@misc {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/99419,
    title ="Tidal Heating: Lessons from Io and the Jovian System - Final Report",
    author = "de Kleer, Katherine and McEwen, Alfred S.",
    
    
    
    
    month = "June",
    year = "2019",
    
    doi = "10.26206/d4wc-6v82",
    
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20191023-151847724",
    note = "© June 2019. \n\nWe especially thank Michele Judd and others at the Keck Institute for Space Studies for supporting this effort. This research was in part carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.",
    revision_no = "14",
    abstract = "Tidal heating is key to the evolution and habitability of many worlds across our solar system and beyond. However, there remain fundamental gaps in our understanding of tidal heating and coupled orbital evolution, which motivated a Keck Institute for Space Studies (KISS) workshop on this topic. The Cassini mission has led to many recent results about ocean worlds and what may become a new paradigm for understanding orbital evolution with tidal heating, the model of resonance locking in the parent planet (Fuller et al., 2016). Resonance locking explains how subsurface oceans may persist over much of geologic time, even in tiny Enceladus. The discovery\nof the Laplace resonance of Io, Europa, and Ganymede orbiting Jupiter led to the prediction of intense tidal heating of Io (Peale et al., 1979); this system provides the greatest potential for advances in the next few decades. Europa Clipper and JUpiter ICy moons Explorer (JUICE) will provide in-depth studies of Europa and Ganymede in the 2030s. The easily observed heat flow of Io, from hundreds of continually erupting volcanoes, makes it an ideal target for further investigation, and the missing link—along with missions in development—to understand the Laplace system. \n\nWe identified five key questions to drive future research and exploration: (Q1) What do volcanic eruptions tell us about the interiors of tidally heated bodies (e.g., Io, Enceladus, and perhaps Europa and Triton)? (Q2) How is tidal dissipation partitioned between solid and liquid materials? (Q3) Does Io have a melt-rich layer, or “magma ocean”, that mechanically decouples the lithosphere from the deeper interior? (Q4) Is the Jupiter/Laplace system in equilibrium (i.e., does the satellite’s heat output equal the rate at which energy is generated)? (Q5) Can stable isotope measurements inform long-term evolution of tidally heated bodies? \n\nThe most promising avenues to address these questions include a new spacecraft mission making close flybys of Io, missions orbiting and landing on key worlds such as Europa and Enceladus, technology developments to enable advanced techniques, closer coupling between laboratory experiments and tidal heating theory, and advances in Earth-based telescopic observations of solar system and extrasolar planets and moons. All of these avenues would benefit from technological developments. An Io mission should: characterize volcanic processes (Q1); test interior models via a set of geophysical measurements coupled with laboratory experiments and theory (Q2 and Q3); measure the rate of Io’s orbital migration (to complement similar measurements expected at Europa and Ganymede) to determine if the Laplace resonance is in equilibrium (Q4); and determine neutral compositions and measure stable isotopes in Io’s atmosphere and plumes (Q5). No new technologies are required for such an Io mission following advances in radiation design and solar power realized for Europa Clipper and JUICE. Seismology is a promising avenue for future exploration, either from landers or remote laser reflectometry, and interferometric synthetic aperture radar (InSAR) could be revolutionary on these active worlds, but advanced power systems plus lower mass and power-active instruments are needed for operation in the outer solar system.",
}
@techreport {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/59019,
    title ="Probing the Interior Structure of Venus",
    author = "Stevenson, David J. and Cutts, James A.",
    
    
    
    
    month = "April",
    year = "2015",
    
    
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20150727-150921873",
    note = "We would like to thank members of the study team for their contributions to this report during\nthe initial teleconferences, at the workshop itself, and in the preparation of the report. Without\nthe diverse talents and enthusiasm of our study team, this report never could have happened.\nOn behalf of members of the study team, we would like to thank Michelle Judd, Managing\nDirector of the Keck Institute for Space Studies, for her role in creating the collaborative\nenvironment that was so vital to the success of our study.\nWe would also like to thank Prof. Tom Prince, Director of the Keck Institute for Space\nStudies, for his guidance and the KISS Steering Committee for the confidence they placed in our\nteam by selecting our study for funding.\nIn the preparation of this report, we would like to acknowledge Samantha Ozyildirim of JPL\nfor her thorough review and editing and layout of the report. Corby Waste, also of JPL, was\nresponsible for creating the cover art. Dr. Suzanne Smrekar provided insightful comments.\nWe acknowledge NASA’s Jet Propulsion Laboratory and the California Institute of\nTechnology for their support of the study and for making it possible for key study participants to\nbe involved.\nFinally, we would like to thank the W.M. Keck Foundation for their foresight in establishing\nthe Keck Institute for Space Studies and the new facilities, which were so conducive to the\nworkshop process.",
    revision_no = "18",
    abstract = "The formation, evolution, and structure of Venus remain a mystery more than 50 years after the\nfirst visit by a robotic spacecraft. Radar images have revealed a surface that is much younger\nthan those of the Moon, Mercury, and Mars as well as a variety of enigmatic volcanic and\ntectonic features quite unlike those we are familiar with on Earth. What are the dynamic\nprocesses that shape these features, in the absence of any plate tectonics? What is their\nrelationship with the dense Venus atmosphere, which envelops Venus like an ocean? To\nunderstand how Venus works as a planet, we now need to probe its interior.\nConventional seismology for probing the interior of a planet employs extremely sensitive\nmotion or speed detectors in contact with the planetary surface. For Venus, these sensors must be\ndeployed on the surface and must tolerate the Venus environment (460 degrees \nC and 90 bars) for up to a\nyear. The dense atmosphere of Venus, which efficiently couples seismic energy into the\natmosphere as infrasonic waves, enables two alternatives: detection of these infrasonic waves in\nthe middle atmosphere using a string of two or more microbarometers suspended from a floating\nplatform or detection with an orbiting spacecraft of electromagnetic signatures produced by\ninteractions of infrasonic waves in the Venus upper atmosphere and ionosphere. This report,\ndescribing the findings of a workshop, sponsored by the Keck Institute of Space Studies (KISS),\nconcludes that seismic investigations can be successful conducted from all three vantage\npoints—surface, middle atmosphere, and space. Separately or, better still, together, these\nmeasurements from these vantage points can be used to transform knowledge of Venus\nseismicity and the interior structure of Venus.\nUnder the auspices of KISS, a multidisciplinary study team was formed to explore the\nfeasibility of investigating the interior of the planet with seismological techniques. Most of the\nteam’s work was conducted in a five-day workshop held at the KISS facility at the California\nInstitute of Technology (Caltech) campus from June 2–6, 2014. This report contains the key\nfindings of that workshop and recommendations for future work.\nSeismicity of Venus: The study team first performed an assessment of the seismicity of\nVenus and the likelihood that the planet experiences active seismic activity. The morphology of\nthe structural features as well as the youthfulness of the planet surface testifies to the potential\nfor seismic activity. There is plenty of evidence that the crust of Venus has experienced stress\nsince the relief of stress is expressed in a wide range of structural features. However, the\ncontemporary rate of stress release is unknown and it is possible that, as on Earth, much of that\nstress release is aseismic. Two competing conditions on Venus will influence the likelihood of\nstress release. On the one hand, the lack of water would result in a larger fraction of seismic\nenergy release; on the other hand, the higher temperatures would limit the magnitude of stress\nrelease events. Experimental measurements on candidate Venus crustal and mantle materials\nmay help define which effect is more important.\nOther Sources of Seismic Energy: Volcanic events are also a potential source of seismic\nwaves on Venus. Unlike Mars, where volcanic activity appears to have ended, infrared orbital\nmeasurements may indicate that some volcanoes on Venus are still active. Disturbances due to\nlarge bolides impacting the atmosphere may also be recorded but are unlikely to be useful for\nprobing the planetary interior. More useful than these point sources of energy will be energy\ninjected into the subsurface from the dynamic atmosphere by atmosphere-surface coupling. This\ndistributed source may be useful for probing the subsurface using the methods of ambient noise\ntomography. \nAtmospheric Propagation: Acoustic waves from a seismic event are coupled much more\nefficiently into the atmosphere than on Earth. The coupling efficiency is intermediate between\nthat for the Earth’s atmosphere and the ocean. Signals propagating from directly above the\nepicenter or from a surface wave propagating out from the quake epicenter both travel up into the\natmosphere. Because the atmosphere is primarily carbon dioxide, attenuation is higher than it\nwould be in an atmosphere with non-polar molecules. The attenuation is frequency dependent\nand only impacts frequencies well above 10 Hz at the altitude of a floating platform (54 km). For\nobservations from a space platform, it may be important at much lower frequencies to 1 mHz.\nDetection from a Floating Platform: Infrasonic pressure signals emanating either directly\nabove the epicenter of a seismic event or from the (surface) Rayleigh wave can be picked up by\nmicrobarometers deployed from a balloon floating in the favorable environment of the middle\natmosphere of Venus atmosphere. Two or more microbarometers deployed on a tether beneath\nthe balloon will be needed to discriminate pressure variations caused by an upwardly\npropagating surface wave resulting from the effects of altitude changes (updrafts and\ndowndrafts) and changes in buoyancy of the balloon. The platform will circumnavigate Venus\nevery few days enabling a survey of Venus seismicity.\nOrbital Detection: Observations from a spacecraft in orbit around Venus enable a broad\nrange of techniques for investigating the perturbations of the neutral atmosphere and ionosphere\nby seismic waves. Our initial analyses confirm that non-local thermodynamic equilibrium CO_2\nemissions on the day side (at 4.3 µm) will present variations induced by adiabatic pressure and\ndensity variations and energy deposition created by both acoustic and gravity waves. For\ndetection purposes, the advantage of this emission compared to other ones considered during the\nstudy (O_2 night side airglow at 1.27 µm or ultraviolet [UV] day side emission at 220 nm) is a\nsmoothly varying background with solar zenith angle, because of a strong CO_2 absorption at this\nwavelength below 110 km.\nSurface Detection: While important seismic measurements can be made from both balloon\naltitudes and from orbit, the measurement of all three dimensions of the ground motion can only\nbe made by a sensor on the surface of Venus. However, at present, the technology for seismic\nexperiments on the surface of Venus does not exist. Development of a seismic measurement\ncapability equivalent to the Seismic and Interior Structure (SEIS) for the Mars InSight (Interior\nExploration using Seismic Investigations, Geodesy and Heat Transport) spacecraft is many years\nif not decades away. However, useful measurements of the ambient noise on the surface of\nVenus are feasible with existing technology and would be vital for both the design of a future\nseismic station with high sensitivity for teleseismic events and a pair or network of stations that\ncould probe the interior using ambient noise tomography.\nSynergistic Observations in All Three Modes: The synoptic orbital view for a remote\nsensing spacecraft in a high orbit would enable not only sensitive detection and localization of\nVenus quakes with excellent background discrimination but potentially precise measurements of\nthe propagation of the seismic surface wave counterpart in the higher atmosphere.\nComplementary observations of the same event at the much higher frequencies that are possible\nfrom in situ platforms on the surface and in the middle atmosphere would greatly enhance the\nability to survey seismicity and probe the Venus interior.\nThe Path Forward: The first step going forward is to develop the detailed requirements of\nthe proposed payloads and to carry out related technology developments and laboratory or field\ndemonstrations. In undertaking this process, we need to know more about the properties of\npotential Venus crustal and mantle rocks through laboratory studies and the potential of ambient \nnoise tomography at Venus through analysis. Once this is done, our strategy for investigating the\ninternal structure of Venus is built around programmatic realities—the missions that NASA,\nEuropean Space Agency (ESA), Japan Aerospace Exploration Agency (JAXA), and the Russian\nFederal Space Agency (RFSA) are currently flying, are under development, or are being planned.\nA primary goal should be technology demonstration experiments on Venus missions where\nseismology is not currently an objective. These include infrasonic background measurements\nfrom a Venus balloon and infrared and visible signatures from an orbiter that might be\nimplemented under NASA’s Discovery program or as an ESA M-series mission. It would also\ninclude seismic background signals and a potential active seismic experiment from a short duration\nlander such as NASA’s proposed New Frontiers Venus In Situ Explorer (VISE)\nmission. This would be followed with a much more capable mission equipped to investigate\nseismicity and interior structure. The orbital and balloon platforms needed for such a mission are\nalso features of the Venus Climate Mission (VCM), a Flagship mission endorsed by the\nPlanetary Science Decadal Survey in 2011. The study team recommends study of a Venus\nClimate and Interior Mission (VCIM), which could benefit from commonalities in spacecraft\nsystems, and secure the support of the broad planetary science community for its Flagship\nmission for the next decade.",
}
@techreport {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/51025,
    title ="LIGO Physics Environmental Monitoring at the 40-meter Prototype",
    author = "Tsai, Victor C. and Weinstein, Alan J.",
    
    
    
    
    month = "October",
    year = "2001",
    
    
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20141029-142001261",
    note = "© 1991\n\nFinally, I would like to extend many thanks to Alan J. Weinstein, Dennis Ugolini, Ben Abbott, Steve Vass, Ken Libbrecht, NSF and SURF.",
    revision_no = "14",
    abstract = "When Einstein formulated General Relativity, he made numerous predictions including the existence of gravitational waves. Until now, though, they have been impossible to detect. LIGO, the Laser Interferometer Gravitational-Wave Observatory, has been built to overcome\nthis. Major difficulties arise as a result of the fact that gravitational waves are inherently weak; LIGO is expected to detect stretching on the order of 10-18 meters.\nWith the need for such precise measurements, a very large number of unwanted effects have to be minimized. Thus, physical environmental effects must be monitored with care and analyzed. Among the tools needed are a weather monitor, accelerometers and seismometers, and vacuum monitors. Each of these devices must be connected to the network and queried by the database, and the data coming from them must be analyzed. In order to accomplish all this, we must setup\nthe hardware; write code to query each device and format the data; create GUIs to display the data; and design data analysis programs. Such systems have been designed and built for the two LIGO observatory sites. In this project I\nimplement a Physical Environmental Monitoring system for the Caltech 40-meter Interferometer Prototype Laboratory, and analyze the data obtained.",
}