Exploring Venus: A Surprising Similarity to Earth’s Early History

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Exploring Venus: A Surprising Similarity to Earth’s Early History

Venus, the second planet from the sun, has long been considered Earth’s evil twin. With a thick atmosphere of carbon dioxide and sulfuric acid, surface temperatures hot enough to melt lead, and no visible signs of water or life, Venus seems like a hellish world compared to our blue and green oasis. However, a new study published in the journal Proceedings of the National Academy of Sciences (PNAS) suggests that Venus may have shared more than just a size and a composition with Earth in the past.

The study, led by Paul Byrne, a planetary geologist at North Carolina State University, analyzed data from NASA’s Magellan mission, which mapped Venus’s surface with radar in the 1990s. The researchers focused on the tesserae, large and complex landforms that cover about 7% of Venus’s surface and have puzzled scientists for decades. Tesserae are characterized by their high elevation, sharp edges, and intersecting ridges, which resemble a jigsaw puzzle or a mosaic. Some tesserae are as big as Texas and rise up to 5 kilometers above the surrounding plains, making them the highest mountains on Venus.

Byrne and his colleagues used a new technique called topographic roughness analysis to measure the complexity of the tesserae at different scales. They found that the tesserae were not only rougher than the surrounding terrain, but also exhibited a fractal pattern of self-similarity, meaning that they looked similar at different levels of magnification. This pattern is typical of natural systems that undergo a process called self-organization, in which small perturbations or instabilities lead to the emergence of larger structures or patterns.

The researchers also compared the tesserae on Venus to the cratons, the oldest and most stable parts of Earth’s continents, which are made of granite and other felsic rocks that formed through partial melting and differentiation of the mantle. The cratons are known for their high elevation, low seismicity, and thick lithosphere, which make them resistant to erosion and deformation. The cratons are also surrounded by younger and more active tectonic zones, where plates collide, subduct, or rift apart, creating mountains, volcanoes, and earthquakes.

To their surprise, the researchers found that the tesserae on Venus shared many features with the cratons on Earth. Both had similar elevations, roughness, and fractal patterns, as well as low seismicity and thick lithosphere. The tesserae on Venus also showed signs of deformation and faulting, which suggested that they had been subjected to intense tectonic activity in the past. This activity could have created the tesserae by uplifting and folding the crust, or by melting and solidifying the mantle, which would have produced a different composition and texture than the surrounding plains.

The researchers proposed that the tesserae on Venus were remnants of an ancient continent or supercontinent, which formed about 2 to 3 billion years ago and broke apart due to plate tectonics. This continent, called “Euramerica,” would have covered about 10% of Venus’s surface and contained most of the tesserae. The rest of the surface would have been covered by a global ocean or a series of smaller seas, which would have evaporated or sublimated over time due to the greenhouse effect of the atmosphere. The tesserae would have survived because they were too thick and rigid to be subducted or eroded by the mantle or the atmosphere.

The researchers also suggested that the tectonic activity on Venus may have been similar to that on Earth during the Archean eon, which lasted from about 4 to 2.5 billion years ago and saw the formation of the first continents and the emergence of life. During this time, Earth’s mantle was hotter and more convective than it is now, and the crust was thinner and more prone to deformation and melting. The tectonic activity on Venus may have been driven by a similar mechanism, such as mantle plumes or subduction zones, which would have created a cycle of crustal growth and recycling.

The implications of this study are significant for our understanding of how planets evolve and how they can support life. If Venus had a continent or supercontinent in the past, it could have had a more diverse and stable geology than previously thought, with different types of rocks, minerals, and environments. This could have provided niches for microbial life to emerge and evolve, even if the surface was inhospitable to complex organisms. The tectonic activity on Venus could also have influenced the climate and the atmosphere, by releasing gases from the mantle or by creating volcanic aerosols that reflect sunlight and cool the planet.

The study of Venus is still in its infancy, but it is gaining momentum and attention from scientists and space agencies around the world. NASA and ESA are planning new missions to Venus in the next decade, which will use advanced instruments and technologies to explore the planet’s surface, atmosphere, and interior. These missions will also search for signs of life, past or present, by looking for biosignatures in the rocks, gases, or clouds of Venus. The discovery of tesserae on Venus is a reminder that even the most familiar and seemingly hostile worlds can surprise us with their secrets and similarities.