When it comes to literary allegories, Venus is about as close to Dante's description of hell as one can get! Its atmosphere is 93 times as dense as Earth's, which is equal to the pressure found 900 m (3,000 ft) underwater, enough to crush the human body. It's also the hottest planet in the Solar System, with temperatures reaching 467 °C (872 °F), which is hot enough to melt lead. Unlike Earth, its surface is not composed of tectonic plates that are constantly shuffling around, but a single-piece crust.

Until recently, scientists believed that this meant Venus was geologically inactive, though recent findings have challenged this. According to a new study by ETH researchers, Venus is not only geologically "alive" but hosts many active volcanoes. This is evident from Venus' rift valleys (aka chasmata), lowland features similar to those on Earth that form when tectonic plates move apart. These features show that Venus also experiences tectonic activity, creating rifts that can measure up to 10,000 km (~6,200 mi) in diameter.

The research was led by Xi Yang, a graduate student from the Department of Earth and Planetary Sciences (DEPS) at ETH Zürich as part of his Master's studies. He was joined by Taras V. Gerya, a Professor of Geodynamics in the DEPS (and Yang's supervisor), and Dr. Anna J. P. Gülcher, a Geosciences researcher from the University of Freidburg and the Center for Space and Habitability at the University of Bern. Their results are published in a paper that appeared in Nature Geosciences.

Current research reveals that Venus is not only geologically active, but has active volcanoes on its surface.

Credit: NASA/JPL-Caltech/Peter Rubin

Previous models of Venus' geological evolution, along with data provided by NASA's Magellan probe (which observed Venus between 1990 and 1994), have confirmed that large rift valleys exist on Venus. Previous models indicated that broad ridges (rift flanks) form along the edges of rift valleys when they are geologically young and are either still moving or have only recently ceased.

Until now, geoscientists believed that they formed more than 100 million years ago, but this has remained unconfirmed. What's more, earlier models had relied on simplified material assumptions and been mostly two-dimensional. As a result, the question of whether Venus is still geologically active or not has remained unresolved. To address this, Yang and his team employed a new computer model to create the first high-resolution 3D models of Venus' surface, focusing on the Ganis, Dali, and Devana Chasmata.

This allowed them to accurately replicate these rift structures and provide better explanations of their formation. Their model shows that rift flanks on Venus tend to flatten rapidly after movement ceases, meaning that systems become less steep and narrow their flanks with age. Unlike Earth, where erosion gradually wears down features, Venus’s flanks subside due to crustal relaxation. Their simulations also suggest that these rifts widen at a rate of 3 to 10 cm (~1.2 to 4 inches) a year, which is faster than previous models suggested.

Based on their modeling and observational data from Magellan and other missions, the researchers conclude that Venus remains geologically active and has a more dynamic interior than previously thought. “The results help us to better assess the tectonic activity on Venus,” says Gerya. This is particularly important considering that NASA and the ESA are preparing multiple missions to explore Venus' atmosphere, surface, and interior structure in the near future.

Comparison between the crustal model at 700,000 years (top figure) and the actual Dali Chasma rift system (bottom).

Credit: Xi Yang/ETH Zürich

The results of their model could help mission planners pinpoint geologically active regions for these missions to study. Interestingly, Taras Gerya and fellow ETH geophysics professor Paul Tackley (and their colleagues) are participating in mission planning for ESA's EnVision mission, a probe that is scheduled to launch in the 2030s to study Venus' atmosphere, surface and interior, and how they interact with each other.

Similarly, the team's findings are shaking up what scientists know about how rocky planets in our Solar System formed, and could have applications in the search for habitable exoplanets.

Further Reading: 

• ETH Zurich, Nature Geoscience

Rover data from more than 20 years ago has revealed clues to the existence of liquid water on ancient Mars. The NASA Spirit Rover carried a specialized instrument called a Mössbauer Spectrometer that performed mineralogical analyses of soil, rock, and dust on the surface of the Red Planet at Gusev Crater. Individual measurements didn't always indicate definitive proof of water, but when scientist Paolo de Souza of Edith Cowan University in Australia examined years' worth of measurements together, a definite pattern began to show up in the existence of minerals that could only exist in the presence of water. His analysis shows that Mars used to sport a lot more water than scientists expected and that the data showing its existence was in the data all along.

A panorama of the region where the Spirit rover landed inside Mars's Gusev Crater. Dust and soil at the site show traces of water-related minerals, including altered magnetite and hematite.

Credit: NASA/JPL-Caltech/Cornell

De Souza was particularly interested in the existence of hematite and altered magnetite measured in the Martian soil. These two minerals often form when rocks interact with water. Hematite, in particular, is at the heart of the amazing "blueberries" found on Mars at Meridiani Planum by the Opportunity rover. The traces of hematite in de Souza's study were excavated from 32 Gusev soil sites that were undisturbed. The result of de Souza's work is the most detailed iron-mineral profile of Martian soil done to date. Scientists didn't expect to find hematite in the soils at the site, so the finding was a surprise. It turns out it was there all along, just in amounts too small in each rover sample measurement.

"One of the most important discoveries was finding crystalline hematite in ordinary Martian soil," Professor de Souza said. "This mineral's widespread presence suggests not only that water was present, but that significant areas of Mars may have once been covered by water."

Hematite, Magnetite and Water on Mars

Hematite is what's called an "iron oxide". It forms in the presence in liquid water, as well as in volcanic regions. On Mars, both types of environments exist, but the regions where the hematite is found appear to be largely shaped by past contact with water. That's why de Souza and others suspect that these areas of Mars were once inundated with water.

Magnetite occurs in both igneous (volcanic) rocks as well as in sedimentary rocks here on Earth. It's also an iron-bearing mineral, and on Mars, its presence indicates that water and rocks interacted. The fact that it's also found in widespread areas indicates a warmer, wetter past on Mars.

Martian "blueberries" as seen by the Opportunity Rover at Meridiani Planum during its exploration. These hematite orbs likely formed in contact with water.

Credit: NASA/JPL Public Domain.

The layers of dust that the rover studied in Gusev Crater that contain traces of the water-related minerals are found across the planet. De Souza's findings suggest that the layer of dust extends across huge areas of Mars. It likely formed over millions of years thanks to constant wind erosion, temperature changes, and storms that moved huge quantities of dust across the Martian surface.

Revisiting Past Data

According to de Souza, each rover measurement wasn't enough to come to a definitive conclusion about water on Mars. But, taken together, they paint a striking picture of Mars's past. "Many measurements were not detailed enough on their own to identify minerals present in very small quantities," he said. "By bringing the data together and analysing it in a new way, we were able to reveal information that had been hidden for years."

It took de Souza several years of painstaking work, sifting through all the measurements, to construct the picture of water on Mars, particularly at Gusev Crater. He had to take into account a number of factors at play during the measurements, including temperature conditions, samples from different soil regions, physical and chemical weathering of the surface materials, and the effects of millions of years of global dust storms. He described the details in a paper submitted to Springer Nature (cited below).

In the future, de Souza will do a similar analysis of data from soils studied by the Opportunity rover at Meridiani Planum. If it works out as expected, hundreds of measurements will be analyzed and combined to form a "big picture" assessment of water on Mars in that region, as well. The work on the Gusev Crater and Meridiani Planum soils also points out the need for future missions to the Red Planet to carry spectrometers to do longer-term studies of the soil than the Opportunity and Spirit instruments were able to do.

For More Information

• New ECU Discovery Adds to Evidence Mars Once Had Water
• A Consolidated Mössbauer Spectrum for Undisturbed Soils from Gusev Crater, Mars