In the chaotic early days of the Solar System planets endured a relentless barrage of cosmic collisions. Most of the rocky worlds including Mercury, Mars, and Earth’s Moon still bear scars of these ancient impacts in the form of vast craters and impact basins. However, Venus has been a strange outlier, with scientists finding no evidence of large craters over 300 kilometers wide. This missing piece of Venus’s violent past has puzzled researchers for years.
A recent study now suggests that these long-sought impact structures may indeed exist on Venus but look very different from our expectations. Geologist Vicki Hansen of the Planetary Science Institute and her team propose that a peculiar formation called the Haastte-Baad Tessera could be Venus’s largest and oldest impact structure. Located on a series of concentric rings spanning about 1,500 kilometers, this tessera terrain may have formed around 3.5 billion years ago due to two massive impacts that struck Venus in quick succession.
The Mystery of Venus’s Tessera Terrain
On Venus, unlike most planets, the lack of traditional, vast impact basins may be linked to the planet’s unique geological evolution. Tessera terrain crumpled, tile-like structures may offer new insights into this early history. Hansen and her colleagues used models to investigate the Haastte-Baad Tessera’s origin, ultimately concluding that the double impact of large asteroids could have breached Venus’s thin crust and triggered magma flows from the molten mantle. This process likely created the terrain’s concentric rings.
“When a bolide collides with a planet, the nature of both the impactor and the target planet matter,” Hansen said. She explained that young rocky planets were far warmer internally, with thin crusts overlaying their molten mantles. On Venus, this thin lithosphere meant impacts could produce less familiar crater shapes.
Comparing Venus to Other Celestial Bodies
Such unusual impact structures are rare but not unprecedented in the Solar System. A similar multi-ringed structure, Valhalla Crater, is visible on Jupiter’s moon Callisto. However, the icy composition of Callisto allowed water from below to fill the impact zone, creating a different formation process than on Venus.
Venus’s hot, volcanic surface created additional complexities. If large impacts left melted mantle material beneath the crust, it would eventually harden and rise due to its buoyancy – a phenomenon Hansen compares to an “air mattress” beneath a lava pond. In some cases, this molten rock may even lift the terrain, explaining why some tesserae appear on elevated plateaus.
Impact Studies Open New Doors to Planetary History
The modeling indicates that the impactors that shaped Haastte-Baad Tessera were approximately 75 kilometers across. The geological evidence suggests this rare formation process may have occurred on Earth, too, such as the dike swarm near Africa’s Lake Victoria. However, Earth’s plate tectonics and erosion have mostly erased evidence of these early impacts.
These findings offer a fresh perspective on the formation of early rocky planets, revealing that a thin lithosphere could result in more complex, unexpected impact structures. “We had been looking for big holes in the ground, but for that to happen, you need a thick lithosphere, and early Venus didn’t have that,” Hansen explained.
This research, published in Journal of Geophysical Research: Planets, not only reshapes our understanding of Venus’s surface but also helps scientists piece together the early history of rocky planets across the Solar System.
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Reference: https://www.sciencealert.com/a-hidden-breed-of-impact-craters-has-been-lurking-on-venus-undetected
