Venus is nearly identical to Earth in terms of size, mass, and density. Inferring that its internal heat generation (from the disintegration of radioactive atoms) is roughly equal to that of Earth. One of the most significant ways this heat escapes from Earth is through volcanic eruptions. If a typical year is anything to go by, at least fifty volcanoes will erupt.
But, until recently, there were no obvious traces of volcanic eruptions on Venus, despite decades of searching. The University of Alaska, Fairbanks geophysicist Robert Herrick presented the results of a new study at this week’s Lunar & Planetary Science Conference in Houston, Texas, and the findings were published in the journal Science.
Because of its thick atmosphere, which includes an uninterrupted cloud layer at a height of 45–65 km and is opaque to most wavelengths of radiation, including visible light, studying Venus’s surface presents a number of challenges. In order to see the ground clearly from above the clouds, radar beams must be sent downward from an orbiting spacecraft.
In order to piece together a picture of the surface, a process called aperture synthesis is employed. This incorporates the time lag between sending a radar signal and receiving an echo back from the ground, as well as the frequency shift that occurs as a spacecraft approaches or departs from the source of an echo. Similar to a black-and-white photograph, the end product has lighter parts representing rougher surfaces and darker areas representing smoother ones.
With a spatial resolution of around a hundred meters at most, this radar method was utilized by NASA’s Magellan probe while it orbited Venus from August 1990 to October 1994. This discovery revealed that more than 80% of the landmass is covered by lava flows, but for the following three decades, scientists were unable to determine how recently the youngest lava flows erupted or if any eruptions are still occurring.
Spacecraft have seen numerous signs of activity through the clouds, which suggests the rocks there are so young that their minerals have not yet been changed by reactivity with the acidic atmosphere and are therefore freshly erupted lava.
As well as these thermal anomalies, which may indicate ongoing lava flows, scientists have also picked up on temporary local fluctuations in the concentration of sulfur dioxide in the atmosphere, which is another possible marker of volcanic eruptions. In spite of this, none of them were entirely persuasive.
Observation of a Volcanic Eruption
The current study appears to have put an end to the debate by identifying surface alterations that can only have been caused by volcanic activity. Hundreds of hours were spent comparing Magellan radar photos of previously observed regions of Venus for new or altered features by the authors.
They zeroed down on the most plausible volcanic locations and found an instance when data from two images taken in the same year, but months apart (October and February) were inconsistent. A volcanic explosion around that time period is the most likely explanation for the alterations they saw.
Radar pictures present challenges for verifying surface changes due to the fact that the appearance of even a stable surface can vary with surface slopes and direction of view. Researchers used simulations to rule out these potential causes for the observed shifts.
The two photos reveal a 1.5-kilometer-wide volcanic crater that expanded eastward by half and doubled in size between February and October. The scientists speculate that the crater is a collapsed volcanic vent that was largely filled by fresh lava in the month of October and that it has shrunk in size as a result.
New lava flows, which may have flowed over the crater rim or seeped out of an adjacent fissure, may stretch several kilometers down the slope, north of the crater. Maat Mons, one of Venus’s greatest volcanoes, with an active crater that rises around 5 kilometers above the surrounding plains.
Destinations for future missions
Volcanic activity on Venus was already known to be the norm among planetary scientists. How frequently and where on Venus eruptions are taking place will now likely be the center of interest. The fact that it took 30 years for Magellan data to finally yield evidence of surface changes is the biggest surprise.
Both the Veritas and EnVision missions are motivated in large part by the hope of discovering and researching active volcanism (both approved in 2021). Each one will have an imaging radar superior to that of Magellan. In 2034, EnVision is scheduled to enter Venus orbit. Although Veritas was expected to arrive early, timetable slips have pushed back the arrival date by several years. The video clip for “Venus’s First Evidence of Active Volcanoes” may be found down below-
About ten years from now, we’ll be in for an exciting moment, with NASA’s DaVinci mission arriving a year or two ahead of them to provide optical photographs from below the clouds during its descent.