by Leandra Xochitl Marshall, published on July 25, 2022
Venus. Photo credit: NASA.
Venus is a terrestrial planet and the second planet from the Sun, known as Earth’s “sister planet” due to its similar size, gravity, and bulk composition.
surface conditions
Toxic clouds that darken the surface of Venus. Photo credit: NASA.
Conditions on the surface of Venus are extreme due to the planet’s proximity to the sun, lack of water, and atmospheric composition. Venus originally had a small terrestrial ocean, but due to the immense heat, the ocean evaporated and the planet’s hydrogen (H2) was lost to space. Venus is now dry and covered in reflective clouds of sulfuric acid that obscure its surface. The temperature is approximately 450 degrees Celsius and the atmosphere is 90 standard atmospheres (atms) thick. Much of the planet’s atmosphere is made up of carbon dioxide (CO2). Probes sent to Venus don’t last long in such conditions. The surface of Venus was a mystery before NASA’s Project Magellan first mapped it in 1990 and 1991.
The Magellan spacecraft sent short-wavelength gravity measurements and radar images back to Earth. As a result, a great deal of work has been produced on crustal and tectonic processes on Venus, and much remains to be learned. The planet’s surface is different from Earth’s because the absence of water has reduced erosion. About 80% is covered by volcanic plains. 70% of these plains contain rough ridges, while 10% of the flows are lobed. Two continental highlands make up the rest of its surface. One mountain is in the planet’s northern hemisphere, while the other is just south of the equator. The northern continent is called Ishtar Terra. The southern continent is called Aphrodite Terra.
Volcanism is the most important geological phenomenon on Venus. Volcanic deposits cover most of the surface and occur in a variety of forms. Sulfur in the atmosphere can mean that eruptions have occurred recently. Some forms of Venusian volcanism have terrestrial analogs, while others do not. Not all volcanic activity on Venus is well understood.
Earth-style volcanism
Venus shares some similar planetary features with Earth. The planet has a basaltic crust 25 to 30 km thick. Its mantle is about 1300 degrees Celsius. Mantle convection is dynamic and produces plumes that cause uplift, rupture, and volcanism. However, apart from its unusual global resurfacing events, Venus does not have regular large-scale plate tectonics.
The composition of the surface of Venus is mainly basaltic. Satellite Aperture Radar (SAR) images show basaltic flows similar to those on Earth, as well as volcanic flows covering surface areas similar in size to terrestrial flood basalt provinces. However, these basaltic flows are more viscous than those found on Earth. Some of the flows, festoons, are lobed flows with crests. These characteristics indicate an extraordinarily high viscosity. Like Earth, Venus has cinder cones, shield volcanoes, and calderas.
Shield volcanoes on Venus
Venusian shield volcano and cinder cones. Photo credit: NASA.
The shield volcanoes of Venus are several hundred kilometers in diameter and less than 2 km high. They are low compared to Earth’s shield volcanoes due to the density contrast between lava and source and surface rocks. Density differences may be smaller on Venus than on Earth because the higher temperature gradient leads to shallower magma sources and volatile dissolution is restricted during magma ascent.