Advances in Planetary Seismology Using Infrasound and Airglow Signatures on Venus

Transcription

1 Advances in Planetary Seismology Using Infrasound and Airglow Signatures on Venus 1 Attila Komjathy, 1 Siddharth Krishnamoorthy 1 James Cutts, 1 Michael Pauken,, 1 Sharon Kedar, 1 Suzanne Smrekar, 1 Jeff Hall, 1 Alan Didion, 1 Balthasar Kenda, 1 Xing Meng, 1 Olga Verkhoglyadova, 1 Walton Williamson, 2 Jennifer Jackson, 3 David Mimoun, 3 Raphael Garcia and 4 Philippe Lognonné 1 JPL/Caltech; 2 Caltech, Pasadena, CA, USA; 3 ISAE, Toulouse; France 4 IPGP, Paris, France Attila.Komjathy@jpl.nasa.gov 1

2 Introduction Motivation Balloon infrasound technique for Venus Earth-based experience Modeling background on Earth Planned Phase 1 to 3 experiments on Earth Airglow measurements on Venus Conclusions Acknowledgements 2

3 Motivation The planetary evolution and structure of Venus remain uncertain more than half a century after the first visit by a robotic spacecraft. To understand how Venus evolved it is necessary to detect the signs of seismic activity. Due to the adverse surface conditions on Venus, with extremely high temperature and pressure, it is infeasible to place seismometers on the surface for an extended period of time. Due to dynamic coupling between the solid planet and the atmosphere, the waves generated by quakes propagate and can be detected in the atmosphere itself. Our goals are: Detect seismicity using infrasound measurements and characterize seismic wave propagation in order to determine crustal structure Conduct complementary investigation of airglow phenomenology, atmospheric gravity waves and ionospheric disturbances 3

4 Three Techniques Defined at KISS Workshop at Caltech to Detect Seismicity on Venus 1) Infrasound observation s at 55km and -10 C 2) Classical seismic measurements with surface temp of 465 C 2) Airglow imaging from orbit 1) Infrasound measurements 2) Airglow imaging and 3) Seismometer on ground (currently infeasible). 4

5 Earth: Generation of Infrasound by Quakes Earthquakes and volcanoes on Earth can be detected using infrasound techniques in situ or from space Measuring and modeling techniques of infrasound signals on Earth are well understood 5

6 Venus Epicentral and Rayleigh Infrasound Waves Venus: Epicentral Seismic signals Infrasound couple 60X more efficiently into the atmosphere on Venus than on Earth Infrasound wave replicas of seismic waves are near perfect Almost no attenuation below 80 km for frequency < 1Hz, hence use balloons Secondary Rayleigh Infrasound 150 km 60 km 6

7 Completed Aerostat Experiment: Altitude Up to 1300 Feet on June 28, 2017 (photos of actual experiment) Source: Seismic hammer Objective: Detect highly reproducible signal Benefit: Validate 2-barometer signal processing using point source Barometer 1 Infrasound signatures associated with Rayleigh waves Barometer 2 7

8 Completed Piloted Hot Air Balloon Experiment: Altitude Up to 3000 Feet on June 28, 2017 Need of syncrhonization Altitude H max < 1 km T 2-3 hours Phase 1 Balloon Climbing Phase 2 Tether / Baro Deployment Phase 3 Measurement Time Phase 4 Tether / Baro withdrawal ISAE Seismic hammer with the hot air balloon monitoring ground strikes Trillium x 2 Microphones x 2 Barometer Acquisition JPL Seismic line 8

9 Phase 2 on Earth Super Pressure Balloon Flight Conduct tropospheric test flight collecting infrasonic data over remote area Develop payload system Complete test data analysis Compare measured and modeled infrasound signatures 9

10 Station ID distant stations also correspond to ground-air coupled infrasound resulting from Rayleigh waves (see Figure 4-10). Prior These investigations Evidence provide great of insight Ground on the mechanisms Detection of generating seismic of Seismo- waves for earthquakes of smaller amplitude. Although a much smaller fraction of the seismic energy is Acoustic Waves Generated by Earthquakes coupled into the Earth s atmosphere than would be the case on Venus, it is still sufficient for detection of comparatively small events. Accordingly, the instrumental and analytical framework is in place for 0applying seismoacoustic 15techniques Time on (Min) Venus Local infrasound Epicentral infrasound Centerville Earthquake 2011 M 4.7. Signals from the nine stations in the University of Utah infrasonic array (1 to 5 Hz) Figure 6-2. Centerville earthquake Signals from the nine stations in the University of Utah array are shown. This is filtered data in the 1 to 5 Hz passband. Epicentral infrasound from a M 4.7 earthquake was detected Probing the Interior Structure of Venus 34 at six infrasound stations extending up to 500 km from the source Reproduced from the paper by Arrowsmith et al 2012) 10

11 Proposed Oklahoma Test Site Notional Stratollite footprint Map of Oklahoma The site chosen for this test is the north-eastern corner of the state of Oklahoma where the frequency of earthquakes is the highest in the nation as a result of pumping of waste water from oil drilling into geological formations. 11

12 Perspectives for Venus A B Use of two barometers (A) enables spatial filtering for separating an upward traveling wave associated with a quake from other sources of pressure variability. (B) In addition, infrasound waves generated by Venus quakes are faithful replica of seismic waves. 12

13 Looking Ahead: Airglow Mission Our mission concept VAMOS (Venus Airglow Measurement and Orbiter for Seismicity) will measure atmospheric perturbations from an orbiting platform that could provide a breakthrough in detecting seismicity on Venus and in the monitoring of seismic wave propagation. 13

14 Simulation of Signal from Venus Seismic Event 14

15 Conclusions Balloon Experiments: We develop a novel technique and a balloon mission opportunity for studying the seismicity and interior structure of Venus. The new technique will help discriminate for the first time between quakes-induced signals and background with magnitudes ~3 and above on Venus. Airglow Mission Concept: We expect to launch SmallSat (<180 kg) into high earth orbit as rideshare with larger spacecraft Our mission concept VAMOS (Venus Airglow Measurement and Orbiter for Seismicity) will measure atmospheric perturbations from an orbiting platform that could provide a breakthrough in detecting seismicity on Venus and in the monitoring of seismic wave propagation. 15

16 Acknowledgements The research is funded by KISS and JPL R&TD program and carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. Copyright All rights reserved. Government sponsorship acknowledged. 16

17 BACKUP SLIDES 17

18 Balloon Infrasound Objectives JPL in collaboration with ISAE and Caltech Campus is in a process of developing an instrument to measure seismic activity on Venus by detecting infrasonic waves in the atmosphere. The overall objective of this research is to demonstrate the feasibility of using sensitive barometers to detect infrasonic signals from seismic and explosive activity on Venus from a balloon platform. Because of Venus dense atmosphere, seismic signatures from even small quakes (magnitude ~3) are effectively coupled into the atmosphere. The seismic signals are known to couple about 60 times more efficiently into the atmosphere on Venus than on Earth. Our specific objective is to use two or more infrasonic sensors using barometers on a tether deployed from the balloon in a series of Earth-based tests. 18

19 VWE Stated Stratollite Capabilities Courtesy: 19

20 Using Seismic Waves to Map Interior Structure of Venus 55 km Nightside Airglow imaging KISS VENUS-11 20

21 Wave-Propagation Global Ionosphere-Thermosphere Model (WP-GITM) Derived TEC Perturbations [not to scale] For Tsunamis For Earthquakes Input I solar wind conditions, solar irradiance, auroral particle precipitation Output Ionospheric and thermospheric disturbances Input II Tsunami wave characteristics Input II vertical velocity data Meng et al., 2015 Meng et al., 2017 (in preparation) 21