Imagine a hellishly hot world covered with thick clouds shedding acid rain over a volcanic landscape. Think it couldn't exist? Well, it does, and its name is Venus. That uninhabitable world is the second planet out from the Sun and misnamed Earth's "sister". It's named for the Roman goddess of love, but if humans wanted to live there, we wouldn't find it at all welcoming, so it's not quite a twin.
Venus from Earth
The planet Venus shows up as a very bright dot of light in Earth's morning or evening skies. It's very easy to spot and a good desktop planetarium or astronomy app can give information on how to find it. Because the planet is smothered in clouds, however, looking at it through a telescope only reveals a featureless view. Venus does, however, have phases, just as our Moon does. So, depending on when observers look at it through a telescope, they will see a half or crescent or a full Venus.
Venus by the Numbers
The planet Venus lies more than 108,000,000 kilometers from the Sun, just about 50 million kilometers closer than Earth. That makes it our nearest planetary neighbor. The Moon is closer, and of course, there are occasional asteroids that wander closer to our planet.
At approximately 4.9 x 1024 kilograms, Venus is also nearly as massive as Earth. As a result, its gravitational pull(8.87 m/s2) is nearly the same as it is on Earth (9.81 m/s2). Additionally, scientists conclude that the structure of the planet's interior is similar to Earth's, with an iron core and a rocky mantle.
Venus takes 225 Earth days to complete one orbit of the Sun. Like the other planets in our solar system, Venus rotates on its axis. However, it doesn't go from west to east as Earth does; instead it spins from east to west. If you lived on Venus, the Sun would appear to rise in the west in the morning, and set in the east in the evening! Even stranger, Venus rotates so slowly that one day on Venus is equivalent to 117 days on Earth.
Two Sisters Part Ways
Despite the stifling heat trapped under its thick clouds, Venus does have some similarities to Earth. First, it's roughly the same size, density, and composition as our planet. It's a rocky world and appears to have been formed at about the time as our planet.
The two worlds part ways when you look at their surface conditions and atmospheres. As the two planets evolved, they took different pathways. While each may have started out as temperature and water-rich worlds, Earth stayed that way. Venus took a wrong turn somewhere and became a desolate, hot, unforgiving place that the late astronomer George Abell once described it as being the closest thing we have to Hell in the solar system.
The Venusian Atmosphere
The atmosphere of Venus is even more hellish than its active volcanic surface. The thick blanket of air is very different than the atmosphere on Earth and would have devastating effects on humans if we attempted to live there. It consists mainly of carbon dioxide (~96.5 percent), while only containing about 3.5 percent nitrogen. This is in stark contrast to Earth's breathable atmosphere, which contains primarily nitrogen (78 percent) and oxygen (21 percent). Moreover, the effect the atmosphere has on the rest of the planet is dramatic.
Global Warming on Venus
Global warming is a great cause for concern on Earth, specifically caused by the emission of "greenhouse gases" into our atmosphere. As these gases accumulate, they trap heat near the surface, causing our planet to heat up. Earth's global warming has been exacerbated by human activity. However, on Venus, it happened naturally. That's because Venus has such a dense atmosphere it traps heat caused by sunlight and volcanism. That has given the planet the mother of all greenhouse conditions. Among other things, global warming on Venus sends the surface temperature soaring to more than 800 degrees Fahrenheit (462 C).
Venus Under the Veil
The surface of Venus is a very desolate, barren place and only a few spacecraft have ever landed on it. The Soviet Venera missions settled onto the surface and showed Venus to be a volcanic desert. These spacecraft were able to take pictures, as well as sample rocks and take other various measurements.
The rocky surface of Venus is created by constant volcanic activity. It doesn't have huge mountain ranges or low valleys. Instead, there are low, rolling plains punctuated by mountains that are much smaller than those here on Earth. There are also very large impact craters, like those seen on the other terrestrial planets. As meteors come through the thick Venusian atmosphere, they experience friction with the gases. Smaller rocks simply vaporize, and that leaves only the largest ones to get to the surface.
Living Conditions on Venus
As destructive as the surface temperature of Venus is, it's nothing compared to the atmospheric pressure from the extremely dense blanket of air and clouds. They swaddle the planet and press down on the surface. The weight of the atmosphere is 90 times greater than Earth's atmosphere is at sea level. It's the same pressure we would feel if we were standing under 3,000 feet of water. When the first spacecraft landed on Venus, they only had a few moments to take data before they were crushed and melted.
Since the 1960s, the U.S., Soviet (Russian), Europeans and Japanese have sent spacecraft to Venus. Aside from the Venera landers, most of these missions (such as the Pioneer Venus orbiters and European Space Agency's Venus Express) explored the planet from afar, studying the atmosphere. Others, such as the Magellan mission, performed radar scans to chart the surface features. Future missions include the BepiColumbo, a joint mission between the European Space Agency and the Japanese Aerospace Exploration, which will study Mercury and Venus. The Japanese Akatsuki spacecraft entered orbit around Venus and began studying the planet in 2015.
Edited by Carolyn Collins Petersen.