http://www.c3.lanl.gov/~cjhamil/SolarSystem/mercury.html (Einblicke ins Internet, 10/1995)
Mercury
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 inner most 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/cm^3 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).
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%
Animations of Mercury
Mercury
(GIF, 488K)
This photomosaic of Mercury was constructed from photos taken by
Mariner 10 six hours after the
spacecraft flew past the planet on March 29, 1974.
The north pole is at the
top and the equator extends from left to right about two-thirds
down from the top. A large circular basin, about 1,300
kilometers (800 miles) in diameter, is emerging from the day-
night terminator at left center. Bright rayed craters are
prominent in this view of Mercury. One such ray seems to join in
both east-west and north-south directions.
(Courtesy NASA/JPL)
Hills of Mercury
(GIF, 491K)
"Weird terrain" best describes this hilly, lineated region of Mercury.
This area is at the antipodal point
from the large Caloris basin. The shock wave produced by
the Caloris impact was reflected and focused to this antipodal point,
thus jumbling the crust and breaking it into a series of complex blocks.
The area covered is about 100 km (62 mi) on a side.
(Courtesy NASA/JPL)
Southwest Mercury
(GIF, 133K)
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.
(Courtesy NASA/JPL)
Mercury Close Up
(GIF, 137K)
Mercury's surface is similar to that of Earth's
Moon, where a history
of heavy cratering is followed by volcanic filling. The small, bright
halo crater in the center is 10 km (6 mi) in diameter, while the prominent
crater farther left has a central peak
30 km (19 mi) across. The darker,
lightly cratered area (upper left) may be an ancient lava flow.
(Courtesy NASA/JPL)
Caloris Basin
(JPG, 102K)
This mosaic shows the Caloris Basin (located half-way in shadow on
the terminator). Caloris is Latin for heat and the basin
is named this because it is near the subsolar point (the point closest
to the sun) when Mercury is at aphelion.
(Courtesy NASA/JPL)
Large Faults on Mercury
(GIF, 525K;
JPG, 105K)
This Mariner 10 image shows Santa Maria
Rupes, the sinuous dark feature
running through the crater at the center of this image. Many such features
were discovered in the Mariner images of Mercury and are interpreted to be
enormous thrust faults where part of the mercurian crust was pushed slightly
over an adjacent part by compressional forces. The abundance and length of
the thrust faults indicate that the radius of Mercury decreased by 1-2 km
after the solidification and impact cratering of the surface. This volume
change probably was due to the cooling of the planet, following the
formation of a metallic core three-fourths the size of the planet.
Discovery Quadrangle
(JPG, 68K)
Mosaic of the Discovery quadrangle of Mercury.
(Courtesy NASA/JPL)
Return to the Sun
Voyage to Venus
