@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/106365, title ="No phosphine in the atmosphere of Venus", author = "Villanueva, G. L. and Cordiner, M.", journal = "arXiv", month = "October", year = "2020", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201030-142420466", revision_no = "9", abstract = "The detection of phosphine (PH₃) has been recently reported in the atmosphere of Venus employing mm-wave radio observations (Greaves et at. 2020). We here demonstrate that the observed PH₃ feature with JCMT can be fully explained employing plausible mesospheric SO₂ abundances (~100 ppbv as per the SO₂ profile given in their figure 9), while the identification of PH₃ in the ALMA data should be considered invalid due to severe baseline calibration issues. We demonstrate this by independently calibrating and analyzing the ALMA data using different interferometric analysis tools, in which we observe no PH₃ in all cases. Furthermore, for any PH₃ signature to be produced in either ALMA or JCMT spectra, PH₃ needs to present at altitudes above 70 km, in stark disagreement with their photochemical network. We ultimately conclude that this detection of PH₃ in the atmosphere of Venus is not supported by our analysis of the data.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/106366, title ="ALMA Observations of Io Going into and Coming out of Eclipse", author = "de Pater, Imke and Luszcz-Cook, Statia", month = "September", year = "2020", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201030-143700771", note = "We are grateful for in-depth reviews by David Goldstein\nand one anonymous referee, which helped improve\nthe manuscript substantially. This paper makes\nuse of ALMA data ADS/JAO.ALMA#2017.1.00670.S.\nALMA is a partnership of ESO (representing its member\nstates), NSF (USA) and NINS (Japan), together\nwith NRC (Canada), MOST and ASIAA (Taiwan), and\nKASI (Republic of Korea), in cooperation with the Republic\nof Chile. The Joint ALMA Observatory is operated\nby ESO, AUI/NRAO, and NAOJ. The National\nRadio Astronomy Observatory is a facility of the National\nScience Foundation operated under cooperative\nagreement by Associated Universities, Inc. The data\ncan be downloaded from the ALMA Archive. This research\nwas supported by the National Science Foundation,\nNSF grant AST-1313485 to UC Berkeley. PMR\nacknowledges support from ANID basal AFB170002.\n", revision_no = "11", abstract = "We present 1-mm observations constructed from ALMA [Atacama Large (sub)Millimeter Array] data of SO₂, SO and KCl when Io went from sunlight into eclipse (20 March 2018), and vice versa (2 and 11 September 2018). There is clear evidence of volcanic plumes on 20 March and 2 September. The plumes distort the line profiles, causing high-velocity (≳500 m/s) wings, and red/blue-shifted shoulders in the line profiles. During eclipse ingress, the SO₂ flux density dropped exponentially, and the atmosphere reformed in a linear fashion when re-emerging in sunlight, with a \"post-eclipse brightening\" after ∼10 minutes. While both the in-eclipse decrease and in-sunlight increase in SO was more gradual than for SO₂, the fact that SO decreased at all is evidence that self-reactions at the surface are important and fast, and that in-sunlight photolysis of SO₂ is the dominant source of SO. Disk-integrated SO₂ in-sunlight flux densities are ∼2--3 times higher than in-eclipse, indicative of a roughly 30--50% contribution from volcanic sources to the atmosphere. Typical column densities and temperatures are N ≈ (1.5±0.3)×10¹⁶ cm⁻² and T ≈ 220−320 K both in-sunlight and in-eclipse, while the fractional coverage of the gas is 2--3 times lower in-eclipse than in-sunlight. The low level SO₂ emissions present during eclipse may be sourced by stealth volcanism or be evidence of a layer of non-condensible gases preventing complete collapse of the SO₂ atmosphere. The melt in magma chambers at different volcanoes must differ in composition to explain the absence of SO and SO₂, but simultaneous presence of KCl over Ulgen Patera.", } @misc {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/105293, title ="Mapping satellite surfaces and atmospheres with ground-based radio interferometry", author = "de Kleer, Katherine and Butler, Bryan", month = "July", year = "2020", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200909-102651170", note = "NASA Planetary Decadal Survey. \n\nThe authors acknowledge ideas generated in the Next-Generation Planetary Radar workshop organized by the W.M. Keck Institute for Space Studies.", revision_no = "12", abstract = "Ground-based interferometry at mm-cm wavelengths provides a powerful tool for characterizing satellite surfaces and atmospheres. We present the science enabled by the ALMA (current) and ngVLA (proposed) arrays, including recent results as well as future work in the context of planned and proposed spacecraft missions.", } @misc {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/104980, title ="EarthFinder Probe Mission Concept Study: Characterizing nearby stellar exoplanet systems with Earth-mass analogs for future direct imaging", author = "Plavchan, Peter and Vasisht, Gautam", journal = "arXiv", month = "June", year = "2020", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200817-122112681", note = "© 2019. \n\nNASA Probe Mission concept white paper for 2020 Astrophysics National Academies Decadal Survey. \n\nThis research was carried out at George Mason University and the Jet Propulsion\nLaboratory, California Institute of Technology, under a contract with the National\nAeronautics and Space Administration.\nReference herein to any specific commercial product, process, or service by trade\nname, trademark, manufacturer, or otherwise, does not constitute or imply its\nendorsement by the United States Government or the Jet Propulsion Laboratory,\nCalifornia Institute of Technology.", revision_no = "8", abstract = "EarthFinder is a NASA Astrophysics Probe mission concept selected for study as input to the 2020 Astrophysics National Academies Decadal Survey. The EarthFinder concept is based on a dramatic shift in our understanding of how PRV measurements should be made. We propose a new paradigm which brings the high precision, high cadence domain of transit photometry as demonstrated by Kepler and TESS to the challenges of PRV measurements at the cm/s level. This new paradigm takes advantage of: 1) broad wavelength coverage from the UV to NIR which is only possible from space to minimize the effects of stellar activity; 2) extremely compact, highly stable, highly efficient spectrometers (R>150,000) which require the diffraction-limited imaging possible only from space over a broad wavelength range; 3) the revolution in laser-based wavelength standards to ensure cm/s precision over many years; 4) a high cadence observing program which minimizes sampling-induced period aliases; 5) exploiting the absolute flux stability from space for continuum normalization for unprecedented line-by-line analysis not possible from the ground; and 6) focusing on the bright stars which will be the targets of future imaging missions so that EarthFinder can use a ~1.5 m telescope.", } @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.", } @misc {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94943, title ="Astro2020 Science White Paper: Triggered High-Priority Observations of Dynamic Solar System Phenomena", author = "Chanover, Nancy and Wong, Michael H.", journal = "arXiv", month = "March", year = "2019", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190424-142121489", revision_no = "9", abstract = "Unexpected dynamic phenomena have surprised solar system observers in the past and have led to important discoveries about solar system workings. Observations at the initial stages of these events provide crucial information on the physical processes at work. We advocate for long-term/permanent programs on ground-based and space-based telescopes of all sizes - including Extremely Large Telescopes (ELTs) - to conduct observations of high-priority dynamic phenomena, based on a predefined set of triggering conditions. These programs will ensure that the best initial dataset of the triggering event are taken; separate additional observing programs will be required to study the temporal evolution of these phenomena. While not a comprehensive list, the following are notional examples of phenomena that are rare, that cannot be anticipated, and that provide high-impact advances to our understandings of planetary processes. Examples include: new cryovolcanic eruptions or plumes on ocean worlds; impacts on Jupiter, Saturn, Uranus, or Neptune; extreme eruptions on Io; convective superstorms on Saturn, Uranus, or Neptune; collisions within the asteroid belt or other small-body populations; discovery of an interstellar object passing through our solar system (e.g. 'Oumuamua); and responses of planetary atmospheres to major solar flares or coronal mass ejections.", } @misc {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/95003, title ="Solar system Deep Time-Surveys of atmospheres, surfaces, and rings", author = "Wong, Michael H. and Cartwright, Richard", journal = "arXiv", month = "March", year = "2019", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190425-160735433", revision_no = "11", abstract = "Imaging and resolved spectroscopy reveal varying environmental conditions in our dynamic solar system. Many key advances have focused on how these conditions change over time. Observatory-level commitments to conduct annual observations of solar system bodies would establish a long-term legacy chronicling the evolution of dynamic planetary atmospheres, surfaces, and rings. Science investigations will use these temporal datasets to address potential biosignatures, circulation and evolution of atmospheres from the edge of the habitable zone to the ice giants, orbital dynamics and planetary seismology with ring systems, exchange between components in the planetary system, and the migration and processing of volatiles on icy bodies, including Ocean Worlds. The common factor among these diverse investigations is the need for a very long campaign duration, and temporal sampling at an annual cadence.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/95016, title ="Potential for Solar System Science with the ngVLA", author = "de Pater, Imke and Butler, Bryan", journal = "arXiv", month = "October", year = "2018", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190426-092643133", revision_no = "9", abstract = "Radio wavelength observations of solar system bodies are a powerful method of probing many characteristics of those bodies. From surface and subsurface, to atmospheres (including deep atmospheres of the giant planets), to rings, to the magnetosphere of Jupiter, these observations provide unique information on current state, and sometimes history, of the bodies. The ngVLA will enable the highest sensitivity and resolution observations of this kind, with the potential to revolutionize our understanding of some of these bodies. In this article, we present a review of state-of-the-art radio wavelength observations of a variety of bodies in our solar system, varying in size from ring particles and small near-Earth asteroids to the giant planets. Throughout the review we mention improvements for each body (or class of bodies) to be expected with the ngVLA. A simulation of a Neptune-sized object is presented in Section 6. Section 7 provides a brief summary for each type of object, together with the type of measurements needed for all objects throughout the Solar System.", }