Earth’s nearest planetary neighbor, Venus, is similar to our world in size, but its environment it truly alien. The weather on Venus is ruled not by water, but by battery acid. Venus seems endowed with more than its share of sulfur, and that sulfur combines with other elements to form complex things like sulfuric acid hazes. Acid rain is a real issue on Venus.
What can we learn from our cosmic neighbor, and how can it help us better care for our own world?
For the answer to this and other questions, researchers like the Jet Propulsion Laboratory’s Viktor Kerzanovich have been working to send an ambitious balloon mission to the hothouse world. The probe is called VALOR, for Venus Atmospheric Long-duration Observatory for in-situ Research.
In interviews conducted by the author with several project scientists for a forthcoming book, Kerzanovich said:
We have been working for several years to fly a new type of balloon on Venus that will last for about 30 days, so we hope that this will be a very spectacular and very science-rich project. VALOR is a big balloon that can carry about 400 kilos above the Venus surface.
VALOR would be the third balloon to visit the skies of Venus. In 1985, two comet-bound Soviet probes dropped off landers at Venus, each carrying an “aerostat” balloon probe designed by Soviet and French engineers. As the landers descended, they released their helium-filled balloons some 33 miles above the ground. The altitude was important, says balloon designer Jacques Blamont:
Venus ballooning is very easy above 50 kilometers [31 miles] altitude. It is more cool up there. At lower levels, it is still possible, but has not been done.
Each Teflon balloon spanned 11½ feet in diameter and carried a battery-powered instrument gondola to observe pressure, temperature, light levels, windspeeds, and mist density. The missions lasted until their batteries gave out, nearly 48 hours into each flight.
VALOR has distinct advantages over its predecessors. The key to VALOR’s success will be longevity — the mission calls for a thirty-day cruise. To that end, the system must be robust, explains Kerzhanovich:
The whole idea is to make it impermeable so it will not lose the gas in a month and maybe forever. It will be built of very strong material, the same material that MER (Mars Exploration Rover) air bags were made of. And remember on Mars when you dropped this 400 kilos of MER experiments with the speed of about 20 meters per second they didn’t pop.
VALOR carries six times the payload of earlier balloons, and will return 100 times the data in a mission lasting 15 times as long.
JPL’s Kevin Baines believes the next generation of science for Venus must come from within its environment:
You have to do what I call “experiencing Venus” to get all the answers. We try to do chemistry from orbit, and we do, but it’s all model-dependent on knowing the clouds. For example, if you have a high cloud with so many molecules of sulfuric acid, you assume that the cloud itself is made of it. But inside the cloud itself, you can get light rattling around and different things going on. When you try to derive the abundances of things, it can really be mucked up by the clouds. It also depends on lighting conditions, time of day. It’s much better to be in situ where you can float around and actually measure and count up the molecules accurately and not have to worry about modeling.
Venus is a chemically violent world with many different reactions going on compared to the Earth’s atmosphere. Baines calls it “a laboratory for understanding all sorts of chemical atmospheric processes”:
We really want to watch these chemical cycles going on in the atmosphere. It’s very much temperature and pressure dependent as well, so as the balloon bobs up and down just a couple kilometers, we expect the sulfur dioxide, for example, to change by almost a factor of ten. We can use that information together with other chemical species to find out what the most important cycles on Venus are.
Baines agrees with Kerzhanovich that the mission is one of potentially great discovery:
It’s like sailing the seas for the first time. I feel like Magellan. I don’t know what’s going to be on the other side.