Volcanism on Venus fueled by powerful ancient impacts

Earth and Venus are almost the same size and density. But they’re drastically different worlds. One of the biggest differences is that Earth has an outer crust, broken into ocean- and continent-sized “plates.” And, according to the theory of plate tectonics, these great plates move relative to each other. On Earth, plate tectonics keeps our world’s surface geologically young. Meanwhile, Venus lacks plate tectonics. Yet, somehow, Venus also has a geologically young surface. Indeed, there’s recent evidence that Venus is still volcanically active, even today. How is this possible?

A new study released July 20, 2023, suggests that ancient, high-speed impacts of rocky debris helped power volcanoes on Venus, and help keep it geologically youthful today. The research comes from scientists at Southwest Research Institute (SwRI) in San Antonio, Texas. Read the full statement.

The researchers, led by Simone Marchi at SwRI, published their peer-reviewed results in Nature Astronomy on July 20, 2023.

2 very different worlds

Despite being similar in size and density, Earth and Venus took very different evolutionary paths. On Earth, plate tectonics helps form mountain ranges and creates volcanism. The constant re-shaping of our planet’s surface keeps it youthful, geologically speaking.

Venus, however, doesn’t have plate tectonics. Yet it still features mountain ranges and is a highly volcanic world. In fact, it has more volcanoes than Earth: over 80,000. As the paper explained:

The geodynamics of Earth and Venus operate in strikingly distinct ways, in spite of their similar size and bulk density, resulting in Venus’ absence of plate tectonics and young surface age (0.2 – 1 billion years). Venus’s geophysical models have sought to explain these observations by invoking either stagnant lid tectonics and protracted volcanic resurfacing, or by a late episode of catastrophic mantle overturn. These scenarios, however, are sensitive to poorly understood internal initial conditions and rheological properties, and their ability to explain Venus’ young surface age remains unclear.

Marchi stated:

One of the mysteries of the inner solar system is that, despite their similar size and bulk density, Earth and Venus operate in strikingly distinct ways, particularly affecting the processes that move materials through a planet.

How could Venus be so active and maintain a young surface without plate tectonics?

Volcanism on Venus fueled by ancient impacts

The new study suggests that high-speed, energetic impacts fueled volcanism on early Venus. Co-author Jun Korenaga at Yale University said:

Our latest models show that long-lived volcanism driven by early, energetic collisions on Venus offer a compelling explanation for its young surface age. This massive volcanic activity is fueled by a superheated core, resulting in vigorous internal melting.

The paper elaborated:

Here we show that long-lived volcanism, driven by early, energetic collisions on Venus, offers an explanation of its young surface age with stagnant lid tectonics. This volcanic activity is fueled by a superheated core, resulting in vigorous internal melting regardless of initial conditions.

But why did Venus experience high-speed, more energetic impacts than Earth? Both planets formed in the same neighborhood of the solar system. However, the relatively small difference in their distance from the sun was enough to make a difference. Since Venus is closer to the sun, and therefore moves faster in its orbit as a result, impacts were more powerful.

In addition, impactors originating from beyond Earth’s orbit require higher orbital eccentricities to collide with Venus. This too results in more powerful impacts.

So how does this affect volcanism on Venus?

As co-author Raluca Rufu at SwRI explained:

Higher impact velocities melt more silicate, melting as much as 82% of Venus’ mantle. This produces a mixed mantle of molten materials redistributed globally and a superheated core.

A few large impacts could have big consequences

As the researchers explained, even a few large impacts could have had a significant effect on Venus’ volcanism and the long-term evolution of the planet. The new study incorporated expertise in large-scale collision modeling and geodynamic processes. Those research specialties can help assess the consequences of the collisions. Korenaga said:

Venus’ internal conditions are not well known, and before considering the role of energetic impacts, geodynamical models required special conditions to achieve the massive volcanism we see at Venus. Once you input energetic impact scenarios into the model, it easily comes up with the extensive and extended volcanism without really tweaking the parameters.

The significant takeaway here is that rocky planets don’t always need plate tectonics to be active worlds. It will be interesting to see how that applies to exoplanets as well.

Bottom line: A new study says that high-speed impacts fueled early volcanism on Venus, explaining why Venus’ surface is geologically young despite a lack of plate tectonics.

Source: Nature Astronomy

Via SwRI

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