202 These creases formed from wrinkling caused when Mercury cooled and shrank.
203 The Surface of Mercury Very similar to Earth’s moon: Heavily battered with craters, including some large basins.Largest basin: Caloris BasinTerrain on the opposite side jumbled by seismic waves from the impact.
204 Curved cliffs, probably formed when Mercury shrank while cooling down Lobate ScarpsCurved cliffs, probably formed when Mercury shrank while cooling down
205 The Plains of Mercury No large maria, but intercrater plains: Marked by smaller craters (< 15 km) and secondary impactsSmooth plains:Even younger than intercrater plains
225 Mercury’s temperature range is the greatest of any planet.
226 Its daytime temperature can reach 700o Fahrenheit.
227 And its nighttime temperature can reach -100o Fahrenheit.
228 All planets without atmospheres get very cold at night. 700o F-100o FAll planets without atmospheres get very cold at night.
229 But because Mercury is so close to the Sun… 700o F-100o FBut because Mercury is so close to the Sun…
230 …its daytime temperatures exceed those of all other planets.
231 So Mercury ranges nearly 800o F between daytime and nighttime. +700o F – (-100o) = 800o F700o F-100o FSo Mercury ranges nearly 800o F between daytime and nighttime.
232 Mercury Mercury Statistics Mass (kg) 3.303e+23 Mass (Earth = 1) e-02Equatorial radius (km) 2,439.7Equatorial radius (Earth = 1) e-01Mean density (gm/cm^3) 5.42Mean distance from the Sun (km) 57,910,000Mean distance from the Sun (Earth = 1)Rotational period (days)Orbital period (days)Mean orbital velocity (km/sec) 47.88Orbital eccentricityTilt of axis (degrees) 0.00Orbital inclination (degrees) 7.004Equatorial surface gravity (m/sec^2) 2.78Equatorial escape velocity (km/sec) 4.25Visual geometric albedo 0.10Magnitude (Vo) -1.9Mean surface temperature 179°CMaximum surface temperature 427°CMinimum surface temperature -173°CAtmospheric compositionHelium 42%Sodium 42%Oxygen 15%Other 1%The southwest quadrant of Mercury is seen in this image taken March 29, 1974, by the Mariner 10 spacecraft. The picture was taken four hours before the time of closest approach when Mariner was 198,000 km (122,760 mi) from the planet. The largest craters seen in this picture are about 100 km (62 mi) in diameter.Mercury has been visited by only one spacecraft, Mariner 10. It flew by three times in 1974 and Only 45% of the surface was mapped (and, unfortunately, it is too close to the Sun to be safely imaged by HST). A new discovery-class mission to Mercury, MESSENGER was launched by NASA in 2004 and will orbit Mercury starting in 2011 after several flybys.