Is Venus a Rocky Planet or a Gas Giant?

Venus, popularly known as Earth’s twin sister and our closest planet, is the second planet from the sun in our solar system.

From the volcanic eruptions on its surface to its thick, impenetrable atmosphere, this article explores Venus in detail to explain how and why the planet is both strikingly similar and starkly different to Earth.

Rocky Planets vs. Gas Giants

While all the planets formed around the same time, their formation history provides important clues about their compositions and why they orbit at their particular positions. 

Find out if Venus is one of the planets visible tonight.

As you may know, all the planets formed out of the disk of gas leftover from the sun’s formation. According to the most widely accepted core accretion theory, when clumps of material began fusing together through gravity, the elements that had high melting point and density (silicate rocks and metals) formed planets close to the sun.

Learn more about a black hole’s accretion disk

Terrestrial Planets

The innermost four planets: Mercury, Venus, Earth, and Mars are made of rocky, solid materials with distinct, compact surfaces. Thus, they are called terrestrial planets.

All terrestrial planets have a metallic core in their center made of iron. They also have common geological features such as mountains and craters.

Another major distinction of rocky planets is a very definite boundary between the surface of the planet, which is solid, and its atmosphere, which is gaseous.

Yet, there are significant differences between the terrestrial planets, which you can read about here.

Gas Giants

The other planets in our solar system are known as gas giants. Lighter elements, such as hydrogen, methane and ammonia, couldn’t fuse near to the sun and were pushed outwards by solar wind where they formed gaseous planets.

These behemoths, such as Jupiter and Saturn, are so big because they are comprised of low-density substances.

Gas giants also tend to have more moons than terrestrial planets. Saturn has over 60 moons and Jupiter more than 70.

This is believed to have two causes. Firstly, ice and dust left over when the gas giants formed readily accretes to form larger bodies which circle the planet. Secondly, huge planets have a big gravitational pull which draws in rocks and dust that strays too close.

The main differences between terrestrial and gas planets are summarized in the table below:

How did Planet Venus Form? 

Venus formed 4.5 billion years ago from accreted dust and gas. Like Earth, Venus’s metallic core formed first, after which lighter elements accumulated around it to form the mantle and atmosphere.

Venus is theorized to have had an Earth-like atmosphere in the early stages of its life but, unlike Earth, it’s believed its proximity to the sun caused all the water to evaporate from the Venusian surface within 2 billion years into its formation, leading to an increase in temperature.

In a concept called runaway greenhouse effect, the heat being released from Venus’s surface is now being trapped within its thick atmosphere, increasing the surface temperature up to 880 degrees Fahrenheit.

Today, the carbon dioxide and nitrogen in Venus’s atmosphere is hot enough to melt lead (and is also the reason why Venus shines so brightly and spacecraft circuitry melts when they try to land).

Bizzarely, Venus also rotates backwards, from east to west, and one day on Venus lasts 117 Earth days. 

How Old is the Surface of Venus? 

The first stop to approximate the age of a planet (or moon) is the number of craters on its surface and how eroded or well preserved they are. The greater the number or density of craters, the older the planet’s age.

To do this, it is assumed that Venus is exposed to a similar number of asteroids as other planets in the vicinity. However, NASA’s Magellan spacecraft found that there are only 1000 craters rather than the expected 5000.

These findings suggest that the surface of Venus is aged between 500 million and 1 billion years old.

Is Venus Geologically Active?

Yes, Venus is geologically active. 

The existence of only 1,000 craters on Venus is a clear indication that the planet is geologically active. If there was no geological activity, there would be many more impact craters given the number of asteroids that must have impacted the planet.

This lack of craters suggests that a process is smoothing the planet’s surface time and again, with the most recent smoothing occurring 500 million years ago.

Since then, there has been very little geological activity, preserving the 1,000 craters we see today. Moreover, studies have determined that the entire planet is not of the same age. The surface near volcanic plains is much younger than the surface elsewhere, indicating that it is recycling time and again. 

Unlike Earth, Venus does not have water, ice, or high surface winds, eliminating the chance of surface erosion due to these factors. The main source of geological activity is volcanoes, which make up 75% of the planet’s surface.

Does Venus have craters on its surface?

There are many craters on the surface of Venus. We see a random but uniform distribution of around 1,000 impact craters, much fewer than the expected 5,000. 

Venus, like all other planets, was subjected to numerous asteroid impacts during its early formation. While the smaller asteroids evaporated in its thick atmosphere, the large ones hit the surface, creating impact craters.

As we’ve already seen in this article, the presence of fewer than expected craters suggests that the planet is recycling its surface by being geologically active.

Unlike on Earth, the craters that are currently present on Venus are pristine, meaning there has been very little weathering on the surface to degrade them. 

Does Venus have mountains? 

Yes. There are four main Venusian mountain ranges: Maxwell Montes, Frejya Montes, Akna Montes, and Danu Montes.

These mountains were formed due to folding and unfolding of Venus’ crust, in a process called Faulting.  

What Would Venus Look Like Without its Atmosphere? 

Venus would be a harsh, dry world, void of water and life if we could see it without its atmosphere.

One of the best known features of Venus is its atmosphere and, for astronomers pointing a telescope at it, it is all we see. That thick atmosphere is what makes Venus such a hot planet.

There is a lot of carbon dioxide encircling the planet. You’d have to be some 30 miles above the surface before pressures are the same as we experience at sea level, but temperatures would still cook us!

However, we have used radar imaging to get a view of the surface of Venus, so we know exactly what it looks without an atmosphere. Take a look for yourself:

Why doesn’t Venus have a magnetic field? 

Venus once had a magnetic field, during the first billion years of its formation.

Magnetic fields in terrestrial planets are created via the dynamo process. In this, the molten core swirls as a result of the planet’s rotation, its movement generating a global magnetic field.

The rotation of a molten core is critical to the creation and evolution of magnetic fields, as shown in this explanatory video.

Venus’ formation, it was created not by a molten core (Venus has one, but it rotates at a very slow rate of once every 243 Earth days), but by the heat leftover from planet formation.

With time, the heat dissipated and the already weak field was eroded by solar winds. Since there is no internal process to generate the field, whatever weak field Venus might have comes from the interaction of upper layers of atmosphere with solar winds. 

Why Does Venus Not Have Rings Around it? 

In our solar system, only the outer planets have ring systems: Jupiter, Saturn, and Neptune.

The rings are composed of icy rocks: debris from materials that were too light and could not clump together to form complete planets, and were thus attracted by gas giants’ gravity wells.

This debris cannot exist nearer to the Sun, since it would either vaporize or be pushed outward. Thus, Venus is too near the sun to have a moon or a ring system. Any left over debris from its formation must have been pushed towards the outer edge of the solar system by solar winds. 

Summary

Planet Venus is a rocky planet covered with extremely thick layers of atmosphere, making it impossible to glance its surface from Earth.

It was once similar to Earth in many aspects: temperature, water, geological activity, core, magnetic field, etc. However, the runaway greenhouse effect caused Venus’s temperatures to soar which now is at the point that it can melt lead.

All in all, Venus is a fascinating planet with a rich history and equally fun to point a planet-watching telescope at!