Art Courtesy of Kara Tao.
Beneath the endless search for the perfect skincare routine is a desire to maintain our youth against the ravages of time. Yet despite the wealth of commercially available aloe creams and collagen powders, the march of age inevitably slows the skin renewal process, leaving wrinkles and rough, dry skin. Likewise, the history and age of a planet can be deciphered from its surface by, for instance, dating the oldest rocks and crystals in its bedrock. But what if a planet’s surface appears much younger than its actual age?
Venus, the second planet from the sun, is estimated to be 4.5 billion years old. It is theorized that the planet was named after the Roman goddess of beauty due to its dazzling brightness in the night sky. However, Venus has another claim to its name: its youthful appearance. The planet’s surface is less than one billion years old, which is young considering the long history of the geophysical time scale. According to a recent paper published in Nature Astronomy, the secret to Venus’ strikingly young surface may lie in volcanic events triggered by early energetic collisions.
These interplanetary collisions have always fascinated Simone Marchi, a planetary scientist at the Southwest Research Institute (SwRI), who teamed up with Yale geophysicist Jun Korenaga and SwRI Sagan Fellow Raluca Rufu to investigate the effects of early collisions on Venus’ surface. “Venus comes with its own mystery and there are a lot of things that we don’t know,” Marchi said. “So I thought, maybe there is something we can say about Venus by studying these early processes.”
Are Collisions The New Collagen?
Imagine an object just short of the mass of the moon colliding with the surface of Venus. This is the scale at which high-velocity collisions occur on Venus’ surface. When such objects collide with planets at this scale, it adds to the surface in a process called accretion. The team’s research suggests that late accretion events—the buildup of new matter in and throughout a planet—greatly contributed to Venus’ overall geological makeup.
Earlier projects conducted by Marchi and colleagues examined the consequences of these large-scale impacts on Mars and Earth, but Marchi had something different in mind for Venus. To understand the effect of late accretions on Venus, Marchi was interested in studying the planet through the lens of geophysics—the study of a planet’s structure and atmosphere. In doing so, the team could figure out how Venus’ volcanic activity, which appeared to play a major part in its youthful surface, was linked to the collisions. “Processes like [volcanism] are connected to the geophysics of the planet, so that gives us the motivation to try to understand how this early energetic event could affect the geophysical evolution of the planet,” Marchi said, referring to the collisions that produced late accretions. His work on Venus explored the relationship between these late accretion events and the planet’s prolonged volcanic activity, particularly noting that the connection between these two phenomena lies in Venus’ superheated core.
Hot To The Core
Venus has the most volcanoes out of all planets in our solar system. Through simulations, the researchers were able to draw some important conclusions that alter how we think about the relationship between a planet’s geological makeup and planetary accretion.
The team found that the early high-velocity collisions not only created a magma ocean on Venus’ surface, but also led to a dramatic heating of the planet’s core. Furthermore, due to the insulating nature of Venus’ surface, the planet’s super-heated core could remain at very high temperatures. This possibility is particularly intriguing because it differs from Earth, where the presence of plate tectonics cools down the planet’s interior very efficiently. Venus, however, lacks tectonic plates, creating a different geological composition.
When choosing a model, the researchers assumed stagnant lid convection on Venus, meaning these tectonic plates were completely absent. Their results of simulating stagnant lid convection starting from high-velocity impacts on Venus suggest that the planet’s core remains super-heated, which helped sustain volcanism for billions of years. Geological features such as vast volcanic plains and volcano domes found on Venus are the result of these conditions that can all be traced back to late-accretion events which heated up the core in the first place. Venus’ youthful appearance is thus the culmination of these features, perceived as a result of the constant magma flow that smooths the surface over time.
While there have been hypotheses about Venus’ youthful surface before, none have attempted to explain it through the planet’s internal core temperature and dynamics. “Simone was interested in combining [these] very short-time scale impact dynamics with long-time scale metal dynamics,” Korenaga said.
What About Earth?
Like Earth, Venus is a terrestrial planet, and is often regarded as Earth’s “sister planet” due to their similarities in size and orbit around the Sun. Why, then, did Earth’s surface fail to fight the passage of time? By comparing these findings to the relatively well-known composition of Earth, it is plausible to conclude that Earth, unlike Venus, did not experience late accretion events that affected its core temperature to such a great extent.
While Earth’s large volume of surface water broke down the crust and uppermost mantle of the planet to form tectonic plates, Venus is closer to the Sun than the Earth, causing Venus to rapidly lose surface water through evaporation. This geophysical difference is significant, as plate tectonics reduce internal heat. In addition, the researchers ran a simulation and found that the mean impact velocities of late accretions on Venus were larger than those of Earth. In other words, small celestial bodies called planetesimals hit Venus harder and faster. The lower-velocity impacts on Earth would lead to less core heating and an inability to sustain the long-lived volcanic activity seen on Venus. These key differences are what lends the ‘planet of beauty’ its distinct, youthful surface.
Marchi and Korenaga hope to use their model to make predictions and further explain the mystery of Venus. “This difference in late accretion by itself may not explain all the differences [between Earth and Venus], but it may help to push it towards the right direction,” Korenaga added. The collaboration with Korenaga, who has studied the origin of life on terrestrial planets for over a decade, highlights a key link between late accretion and the early history of planets. As it did for Venus, late accretion played a significant role in Earth’s early history and has a lasting impact on its present surface features, contributing substantially to the geological record of the planet. Thus, understanding late accretions has other far-reaching implications for related projects.
According to Marchi, these energetic events could drastically alter the chemistry of the atmosphere. For example, large-scale impacts can lead to the heating of the crust, generating a hydrothermal system that could serve as a possible reservoir for microbes to thrive. “We strive to understand whether or not these early impacts could have had anything to do with the origin of life on Earth,” Marchi said.
Much of Korenaga’s work in the past has focused on early Earth and investigating the geophysical catalysts for life. “The role of late accretion is important to discuss generally, for how you can build a habitable planet,” Korenaga said. He argues that late-stage cosmic collisions have a large impact on whether or not a planet can produce life. In particular, this research helps us better understand the geological makeup and formation of planets, a key ingredient for a given planet’s potential to sustain life.
As a planetary scientist, Marchi is also involved in space missions and is currently one of the leaders of the Lucy Mission, a NASA space probe with the goal of reaching Trojan asteroids near Jupiter. Recently, there has been a revival of interest in Venus in space exploration. NASA selected two future space missions to explore Venus in the coming decade, and the European Space Union has proposed its own mission.
For next steps, the authors hope to build off of this work and potentially explore the geophysics of Earth and Mars, which could hold more mysteries of their own. “The work for Venus is definitely not done,” Marchi said. “But we’ll try to push the new idea forward to make predictions and try to test that as much as possible—with new missions as well.”