The hills are alive with the sounds of Venus and Mars. At least that's the case at the Astrium Planetarium at INTECH near Winchester in the UK, where a new exhibit showcases sounds from some of our cosmic neighbours.Humans have been sending probes to Venus and Mars since the early 1960s, but their instrument payload has always focused on gathering atmospheric data and images. Of the few that did carry microphones, none managed to record any sound. NASA's Mars Polar Lander carried a microphone but the spacecraft crashed during its descent towards the surface in 1999. A French mission designed to record sound on Mars never flew. NASA's successful Mars Phoenix Lander carried a microphone, but it didn't return any during the 2008 mission.But just because we haven't captured sounds from neighboring worlds doesn't mean there isn't any. We just have to be a little creative to hear them. Here's where Tim Leighton comes in, an acoustician from the University of South Hampton in England. He's adjusted natural sounds — lightning like you'd find on Venus, strong winds like on Mars, and a volcanic eruption reminiscent of Saturn's moon Titan — to suggest what they might sound like on these other worlds.Leighton's results aren't speculative. He uses physics to adjust his sound clips. Knowing the atmospheric pressure and composition of these worlds and the effects different environments have on sound waves, he has been able to get a pretty good idea of what these natural phenomena would sound like on other worlds. He's even figured out what we might sound like if we went for a stroll and a chat on, say, Venus.Venus' atmosphere is dense, about 90 times more so than Earth's. Human vocal cords would vibrate much more slowly in that environment, but the sound waves would travel much faster. This would affect how our brains interpret the size of the speaker. A voice on Venus, says Leighton, would invoke the image of a small person with a deep bass voice.This isn't Leighton's first foray into creating otherworldly sounds. In 2004, he gained notoriety for his approximation of a methane waterfall on Titan, a project NASA commissioned to commemorate the Cassini-Huygens mission. In this case, he calculated the relative properties of water and methane. He then took a recording of a waterfall in Hampshire and adjusted each sound to reflect the difference between water on Earth and methane on Titan.Over the past few years, Leighton has been taking his extraterrestrial sound work into the realm of music, partnering with Dr. Andi Petculescu of the University of Louisiana in Lafayette. Together they have determined exactly how voices and different instruments might sound on other worlds. This has a practical application, says Leighton. "If astronauts are based on Mars for several months, they might just take musical instruments along, or build one there. What would they sound like?" It's also different, he says. "As a scientist, I reckon the most exciting thing to work on is a completely new idea, something that’s never been done before."For the time being, simulated sounds like Leighton's are all we have. Planetariums show amazing images we've captured from around the Solar System, but there aren't any real extra terrestrial sounds to accompany the visuals. Nevertheless, hearing simulated liquid falling on another planet adds a new level of reality — on unreality, maybe — to the alien landscapes of our cosmic neighbors.
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