Data from NASA’s long-canceled Magellan Radar Imaging Mission to Venus provides the first indirect detection of large lava tubes (pyroducts) on the western flank of the sister planet’s giant Nyx Shield volcano.
In a new paper just published in the journal *Nature Communications*, the authors detail how they used a new technique to extract data from Magellan’s Synthetic Aperture Radar (SAR). This new analytical technique reveals the existence of a huge open skylight above a large underground lava tube conduit.
The lava tubes are the result of ancient volcanic activity on Venus, Lorenzo Bruzzone, one of the study’s co-authors and a radar and remote sensing scientist at the University of Trento in Italy, told me via email. Lava tubes form within basaltic lava flows, and low-density lava continues to move beneath the solidifying surface, Bruzzone said.
How can this happen?
Sometimes a hard crust grows inward from the edges of the lava channel, sometimes the overflow of lava builds up the channel’s banks and forms a roof, and sometimes floating pieces of cooled lava coalesce and solidify to form a continuous ceiling, Bruzzone said.
Perhaps one of the reasons it took so long to identify such lava tubes on Venus is simply because Venus is surrounded by an extremely dense cloudy atmosphere, making it impossible to see its hellish surface with regular optical telescopes.
NASA’s Magellan spacecraft was the first orbital mission to use radar imagery to map nearly the entire surface of Venus. In fact, during its four-year mission from 1990 to 1994, the spacecraft mapped about 98 percent of Earth’s surface.
How did Magellan’s SAR instrument enable such mapping?
The authors point out that SAR works by sending radio waves toward the Earth’s surface and measuring the time it takes for the radio waves to return after interacting with the terrain. By processing the returned radar signals, a detailed backscatter map of Venus’s surface was created, they wrote. Magellan therefore detected the presence of several shaft chains on Venus, revealing one of the main indicators of the possible existence of lava tubes, the authors write.
*This overall view of Venus’ surface is centered at 180 degrees east longitude. A Magellan synthetic aperture radar mosaic from the first cycle of Magellan mapping is mapped onto a computer-simulated globe to create this image. Gaps in the data will be filled with data from the Pioneer Venus Orbiter, or with certain intermediate values. Simulated colors are used to highlight small-scale structures. The simulated hues are based on color images recorded by the Soviet Union’s Venera 13 and 14 spacecraft. NASA/JPL-California Institute of Technology*
Until now, lava tubes on Venus have been hypothesized, but never confirmed, even indirectly.
In some cases, lava tubes can develop as fresh, hot lava flows underneath and the cooled lava layer gradually expands, Bruzzone said. Once a lava tube forms, he says, if the lava supply dwindles or completely stops, it can leave partially or completely drained underground conduits.
Lava tubes are also known to be widespread on Earth (Hawaii and Spain), Mars, and the Moon.
The average diameter of this Venusian lava tube is approx. It is approximately 525 meters deep, 375 meters high, and covered with a roof approximately 150 meters thick.
Magellan radar data indicates that this tube is at least 300 meters long, but probably much longer. The researchers hypothesize that other similar underground conduits on Venus could extend tens of kilometers further.
The authors say they hypothesize that there is a pile of rocks on the floor of the pit due to the collapse of the roof. However, they write, the height of the cavity, measured from the top of the rock, is about 300 meters.
The identified lava tubes appear to be wider and taller than those observed on Earth or predicted for Mars, Leonardo Carrere, lead author of the paper and a radar and remote sensing scientist at the University of Trento in Italy, told me via email. And that’s on the upper end of what scientists have suggested (and in some cases have observed) on the moon, he told me.
It remains to be seen whether the detection of these underground tubes will change current thinking about Venus. But it’s a start.
Until now, researchers have not had the opportunity to directly observe the processes occurring beneath the surface of Earth’s twin planet, Carrère said.
Chronology of the geological evolution of Venus
The discovery adds a new element to the reconstruction of Venus’s geological evolution, Carrère said. The findings confirm that Venus also has underground caverns, and that these caverns can reach enormous dimensions, he said.
Over the next decade, planetary scientists hope to learn more about Venus’ potentially vast network of ancient lava tubes.
Future missions to Venus planned over the next decade, including the European Space Agency’s Envision and NASA’s Veritas, will carry advanced radar systems capable of capturing high-resolution images, allowing scientists to study tiny holes in the surface in more detail, according to the University of Trento.
Envision will also carry an orbital ground-penetrating radar that can probe Venus to depths of hundreds of meters and potentially detect conduits even when there are no openings on the surface, Trento University notes.
What is the conclusion?
This is further evidence that our brother planet is geologically alive and that Earth continues to interact with and build up its already massive atmosphere, Stephen Cain, a planetary astrophysicist at the University of California, Riverside, who was not involved in the study, told me via email. This is important information for understanding the large number of Venus- and Earth-sized planets orbiting other stars, many of which are about the same age as the twin planets, Cain said.