Science News looks at the recent breakthroughs in planetary research using an often-overlooked kind of vehicle, a lighter-than-air balloon, as a research platform in alien skies:
“Venus is the sister planet of Earth, but it’s the evil twin sister,” says David Mimoun, a planetary scientist at the University of Toulouse in France. “We don’t know why the two planets are so different. That’s why we need measurements.”
The idea of using balloons to study far-off rumblings on Earth has its roots in the Cold War. In the 1940s, the U.S. military launched a top secret project to spy on Soviet nuclear weapons testing using microphones attached to balloons floating high in the atmosphere. When the ground shakes, it releases low-frequency sound waves that can travel long distances in the atmosphere. The military planned on using the microphones to pick up on the sound of the ground shaking from a nuclear explosion. But the project was eventually deemed too expensive and dropped — though not before one of the balloons crashed in New Mexico, launching the Roswell conspiracy.
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Landers have made it to the surface of Venus before. But these probes lasted only a few hours before succumbing to the extreme heat and pressure. The chances of measuring a quake in that short time frame are slim, says Siddharth Krishnamoorthy, a research technologist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., who wasn’t involved in the study. So while radar images of Venus have revealed a world dotted with volcanoes, scientists still don’t know for sure if Venus is geologically active, he says.
Scientists have previously experimented with the idea of detecting quakes on Venus using orbiters. But quake-detecting balloons have better resolution, says Mimoun, meaning they could provide the key to revealing the planet’s interior life. But first Mimoun and his colleagues had to show that they could design devices small enough to be carried by balloons but sensitive enough to pick up earthquakes far below.
In 2021, the team attached micro-barometers to 16 balloons launched from the Seychelles Islands, off the coast of East Africa. In December, four balloons — having drifted thousands of kilometers apart — recorded similar, low-frequency sound waves. These changes in air pressure resembled ground readings of a 7.3 magnitude earthquake near the Indonesian island of Flores, indicating that the sound waves were produced by the earthquake. The researchers were able to use the changes in air pressure to pinpoint the epicenter of the quake and calculate its magnitude.