Caloris Basin Floor
Back to: Mercury
This image is
a high resolution view of the Caloris Basin shown in the previous
image. It shows ridges and fractures that increase in size towards
the center of the basin (upper left). (Credit: Calvin J. Hamilton,
and NASA; FDS 126)
Mercury was named by the Romans after the messenger of the gods
because it seemed to move more quickly than any other planet.
Mercury is the innermost planet in our solar system and is the
second smallest one. Pluto is the smallest. Both Saturn and Jupiter
have moons that are larger than Mercury, such as Titan and Ganymede.
Jupiter's moons Io, Europa, and Callisto are very close in size
to Mercury.
Mercury resembles our moon with lunar-like terrain but differs
with respect to its density. Mercury has a density of 5.43 gm/cm3
which is similar to the density of the Earth. This density indicates
that its core has an iron composition like the Earth. The core
probably takes up about 70% to 80% of the planet's radius with
the outer region largely composed of silicate rocks.
Mercury has almost no atmosphere. The atmosphere on Earth helps
keep a uniform temperature from day to night. On Mercury, due
to its closeness to the Sun, the temperature rises to over 400°
C (750° F) during the day. At night, because of the lack of
atmosphere to help retain heat, the temperature drops to -180°
C (-300°F).
Mercury Statistics:
Mass (kg) 3.303e+23
Mass (Earth = 1) 5.5271e-02
Equatorial radius (km) 2,439.7
Equatorial radius (Earth = 1) 3.8252e-01
Mean density (gm/cm^3) 5.42
Mean distance from the Sun (km) 57,910,000
Mean distance from the Sun (Earth = 1) 0.3871
Rotational period (days) 58.6462
Orbital period (days) 87.969
Mean orbital velocity (km/sec) 47.88
Orbital eccentricity 0.2056
Tilt of axis 0.00°
Orbital inclination 7.004°
Equatorial surface gravity (m/sec^2) 2.78
Equatorial escape velocity (km/sec) 4.25
Visual geometric albedo 0.10
Magnitude (Vo) -1.9
Mean surface temperature 179°C
Maximum surface temperature 427°C
Minimum surface temperature -173°C
Atmospheric composition
Helium 42%
Sodium 42%
Oxygen 15%
Other 1%