Venus is a puzzle: Our nearest planetary neighbor probably started out looking much the same as Earth, but somewhere along the line the two planets’ paths diverged. Several spacecraft have studied Venus from orbit, and even a few have studied it from the ground, but there’s still much we don’t know. Does Venus currently have lightning, quakes, or active volcanoes? How does its atmosphere move and interact with the surface? Is it possible for life to exist in its clouds?
The planet’s surface is dry and barren, smothered by a thick, poisonous atmosphere, and baked by a hellish heat. Instruments placed on the surface have been destroyed in a matter of hours, and orbiting craft have struggled to get a complete, detailed picture of the surface at all wavelengths. Aerobots (balloons), however, can conduct a wide array of scientific investigations without experiencing harsh conditions on the surface or the limitations of orbital craft.
What Is an Aerobot?
Aerobots are robotic balloons. Some can change their altitude by becoming more or less inflated and move through the air directed by autonomous guidance systems. A Venus aerobot would likely be roughly 10 meters in diameter and carry a payload of more than 20 kilograms of scientific instruments.
An aerobot, like the Soviet Union’s Vega balloons in 1985, could map the planet’s surface features, gravity, and magnetic field as it travels the friendly Venusian skies. It could also act as a relay station between a ground-based instrument and an orbiting spacecraft. Several current Venus mission ideas include an aerobot component that acts as both an independent investigator and a support craft.
Ground to Air
Can an airborne balloon detect seismic activity happening below ground? It’s possible because Venus’s surface and its dense atmosphere have a strong connection. An underground quake would cause vibrations that would travel upward through the air as acoustic waves. Those waves could then be measured and decoded by balloon-borne instruments. Several groups are currently testing the technique, called infrasound, on Earth to better understand how to make it work on Venus, too.
Venus has many volcanoes and volcanic features, but is the planet volcanically active today? This is one of the major unanswered questions about Venus, and a network of balloons could help answer it. If the planet rumbles with any volcanic activity, the rumbles travel through the atmosphere as acoustic waves. A trio of aerobots carrying infrasound microphones could then triangulate the signal and pinpoint the location of volcanic activity, which could then be studied by an orbiting satellite.
Up in the Clouds
The clouds in Venus’s lower and middle atmosphere might be prime real estate for microbial life. Venusian clouds have temperatures between 0°C and 60°C, atmospheric pressures 0.4–2 times that at Earth’s sea level, aerosols, and liquid water droplets. With the right analysis tools on board, an aerobot flying about 50 kilometers up could measure the chemistry of the clouds and collect samples of aerosols or droplets. As the bot moved around, it could map how the chemistry, and the potential for life, varies in three dimensions.
Flying through Venus’s atmosphere would provide a golden opportunity to study it in situ. Spectroscopic instruments could measure atmospheric chemistry with unprecedented detail. A balloon could help build 3D maps of Venus’s wind patterns, its atmospheric temperature and pressure, how it filters sunlight down to the surface, and how gravity waves and planetary waves travel through the air. Each of these measurements also would be essential for the aerobot’s navigation and for interpreting other discoveries, balloon based or otherwise, of the planet.
—Kimberly M. S. Cartier (@AstroKimCartier), Staff Writer
Cartier, K. M. S. (2021), Exploring Venus by balloon, Eos, 102, https://doi.org/10.1029/2021EO156737. Published on 01 April 2021.
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