Insight September 12Th 2019

InSight September 12th 2019

Medium and long-term perspectives of seismology for the study and characterization of planetary and satellite interiors D. Mimoun1*, R. Garcia 1 ,Ph. Lognonné2

1ISAE-SUPAERO, 10, av Belin, 31400 Toulouse France 2 Institut de Physique du Globe de Paris-Sorbonne Paris Cité Université Paris Diderot (UMR 7154 CNRS), *[email protected]

Sept 12th, 2019 May 5th 2018 : Start of a new era for planetary seismology

Ground Seismometer

InSight !

Apollo

1970 1975 2020 Nov 26th 2018 : Start of a new era for planetary seismology

NASA/JPL/Caltech 2018 : Start of a new era for seismology

Ground Seismometer

NASA NASA/JPL/Caltech NASA/JPL/Caltech

InSight !

Apollo

1970 1975 2020 Summary of Past Missions Involving Seismology

MISSION Launch Major mission events Instrument description Seismometer deployment Reference Ranger 3 1962-01-26 Failure due to the booster. Moon missed Vertical axis seismometer, with a free Seismometer in a lunar capsule designed Lehner et al. Ranger 4 1962-04-23 Failure of spacecraft central processor. Moon crash. frequency of 1 Hz. (Mass: 3.36 kg) for a 130-160 km h-1 landing. Batteries (1962) Ranger 5 1962-10-18 Failure in the spacecraft power system. Moon missed. powered for 30 days of operations Surveyor 1966-1968 The seismometer was finally deselected from the payload of the Single short period vertical axis Fixed to the lander. Sutton and Surveyor missions seismometer (mass: 3.8 kg, power: Steinbacher 0.75 W ) (1967). Apollo 11 1969-7-16 Successful installation. Powered by solar panel, worked during the first Passive seismic experiment (PSE). Installation performed by crew. Latham et al. lunation and stopped after 21 days Triaxis Long Period seismometer Seismometers were manually leveled and (1969, 1970a, Apollo 12 1969-11-14 Successful installation of a network of 4 stations. For all but the Apollo (LP) and one vertical Short Period oriented with bubble level and sun 1970b). Apollo 14 1971-01-31 12 SP seismometer and Apollo 14 vertical LP seismometer operated until (SP) seismometer, with resonance compass. A sun protection/thermal shroud Apollo 15 1971-07-26 the end of September 1977, when all were turned off after command periods of 15 sec and 1 s respectively. was covering the instruments. Power was Apollo 16 1972-04-16 from the Earth. 26.18 active station years of data collected. (mass: 11.5 kg , power: 4.3 -7.4 W) delivered by a Plutonium thermal generator Apollo 13 1970-4-11 Moon landing aborted. No installation of the PSE experiment but lunar for A12-14-15-16 crash of the Apollo 13 Saturn-IV upper stage recorded by the A12 PSE. Apollo 14 1971-01-31 Successful installation and operation of the active seismic experiments. String of 3 geophones on A-14 and Geophones were anchored into the surface Watkins and Apollo 16 1972-04-16 Seismic sources were thumper devices containing 21 small explosive A16 and on 4 geophones on A-17. by short spikes as they were unreeled from Kovach (1972) Apollo 17 1972-12-07 sources and a rocket grenade launcher with 4 sources exploding up to Frequency was 3Hz-250 Hz. the thumper/geophone assembly. Kovach and 1500 m on A-14 and A-16. 8 sources were used containing up to 2722 g Watkins (1973a) of explosive and deployed at 3500 m by astronauts Apollo 17 1972-12-07 Deployment of the Lunar Surface Gravimeter. The gravimeter was Gravimeter designed for gravity Installation performed by crew. Weber (1971) unable to operate properly due to an error in the design of the proof waves detection. Additionnal long mass. period vertical seismic output (10-11 lunar g resolution) for free oscillation detection, with a 16 Hz sampling. Viking 1975-08-20 Successful landing but instrument failure. Short period instrument, with an The seismometer was installed on the Anderson et al. Lander 1 undamped natural period of 0.25 s, a Lander platform. No recentering was (1977a, 1977b) Viking 1975-09-09 Successful landing and 19 months of nearly continuous operation. Too mass of 2.2 kg, a size of 12x15x12 necessary since the 3 axis seismometer had Lander 2 high wind sensitivity associated to the elastic recovery of the Viking cm and a nominal power consumption been designed to function even when tilted landing legs to the loading of the station by pressure fluctuations induced of 3.5 W. to up to 23 degrees. by the wind. Phobos 1-2 1988-07-07 Respecivelly:Lost during transfer to Mars and Phobos ; Contact lost just Instrument onboard the long-service lander. Surkov (1990) 1988-07-12 before the final phase of lander deployment, after Mars orbit insertion Mars 96- 1996-11-16 Failure of the Block-D propulsion system in parking orbit. Earth re- Long period vertical axis seismometer Seismometer in the small surface station. Lognonné et al. Small entry. 2 small stations and 2 penetrators lost. (0.1-4Hz, 0,405kg for the sensor) Semi-hard landing (200g-20 ms). Nominal (1998a) surface combined to a magnetometer. 55 mW operations of one Martian year with 90th stations of power first days of nearly continuous mode with internal batteries Mars 96 High frequency seismometer Seismometer in the penetrator. Hard Kravroshkin and Penetrators (10-100Hz, 0.3kg, 20 mW) landing. Nominal operations of one Martian Tsyplakov year. (1996) Rosetta 2004-03-04 Landing on the comet 67P/Churyumov-Gerasimenko planned a few CASSE/SESAME experiment: High Instrument mounted on the lander (Kochan et al. months after rendez-vous, expected on 22-05-2014 frequency accelerometer covering the 2000) frequency bandwidth ~10 Hz-20 kHz.

Table 1: Summary and History of Planetary seismology experiments. Successfull experiment, leading to detection and interpretationLognonné of data in terms of quaetkes aal,re ind i2007cated by their name in bold, in the Mission column. Bold and italic names are for successfull deployment, but without clear event detection or interpretation.

Why Seismology ?

(Surface Waves) IPGP/Ducros

Seismic S Waves Station

Core

(Mantle) P Waves

Seismology is the best (if not the only) only way to investigate the internal structure of a telluric planet It can help with Oceans Worlds, too ! Planetary Seismology : current status

≃0 (NASA) 3 (1970’s) > 20000 1 (2018)

1969-1977: 2019- … 1x10 -8 1889-1910 LPX 5x10 -9 0 [m] ? -5x10 -9 -1x10 -8 1x10 -8 LPY 5x10 -9 0 [m] -5x10 -9 -1x10 -8 1x10 -8 LPZ 5x10 -9 0 [m] -5x10 -9 -1x10 -8 1x10 -8 SPZ 5x10 -9 0 [m] -5x10 -9 -1x10 -8 2000 3000 4000 5000 6000 7000 8000 9000 10000 [s] Science Questions ?

NASA

400°C, 90 atm 15°C, 1 atm -50°C, 0.005 atm

Solar System Formation

Walkers et al. 2006 JPL/Caltech Science Questions ?

NASA Planetary Main Associated Seismometer Main Instrument Reference Body Science Question Type Constraint Moon Core size, Earth Moon Long Period, Lunar night (Mimoun et al history, High sensitivity 2012) Mars Formation, history, Long Period, Instrument sensitivity (Mimoun et al habitability High sensitivity to environment 2017) Network ? Mercury Formation process Long Period, Strong temperature High sensitivity variations

Venus Formation processes, Long Period, Extremely harsh (Cutts, Mimoun et coupling with atmosphere, High sensitivity environment al, 2015) habitability Small Internal structure Short period, Size and mass, low (Murdoch et al, Boday “Planetary defense” autonomy gravity, coupling 2017) Oceans Internal Structure Short period Radiations, (Lee et al, Worlds Ice sheet width temperature 2003) Ocen depth STEP 1 : New generation of ALSEP and Seismology as a tool for ISRU

• The Moon holds a particular place on this prospective exercise, including with the context of human mission. • Establishing a seismic network operating several years on the Moon must be the first priority, with the development of a new generation of Artemis Lunar Surface module. • Beside of the completion of the Moon structure understanding, which may be done in the next few years thanks to the effort of US and (or) China we expect the seismology to become also (as it is on Earth) a standard tool for In Situ Resources Utilization (ISRU), for mining water ice of other minerals of interest.

Science Objectives Preparing for human occupation Crust Water Confirm the GRAIL lunar crustal models and better anchor it with seismic data ? Find sustainable sources of water in the subsurface What is the vertical & lateral structure of the lunar crust interior and how did it develop? What is the nature of the Moon's crustal asymmetry, Minerals what caused it ? Find Minerals in the subsurface Mantle What is the composition, structure, and variability of the lunar mantle? Is there an undifferentiated lower mantle ; if so, what was its role in lunar magmatism? Core Precise the radius of central metallic (molten) core, and if it does, how large is it and what is its composition? Discovery of the inner core remains to be done… Step 1 : New generation of ALSEP and Seismology as a tool for ISRU

RFI Lunar Exploration Campaign Science and Technology Payloads

Cover Page for Proposal NASA Proposal Number Submitted to the 18-PMCS18-0055 National Aeronautics and

Space Administration

NASA PROCEDURE FOR HANDLING PROPOSALS

This proposal shall be used and disclosed for evaluation purposes only, and a copy of this Government notice shall be applied to any reproduction SEIS or abstract thereof. Any authorized restrictive notices that the submitter places on this proposal shall also be strictly complied with. Disclosure of this proposal for any reason outside the Government evaluation purposes shall be made only to the extent authorized by the Government. The InSight seismometer adapted to the Moon context by a European & Chinese consortium will uncover the Moon internal structure. SECTION I - Proposal Information Principal Investigator E-mail Address Phone Number

Clive Neal [email protected] 574-631-8328 Street Address (1) Street Address (2) 156 Fitzpatrick Hall

City State / Province Postal Code Country Code Notre Dame IN 46556 US

Proposal Title : Developing the Lunar Geophysical Network Mission

Proposed Start Date Proposed End Date Total Budget Year 1 Budget

10 / 15 / 2019 06 / 30 / 2020 99,993.00 99,993.00 SECTION II - Application Information

NASA Program Announcement Number NASA Program Announcement Title NNH18ZDA001N-PMCS Planetary Mission Concept Studies

For Consideration By NASA Organization (the soliciting organization, or the organization to which an unsolicited proposal is submitted) NASA , Headquarters , Science Mission Directorate , Planetary Science Chang’E 7 workshop Date Submitted Submission Method Grants.gov Application Identifier Applicant Proposal Identifier

05 / 31 / 2019 Electronic Submission Only NNH18ZDA001N-PMCS Type of Application Predecessor Award Number Other Federal Agencies to Which Proposal Has Been Submitted New

International Participation Type of International Participation Ref : Moon-SEIS-PP-21012 INSTITUTE OF GEOLOGY AND GEOPHYSICS Yes CO-I Collaborator Issue : 3.0 Date of issue : 14/12/2018 CHINESE ACADEMY OF SCIENCES SECTION III - Submitting Organization Information Status : Validated DUNS Number CAGE Code Employer Identification Number (EIN or TIN) Organization Type 中国科学院地质与地球物理研究所 824910376 5B002 8H P.O.BOX 9825, BEIJING 100029, CHINA Organization Name (Standard/Legal Name) Company Division Tel: 86-(0)10-82998001 Fax: 86-(0)10-62010846 University Of Notre Dame OFFICE OF RESEARCH

Organization DBA Name Division Number 《中法月震仪研讨会》会议纪要 OFFICE OF RESEARCH 2017 年 9 月 22 日，中国科学院地质与地球物理研究所、北京大学、华中科技大学等单位的 Street Address (1) Street Address (2) 中方专家参加了火星地震仪、月震仪布设和科学问题有关的研讨会，会议特邀法方专家 Institut 940 GRACE HALL de Physique du Globe de Paris （IPGP）, University Paris Diderot 研究所的 Philippe Lognonné City State / Province Postal Code Country Code 教授对他所带领团队研制的 InSight 火星地震仪相关技术做了详细介绍。中方代表中国科学院地 NOTRE DAME IN 46556 USA 质与地球物理研究所（IGGCAS）地震学组长张金海研究员代表中方介绍了单位概况和月震仪设计和布设有关方面的技术现状和科学设想。中方代表华中科技大学的屈少波博士介绍了空间 SECTION IV - Proposal Point of Contact Information 惯性传感器研制的技术现状、悬挂摆式隔振测试平台的性能及用于下一步月震仪地面测试的设 Name Email Address Phone Number 想。北京大学地球与空间科学学院的法文哲研究员、中国科学院地质与地球物理研究所科技处 Clive Neal [email protected] 574-631-8328 处长赵亮研究员、地震仪专业技术人员汪广浠工程师、地震震源过程专家郝金来博士等业界代 SECTION V - Certification and Authorization 表也参加了会谈。由于时间原因未能参会的专家和代表也希望加入中法双方的合作，他（她）们是：中国地质大学（武汉）大学的朱培民教授，北京大学的王彦宾教授，中国科技大学的孙 Certification of Compliance with Applicable Executive Orders and U.S. Code 道远教授，台湾海洋科技研究中心的林佩莹博士，中国科技大学的杨欣颖博士，中国科学院院 By submitting the proposal identified in the Cover Sheet/Proposal Summary in response to this Research Announcement, the Authorizing Official of the proposing organization (or the individual 刊副编审辛玲，Dr. Raphael Garcia, Institut de l’Aéronautique et de l’Espace, Dr. Mark proposer if there is no proposing organization) as identified below: Wieczorek, Observatory of Nice. • certifies that the statements made in this proposal are true and complete to the best of his/her knowledge; 双方代表就月震仪和火星地震仪设计方面的异同点进行了详细探讨，双方认为可以在如下 • agrees to accept the obligations to comply with NASA award terms and conditions if an award is made as a result of this proposal; and 几个方面进行深入合作： • confirms compliance with all provisions, rules, and stipulations set forth in this solicitation. Willful provision of false information in this proposal and/or its supporting documents, or in reports required under an ensuing award, is a criminal offense (U.S. Code, Title 18, Section 1001). 1. 充分借鉴 IPGP 课题组在火星地震仪设计方面的成功经验，为中国探月计划后续任务的月震仪设计和布设提供强有力的技术支撑； Authorized Organizational Representative (AOR) Name AOR E-mail Address Phone Number 2. 建立长效持久的合作机制，双方保持紧密联系，不定期召开学术研讨会，就有关问题进行深 Liz Rulli [email protected] 574-631-7432 入探讨，探索最优解决方案； 3. 在数据处理方面进行深入合作，探索发掘微弱信号的新方法和新技术，为解译月球和火星内 AOR Signature (Must have AOR's original signature. Do not sign "for" AOR.) Date 部圈层结构奠定基础； 4. 发挥中方长期以来在地震震源过程和地震偏移成像等方面的累积优势，预研火星地震研究可 FORM NRESS-300 Version 3.0 Apr 09 能遇到的特殊问题，为 InSight 采集的火星地震数据处理做好技术储备。

中方代表：法方代表： Prof. Philippe Lognonné 林杨挺研究员

张金海研究员

With the Chinese and American community

11 Commercial Missions : Seismology as a tool for ISRU

3 commercial lander candidates Step 1 : Exploration of Small Bodies with seismometers

• Several studies : AGEX, SEISCube … for AIM/AIDA, HERA, MMX • Objective : determination of Asteroid internal structure • Origins, Planetary Defense

Chipsat

Geophones + Rotation Gravimeter

Walkers et al. 2006 STEP 2: “finish the job” and reveal the solar systems rocky planets interior structure.

• Formidable questions but formidable difficulties

• Knowledge of its interior may hold the key to the understanding of its unique properties, such as its dense and hot carbon dioxide atmosphere and apparent lack of plate tectonics

• However, the temperature (400°C) and pressure (90 atm) at the Venus surface are not compatible with the state of the art of planetary seismometer

• Several options are open

(Cutts, Mimoun et al, 2015) Step 2: “finish the job” and reveal the solar systems rocky planets interior structure.

• Possible options for Venus Seismology

Atmospheric TEC Measurements Density Variations Airglow

Drag UV (day) Faraday “GNSS like” signal Doppler/S measurement IR – VIS (night) Rotation delay AR radar (SAR)

Several physical quantities can be used to monitor the perturbations in upper atmosphere

EMC perturbation

Sensor Noise Temperature

Pressure effect on ground

Noise induced by lander coupling (tether ?) Wind Lander Mechanical Noise Electronics (ASRG, wind) Noise

(Cutts, Mimoun et al, 2015) Step 3: Ocean worlds internal structure

• Determination of ice shell thickness

• Tectonics-related activity ?

• Plume / cryovolcano events ?

• Asteroid Impact Rates (Image via Slate) Step 3: Ocean worlds internal structure

• Several signals sources are expected to be measured by geophones • Ice crack signals related to excentricity tidal stresses • Ice crack signals related to plate tectonics • Signal related to cryovolcanoes/plumes • Meteoritic impacts

Moonquakes vs tidal stresses 50

014 1970 1974 0-12 0.10 0-08 0-08 0-06 U) Cl) 0-04 0-04 0-02

~“ U) -0-040-00 -.140 -0-06-0-08-0-02-0-04o-oo -0-08 -0-10 A NORMAL EVENTS -0-12 A NORMAL EVENTS • INVERTED EVENTS _U.100 200 300 100 200 300 DAY NUMBER DAY NUMBER

1971 014 1975 0-06 0-12 0-10 0-04 0-08 0-06 0-02 ~0-04 0-02

I 0-000 04 ~ -0-0600-0010 In -0-02 -0-04-0-02-0-08 A NORMAL EVENTS A NORMAL EVENTS I I - —012 I I 100 200 300 100 200 300 DAY NUMBER DAY NUMBER 0-12 1972

Kattenhorn et al, 2014 ~ 4 0-08 0-04 T.A. Minshull0-06 et al, 1987 0-04 ~ 0-020 08 w 0 10 1976 0-02 ~0-00 0-00 ~-0-02 -0-02 I U) ‘~-0-04 -0-04 0 ~-0-06 ~ -0-06 -0-08 A NORMAL EVENTS U INVERTED EVENTS -0-08 A NORMAL EVENTS 100 200 300 100 200 300 DAY NUMBER DAY NUMBER

0-12 - 1973 0-05 1977 0-10 ~ 0-04 0-08 0-03 0-06 Cl) 0-04 0-02 0-02 ‘Ii ~ 0~01 0-00 In ~ 0-00 ~ -0-02 4 ILl -0-04 -0-01 In -J -0-06 -0-02 a ~-0-08 -o-io ~ 003

—0-12 A NORMAL EVENTS U INVERTED EVENTS - I -0-04 A NORMAL EVENTS I I 100 200 300 - 100 200 300 DAY NUMBER DAY NUMBER Fig. 6. Correlationof Al moonquake activity over the period 1970—1977 with peaks in the tidal shear stress sympathetic to failure for a fault with strike N30°E, dip 300 to the SE, and left-lateral strike slip. 150 S. Lee et al. / Icarus 165 (2003) 144–167 are visible as are modal interference patterns in the ice layer. at a receiver simultaneously since their ray paths are sym- These patterns are a function of frequency, and are not read- metric. Also, an S wave from a source to a receiver on the ily observable for a typical broadband ice-crack or impact ice-vacuum surface is a Rayleigh wave. source. As expected, the horizontal particle velocity field in Some labelled ray geometries are shown in Fig. 8. A ray the ocean directly beneath the source is very weak due to path follows a straight line in an iso-speed medium. How- the almost total reflection of the shear wave at the ice–water ever, if the sound speed in the medium varies along the ray interface, which cannot support horizontal shear. path, the ray must satisfy Snell’s law where reflection and Figure 7 illustrates how efficiently seismic waves propa- transmission will occur at the boundary between iso-speed gate through the ice shell as do acoustic waves through the layers, and a continuous bending of a ray path, or refrac- subsurface ocean, and how a geophone located at the top of tion, will occur given a continuous sound speed gradient. For the ice shell will be able to detect multiple reflections from ahorizontallystratifiedmediumwheresoundspeedvaries the ice–water interface as well as the water–mantle interface. only in the z-direction, the radius of curvature rc of a re- The Rayleigh wave is a surface wave that travels at fracting ray is roughly 90% of the medium shear speed for a homogeneous 1 c0 dc − halfspace, and suffers only cylindrical spreading in horizon- rc , (18) = sin θ dz tal range but is attenuated exponentially with depth from 0 ! ! ! ! the surface it travels on. It will be strongly excited on the where θ0 is! the! incident angle at some fixed depth as in Fig. 8 ! ! ice-vacuum interface by sources of shallow depth, such as and c0 is the sound speed at the same depth. For the 20-km surface cracking events, impacts and the near-surface source convective ice shell model, the minimum radius of curvature of the given example. It can be seen in Fig. 7 as a strong ver- of a compressional wave in upper thermal boundary layer tical velocity field trapped near the surface. Characteristic regime is 51 km, which is not perceptible in Fig. 7. Re- differences between the Rayleigh wave and direct compres- fracted propagation of sound is a common feature in terres- sional wave arrivals will prove to be useful in determining trial oceans. In mid-latitudes deep sound channels typically the range of surface sources of opportunity. The frequency- form due to thermal heating above and increasing pressure dependent characteristics of a Rayleigh wave may also be below. These enable sound waves to propagate for thousands used as another possible tool to probe the interior structure of kilometers without ever interacting with the sea surface or of the ice shell, and will be described in Section 7.2. If the bottom (Urick, 1983). Without more evidence, however, it is wavelength of the Rayleigh wave is long compared to the difficult to speculate on what sound speed profiles may exist thickness of the ice shell, it will propagate as a flexural wave in a potential Europan ocean. on a thin plate. The travel time from a source to receiver depends on the ray path. Travel time differences between ray paths can be 4.2. Nomenclature of acoustic rays used to infer Europa’s interior structure. The range between asurfacesourceeventandasurfacegeophonecanbeob- The analysis of seismo-acoustic wave propagation fromNous netained pouvons from pas direct afficher P and S wave arrivals given the compres- asourcetoreceivercanbeintuitivelyunderstoodbyapply-lʼimage.Stepsional3: and Ocean shear wave speedsworlds in ice, whichinternal can be estimatedstructure ing ray theory which is valid when the wavelength is small with reasonable accuracy based on aprioriinformation (see compared to variations in the medium. Rays are defined as Appendix A). With the additional travel time measurement afamilyofcurvesthatareperpendiculartothewavefronts of a single ice–water reflection, such as PP, PS, or SS, the emanating from the source, and are obtained by solving the 154 S. Lee et al. / Icarus 165 (2003) 144–167 eikonal equation (Brekhovskikh and Lysanov, 1982; Frisk, 1994; Medwin and Clay, 1998). In order to describe the various seismo-acoustic rays propagating in ice and water layers, a nomenclature is adopted where P represents a compressional wave in the ice shell, S a shear wave in the ice shell, and where C is an acoustic wave in the subsurface ocean that includes reflection from water–mantle interface. Following this convention, appropriate letters are added consecutively when an acoustic ray reflects from or transmits through a given environmental interface. A PS wave, for example, is a compressional wave that departs from the source, reflects as a shear wave at the ice–water interface and arrives at the receiver. A PCS wave (Lee et al, 2003) Fig. 8. Nomenclature of acoustic rays. PP, PS, SS waves are single re- is a compressional wave that transmits through the ice–water flections from the ice–water interface, and PPPP, SSSS waves are double interface, reflects from the water–mantle interface, returns to reflections from the ice–water interface. PCP, PCS, and SCS waves are the the bottom of the ice shell, and transmits back into the ice as reflections• fromDistance the water–mantle between interface. Sound P,PP,PS speeds in ice layer and and S waves arrivals depends on ashearwave.ItshouldbenotedthatSPandPSwavesarrive ocean layer areice assumed shell constant width in this figure. • Only requirement is to have « seismic » events big enough to be detected by the geophones • PCP and PCS arrivals could also in principle sound the sug- Fig. 14. Bottomsurface reflections atocean 2-km range for (likely the 20-km convective very ice shellbig, closeFig. 15. Ice-water events reflections only at 50-km ) range for the 20-km convective ice model. The bottom reflections for short range propagation are mostly com- shell model. Travel time differences between the direct P wave and the pressional wave reflections, and are more prominent in the vertical particle Rayleigh wave can be inverted for the range between the source and re- velocity components. The weak precursor before the PCP reflection is the ceiver, and multiple reflections from the ice–water interface can be inverted reflection from the sediment layer overlying the basalt halfspace. for the thickness of the ice shell.

to-receiver travel time of ice–water reflected paths can be determined as a function of two nondimensional parameters Rayleigh wave. The Rayleigh wave can be easily identified ξ and R/H,asshowninAppendixB.Thetraveltimecurves by its high amplitude and retrograde particle motion where become functions of only one nondimensional parameter vertical and horizontal components are 90◦ out of phase. R/H,ifweassumethetypicalvalueξ 2. Nondimensional To also estimate the thickness of the ice shell, at least one = travel time curves for the simplified Europa model are plot- reflection from the ice–water interface must also be identi- ted in Fig. 18 where the travel time for paths including up to fied. The PP wave arrival can be readily identified since it double reflections from the ice–water interface are shown. arrives the soonest after the direct P wave except when R/H This figure can be used to analyze arrivals from ice–water is less than one, as shown in Fig. 18. Even in this case, how- reflections in Figs. 9 to 12. ever, the PP wave can be easily identified, since, besides the Similarly, the general source-to-receiver travel time of direct P wave, the Rayleigh wave is the only wave that can paths involving water–mantle reflections can also be deter- arrive before it. mined in terms of the additional nondimensional parame- If, for example, we measure the travel time differences ters ξw cp/cw,theratiobetweenthecompressionalwave ts tp ∆s ,andtpp tp ∆pp ,wheretp, ts ,andtpp are ≡ − ≡ − ≡ speed in ice and water, and Hw/H , the ratio between the the travel times of the direct P, the Rayleigh, and PP waves, ocean depth and the ice shell thickness, assuming an iso- speed water column. This is also shown in Appendix B. 1 1 1 ξ Nondimensional travel time curves for these paths are also ∆s R 1 R, (19) = 0.93 cs − cp = cp 0.93 − plotted in Fig. 18, assuming Hw/H 4andξw 4/1.5. ! " ! " = = 1 2 2 ∆pp 4H R R , (20) 5.3. Estimating interior structure = cp + − #$ % The range between the source and receiver can be deter- and R/cp and H/cp are uniquely determined by, mined with a single triaxial geophone on Europa’s surface without knowledge of the ice thickness by measuring the R ∆s , (21) travel time difference between the direct P wave and the cp = ξ/0.93 1 − Step 3: Ocean worlds internal structure

Lorenz et al 2009 • Temperature

• The radiation challenge for galilean satellites (MRad level !)

• 3 seismometers on DragonFly !

Oceans Internal Structure Short period Radiations, (Lee et al, Worlds Ice sheet width temperature 2003) Ocen depth PIONEERS : the next generation of planetary seismometers

• SEIS : an outstanding achievement • Use of optical technologies • …. but 1990’s technologies • Displacement transducer : x100 perf. improvement • Fiber Optics Gyrolaser : translation & rotation

Airbus/ixBlue

JPL/Caltech SODERN/IPGP

• PIONEERS is the acronym of Planetary Instruments based on Optical technologies for an iNnovative European Exploration using Rotational Seismology • It is about developing the new generation of planetary seismometers which will fly on the next missions of exploration of the solar system • A project of 4 years and 3 millions Euros • « Small » CubeSat size Instrument • Small bodies • Two instruments are developped • Ocean worlds • Planetary size Instruments:

• Moon MissionsNASA • Mars Missions PIONEERS : a breakthrough for the performance level

Impacts with Apollo Impacts with VBB and PIONEERS

DU= 5 x 10-10 ms-2 RMS= 5x10-11 ms-2

Apollo

VBB ( 2022+)

PIONEERS ( 2025+) Summary of Present / Future Missions Involving Seismology

Mission Launch Major Mission Instrument description Seismometer deployment Reference event SEIS May 5th Arrival on Mars Hybrid 6- axis instrument VBB and SP. [0.01 1 Hz] Instrument deployed on the ground by Lognonné et al (Mars) 2018 November 26th Noise floor < 0.5 10-9 m/s2/ÖHz - about 30 kg all robotic arm. Protected from environment (2019) 2018. First included by Wind and Thermal shield Marsquake detection DragonFly launch Arrival Lunar-A vertical seismometer (see Yamada Seismometer lowered with a windshield Lorenz et al, 2009 (Titan) in 2026 foreseen in paper) lowered with a windshield. Mass 0.4 kg underneath UAV. Geophones 2034 Two small (10Hz) geophones . implemented on both skid MMX Rover Sept Rover landing PIONEERS PFM instrument. High sensitivity Used as an IMU by the Rover Mimoun et al, 2019 (Phobos) 2024 foreseen accelerometer plus fiber optics gyro. March 2025 LGN TBD Launch 2025- Lunar Version of SEIS or Silicon Audio (SiA) Ultra Deployed by robotic arm or lowered Neal et al, 2019 Chang’E 7 2030 ? Low Noise optical/mechanical sensor is a force below lander. (Moon) feedback accelerometer that allows for very broadband detection and uses a laser interferometer Europa TBD Mission Instrument derived from SP seismometer Instrument in the lander warm box (Pike et al, 2016) Lander candidate for (radiation, temperatures …) (Europa) NF5 SEM Mars Arrival October 3-axis trihedron seismometer based on bronze- Instrument in the lander warm box ( Manoukian et al ExoMars 2021 2021 beryllium moving mass temperatures …) (Mars) Chandrayiian- 22 juillet ILSA is a triple axis, MEMS-based seismometer Instrument in the lander warm box ( https://www.isro.gov.i 2 2019 that can detect minute ground displacement, temperatures …) n/chandrayaan2- Seismometer velocity, or acceleration caused by lunar quakes. payloads (Moon) Its primary objective is to characterize the seismicity around the landing site. ILSA has been designed to identify acceleration as low as 100 ng /√Hz with a dynamic range of ±0.5 g and a bandwidth of 40 Hz. The dynamic range is met by using two sensors — a coarse-range sensor and a fine-range sensor. Venus 2025- Mission Microbarometer netwok to detect seismo-gravity Two barometers deployed below a Climate 2030 candidate for waves balloon gondola. Geophysics NF5 (Venus) Step 4 : Long term : planetary defense system

• Deriving from small bodies exploration

• Another use of the understanding of small bodies seismology is planetary defense;

• By helping to determine the internal structure of potentially hazardous asteroids (PHAs), seismic techniques can help evaluate the threat and the potential efficiency of a planned mitigation action

• A systematic survey of PHAs (as soon as they are discovered) with small CubeSat size probes including a seismometer a gyroscopic payload and a beacon to precisely track their location would definitely be a part of a planetary wide defense system. Step 4 : Long, long term : planetary wide sensors

• In the previous discussion, we have considered the use of seismic techniques with a performance level close to what has already been achieved for Apollo or Insight (typically 10-10 m/s2/Hz). Improving the detector performance by several orders of magnitude -which is technically possible with optical interferometry techniques - would enable the measurement of gravitational waves – on a planetary scale.

• All planets without atmosphere can be the place of remote sensing long period seismology, if very precise ranging ( below nm) can be made between slow orbiting S/C and surface reflectors.