Archival images of Venus show that part of the surface has changed quite a bit in eight months. Two planetary scientists think this is a likely sign that the long-sought volcanic activity on Venus happened as recently as 30 years ago, giving an extra boost to plans for future missions that are still being considered.
Some frozen moons and other icy worlds show signs of cryovolcanoes, but true volcanism is rare in the solar system. Aside from Earth, the only place it’s been observed is Io, although some lava flows on Mars look fairly fresh. Venus was certainly once volcanically active — huge mountains like Maat Mons bear witness to this, but planetary scientists are unsure whether robotic emissaries will witness it.
Even if Venusian volcanism returns, such events could now be so rare that our chances of observing them are slim. However, a more hopeful scenario is presented in the journal Science, based on a comparison of images taken by the Magellan spacecraft.
Magellan spent four years in orbit around Venus, measuring its gravitational field and mapping the surface with radar. In that time, it completed three radar mapping cycles of parts of the planet’s surface from different altitudes, but only 8 percent were mapped all three times and 42 percent twice. No obvious eruptions were detected in the images, suggesting that when activity is present, it is much more sparse than on Io.
Thirty years later, Professor Robert Herrick of the University of Alaska, Fairbanks, and Dr. JPL’s Scott Hensley images for the Atla Regio region and found what they believe to be a volcanic vent. More importantly, the vent is larger and has a different shape in the second set of images than in the first.
Herrick and Hensley believe the most likely explanation is that lava erupted from the vent and reshaped the surface in the meantime.
In the first image, the vent is about 2.2 square kilometers (0.9 sq mi) and roughly circular. In the later it is nearly 4 square kilometers (1.5 sq mi) and more irregular, with apparently shorter walls.
On Earth, the most likely cause of such changes would be the appearance of a lava lake. The authors believe the same is true on Venus, although they are unsure whether the second image shows a liquid or something that has managed to cool to a solid despite the blisteringly hot environment.
Herrick and Hensley concede that a Venusquake could trigger similar changes, but even that would likely indicate volcanic activity, such as B. Magma escaping from a reservoir beneath the vent.
If the volcanic activity is real, Magellan may have been lucky, but it’s more of a sign that such things are common on Venus. That would be interesting because the majority of volcanoes on Earth form at plate tectonic boundaries, which Venus does not have. A hotspot like the one that created Hawaii is the most likely cause.
“We can now say that Venus is currently volcanically active, in the sense that there are at least a couple of eruptions per year,” Herrick said in a statement. “We can expect that the upcoming Venus missions will observe new volcanic flows that have occurred since the end of the Magellan mission three decades ago, and we should monitor some activity while the two upcoming orbital missions collect imagery.”
It may seem odd that the authors would have discovered something that had been overlooked for so long, but differences in the heights and angles at which the images were taken make comparisons difficult. Herrick explained, “Actually, only in the last ten years has the Magellan data been available in full resolution, mosaicked, and easily manipulated by an investigator with a typical personal workstation.”
Still having to search manually, the authors focused on the area around the largest volcanoes, which are similar in size to the largest on Earth but much smaller than Olympus on Mars.
The study was published in Science.