Venus’ Retrograde Rotation May Stem From High-Speed Impact, New Simulations Suggest
New simulations presented at the European Geosciences Union General Assembly in Vienna propose that Venus’ peculiar backward rotation could result from a high-angle collision with an object roughly one-tenth the planet’s mass, according to a study led by Cedric Gillmann, a planetary scientist at ETH Zurich. The impact, theorized to have occurred within the first 50 million years of Venus’ formation, may have slowed the planet’s spin and melted nearly its entire mantle, as reported by Universe Today.
How Did the Collision Affect Venus’ Rotation?
Gillmann and colleagues’ models suggest that a moon-sized impactor striking Venus at a high angle could have drastically altered its rotation. The simulations indicate that such an event could slow a rapidly spinning early Venus to its current retrograde rotation, which takes 248 Earth days to complete. “Depending on impact parameters, we can slow down a rapidly rotating early Venus to rotation rates compatible with long-term evolution toward a slow-rotating planet,” Gillmann said. In some scenarios, the collision might have even reversed the planet’s spin, leading to its current backward motion.
What Evidence Supports the Impact Theory?
The study highlights that giant impacts typically produce surface magma oceans, with depths ranging from 100 km to a fully molten mantle. If Venus’ surface could radiate heat efficiently, these magma oceans would cool within a few hundred million years, leaving a planetary structure indistinguishable from one without a major impact. Gillmann noted that the impact likely melted 99% of Venus’ mantle, though the heat dissipates over time, making the event difficult to detect in the planet’s current geological state.
How Does This Relate to Venus’ Lack of Plate Tectonics?
While the collision may explain Venus’ rotation, its role in the planet’s absence of plate tectonics remains unclear. Scientists hypothesize that Venus lacks a large-scale carbon recycling mechanism, contributing to its runaway greenhouse effect. However, the study does not directly link the impact to this feature, leaving the connection open for further research.
Why Is This Discovery Significant?
Understanding Venus’ formation and evolution provides insights into planetary dynamics and the conditions necessary for habitability. The collision theory aligns with broader research on giant impacts shaping planetary systems, including Earth’s own moon-forming event. “This work underscores how extreme events can drastically alter a planet’s trajectory,” said Gillmann.
What Are the Next Steps for Research?
Future studies will focus on refining impact models and comparing them with data from upcoming missions, such as NASA’s VERITAS and ESA’s EnVision, which aim to map Venus’ surface and geology. These missions could provide critical evidence to validate or challenge the collision hypothesis.
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