Data from NASA’s long defunct Magellan radar-imaging mission to Venus has made the first indirect detection of a large lava tube (pyroduct) on the Western flank of our sister planet’s massive Nyx Mons shield volcano.
In a new paper just published in the journal *Nature Communications*, the authors detail how they used a new technique to tease out data from Magellan’s Synthetic Aperture Radar (SAR). This new analysis technique revealed the existence of a massive open skylight above a large subsurface lava tube conduit.
The lava tube is the result of ancient volcanism on Venus, Lorenzo Bruzzone, one of the paper’s co-authors and a radar and remote sensing scientist at the University of Trento in Italy, tells me via email. Lava tubes form within basaltic lava flows, where low-density lava continues to move beneath a solidifying surface, Bruzzone tells me.
How does this happen?
In several ways: a solid crust may gradually grow inward from the edges of a lava channel, lava overflows can build up the channel’s levees until they form a roof, or floating fragments of cooled lava can merge and solidify into a continuous ceiling, says Bruzzone.
Arguably, one reason such lava tubes on Venus took so long to confirm is simply because Venus is cloaked in a hyperdense cloud-covered atmosphere that doesn’t permit normal optical telescopes to view its hellish surface.
NASA’s Magellan spacecraft was the first orbital mission to map almost the whole of Venus’ surface using radar imagery. In fact, during its four-year mission from 1990 to 1994, the spacecraft mapped some 98 percent of the planet’s surface.
How did Magellan’s SAR instrument enable such mapping?
SAR works by transmitting radio waves towards the surface and then measuring the time it takes for waves to bounce back after interacting with the terrain, the authors note. By processing the returned radar signals, a detailed backscattering map of the Venusian surface has been produced, they write. Thus, Magellan detected the presence of several pit chains on Venus, revealing one of the main indicators for the possible presence of lava tubes, the authors write.
*This global view of the surface of Venus is centered at 180 degrees east longitude. Magellan synthetic aperture radar mosaics from the first cycle of Magellan mapping are mapped onto a computer-simulated globe to create this image. Data gaps are filled with Pioneer Venus Orbiter data, or a constant mid-range value. Simulated color is used to enhance small-scale structure. The simulated hues are based on color images recorded by the Soviet Venera 13 and 14 spacecraft. NASA/JPL-Caltech*
Until now, such Venus lava tubes have been hypothesized but never confirmed, even indirectly.
In some cases, lava tubes develop through the gradual inflation of cooled lava layers as fresh, hot lava flows beneath them, says Bruzzone. Once a lava tube has formed, a reduction or complete halt in lava supply can leave behind a partially or fully drained underground conduit, he says.
Lava tubes are known to be prevalent on earth (in Hawaii and Spain) and on Mars as well as our Moon.
This Venus lava tube has an average diameter of about a diameter; lies at a depth of about 525 meters, has a height of about 375 meters, and is covered by a roof approximately 150 meters thick.
Magellan’s radar data indicates that the tube is at least 300 meters in length yet is likely much longer. The team hypothesizes that other such Venus subsurface conduits could extend for an additional tens of kilometers.
We hypothesize the presence of a rock pile on the pit floor, originating from the roof collapse, say the authors. Yet the cavity height measured from the top of the rock pile is about 300 meters, they write.
The lava tube that has been identified appears to be wider and taller than those seen on Earth or predicted for Mars, Leonardo Carrer, the paper’s lead author and a radar and remote sensing scientist at the University of Trento in Italy, tells me via email. And it falls at the upper end of what scientists have suggested (and in one case observed) on the Moon, he tells me.
It’s still unclear whether the detection of these subterranean tubes will change our current ideas about Venus. But it’s a start.
Before now we have never had the opportunity to directly observe processes occurring beneath the surface of Earth’s twin planet, says Carrer.
This discovery adds another piece to the reconstruction of the geological evolution of Venus, says Carrer. We can now confirm that Venus also hosts subsurface caves, and that these caves can reach huge dimensions, he says.
In the next decade, planetary scientists hope to learn much more about Venus’ potentially extensive network of ancient lava tubes.
Future Venus missions planned for the next decade, such as the European Space Agency’s Envision and NASA’s Veritas which will carry advanced radar systems capable of capturing high resolution images, allowing scientists to study small surface pits in greater detail, says the University of Trento.
Envision will also carry an orbital ground penetrating radar (Subsurface Radar Sounder) capable of probing Venus’s subsurface to depths of several hundred meters and potentially detecting conduits even in the absence of surface openings, the University of Trento notes.
The Bottom Line?
This is further evidence that our sibling planet is geologically alive and well, and that the planet is continuing to interact with and build its already massive atmosphere, Stephen Kane, a planetary astrophysicist at the University of California, Riverside (who was not part of the study) told me via email. This is important information for understanding the plethora of Venus/Earth-size planets orbiting other stars, many of which are a similar age to our twin planets, says Kane.
