Venus may have been without active tectonic plates for a billion years
Venus may not have had Earth-like tectonic plates for the last billion years, according to the results of a new study. Instead, the planet, which is often referred to as Earth’s twin, may be covered in a single thick outer plate.
The planet Venus remains one of the most fascinating and mysterious bodies in our solar system. Despite the fact that it is Earth’s closest planetary neighbor, and shares many characteristics with our home world, we know relatively little about it.
This is largely down to the fact that the Venusian surface is obscured from view by a super dense, carbon-dioxide-dominated atmosphere. This atmospheric veil prevents observation of the surface by telescopes attempting to explore the planet in the visible part of the electromagnetic spectrum, which can be seen by the human eye.
However, spacecraft have been able to map the Venusian surface using radio waves, revealing a tortured surface etched with fascinating and sometimes familiar geographical features. Among these features, scientists have identified ridges on the planet’s surface that appear similar to those created by tectonic movement on Earth.
Back on Earth, the rigid outer part of our planet, known as the lithosphere, is broken into curved sections known as tectonic plates. These plates are in a state of constant motion relative to one another, with their movement driven by powerful subsurface processes.
Interactions between the plates create geological features such as rifts and ridges on Earth's surface. Similar surface features spotted on the Venusian surface were taken by some as indicators that the alien world had also been tectonically active in the relatively recent geological past.
The new study sought to approach the question of Venus’s potential ongoing tectonic activity by analyzing the crater remains of a massive impact event that still scars the planet’s tortured surface to this day. It is thought that the impact site, officially known as Mead crater, was formed between 300 million to 1 billion years ago, when a huge impactor smashed through the ancient Venusian atmosphere to carve an enormous scar out of the planet’s surface.
In the present day, this impact crater measures over 170 miles (274 km) in diameter, and features a set of two circular cliff-like faults that formed in the wake of the cataclysmic event.
The researchers behind the study used computer modeling to recreate the process that could have created the Mead crater, and the distinctive ridges. Earlier research suggested that the positions of the rings relative to the center of an impact crater is linked to the thermal gradient of the rock below.
In this context, a thermal gradient is essentially the rate at which the temperature of rock increases the further it is from the surface. This can affect how a crater forms, as the temperature of a rock deposit is a significant factor in dictating how it will deform upon impact, and so how ring features will form on the crater above.
A combination of the computer modeling and the physical location of the rings in the crater basin led the team to conclude that Venus must have a low thermal gradient. This in turn suggests that the planet has a very thick lithosphere, and that it likely doesn’t play host to drifting tectonic plates. Furthermore, according to the authors of the study, it may not have done so since the creation of the crater, up to a billion years ago.
An analysis of other ringed craters examined by the team offered similar indications.
"This tells us that Venus likely had what we'd call a stagnant lid at the time of the impact," says Evan Bjonnes, a graduate student at Brown University, and lead author of a paper on the new study. "Unlike Earth, which has an active lid with moving plates, Venus appears to have been a one-plate planet for at least as far back as this impact."
The paper has been published in the journal Nature Astronomy.
Source: Brown University