Venus is sometimes called Earth’s sister planet because of their shared physical, geological, and atmospheric features. Scientists have discovered something new about Venus’ geology that’s reminding us of the similarities between the two planets. We have to look deep inside both planets to see what the researchers found.

There are a few reasons why the pair of planets are sometimes called twins. They have several characteristics in common:

• They’re inner Solar System neighbours.
• They’re both rocky.
• They’re roughly the same size and mass.
• They both have few craters, implying young surfaces.
• They both have atmospheres and dense clouds.
• They both have geological similarities and surface features like volcanoes, mountains, plateaus, and plains.

New research published in Nature Geoscience focuses on the last item in that list. Its title is “Ishtar Terra highlands on Venus raised by craton-like formation mechanisms.” The lead author is Fabio Capitanio, an Associate Professor from the Monash University School of Earth, Atmosphere and Environment.

Ishtar Terra is one of three large highland regions on Venus. Its topography includes mountains, plains, and plateaus. The Maxwell Montes mountain chain is in Ishtar Terra, and it’s about 11 km (6.8 mi) high, compared to Mt. Everest, which is 8.8 kilometres (5.5 mi).

Ishtar Terra has highly complex terrain and appears to be heavily deformed. These are indications that Venus underwent powerful geological activity in its past.

Ishtar Terra also contains Lakshmi Planum, a two million square kilometre plateau about four km high and surrounded by extremely deformed terrain. It’s made of smooth lava flows and features two large shield volcanoes. Colette Patera is about 130 km in diameter, and Sacajawea Patera is about 200 km across and 1-2 km deep. Though Venus is tectonically inactive now, scientists think that ancient tectonic activity is responsible for the region’s wild topography.

The new research in Nature Geoscience zeroes in on a specific part of geology called cratons. Cratons are the ancient geological cores of Earth’s continents. They’re stable parts of Earth’s lithosphere that are usually found in the center of the planet’s continental plates. Cratons have survived Earth’s extensive history of continental rifting and merging. They’re typically composed of extremely durable basement rock and have deep roots that can extend several hundred kilometres into the planet’s mantle.

Some cratons date from the Precambrian era, more than 2.5 billion years ago. Others may be even older and could date back to the Earth’s early days during the Hadean and Archaean Eons.

In this new work, Capitanio and his co-researchers used data from NASA’s Magellan spacecraft and high-performance computer simulations to investigate the formation of Ishtar Terra more deeply. They found that Ishtar Terra may have formed the same way that Earth’s cratons may have formed.

“The structures emerging in this model provide topography, gravity and crustal thicknesses remarkably comparable to the plateaus of Venus.”

From “Ishtar Terra highlands on Venus raised by craton-like formation mechanisms.”

On Earth, plateaus and belts of mountains like Ishtar Terra would clearly result from colliding continental plates. Ishtar Terra is similar to the Tibetan Plateau, and continental collision is the primary driver behind its formation. Something else must be behind Ishtar Terra and Venus’s other terrae because the planet lacks plate tectonics. But Ishtar Terra shares something particular with Earth. It has a thick crustal floor similar to Earth’s cratons.

This suggests that the planets have or had processes in common. Ishtar Terra and Venus’ other terrae may have risen from the planet’s hot interior. While there are several competing explanations for the formation of Earth’s cratons, one is the molten plume model. It states that rising plumes of molten rock came from deep within Earth’s mantle and built up thick layers with the cratons on top.

“The study challenges our understanding of how planets evolve,” lead author Capitanio said. “We did not expect Venus, with its scorching 460°C surface temperature and lack of plate tectonics, to possess such complex geological features.”

While Venus doesn’t have plate tectonics, it does have a hot lithosphere. The planet’s surface temperature is about 460°C (860°F). The heat extends into the lithosphere, which is hotter than Earth’s due to Venus’s runaway greenhouse effect. The surface simply can’t shed heat the way Earth does. The high heat means that Venus’s lithosphere is probably thinner than Earth’s. While Earth’s lithosphere can be as thick as 200 km, maybe even thicker, Venus’s is only about 50-100 km thick. Since it’s so much thinner, it’s also weaker.

“Venus’s hot lithosphere might make it a good analogue of early Earth and might enable the same types of continent-forming processes that occurred on Earth,” the researchers write in a briefing from Nature. “Our focus was on Ishtar Terra, the broadest of the plateaus, for which we found that the topography, crustal thicknesses and gravity signals are consistent with our simulations when the modelled lithosphere is about 10–50 times weaker than Earth’s.”

The thin lithosphere favours “the emplacement of a thick magmatic crust on top of a deep residual
depleted mantle,” the authors write in their research.

“This finding provides a fascinating new perspective on Venus and its potential links to early Earth,” Capitanio said. “The features we found on Venus are strikingly similar to Earth’s early continents, suggesting that the dynamics of Venus’ past may have been more similar to Earth’s than previously thought.”

The research shows that despite their differences, divergent rocky planets can share underlying mechanisms. Spotting these cratons or craton-associated mechanisms on another planet can help scientists understand Earth. “By studying similar features on Venus, we hope to unlock the secrets of Earth’s early history,” Associate Professor Capitanio said.

Venus is like the Solar System’s plan B. If life couldn’t make it work on Earth, maybe it could’ve worked on Venus. There’s evidence that Venus may have once had liquid water and used to be in the habitable zone, though that’s not certain. In any case, while Earth is resplendent with life, Venus is far too hot.

Earth’s ancient cratons are a part of Earth’s story. On our planet, geology, life, and the planet’s atmosphere are all intricately connected. By recognizing what Earth and Venus have in common and how they are also so different, researchers can learn more about Earth’s trajectory toward a living planet.

Future missions to Venus are in the works, and they should provide even more explanations for the sister planets’ divergent outcomes.

“Our research has paved the way for future missions to Venus, such as DAVINCI, VERITAS, and EnVision,” Capitanio said. “These missions will provide further insights into Venus’ geological history and its connection to Earth.”