During the Cold War, the US military launched a secret project to spy on the Soviet Union by sending microphones attached to balloons floating at high altitudes. The idea behind this project was that when the ground shakes, it would release low-frequency sound waves that travel long distances in the atmosphere. The US used it to get information on the Soviet’s nuclear weapon testing sites. Many decades later in the early 2000s, David Mimoun, an astronomer at the University of Toulouse, France started working with this idea to investigate the atmospheres of planets in our Solar System.
This kind of experiment would work the best for planets like Venus where the surface temperature is hot enough to melt lead. Therefore, a balloon floating at a high altitude would be a great option to measure any seismic activity there. In other words, they could reveal a lot about the interior of this planet. Scientists often wonder why Earth and Venus are drastically different even when they are close together in our Solar system. What made Venus a factory of the greenhouse effect and Earth home to all of us? Please note that it is not the distance of Venus from the Sun which makes it burn like this but the dense atmosphere which causes the greenhouse effect. This kind of investigation is extremely important to understand the early stages of the formation of our Solar system and therefore it is deemed crucial in the scientific community. See the video below to learn some basic facts about the planet Venus, which is also fondly known as the Earth’s evil twin sister.
In 2021, Mimoun and the team attached micro-barometers to 16 balloons launched from the Seychelles Islands, off the coast of East Africa. On December 14, 2021, four of these balloons which drifted far apart in the air recorded similar low-frequency waves. These waves were coincident with a 7.3 magnitude earthquake near the Indonesian Island of Flores. This team was able to locate the epicenter of this earthquake by just using their calculations from these balloons.
This study is a major milestone towards making progress in investigating the interiors of planets like Venus where landing a rover on the surface is almost an impossible task (850 °F surface temperature). This work was published in the Geophysical Research Letters in July 2022.