Venus, Earth's "Sister" Planet

Venus radar view
A radar map of the surface of Venus, made by the Magellan spacecraft. Radar was able to punch through the clouds to give scientists an idea of the volcanic surface of the planet. NASA

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, why is Venus called Earth's sister?

Despite the stifling heat trapped under its thick clouds, it turns out that Venus has some similarities to Earth. First, Venus is roughly the same size, density and composition as our planet. It's a rocky planet — a terrestrial world. It orbits a bit closer to the Sun than Earth does, and it appears to have been formed at about the time as our planet.

Two Sisters Part Ways

The two worlds part ways when you look at their surface conditions and atmospheres. As the two planets evolved, they took different pathways. While they may both 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 in textbook as being the closest thing we have to Hell in the solar system.

Location

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. In fact, Venus is so close to us, and so bright (due to the Sun's reflection off its atmosphere), that it's only object besides our Moon that can be seen from Earth during the evening and during the day!

Rotation

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.

Size

At approximately 4.9 x 1024 kilograms, Venus is also nearly as massive as Earth. As a result, the gravity on Venus (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 mantel.

The Volcanic Venusian Surface

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 sculpted through constant volcanic activity, and is comprised of low, rolling plains punctuated by mountains that are much smaller than those here on Earth.

There is also a lack of small impact craters, like those seen on the other terrestrial planets. This is due to the thickness of the Venusian atmosphere. It prevents all but the largest meteors from reaching the surface.

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%), while only containing about 3.5% nitrogen. This is in stark contrast to our breathable atmosphere, which contains primarily nitrogen (78%) and oxygen (21%). 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). 

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 that swaddle the planet. 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. This pressure is so high, that when the early Venera spacecraft landed, they only had a few moments to take data before they were crushed and melted.

Exploring Venus

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.