise | 175.9 days |
| How big it looks | 4.5 to 13 arcseconds, depending on how far away it is — the full Moon is about 1,800 |
| Temperature | 167 °C (from −173 to 427) |
| Also found there | water |
Show Mercury in the model
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