Mercury

Mercury - Rotating Model
Credit: Almond/NASA

Mercury is the closest planet to the Sun. It is also the smallest planet in the Solar System and has the slowest rotation speed (or spin). Curiously, visitors to Mercury would find that its day is about twice as long as its year.

It is quite similar to the Moon, with lots of craters, but it has no moon of its own.

The name Mercury comes from the Roman god of travel, and was probably given because the planet appears to move the fastest across the night sky.

The first spacecraft to visit Mercury was Mariner 10 in 1973, and again in 1974, but it only mapped about half of the surface. More recently (January 2008) the Messenger spacecraft captured more of the rocky planet's surface during a close approach.

Planet Data Sheet show »

Facts and Figures	Mercury	Venus	Earth	Mars	Jupiter	Saturn	Uranus	Neptune
Orbital Distance (AU)¹	0.38	0.72	1.0	1.52	5.2	9.45	19.2	30.06
Radius (KM)	2,440	6,052	6,378	3,397	71,492	60,268	25,559	24,746
Mass (Earth Masses)²	0.055	0.82	1.0	0.11	318	95.2	14.5	17.1
Year Length (Earth Days)	88	225	365.25	687	11.9 Years	29.45 Years	84.0 Years	164.8 Years
Day Length (Earth Days)	176	117	1.0	1.03	0.41	0.43	0.75	0.67
Surface Gravity (g)³	0.38	0.91	1.0	0.38	2.34	0.93	0.92	1.12
Surface Temperature	-200 to 400 °C	460 °C	-80 to 50 °C	-150 to 20 °C	-110 °C	-140 °C	-190 °C	-200 °C
Number of moons	0	0	1	2	63	60	27	13

Notes: ¹ 1 AU (or Astronomical Unit) = 149,600,000 KM and is the mean distance from the Earth to the Sun
² 1 Earth Mass = 5,980,000,000,000,000,000,000,000 KG : ³ 1 g = 9.8 m/s²

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