Some students see a resemblance between this corona and Miss Piggy of the Muppets her left ear, at the top of the picture, is the pancake volcano in the upper center of the image. Figure 4. Ridges and Cracks: This region of the Lakshmi Plains on Venus has been fractured by tectonic forces to produce a cross-hatched grid of cracks and ridges.
Be sure to notice the fainter linear features that run perpendicular to the brighter ones. As this is a radar image, the brightness of the ridges indicates their relative height.
This image shows a region about 80 kilometers wide and 37 kilometers high. Lakshmi is a Hindu goddess of prosperity. Convection currents of molten material in the mantle of Venus push and stretch the crust. Such forces are called tectonic , and the geological features that result from these forces are called tectonic features.
In a few places, the crust has even torn apart to generate rift valleys. The circular features associated with coronae are tectonic ridges and cracks, and most of the mountains of Venus also owe their existence to tectonic forces. The Ishtar continent, which has the highest elevations on Venus, is the most dramatic product of these tectonic forces.
Both are the product of compression of the crust, and both are maintained by the continuing forces of mantle convection. The successful Venera landers of the s found themselves on an extraordinarily inhospitable planet, with a surface pressure of 90 bars and a temperature hot enough to melt lead and zinc.
Despite these unpleasant conditions, the spacecraft were able to photograph their surroundings and collect surface samples for chemical analysis before their instruments gave out. The diffuse sunlight striking the surface was tinted red by the clouds, and the illumination level was equivalent to a heavy overcast on Earth.
The probes found that the rock in the landing areas is igneous, primarily basalts. Examples of the Venera photographs are shown in Figure 5. Each picture shows a flat, desolate landscape with a variety of rocks, some of which may be ejecta from impacts. Other areas show flat, layered lava flows. There have been no further landings on Venus since the s. Figure 5. Surface of Venus: These views of the surface of Venus are from the Venera 13 spacecraft.
Everything is orange because the thick atmosphere of Venus absorbs the bluer colors of light. The horizon is visible in the upper corner of each image. Venus has been mapped by radar, especially with the Magellan spacecraft. The planet has been modified by widespread tectonics driven by mantle convection, forming complex patterns of ridges and cracks and building high continental regions such as Ishtar.
The surface is extraordinarily inhospitable, with pressure of 90 bars and temperature of K, but several Russian Venera landers investigated it successfully. Skip to main content. Earthlike Planets: Venus and Mars. Search for:. The Geology of Venus Learning Objectives By the end of this section, you will be able to: Describe the general features of the surface of Venus Explain what the study of craters on Venus tells us about the age of its surface Compare tectonic activity and volcanoes on Venus with those of Earth Explain why the surface of Venus is inhospitable to human life.
Key Concepts and Summary Venus has been mapped by radar, especially with the Magellan spacecraft. Licenses and Attributions. CC licensed content, Shared previously. The earliest observers had two names for it, the Morning Star and the Evening Star.
Telescopes showed only a brilliant white disk, thick clouds hiding all trace of the planet's surface. More recently radar mappers, landers and other spacecraft studies have lifted Venus's veil to science, but today it remains mysterious. Venus is almost a twin of Earth in terms of size, mass and composition. It's only slightly smaller, formed in the same neighborhood of the solar system, and has a large iron core and rocky silicate mantle.
Like Earth, its crust is largely basalt though in our case the basalt is almost all hidden by the ocean. The key to the geology of Venus seems to be its heat. Start with its thick, choking atmosphere of nearly pure carbon dioxide. Air pressure on Venus's surface is about 90 times Earth's, the same as it would be a full kilometer under the ocean. This greenhouse gas is so effective at trapping the sun's heat that the ground of Venus is literally hot as a furnace, reaching around degrees C or K at the equator, year round.
There is no water anywhere except a little high in the atmosphere. The bright clouds are composed of sulfuric acid. The crust of Venus appears to be almost entirely volcanic and basaltic.
Venus instead has large, bizarre fractured structures called coronae "crowns" and tesserae "mosaic chips". There is no large-scale motion of the crust, no plate tectonics. On Earth, plate tectonics is driven by surface cooling, which makes the plates denser than the soft layer of rock beneath them.
On Venus the surface cannot cool and the crust cannot overturn. This synthetic-aperture radar image shows a crater on the left, a small corona on the right, and the profusion of fractures and wrinkle ridges that cover all of Venus. Nevertheless, the presence of lava everywhere we look means that deep heat from Venus's mantle and core can melt rocks and cause that magma to erupt.
The eruptions appear random, unlike the organized lines and arcs of volcanoes on Earth. Is this all that ever happens? The way to answer that question is to study the geologic history of the planet in detail. The backbone of planetary dating is crater counts.
We have a good idea, from studying the other planets, of how old a surface is based on the number of craters it has. On Venus there are about craters, an unusually small number. The crater statistics tell us that although the planet is 4. A runaway greenhouse effect turned all surface water into vapor, which then leaked slowly into space. The present-day surface of volcanic rock is blasted by high temperatures and pressures. The ingredients are all there, or at least, they used to be.
By studying why our neighbor world went in such a different direction with regard to habitability, we could find out what could make other worlds right. Temperature, air pressure, and chemistry are much more congenial up high, in those thick, yellow clouds. The ancient Romans could easily see seven bright objects in the sky: the Sun, the Moon, and the five brightest planets Mercury, Venus, Mars, Jupiter, and Saturn. They named the objects after their most important gods. Venus, the third brightest object after the Sun and Moon, was named after the Roman goddess of love and beauty.
Persistent, dark streaks appear. Scientists are so far unable to explain why these streaks remain stubbornly intact, even amid hurricane-force winds.
They also have the odd habit of absorbing ultraviolet radiation. The most likely explanations focus on fine particles, ice crystals, or even a chemical compound called iron chloride. Although it's much less likely, another possibility considered by scientists who study astrobiology is that these streaks could be made up of microbial life, Venus-style.
These handy chemical cloaks would also absorb potentially damaging ultraviolet light and re-radiate it as visible light. There is much, it would seem, that she can teach us. Our nearness to Venus is a matter of perspective. The planet is nearly as big around as Earth — 7, miles 12, kilometers across, versus 7, miles 12, kilometers for Earth. From Earth, Venus is the brightest object in the night sky after our own Moon.
The ancients, therefore, gave it great importance in their cultures, even thinking it was two objects: a morning star and an evening star.
At its nearest to Earth, Venus is some 38 million miles about 61 million kilometers distant. One more trick of perspective: how Venus looks through binoculars or a telescope.
The complete cycle, however, new to full, takes days, while our Moon takes just a month. And it was this perspective, the phases of Venus first observed by Galileo through his telescope, that provided the key scientific proof for the Copernican heliocentric nature of the Solar System.
Spending a day on Venus would be quite a disorienting experience — that is, if your ship or suit could protect you from temperatures in the range of degrees Fahrenheit Celsius. For another, because of the planet's extremely slow rotation, sunrise to sunset would take Earth days.
And by the way, the Sun would rise in the west and set in the east, because Venus spins backward compared to Earth. In winter, the tilt means the rays are less direct. No such luck on Venus: Its very slight tilt is only three degrees, which is too little to produce noticeable seasons. A critical question for scientists who search for life among the stars: How do habitable planets get their start? The close similarities of early Venus and Earth, and their very different fates, provide a kind of test case for scientists who study planet formation.
Similar size, similar interior structure, both harboring oceans in their younger days. Yet one is now an inferno, while the other is the only known world — so far — to play host to abundant life.
The factors that set these planets on almost opposite paths began, most likely, in the swirling disk of gas and dust from which they were born. Somehow, 4.
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