Why Not Venus?

Why not Venus?

The planet next door may be rough, but it has a lot of atmosphere

One reason an expedition to Mars is forever two decades away is because of the leap in difficulty between landing to the Moon and going to Mars.

There’s not a big difference in energy between the two destinations. Any rocket that can land on the moon can easily put a crew in Martian orbit. The issue is time.

As we saw recently with Artemis II, a spaceship can get human cargo to the Moon and back in about ten days. But orbital mechanics makes it hard to complete a trip to Mars in less than two years, and rigid launch windows further constrain options for abort or rescue. Bridging the gap between the two weeks we’ve spent on the Moon and the long, committal journey we’d have to make to Mars runs us into a thicket of difficulties.

In other words, the ladder to the stars is missing some rungs.

It would be nice if there was a class of mission intermediate in difficulty between the Moon and Mars, one that didn’t take us so far out of our experience base and had better abort options than ‘press the red button and wait two years’. Even better if the mission had a milder radiation environment, shorter communications delay, and a high potential for scientific discovery.

This class of mission exists, but no one likes to talk about it: Venus.

An orbital trip to Venus is like one of those gorgeous high-rise apartments in Jersey City. Everything about it is perfect except the location. Venus is the biggest heartbreak in the Solar System. The planet could have been Earth’s twin, but instead became an acid-washed nightmare and climatological horror story.

But with Venus, you have to adopt a ‘glass half full’ approach, even if the thing the glass is half full of is concentrated sulfuric acid.

To get the bad stuff out of the way, the surface temperature on Venus is around 470°C, about as hot as a pizza oven, and the pressure is 92 times what we enjoy here on Earth. The high cloud layers, while temperate, are mostly sulfuric acid. And because volcanic activity has reworked the planet’s surface within the last billion years, there is little hope of finding Mars-like relics of the planet’s habitable past.

So that’s the bad part. But once you move past it, you start to notice that everything gets easier on Venus. The atmosphere is great at blocking radiation. Solar panels can be small, and the pressure and temperature in the high clouds are so Earthlike that, if not for the acid, an astronaut could sit in the gondola of a Venusian blimp wearing only an oxygen mask and a swimsuit.

Launch windows to the planet recur every 19 months, compared to 26 months for Mars, and the round trip communications delay is about half of what a Mars-bound crew will face. Abort trajectories are about twice as fast as trying to make it home from Mars. Even the gravity on Venus (0.91g) is homelike, which means that airship habitats and equipment can be developed on Earth instead of forcing us to build stations that simulate Martian gravity.

The Science Case for Venus

There are anomalies in the Venusian atmosphere that are consistent with the presence of life. Unlike on Mars, where any living microbes are presumably deep underground, life on Venus can only exist in the clouds and should be easy to observe with cheap balloons and aerostats.

Maybe the strongest piece of circumstantial evidence is the detection of phosphine, a gas that should degrade rapidly in sunlight. But the presence of phosphine is just part of a larger pattern of anomalies: an ‘unknown absorber’ capturing ultraviolet light, an unexpectedly high proportion of water vapor, and the presence of ammonia and molecular oxygen with no identifiable source.

Venus researchers Janusz Petkowski and Sara Seager have made an intriguing case that all these anomalies can be explained by the presence of microorganisms that produce ammonia. The ammonia would react with sulfuric acid to create a livable environment for acidophiles.

The appeal of this theory is that it’s ridiculously easy to test. Unlike Mars, we can just go look at the clouds on Venus with a party balloon. The mission is simple enough that Petkowski and Seager are flying a private version of it with RocketLab. Missions to the clouds of Venus are either going to find life or some kind of brand new chemistry, either of which will be a breakthrough discovery.