Airborne decoder

Separating signal from noise

What can venusquakes teach us?

Quakes are just one source of infrasound signals — which are the inaudible, low-frequency sound waves that this balloon mission would tune into. These signatures can be quite different depending on what type of event caused them. And by cataloging and analyzing various sources of infrasound signals, researchers can learn to distinguish between them.On Earth, everything from volcanic eruptions to meteors and lightning bolts generate infrasound signatures like those produced by earthquakes. And while astronomers aren’t sure if Venus still has active volcanoes , they do know the planet gets hit with meteorites and has lightning So, with enough data, researchers think they'll be able to tease out the differences between these various signatures, offering insights into the specific events that produced them.If you’ve ever driven on a highway with the windows down, you know exactly how loud the wind can be. The same principle, though pushed to the extreme, is true on Venus. According to data from the ESA’s Venus Express orbiter, although Venus itself takes 243 Earth days to rotate once, its super-rotational winds whip around the planet in just four Earth days , reaching speeds of more than 200 miles (320 kilometers) per hour.That could really complicate things for a floating balloon, but not in the way you may think.Surprisingly, the problem with the wind isn’t necessarily that it moves so quickly, it’s that it doesn’t flow very steadily. The wind speeds on Venus vary drastically depending on altitude, and this leads to instabilities in the atmosphere — turbulence."It will make the balloon vibrate, which is noise,” says Krishnamoorthy.Because addressing wind interference is still one of the biggest challenges facing a balloon mission to Venus, Krishnamoorthy says the infrasound community, though small, is working hard to improve their noise reduction techniques.But the wind isn’t all bad news. According to Krishnamoorthy, "the super-rotating winds sort of gives you this global coverage because you kind of whip around the planet once every few days." This essentially provides a free ride for the balloon, allowing it to study the entire planet rather than just one specific location or region.There’s still a host of complex hurdles the team must clear before a seismic balloon mission to Venus truly gets off the ground. But if researchers can prove whether Venus is (or is not) seismically active, it would be a truly ground-breaking discovery."Any kind of seismic activity [detected on Venus] would be a big deal," Paul Byrne , a planetary geologist at North Carolina State University who is not involved in the balloon research, told Astronomy via email. In addition to proving that Venus is geologically active, Byrne says that if a balloon experiment could measure the strength, direction, and type of seismic signature, it would hint at what kind of event produced it.For example, if the signature matched what you would expect from a meteorite impact, Byrne says it would help us pin down how often Venus gets struck. Alternatively, if the signature appeared to be caused by a moving fault, then even a rough estimate of where the event occurred would shed light on what kind of geological activity caused it.But perhaps the most valuable thing we can learn from a Venus balloon is the ultimate fate of Earth.Although Venus is now an infernal landscape, we don’t know what it was like in the past (though some research suggests it may have been a habitable planet with a water ocean as little as 2 billion years ago .) We do know, however, that Venus is now the hottest planet in the solar system thanks to a phenomenon very familiar to us here on Earth: the greenhouse effect.According to Byrne, Venus once may have had a structure very similar to our planet, but now represents the hellish future we may face should Earth succumb to a runaway greenhouse effect. After all, Venus is so hot because its dense, carbon-dioxide-rich atmosphere is extremely adept at trapping heat."But then, perhaps Venus was always different to Earth," says Byrne. "The fact is that we just don't know, and that’s why we have to continue exploring the second planet."[Editor's Note: An earlier version of this story failed to properly attribute original reporting by Science Magazine.]