Mercury vs Moon: Two Look-Alike Cratered Worlds
In photos, Mercury and the Moon look almost the same: grey, airless and covered in craters. But Mercury is a planet, about 40% wider than the Moon, more than four times heavier, with a giant iron core that takes up most of its inside.
Mercury vs Moon: true size
Mercury vs Moon at a glance
| Mercury | Moon | |
|---|---|---|
| Diameter | 4,879 km | 3,475 km |
| Mass | About 5.5% of Earth | About 1.2% of Earth |
| Gravity | 3.7 m/s², about 38% of Earth’s | 1.6 m/s², about 17% of Earth’s |
| Core | Huge iron core, most of its width | Small core |
| Temperature | About 430 °C by day, −180 °C at night | About 120 °C by day, −130 °C at night |
| Orbits | The Sun, every 88 days | Earth, every 27.3 days |
| Magnetic field | Yes, a weak one | No |
Why they look alike
Both are small, rocky and have almost no atmosphere. With no air or weather to wear craters away, every impact over billions of years leaves its mark. Both were also shaped by ancient lava floods. That is why photos of the two can fool even space fans.
How they differ inside
Mercury is much denser. Its iron core makes up around 85% of its width, so it is more like a ball of metal with a thin rocky skin. The Moon is mostly rock with only a small core, and it is slightly lopsided, with thicker crust on its far side.
Quick facts
- Mercury is the smallest planet, but bigger than our Moon.
- Mercury has ice in deep craters at its poles that never see sunlight.
- Mercury’s gravity is almost the same as on Mars.
- The MESSENGER spacecraft orbited Mercury from 2011 to 2015.
- Jupiter’s moon Ganymede and Saturn’s moon Titan are both bigger than Mercury.
See them in 3D
Mercury vs Moon questions
Is Mercury bigger than the Moon?
Yes. Mercury is 4,879 km across against 3,475 km for the Moon, about 40% wider.
Why do Mercury and the Moon look so similar?
Both are airless, rocky and covered in craters, which have not been worn away by weather.
Which has stronger gravity?
Mercury, at about 38% of Earth’s gravity against about 17% on the Moon.
Does Mercury have a moon?
No. Mercury and Venus have no moons.
Is Mercury the hottest planet?
No. Venus is hotter, because its thick atmosphere traps heat.
More face-offs: see all 3D comparisons.
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