The formation, evolution and structure of Venus are still a mystery, more than 50 years after the first visit by a robotic space probe. Well hidden behind its thick, cloudy cover, the radar images only recently revealed a surface much younger than that of the Moon, Mercury and Mars, as well as a huge variety of enigmatic volcanic and tectonic features, very different from those on Earth.
What dynamic processes create these characteristics in the absence of tectonic plates ? What is their relationship with the dense atmosphere of carbon dioxyde which envelopes Venus like an ocean? Could young Venus have been home to life? In this case, how has it become the furnace that it is today?
In order to answer these questions, we need to probe the interior structure of the planet using highly sensitive seismometers, which alone can enlighten us as to its history.
As of today, only a few soviet space probes have been able to land on the surface of the Earth’s twin sister and they only survived a few tens of minutes due to the extreme conditions: a mean temperature of 400°C, a pressure of 90 atmospheres of carbon dioxide[n1] , (like several kilometers under the oceans).
To survive long enough on the planet for this investigation, there is today only one solution: stay above the clouds of sulphuric acid. At 60 km, the pressure and temperature are nearly terrestrial: 20°C, pressure of 1 bar.
Such a dense atmosphere has nevertheless an interesting particularity: the seismic waves containing information about the structure of the planet propagate upwards in the dense atmosphere and can be recorded in the higher layers of the atmosphere, above the clouds.
To prepare the next missions to Venus, capable of finally determining the history of the Earth’s twin, researchers from the space systems team of the electronics, optronics and signal processing department (DEOS) of ISAE-SUPAERO implemented extremely sensitive pressure sensors and full-scale tested them in the Nevada desert, in collaboration with their peers from the Jet Propulsion Laboratory (JPL/Caltech) and the California Institute of Technology (Caltech).
The experience took place at Pahrump in Nevada and consisted in generating artificial seismic signals with a mass of 30 tons, while the pressure sensors from ISAE-SUPAERO suspended from balloons recorded the sound images of the seismic waves generated. The site was fully instrumented (seismic sensors, microphones) to allow reliable modeling of experimental conditions.
While complete assimilation of data will take several months, the first results show that this method is extremely promising, and the team is preparing a mission for the coming years based on this concept, which will be proposed to NASA.