École Polytechnique’s Student Research probes Venus structure

Understanding the evolution of terrestrial planets such as Venus, Earth, and Mars is an important step in understanding our entire solar system. Venus is particularly interesting because of its similarity to Earth – for example, at an altitude of 55 km, the planet’s atmosphere virtually replicates earth’s, with a pressure of 0.5 atm and a temperature of 27 °C. However, the extreme surface conditions on Venus (460 °C and 92 atm) render it virtually impossible to use exploratory landing vehicles with ground sensors to probe the planet’s structure.

Researchers from ISAE-Supaero and JPL found a solution: deploy barometers on balloons that could get close enough to study the infrasonic waves produced by seismic events on the Venusian surface, while remaining at a safe distance. The DESTINY project tests this solution in Earth’s stratosphere to gauge its potential.

"The Group science project is an integral part of the 2nd year of studies. It offers a first, hands-on, exposure to a concrete research setting. The students are expected to decide on how to approach the chosen scientific problem, to find the right questions to address and to organize their work as a team," explains Pierre Dauchy, Dean of studies for the Ingénieur Polytechnicien program at École Polytechnique.

The stratospheric balloon carrying the X18 students’ experiment lifted off on October 25, 2019, from the Swedish Space Corporation’s Esrange Space Centre and reached a float altitude of 26.7 km. Two aluminum boxes, each carrying a barometer and sensors, had been installed on the balloon: one box inside the gondola (GB), the other box on the flight train (FTB), which is between the cables connecting the gondola to the balloon. Distancing the boxes by 32,5 m, the configuration allowed to register data via barometers located in distinct positions.

The goal of the experiment was to characterize the infrasonic background of the atmosphere in order to recognize specific signals and locate their source, and more precisely the epicenter of a geophysical event. A ground explosion of 800kg TNT equivalent at a distance of 240 km from the experiment was used as the “infrasound event.” The students would measure the phase difference between the signals detected by the balloon-borne barometers, and process them to locate their origin with the help of GPS units.

The freight of the flight, including the two experiment boxes successfully landed some 3.5 hours later in Finland.

The analyzed data revealed that the ground explosion had indeed been registered by one barometer as many as three times. The DESTINY team deduced from this result that the shock wave generated by the explosion had followed three different paths in the stratosphere, rebounding on different strata in the atmosphere.

As only one of the two barometers had sufficiently well registered the signals, it was nevertheless not possible to precisely locate the epicenter of the explosion.

The project DESTINY (Detection of Earthquakes through a STratospheric INfrasound study) is conducted with the Students Space Center and ISAE-Supaero, and aims to demonstrate the possibility to study seismic activity on terrestrial planets from their atmosphere. Carried out within Earth’s atmosphere to recognize and source infrasound events, the experiment results should be applicable to further explorations on Venus, designed to add to the scientific understanding of the solar system.

Further information is available : https://www.polytechnique.edu/en/content/student-space-centers-experiment-carried-out-stratospheric-balloon