Return to Newsletter Index

Seeing the Heat

by Perry Pezzolanella

Images of planets, moons, asteroids, and comets as seen by a spacecraft are stunning and always reveal surprises. All that is required is a suite of superior imaging systems and sunlight. The former is correct, but the later is not. There are situations where night time is the best time. There is a new mission that will look for volcanic activity and determine rock types at night from orbit with the planet completely obscured by clouds.

EnVision is an orbital mission to Venus being developed by the European Space Agency (ESA) that was approved on June 10, 2021. It will perform high resolution radar mapping and atmospheric studies to help scientists understand the relationship between geological activity and the atmosphere and figure out how and why Venus and Earth evolved so differently. The mission’s goals are: 1) Determine the level and nature of current geological activity. 2) Determine the sequence of geological events that generated its range of surface features. 3) Assess whether Venus once had oceans or was hospitable for life. 4) Understand the geological framework that controls the release of internal heat throughout the history of Venus.

EnVision will carry three instruments and a radio-science experiment. The Venus Synthetic Aperture Radar (VenSAR) will do regional and targeted surface mapping from polar orbit along with global topography and altimetry, stereo imaging, surface radiometry and scatterometry, surface polarimetry, and repeat pass interferometry opportunities. It will be able to characterize the processes that shaped the surface past and present including current volcanic, tectonic, and sedimentary activity. The Venus Subsurface Radar Sounder (SRS) will search for subsurface material boundaries such as craters and their infilling, tesserae (tiled ridges) and their edges, plains, lava flows and their edges, and tectonic features to determine their depths and ranges. The Venus Spectrometry Suite (VenSpec) will perform extremely high resolution atmospheric measurements of sulfur, sulfur dioxide, and the mysterious ultraviolet absorber in the clouds. It will also search for variations in surface temperatures and concentration of volcanic gases as evidence for volcanic eruptions. A radio science experiment will allow EnVision to map the gravity field of Venus eliciting clues to the structure of the crust in relation to the topography, and the size and state of the core.

The thick clouds will not hamper EnVision which will use sophisticated instruments that will be able to look for evidence of past oceans by looking for ancient shorelines, not in visible light, but in the infrared. The clouds are transparent to heat at certain infrared wavelengths causing the hot surface to appear bright at night. The hotter canyons and lowlands are brighter and the cooler highlands and mountains appear dimmer in infrared. EnVision will be able to determine the rock types by analyzing the spectra in infrared. Some rock types such as granite form in the presence of water. If Venus has large tracts of granite, then Venus had to have had oceans. That will firmly answer the past, but how did Venus become the hellishly hostile world it is today? The focus will be where there is activity today. Volcanic hot spots, eruptions, and lava flows will show up in the infrared as they will be much hotter and glow brighter at night than the blistering nearly 900ºF surface. Venus Express detected suspected areas as hot as 1300ºF. Volcanic gases in the atmosphere can also be detected and studied, such as the sudden increase in sulfur dioxide that has been occasionally detected by other orbiting spacecraft through the decades. Sulfuric acid breaks down over time, but it is present in the clouds. EnVision will determine if volcanic eruptions are replenishing the acid.

EnVision is scheduled to launch between late 2031 and early 2033 and will join NASA’s Venus missions, DAVINCI+ and VERITAS. Together these missions will determine how the tectonics and geological activity affect the surface and if it affects the atmosphere. Venus has guarded it secrets well and has been a neglected target of extensive and thorough exploration for decades. Now a new armada of spacecraft will usher in the Decade of Venus in the 2030s finally revealing the burning secrets that Venus conceals.