Quentin Brissaud – quentin@norsar.no
X (twitter): @QuentinBrissaud
Research Scientist, NORSAR, Kjeller, N/A, 2007, Norway
Sven Peter Näsholm, University of Oslo and NORSAR
Marouchka Froment, NORSAR
Antoine Turquet, NORSAR
Tina Kaschwich, NORSAR
Popular version of 1pPAb3 – Exploring a planet with infrasound: challenges in probing the subsurface and the atmosphere
Presented at the 186 ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0026837
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Low frequency sound, called infrasound, can help us better understand our atmosphere and explore distant planetary atmospheres and interiors.
Low-frequency sound waves below 20 Hz, known as infrasound, are inaudible to the human ear. They can be generated by a variety of natural phenomena, including volcanoes, ocean waves, and earthquakes. These waves travel over large distances and can be recorded by instruments such as microbarometers, which are sensitive to small pressure variations. This data can give unique insight into the source of the infrasound and the properties of the media it traveled through, whether solid, oceanic, or atmospheric. In the future, infrasound data might be key to build more robust weather prediction models and understand the evolution of our solar system.
Infrasound has been used on Earth to monitor stratospheric winds, to analyze the characteristics of man-made explosions, and even to detect earthquakes. But its potential extends beyond our home planet. Infrasound waves generated by meteor impacts on Mars have provided insight into the planet’s shallow seismic velocities, as well as near-surface winds and temperatures. On Venus, recent research considers that balloons floating in its atmosphere, and recording infrasound waves, could be one of the few alternatives to detect “venusquakes” and explore its interior, since surface pressures and temperatures are too extreme for conventional instruments.
Sonification of sound generated by the Flores Sea earthquake as recorded by a balloon flying at 19 km altitude.
Until recently, it has been challenging to map infrasound signals to various planetary phenomena, including ocean waves, atmospheric winds, and planetary interiors. However, our research team and collaborators have made significant strides in this field, developing tools to unlock the potential of infrasound-based planetary research. We retrieve the connections between source and media properties, and sound signatures through 3 different techniques: (1) training neural networks to learn the complex relationships between observed waveforms and source and media characteristics, (2) perform large-scale numerical simulations of seismic and sound waves from earthquakes and explosions, and (3) incorporate knowledge about source and seismic media from adjacent fields such as geodynamics and atmospheric chemistry to inform our modeling work. Our recent work highlights the potential of infrasound-based inversions to predict high-altitude winds from the sound of ocean waves with machine learning, to map an earthquake’s mechanism to its local sound signature, and to assess the detectability of venusquakes from high-altitude balloons.
To ensure the long-term success of infrasound research, dedicated Earth missions will be crucial to collect new data, support the development of efficient global modeling tools, and create rigorous inversion frameworks suited to various planetary environments. Nevertheless, Infrasound research shows that tuning into a planet’s whisper unlocks crucial insights into its state and evolution.
Applied Ocean Phusics and Engineering, Woods Hole Oceanographic Instuitution., Woods Hole, MA, 02543, United States
Andi Petculescu
University of Louisiana
Department of Physics
Lafayette, Louisiana, USA
Popular version of 3aPAa6 – Calculating the Acoustics Internal Gravity Wave Dispersion Relations in Venus’s Supercritical Lower Atmosphere
Presented at the 186th ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0027303
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Venus is the second planet from the sun and is the closest in size and mass to Earth. Satellite images show large regions of tectonic deformations and volcanic material, indicating the area is seismically and volcanically active. Ideally, to study its subsurface and seismic and volcanic activity, we would deploy seismometers on the surface to measure the ground motions following venusquakes or volcanic eruptions; this will allow us to understand the planet’s past and current geological processes and evolution. However, the extreme conditions at the surface of Venus prevent us from doing that. With temperatures exceeding 400°C (854°F) and a pressure of more than 90 bars (90 times more than on Earth), instruments don’t last long.
One alternative to overcome this challenge is to study Venus’s subsurface and seismic activity using balloon-based acoustic sensors floating in the atmosphere to detect venusquakes from the air. But before doing that, we first need to assess its feasibility. This means we must better understand how seismic energy is transferred to acoustic energy in Venus’s atmosphere and how the acoustic waves propagate through it. In our research, we address the following questions. 1) How efficiently does seismic motion turn to atmospheric acoustic waves across Venus’ surface? 2) how do acoustic waves propagate in Venus’s atmosphere? and 3) what is the frequency range of acoustic waves in Venus’s atmosphere?
Venus’s extreme pressure and temperature correspond to supercritical fluid conditions in the atmosphere’s lowest few kilometers. Supercritical fluids combine gases and fluids’ properties and exhibit nonintuitive behavior, such as high density and compressibility. Therefore, to describe the behavior of such fluids, we need to use an equation of state (EoS) that captures these phenomena. Different EoSs are appropriate for different fluid conditions, but only a limited selection adequately describes supercritical fluids. One of these equations is the Peng-Robinson (PR) EoS. Incorporating the PR-EoS with the fluid dynamics equations allows us to study acoustics propagation in Venus’s atmosphere.
Our results show that the energy transported across Venus’s surface from seismic sources is two orders of magnitude larger than on Earth, pointing to a better seismic-to-acoustic transmission. This is mainly due to Venus’s denser atmosphere (~68 kg/m3) compared to Earth’s (~1 kg/m3). Using numerical simulations, we show that different seismic waves will be coupled to Venus’s atmosphere at different spatial positions. Therefore, when considering measurements from floating balloons, they will measure different seismic-to-acoustic signals depending on their position. In addition, we show that Venus’s atmosphere allows lower acoustic frequencies than Earth’s. This will be useful in 1) preparing the capabilities of the acoustic instruments used on the balloons, and 2) interpreting future observations.
NASA Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA, 91109, United States
Daniel C. Bowman2, Emalee Hough3, Zach Yap3, John D. Wilding4, Jamey Jacob3, Brian Elbing3, Léo Martire1, Attila Komjathy1, Michael T. Pauken1, James A. Cutts1, Jennifer M. Jackson4, Raphaël F. Garcia5, and David Mimoun5
1. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, USA
2. Sandia National Laboratories, Albuquerque, New Mexico, USA
3. Oklahoma State University, Stillwater, OK, USA
4. Seismological Laboratory, California Institute of Technology, Pasadena, CA, USA
5. Institut Supérieur de l’Aéronautique et de l’Espace (ISAE-SUPAERO), Toulouse, France
Popular version of 4aPAa1 – Development of Balloon-Based Seismology for Venus through Earth-Analog Experiments and Simulations
Presented at the 184 ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0018837
Venus has often been described as a “hellscape” and deservedly so – the surface of Venus simultaneously scorches and crushes spacecraft that land on it with temperatures exceeding 460 degrees Celsius (~850 F) and atmospheric pressure exceeding 90 atmospheres. While the conditions on the surface of Venus are extreme, the temperature and pressure drop dramatically with altitude. At about 50-60 km above the surface, temperature (-10-70 C) and pressure (~0.2-1 atmosphere) resemble that on Earth. At this altitude, the challenge of surviving clouds of sulfuric acid is more manageable than that of surviving the simultaneous squeeze and scorch at the surface. This is evidenced by the fact that the two VeGa balloons floated in the atmosphere of Venus by the Soviet Union in 1985 transmitted data for approximately 48 hours (and presumably survived for much longer) compared to 2 hours and 7 minutes, which is the longest any spacecraft landed on the surface has survived. A new generation of Venus balloons is now being designed that can last over 100 days and can change their altitude to navigate different layers of Venus’ atmosphere. Our research focuses on developing technology to detect signatures of volcanic eruptions and “venusquakes” from balloons in the Venus clouds. Doing so allows us to quantify the level of ongoing activity on Venus, and associate this activity with maps of the surface, which in turn allows us to study the planet’s interior from high above the surface. Conducting this experiment from a balloon floating at an altitude of 50-60 km above the surface of Venus provides a significantly extended observation period, surpassing the lifespan of any spacecraft landed on the surface with current technology.
We propose to utilize low-frequency sound waves known as infrasound to detect and characterize Venus quakes and volcanic activity. These waves are generated due to coupling between the ground and the atmosphere of the planet – when the ground moves, it acts like a drum that produces weak infrasound waves in the atmosphere, which can then be detected by pressure sensors deployed from balloons as shown in figure 1. On Venus, the process of conversion from ground motion to infrasound is up to 60 times more efficient than Earth.
Figure 1: Infrasound is generated when the atmosphere reverberates in response to the motion of the ground and can be detected on balloons. Infrasound can travel directly from the site of the event to the balloon (epicentral) or be generated by seismic waves as they pass underneath the balloon and travel vertically upward (surface wave infrasound).
We are developing this technique by first demonstrating that earthquakes and volcanic eruptions on Earth can be detected by instruments suspended from balloons. These data also allow us to validate our simulation tools and generate estimates for what such signals may look like on Venus. In flight experiments over the last few years, not just several earthquakes of varying magnitudes and volcanic eruptions, but also other Venus-relevant phenomena such as lightning and mountain waves have been detected from balloons as shown in figure 2.
Figure 2: Venus-relevant events on Earth detected on high-altitude balloons using infrasound. Pressure waves from the originating event travel to the balloon and are recorded by barometers suspended from the balloon.
In the next phase of the project, we will generate a catalog of analogous signals on Venus and develop signal identification tools that can autonomously identify signals of interest on a Venus flight.
Copyright 2023, all rights reserved. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004).
While there is great interest in studying the structure of Venus because it is believed to be similar to Earth, there are no direct seismic measurements on Venus. This is because the Venus surface temperature is too hot for electronics, but conditions are milder in the middle of the Venus atmosphere. This has motivated interest in studying seismic activity using low frequency sound measurements on high altitude balloons. Recently, this method was demonstrated on Earth with weak earthquakes being detected from balloons flying at twice the altitude of commercial airplanes. Video 1 shows a balloon launch for these test flights. Due to the denser atmosphere on Venus, the coupling between the Venus-quake and the sound waves should be much greater, which will make the sound louder on Venus. However, the higher density atmosphere combined with vertical changes in wind speed is also likely to increase the amount of wind noise on these sensor. Thus development of a new technology to reduce wind noise on a high altitude balloon is needed.
Video 1. Video of a balloon launch during the summer of 2021. Video courtesy of Jamey Jacob.
Several different designs were proposed and ground tested to identify potential materials for compact windscreens. The testing included a long-term deployment outdoors so that the sensors would be exposed to a wide range of wind speeds and conditions. Separately, the sensors were exposed to controlled low-frequency sounds to test if the windscreens were also reducing the loudness of the signals of interest. All of the designs showed significant reduction in wind noise with minimal reduction in the controlled sounds, but one design in particular outperformed the others. This design uses a canvas fabric on the outside of a box as shown in the Figure 1 combined with a dense foam material on the inside.
Figure 1. Picture of balloon carrying the low frequency sound sensors. Compared an early design to no windscreen with this flight. Image courtesy of Brian Elbing.
The next step is to fly this windscreen on a high altitude balloon, especially on windier days and with a long flight line to increase the amount of wind that the sensors will experience. The wind direction at the float altitude of these balloons will change in May and then rapidly increase, which this will be the target window to test this new design.
Low frequency sound, called infrasound, can help us better understand our atmosphere and explore distant planetary atmospheres and interiors.
Venus surface. Image from NASA (
Figure 1: Infrasound is generated when the atmosphere reverberates in response to the motion of the ground and can be detected on balloons. Infrasound can travel directly from the site of the event to the balloon (epicentral) or be generated by seismic waves as they pass underneath the balloon and travel vertically upward (surface wave infrasound).
Figure 2: Venus-relevant events on Earth detected on high-altitude balloons using infrasound. Pressure waves from the originating event travel to the balloon and are recorded by barometers suspended from the balloon.