Impact craters hidden in plain sight on Venus

Oct. 29 () –

Geological mapping of one of the oldest-surface regions of Venus has revealed evidence of two massive back-to-back impact events. with unique features.

The Haastte-baad Tile is home to one of the oldest surfaces on Venus, called the tessera terrain. cut by a unique set of concentric rings of more than 1,500 kilometers in its widest part.

After modeling how their unique features might have formed, the research concluded they look nothing like the traditional-looking craters on the Moon and Mars, and even Venus; This is because the initial conditions of Venus gave rise to impact structures which differ significantly from classical impact craters.

“If this is indeed an impact structure, it would be the oldest and largest on Venus, giving us a rare glimpse into its past and informing early planetary processes,” he said. in a statement study author and senior scientist at the Planetary Scientific Institute (PSI), Vicki Hansen.

“And perhaps even more importantly, it shows us that not all impact structures are the same. Impact structures are the result of a bolide (a body of unspecified composition) colliding with a target planet. The nature of the bolide is important , but so is the nature of the objective.”

The article was published in the Journal of Geophysical Research: Planets.

Tesserae are regions of highly deformed terrain on Venus characterized by wrinkled and corrugated terrain, which forms when a relatively thin but strong layer of material forms over a weak layer capable of flowing and convecting vigorously, like boiling water.

The Venus tessera terrain formed over a huge pool of lava. So, Where could that lava have come from?

While today’s Venus has a 70-mile-thick outer layer called the lithosphere, young Venus was much hotter and probably had a lithosphere about 9 kilometers thick. If a thin lithosphere is hit by a large bolide, it will pass through the thin lithosphere and enter the mantle below, releasing a huge sea of ​​lava to the surface that eventually cools and forms tesserae, Hansen said. The team’s mapping suggests this occurred between 1.5 and 4 billion years ago.

However, an additional mystery is that the tiles can sometimes lie on plateaus. The formation of the enormous volume of lava results in a solution.

“When there are large amounts of partially molten material in the mantle that rushes to the surface, what is left is something called debris. The solid debris is much stronger than the adjacent mantle, which did not experience partial melting. What can result Surprisingly, the solid residue also has a lower density than the entire mantle around it. Therefore, it is stronger, but it is also buoyant. Basically, you have a cushion of air in the mantle beneath your lava pool. and it will just rise and rise that tessera terrain“he explained.

But convection beneath the lithosphere can sometimes move material. If the residue remains in place, the tile remains tall; If the debris is carried away by mantle convection, the overlying tile will be at the same height as the rest of the planet’s surface, Hansen said. This is the case of the Haasttse-baad tile.

Next, the team had to take into account ring structures, which are not seen anywhere else on Venus. The researchers agreed that the rings are reminiscent of Callisto’s Valhalla crater and Europa’s Tire crater. They are believed to have formed by the impact of a thin, strong layer on a weak, fluid layer, very similar to the configuration needed to form tesserae. In Callisto and Europe, That means a thin, tough layer of ice over an ocean or slushy liquid.

Finally, the research team discovered that the formation of the ringed structure of Venus It would have required two large cars to crash into Venus one after the other. The first created the lava pool to form the tessera terrain and the second bolide impacted the lava pool, forming the unique ring structure.

The consecutive bolides may seem too random, but there is evidence in ancient rocks preserved in South Africa that this occurred about 3.5 billion years ago on Earth, Hansen said. Even on the Moon and Mars, there is evidence of many of these huge impacts. In those cases, large bolides, which were not uncommon during the first 2.5 billion years of our Solar System’s history, occurred on Earth about 3.5 billion years ago.