Venus: The Surface

Facts in Brief

Mass	4.87 x 10²⁴ kg
Diameter	12,100 km
Density	5,250 kg/m³
Mean Surface Temperature	482^oC
Surface Gravity	8.87 m/s²
Orbital Eccentricity	0.0068
Surface Pressure	96 bars
Magnetic Field	None

The sixth largest planet in the solar system, Venus has a solid core and a very dense atmosphere. Nicknamed Earth's sister planet, Venus shares many similar characteristics with Earth in terms of mass, size, density, and volume. Furthermore, both planets are believed to have been formed out of the same nebula around the same time. Venus's mass is 4.87 x 10^24 kg with an approximate diameter of 12,100 km, achieving a density of 5,250 kg/m^3 Appropriately, the surface gravity of 8.87 m/s^2 is also very close to that of Earth's 9.80 m/s^2. The planet's iron core is about 6,000 km in diameter, but the majority is molten rocky mantle. Surface material resembles that of granite and is chemically separated by volcanic activity.
The Jewel of the Sky shines very brightly because of its well-known runaway greenhouse effect. This phenomenon is nearly identical to that of Earth's, only on a larger scale. Sunlight penetrates the atmosphere and heats the surface. When the heat is absorbed, however, dense clouds prevent it from escaping, trapping the heat and keeping the surface temperature at a scorching 482 degrees Celsius.

Underneath that unescapable cloud layer, the planet is a large rolling plain with two highland areas the size of Earth continents. The two are named Ishtar Terra and Aphrodite Terra, after a Babylonian and Greek goddess, respectively. The latter wraps more than half way around the equatorial region. The oldest terrains measured are about 800 million years old. As a side note, Maxwell Montes on Ishtar Terra is the planet's highest peak, and iron pyrite, otherwise known as fool's gold, most likely exists in the highlands.
The US probe Magellan (See Missions to Venus.) uncovered much of the terrain, finding huge active volcanoes, large solidified lava flows, and a vast number of meteorite craters. These craters extend from less than 2 km to over 160 km across. These ridges, canyons, craters, and volcanoes allow astronomers to speculate on possible tectonic activity on the planet. Angular rocks present on the surface also point to geologic activity. In fact, over 85 percent of the planetary surface is volcanic rock. There are also over 100,000 small shield volcanoes among the hundreds of larger ones. The largest volcanic cone has a base of over 700 km across. As noted earlier, these volcanoes produce channels that extend for hundreds of kilometers, including one that is 7,000 km long! Calderas are abundent, many over 100 km in diameter.

Three special features are worth noting. Coronae are large circular to ovular features. Like craters, coronae are somewhat dome-shaped, although it may be lower or higher than the surrounding terrain. The circumference of coronae are usually marked by troughs and long chains of mountains or hills. The average diameter of a corona is 250 km, the center of which shows evidence of volcanic activity. Over 360 of these coronae have been identified on the planetary surface. Arachnoids are similar to coronae and also vary from circular to ovular. They feature a central dome or depression. Arachnoid are, on average, 115 km across. At least 259 have been detected. In contrast, over 50 novas have been found. Novas are possibly early coronae with diameters of approximately 190 km.

Copyright © 2000 by Gary Chan and Matthew McDermott. All rights reserved.