Astronomy

Venus, the planet the jewel of the sky, was once know by ancient astronomers as the morning star and evening star. Early astronomers once thought Venus to be two separate bodies. Venus, which is named after the Roman goddess of love and beauty, is veiled by thick swirling cloud cover.

Astronomers refer to Venus as Earth’s sister planet. Both are similar in size, mass, density and volume. Both formed about the same time and condensed out of the same nebula. However, during the last few years scientists have found that the kinship ends here. Venus is very different from the Earth. It has no oceans and is surrounded by a heavy atmosphere composed mainly of carbon dioxide with virtually no water vapor. Its clouds are composed of sulfuric acid droplets. At the surface, the atmospheric pressure is 92 times that of the Earth’s at sea-level.

Venus is scorched with a surface temperature of about 482° C. This high temperature is primarily due to a runaway greenhouse effect caused by the heavy atmosphere of carbon dioxide. Sunlight passes through the atmosphere to heat the surface of the planet. Heat is radiated out, but is trapped by the dense atmosphere and not allowed to escape into space. This makes Venus hotter than Mercury.

A Venusian day is 243 Earth days and is longer than its year of 225 days. Oddly, Venus rotates from east to west. To an observer on Venus, the Sun would rise in the west and set in the east.

Until just recently, Venus’ dense cloud cover has prevented scientists from uncovering the geological nature of the surface. Developments in radar telescopes and radar imaging systems orbiting the planet have made it possible to see through the cloud deck to the surface below. Four of the most successful missions in revealing the Venusian surface are NASA’s Pioneer Venus mission (1978), the Soviet Union’s Venera 15 and 16 missions (1983-1984), and NASA’s Magellan radar mapping mission (1990-1994). As these spacecraft began mapping the planet a new picture of Venus emerged.

Venus’ surface is relatively young geologically speaking. It appears to have been completely resurfaced 300 to 500 million years ago. Scientists debate how and why this occurred. The Venusian topography consists of vast plains covered by lava flows and mountain or highland regions deformed by geological activity. Maxwell Montes in Ishtar Terra is the highest peak on Venus. The Aphrodite Terra highlands extend almost half way around the equator. Magellan images of highland regions above 2.5 kilometers are unusually bright, characteristic of moist soil. However, liquid water does not exist on the surface and cannot account for the bright highlands. One theory suggests that the bright material might be composed of metallic compounds. Studies have shown the material might be iron pyrite (also know as “fools gold”). It is unstable on the plains but would be stable in the highlands. The material could also be some type of exotic material which would give the same results but at lower concentrations.

Venus is scarred by numerous impact craters distributed randomly over its surface. Small craters less that 2 kilometers are almost non-existent due to the heavy Venusian atmosphere. The exception occurs when large meteorites shatter just before impact, creating crater clusters. Volcanoes and volcanic features are even more numerous. At least 85% of the Venusian surface is covered with volcanic rock. Hugh lava flows, extending for hundreds of kilometers, have flooded the lowlands creating vast plains. More than 100,000 small shield volcanoes dot the surface along with hundreds of large volcanoes. Flows from volcanoes have produced long sinuous channels extending for hundreds of kilometers, with one extending nearly 7,000 kilometers.

Giant calderas more than 100 kilometers in diameter are found on Venus. Terrestrial calderas are usually only several kilometers in diameter. Several features unique to Venus include coronae and arachnoids. Coronae are large circular to oval features, encircled with cliffs and are hundreds of kilometers across. They are thought to be the surface expression of mantle upwelling. Archnoids are circular to elongated features similar to coronae. They may have been caused by molten rock seeping into surface fractures and producing systems of radiating dikes and fractures.

Venus Statistics

Characteristic	Measurement
Mass (kg)	4.869e+24
Mass (Earth = 1)	0.81476
Equatorial radius (km)	6,051.8
Equatorial radius (Earth = 1)	0.9488
Mean density (gm/cm^3)	5.25
Mean distance from Sun (km)	108,200,000
Mean distance from the Sun (Earth = 1)	0.7233
Rotational period (days)	-243.0187
Orbital period (days)	224.701
Mean orbital velocity (km/sec)	35.02
Orbital eccentricity	0.0068
Tilt of axis	177.36°
Orbital inclination	3.394°
Equatorial surface gravity (m/sec^2)	8.87
Escape velocity (km/sec)	10.36
Visual geometric albedo	0.65
Magnitude (Vo)	-4.4
Mean surface temperature	482°C
Atmospheric pressure (bars)	92

Atmospheric Composition	Percent
Carbon Dioxide	96%
Nitrogen	3+%
Other	Less than 1%*

*Includes trace amounts of sulfur dioxide, water vapor, carbon monoxide, argon, helium, neon, hydrogen chloride, and hydrogen fluoride.

Views of Venus

Mariner 10 Image of Venus

This beautiful image of Venus is a mosaic of three images acquired by the Mariner 10 spacecraft on February 5, 1974. It shows the thick cloud coverage that prevents optical observation of the surface of Venus. Only through radar mapping is the surface revealed.

Galileo Image of Venus

On February 10, 1990 the Galileo spacecraft acquired this image of Venus. Only thick cloud cover can be seen.

Hubble Image of Venus

This is a Hubble Space Telescope ultraviolet-light image of the planet Venus, taken on January 24, 1995, when Venus was at a distance of 113.6 million kilometers from Earth. At ultraviolet wavelengths cloud patterns become distinctive. In particular, a horizontal “Y” shaped cloud feature is visible near the equator. The polar regions are bright, possibly showing a haze of small particles overlying the main clouds. The dark regions show the location of enhanced sulfur dioxide near the cloud tops. From previous missions, astronomers know that such features travel east to west along with the Venus’ prevailing winds, to make a complete circuit around the planet in four days.

Venus

This is a global view of the surface of Venus centered at 180 degrees East longitude. Simulated color is used to enhance small-scale structure.

Five Global Views of Venus

The surface of Venus is displayed in these five global views. The center image (A) is centered at Venus’ north pole. The other four images are centered around the equator of Venus at (B) 0 degrees longitude, (C) 90 degrees East longitude, (D) 180 degrees and (E) 270 degrees East longitude. The bright region near the center in the polar view is Maxwell Montes, the highest mountain range on Venus. Ovda Regio is centered in the (C) 90 degrees East longitude view. Atla Regio is seen prominently in the (D) 180 East longitude view.

Hemispheric View of Venus

This hemispheric view of Venus, as revealed by more than a decade of radar investigations culminating in the 1990-1994 Magellan mission, is centered at 0 degrees East longitude. The effective resolution of this image is about 3 kilometers. It was processed to improve contrast and to emphasize small features, and was color-coded to represent elevation.

Additional Hemispheric Views of Venus

• View centered at 90 degrees East longitude.
• View centered at 180 degrees East longitude.
• View centered at 90 degrees West longitude.
• View centered at the north pole.
• View centered at the south pole.

Venusian Map

This image is a Mercator projection of Venusian topography. Many of the different regions have been labeled. The map extends from -66.5 to 66.5 degrees in latitude and starts at 240 degrees longitude.

Venusian Topography

This image is a Mercator projection of Venusian topography The highland regions such as Ishtar Terra, Aphrodite Terra, Alpha Region and Beta Regio are shown in yellow and orange. The low-lying regions are shown in blue.

Cylindrical Map of Venus

Venus is displayed in this simple cylindrical map of the planet’s surface. The right and left edges of the image are at 240 degrees East longitude. The top and bottom of the image are at 90 degrees North latitude and 90 degrees South latitude, respectively. The bright region at the top, left of center, is Maxwell Montes, the highest mountain range on Venus. Aphrodite Terra, a large highland region, extends along the equator to the right of center. The scattered dark patches in this image are halos surrounding some of the younger impact craters. This global data set reveals a number of craters consistent with an average Venus surface age of 300 million to 500 million years.

Gula Mons and Crater Cunitz

A portion of Western Eistla Regio is displayed in this three dimensional perspective view of the surface of Venus. The viewpoint is located 1,310 kilometers southwest of Gula Mons at an elevation of 0.78 kilometers. The view is to the northeast with Gula Mons appearing on the horizon. Gula Mons, a 3 kilometer high volcano, is located at approximately 22 degrees North latitude, 359 degrees East longitude. The impact crater Cunitz, named for the astronomer and mathematician Maria Cunitz, is visible in the center of the image. The crater is 48.5 kilometers in diameter and is 215 kilometers from the viewer’s position.

Eistla Regio - Rift Valley

A portion of Western Eistla Regio is displayed in this three dimensional perspective view of the surface of Venus. The viewpoint is located 725 kilometers southeast of Gula Mons. A rift valley, shown in the foreground, extends to the base of Gula Mons, a 3 kilometer high volcano. This view is facing the northwest with Gula Mons appearing at the right on the horizon. Sif Mons, a volcano with a diameter of 300 kilometers and a height of 2 kilometers, appears to the left of Gula Mons in the background.

Eistla Regio

A portion of Western Eistla Regio is displayed in this three dimensional perspective view of the surface of Venus. The viewpoint is located 1,100 kilometers northeast of Gula Mons at an elevation of 7.5 kilometers. Lava flows extend for hundreds of kilometers across the fractured plains shown in the foreground, to the base of Gula Mons. This view faces the southwest with Gula Mons appearing at the left just below the horizon. Sif Mons appears to the right of Gula Mons. The distance between Sif Mons and Gula Mons is approximately 730 kilometers.

Lakshmi Planum

The southern scarp and basin province of western Ishtar Terra are portrayed in this three dimensional perspective view. Western Ishtar Terra is about the size of Australia and is a major focus of Magellan investigations. The highland terrain is centered on a 2.5 to 4 kilometers high plateau called Lakshmi Planum which can be seen in the distance at the right. Here the surface of the plateau drops precipitously into the bounding lowlands, with steep slopes that exceed 5% over 50 kilometers.

Alpha Regio

These images show the Alpha Regio. The bright lineated terrain is a series of troughs, ridges, and faults that are oriented in many directions. The lengths of these features generally range from 10 to 50 kilometers. The topographic elevation within Alpha Regio varies over a range of 4 kilometers. Local topographic lows, whose outlines are generally controlled by structures within the central region, are relatively radar-dark and filled with volcanic lavas. Source vents for this volcanism appear as bright spots within the smooth plains units.

Arachnoids

Arachnoids are one of the more remarkable features found on Venus. They are seen on radar-dark plains in these Magellan image mosaics of the Fortuna region. As the name suggests, arachnoids are circular to ovoid features with concentric rings and a complex network of fractures extending outward. The arachnoids range in size from approximately 50 to 230 kilometers in diameter. Arachnoids are similar in form but generally smaller than coronae (circular volcanic structures surrounded by a set of ridges and grooves as well as radial lines). One theory concerning their origin is that they are a precursor to coronae formation. The radar-bright lines extending for many kilometers might have resulted from an upwelling of magma from the interior of the planet which pushed up the surface to form “cracks.” Radar-bright lava flows are present in the 1st and 3rd image, also indicative of volcanic activity in this area. Some of the fractures cut across these flows, indicating that the flows occurred before the fractures appeared. Such relations between different structures provide good evidence for relative age dating of events. At present, arachnoids are found only on Venus and can now be more closely studied with the high-resolution (120 meter) radar imagery from Magellan.

Parallel Lines

Two groups of parallel features that intersect almost at right angles are visible. The regularity of this terrain caused scientists to nickname it graph paper terrain. The fainter lineations are spaced at intervals of about 1 kilometer and extend beyond the boundaries of the image. The brighter, more dominant lineations are less regular and often appear to begin and end where they intersect the fainter lineations. It is not yet clear whether the two sets of lineations represent faults or fractures, but in areas outside the image, the bright lineations are associated with pit craters and other volcanic features.

Surface Photographs from Venera 9 and 10

The Soviet Venera 9 and 10 spacecraft were launched on 8 and 14 June 1975, respectively, to do the unprecedented: place landers on the surface of Venus and return images. The two spacecraft successfully landed descent crafts on 16 and 23 October 1975. These images were obtained on 22 and 25 October 1975. Venera 9 landed on a slope inclined by about 30 degrees to the horizontal whereas Venera 10 was inclined about 8 degrees. The two spacecraft were separated by about 2,100 kilometers. Most of the rocks in the images are between about 0.3 and 1 meter.

Color Surface Photographs from Venera 13

On March 3, 1982, the Venera 13 lander touched down on the Venusian surface. It was the first Venera mission to include a color TV camera. This image is the left half of the Venera 13 photo.