Size

Mass: 3.303 x 10²³ kg (0.0553 Earths)
Radius (equatorial): 2 439 km
Mean density: 5.42 g cm^-3
Distance from Sun: 57 910 000 km
Rotational period: 58.6 days
Orbital period: 88 days
Escape velocity: 4.25 km s^-1
Apparent magnitude: -1.90
Surface temperature: 179°C (427deg;C, max. -173°C, min.)
Atmospheric composition: Helium (42%), sodium (42%), oxygen (15%). (Mercury really doesn't have a permanent atmosphere)
Number of satellites: None