Moon Io Research Articles

Changes in the longitude polarization dependence of Jupiter's moon Io as evidence of the long-term variability of its volcanic activity

The aim of the work was to investigate the longitude (orbital) dependence of the polarization of Jupiter's moon Io and compare results of our study with what is reported in the literature. We used our published observations and supplemented them with new measurements carried out with the polarimeters mounted on the 2.6 m Shajn telescope of the Crimean Astrophysical Observatory and the 2 m telescope of the Peak Terskol Observatory in the UBVRI bands at phase angles between 10° and 12° in August 2023 – February 2024. We have determined that amplitude of the orbital polarization in the V band does not exceed ≈0.1 %. It is the deepest −0.17 ± 0.03 % at L ≈ 270° and the shallowest −0.07 ± 0.03 % near L ≈ 130°. These parameters differ markedly from that obtained by Zellner and Gradie (1975), which found that the orbital polarization variations from 0.4 to 0.5 % for α > 10°, and the negative branch is the deepest near L = 160° and the shallowest near L = 300°. These differences may be a consequence of changes in the reflective properties of the local areas of Io's surface due to long-term changes in Io's local or global volcanic activity.

Energetic Charged Particle Measurements During Juno's Two Close Io Flybys

AbstractOn days 2023‐364 and 2024‐034, the Juno spacecraft made close passages of Jupiter's moon Io, at altitudes of about 1,500 km. Data obtained from the first flyby, when the spacecraft was on magnetic field lines connected to both Jupiter and Io, revealed deep flux decreases. In addition, Juno's energetic particle detectors observed tens to hundreds of keV electron and proton beams. Such beams could be generated near Jupiter on field lines associated with Io. The second encounter occurred in the plasma wake and a more modest flux decrease was observed. Furthermore, data from both encounters suggest a spatially extensive decrease in >1 MeV electrons that includes regions inward of Io's orbit. In the immediate vicinity of Io, signatures of absorption likely dominate the data whereas diffusion and wave‐particle interactions are expected to be needed to understand MeV electron data in the wider spatial region around Io.

The Vulcan Mission to Io: Lessons Learned during the 2022 JPL Planetary Science Summer School

A mission to Jupiter's moon Io, the most volcanically active body in the solar system, was suggested as a priority for the New Frontiers program in the 2013 Planetary Science Decadal Survey. We present a New Frontiers–class mission concept, Vulcan, that was designed as an educational exercise through the Jet Propulsion Laboratory’s 2022 Planetary Science Summer School. Vulcan would leverage an instrument suite consisting of wide- and narrow-angle cameras, a thermal infrared spectrometer, two fluxgate magnetometers, and ion and electron electrostatic analyzers to conduct the most thorough investigation of Io to date. Using 78 flybys over a 2 yr primary science mission, Vulcan would characterize the effects of tidal forces on the differentiation state, crustal structure, and volcanism of Io and investigate potential interactions between Io's volcanoes, surface features, and atmosphere. Although Vulcan was developed as an academic exercise, we show that a New Frontiers–class mission to Io could achieve transformative science in both geophysics and plasma physics, unifying typically disparate subfields of planetary science. A dedicated mission to Io, in combination with the Europa Clipper and Jupiter Icy Moons Explorer missions, would address fundamental questions raised by the 2023 Planetary Science Decadal Survey and could complete our understanding of the spectrum of planetary habitability. Lessons learned from Vulcan could be applied to a New Frontiers 5 Io mission concept in the near future.

Isotopic evidence of long-lived volcanism on Io.

Jupiter's moon Io hosts extensive volcanism, driven by tidal heating. The isotopic composition of Io's inventory of volatile chemical elements, including sulfur and chlorine, reflects its outgassing and mass loss history, and thus records information about its evolution. We used millimeter observations of Io's atmosphere to measure sulfur isotopes in gaseous SO2 and SO, and chlorine isotopes in gaseous NaCl and KCl. We find 34S/32S = 0.0595 ± 0.0038 (equivalent to δ34S = +347 ± 86‰), which is highly enriched compared to average Solar System values and indicates that Io has lost 94 to 99% of its available sulfur. Our measurement of 37Cl/35Cl = 0.403 ± 0.028 (δ37Cl = +263 ± 88‰) shows that chlorine is similarly enriched. These results indicate that Io has been volcanically active for most (or all) of its history, with potentially higher outgassing and mass-loss rates at earlier times.

Erupting Moon: What heats the prodigious volcanoes on Jupiter's fiery moon Io?

Erupting Moon: What heats the prodigious volcanoes on Jupiter's fiery moon Io?

A HITRAN-formatted UV line list of S2-containing transitions involving X3 Σg-, B3 Σu-, and B″ 3 Πu electronic states

ABSTRACT The sulfur dimer (S2) is an important molecular constituent in cometary atmospheres and volcanic plumes on Jupiter’s moon Io. It is also expected to play an important role in the photochemistry of exoplanets. The ultraviolet (UV) spectrum of S2 contains transitions between vibronic levels above and below the dissociation limit, giving rise to a distinctive spectral signature. Using spectroscopic information from the literature, and the spectral simulation program PGOPHER, a UV line list of S2 is provided. This line list includes the primary $B\, ^{3}\Sigma ^{-}_{u}-X\, ^{3}\Sigma ^{-}_{g}$ (v′ = 0–27, v″ = 0–10) electronic transition, where vibrational bands with v′≥10 are pre-dissociated. Intensities have been calculated from existing experimental and theoretical oscillator strengths, and semi-empirical strengths for the pre-dissociated bands of S2 have been derived from comparisons with experimental cross-sections. The S2 line list also includes the $B^{\prime \prime }\, ^{3}\Pi _{u}-X\, ^{3}\Sigma ^{-}_{g}$ (v′ = 0–19, v″ = 0–10) vibronic bands due to the strong interaction with the B state. In summary, we present the new HITRAN-formatted S2 line list and its validation against existing laboratory spectra. The extensive line list covers the spectral range 21 700–41 300 cm−1 (∼242–461 nm) and can be used for modelling both absorption and emission.

On the Time-Dilation Paradox—Can it be Removed?

In special relativity theory, the velocity of light is assumed to be constant, independent of the reference frame. This creates paradoxes when observations in different reference frames are compared. The so-called twin-paradox is based on a Gedanken experiment with identical twins, one traveling in a spaceship and one remaining on Earth. Due to the time-dilation effect, the traveling twin, when returning to Earth is younger than the other twin. This paradox has been tentatively resolved by inserting asymmetry, but the fully symmetrical twin-paradox remains within the relativity theory. However, if the light velocity, instead of being absolute, is taken to be relative, the paradox can be resolved. By reevaluating the light-clock experiment and performing various other Gedanken experiments, it becomes apparent that constant movement, independent of velocity, is the same as “at rest” for any one reference frame and does not need to involve any relativistic effects. This would make the Lorentz–Voigt factor void, and red- and blue-shifts of electromagnetic (EM) radiation can be explained as true changes in light-velocities. Based on thinking experiments, new rules for light-velocities are proposed, which also could explain anomalous observations regarding Jupiter’s moon Io’s movement. Gravity and its effect on light are examined, and it is argued that planetary lensing of light can be simply explained as refraction in a planet’s atmosphere or by diffraction on the planet itself. Further, the light pressure can resolve the indistinguishability principle. Alternatives to relativity explanations are suggested for several observations that nullify Fresnel dragging and oppose the existence of an aether medium. A modified Mach–Zehnder interferometer is proposed as an instrument for measuring sub-c and super-c velocities of EM-waves. The “old” relativity theories are replaced by a novel postulate that an applied force, leading to changes in velocity, is the reason for time-dilation: what may be called mechanical relativity. A mathematical suggestion of mechanical relativity is presented, along with discussions on connections between time, energy, and gravity.

Геодезическая нутация Юпитера и его галилеевых спутников

In the article, the relativistic effect of geodetic nutation in the rotation of Jupiter and its Galilean moons (Io, Europa, Ganymede and Callisto) was investigated in two ways over an 800-year time interval. As a result, for the first time, the most significant periodic terms of the geodetic rotation of these celestial bodies relative to: a) the barycenter of the Solar system and the plane of the mean orbit of Jupiter of the epoch J2000.0 in the Euler angles, in the disturbing terms of the physical libration and in the absolute magnitude of the angular rotation vector of the geodetic rotation of the body under study; b) (with the exception of Jupiter) the barycenter of the Jupiter satellite system and the mean orbit of the studied satellite of the epoch J2000.0 in the disturbing terms of the physical libration and in the absolute magnitude of the angular rotation vector of the geodetic rotation of the body under study. It is shown that the use of Way II in this study, which uses the numerical integration procedure, is more preferable, and the values of the geodetic nutation terms obtained by this way are more accurate. The accuracy level of calculating the parameters (obtained by Way II) for the geodetic nutation values of the studied celestial bodies was 0.1 microarcseconds. The obtained analytical values of geodetic nutation of the studied celestial bodies can be used for numerical investigation of the rotation of these bodies in the relativistic approximation.

Source of Radio Emissions Induced by the Galilean Moons Io, Europa and Ganymede: In Situ Measurements by Juno

AbstractAt Jupiter, part of the auroral radio emissions are induced by the Galilean moons Io, Europa and Ganymede. Until now, except for Ganymede, they have been only remotely detected, using ground–based radio–telescopes or electric antennas aboard spacecraft. The polar trajectory of the Juno orbiter allows the spacecraft to cross the range of magnetic flux tubes which sustain the various Jupiter–satellite interactions, and in turn to sample in situ the associated radio emission regions. In this study, we focus on the detection and the characterization of radio sources associated with Io, Europa and Ganymede. Using electric wave measurements or radio observations (Juno/Waves), in situ electron measurements (Juno/JADE–E), and magnetic field measurements (Juno/MAG) we demonstrate that the Cyclotron Maser Instability (CMI) driven by a loss–cone electron distribution function is responsible for the encountered radio sources. We confirmed that radio emissions are associated with Main (MAW) or Reflected Alfvén Wing (RAW), but also show that for Europa and Ganymede, induced radio emissions are associated with Transhemispheric Electron Beam (TEB). For each traversed radio source, we determine the latitudinal extension, the CMI–resonant electron energy, and the bandwidth of the emission. We show that the presence of Alfvén perturbations and downward field–aligned currents are necessary for the radio emissions to be amplified.

Зависимость геодезической прецессии от выбора системы координат на примере галилеевых спутников Юпитера

The relativistic effect of geodetic precession in the rotation of Jupiter and its Galilean moons (Io, Europa, Ganymede and Callisto) are investigated. For this purpose, the method developed in (Pashkevich, 2016) was modified, which is applicable for studying any bodies of the Solar System that have long-term ephemeris. As a result of its application, the most significant secular terms of geodetic precession were determined. In this study, the values of the angular velocity vectors of the geodetic rotation of the Galilean satellites of Jupiter relative to the barycenter of the Solar System and relative to the barycenter of the system of Jupiter satellites were calculated. Their differences are shown depending on the choice of coordinate reference system due to the asymmetry of the formula for the angular velocity vector of geodetic rotation for any solar system bodies used for these calculations. The obtained analytical values of the geodetic precession of the rotation parameters of the studied objects can be used for the numerical study of their rotation in the relativistic approximation.

Variability of the Auroral Footprint of Io Detected by Juno‐JIRAM and Modeling of the Io Plasma Torus

AbstractOne of the auroral features of Jupiter is the emission associated with the orbital motion of its moon Io. The relative velocity between Io and the surrounding plasma trigger perturbations that travels as Alfvén waves along the magnetic field lines toward the Jovian ionosphere. These waves can accelerate electrons into the atmosphere and ultimately produce an auroral emission, called the Io footprint. The speed of the Alfvén waves—and hence the position of the footprint—depends on the magnetic field and on the plasma distribution along the field line passing through Io, whose SO2‐rich atmosphere is the source of a dense plasma torus around Jupiter. Since 2016, the Jovian InfraRed Auroral Mapper (JIRAM) onboard Juno has been observing the Io footprint with a spatial resolution of ∼few tens of km/pixel. JIRAM detected evidences of variability in the Io footprint position that are not dependent on the System III longitude of Io. The position of the Io footprint in the JIRAM images is compared with the position predicted by a model of the Io Plasma Torus and of the magnetic field. This is the first attempt to retrieve quantitative information on the variability of the torus by looking at the Io footprint. The results are consistent with previous observations of the density and temperature of the Io Plasma Torus. However, we found that the plasma density and temperature exhibit considerable non‐System III variability that can be due either to local time asymmetry of the torus or to its temporal variability.

Early Stages of Galilean Moon Formation in a Water-depleted Environment

A key feature of the Galilean satellite system is its monotonic decrease in bulk density with growing distance from Jupiter, indicating an ice mass fraction that is zero in the innermost moon Io and about half in the outer moons Ganymede and Callisto. Jupiter-formation models, and perhaps the Juno spacecraft water measurements, are consistent with the possibility that the Jovian system may have formed, at least partly, from ice-poor material. And yet, models of the formation of the Galilean satellites usually assume abundant water ice in the system. Here, we investigate the possibility that the Jovian circumplanetary disk was populated with ice-depleted chondritic minerals, including phyllosilicates. We show that the dehydration of such particles and the outward diffusion of the released water vapor allow condensation of significant amounts of ice in the formation region of Ganymede and Callisto in the Jovian circumplanetary disk. Our model predicts that Europa, Ganymede, and Callisto should have accreted little, if any, volatiles other than water ice, in contrast to the comet-like composition of Saturn’s moon Enceladus. This mechanism allows for the presence of ice-rich moons in water-depleted formation environments around exoplanets as well.

Io: A Unique World in our Solar System

Jupiter’s moon Io is the most volcanically active world in our Solar System. Eruptions on Io sustain its atmosphere, feed the Jovian magnetosphere, and contaminate neighboring moons. This unique volcanic and tectonic activity is powered by tidal heating, caused by its gravitational interactions with Jupiter and other moons. The silicate crust of Io is coated with sulfur compounds, and its interior—one that is exceptional for an outer-planet moon—is composed of a metallic core and a silicate mantle that may host a magma ocean. Such spectacular large-scale volcanism and high heat flow provide insights into the processes that shaped all terrestrial bodies. Future exploration of Io would answer key questions and herald a new era of discoveries about the evolution of terrestrial planets and moons within our Solar System and beyond.

Stationkeeping of halo orbits in Jupiter-Europa-Io system

Europa is one of the most promising exploration targets in search for extraterrestrial life. In the observation of Europa, halo orbits are suitable locations, because they are periodic and three-dimensional, and stationary with respect to Europa. However, halo orbits are naturally unstable and thus need stationkeeping. This study addresses the stationkeeping problem of halo orbits in the Jupiter-Europa system perturbated by another Galilean moon Io, in which case Io’s mass and orbital rate are assumed to be unknown. A tight stationkeeping scheme is proposed while accounting for autonomous navigation. To deal with the unknown gravitational perturbation from Io, the mass and orbital rate of Io are estimated during the flight and are then used to enhance the control robustness and stability, and improve the navigation accuracy. The control saturation problem is addressed by introducing adjustable parameters into the control law. The accuracy and error distribution of estimation is evaluated through Monte Carlo simulation.

On the Relation Between Auroral Morphologies and Compression Conditions of Jupiter's Magnetopause: Observations From Juno and the Hubble Space Telescope

AbstractJupiter displays the most powerful auroral emissions in our solar system, which result from strong energy dissipation in Jupiter's surrounding space environment. Although mass and energy in Jupiter's magnetosphere mostly come from the innermost Galilean moon Io's volcanic activity and Jupiter's rotation, solar wind perturbations can play crucial roles in releasing magnetospheric energy. The systematic response of the aurora to a solar wind compression remains poorly understood because of timing uncertainties. Here we report the analysis of a set of auroral images from the Hubble Space Telescope with contemporaneous in situ magnetopause detections from Juno, allowing for a more direct comparison. By analyzing the dawn side main auroral emission, we distinguish two non‐mutually exclusive types of auroral enhancements: auroral dawn storm (ADS) featured with latitudinal extension in limited longitudes, and a long‐lasting main auroral brightening with limited extension in latitudes while extending over a large longitude range. Only the latter systematically appears under a compressed magnetopause, while the dawn storms could occur whatever the state of the magnetopause. The results could provide important constraints to improve theoretical models and numerical simulations. During expanded magnetopause conditions, Jupiter's aurora displayed either quiet or dawn storm morphology. The result is consistent with recent discovery of the initiation of ADSs in midnight and post‐midnight, possibly driven by magnetic reconnection plasma instabilities in night magnetotail. Our results show that some typical auroral morphologies could be used as a diagnostic of solar wind conditions at Jupiter.

Abiotic molecular oxygen production-Ionic pathway from sulfur dioxide.

Molecular oxygen, O2, is vital to life on Earth and possibly also on exoplanets. Although the biogenic processes leading to its accumulation in Earth’s atmosphere are well understood, its abiotic origin is still not fully established. Here, we report combined experimental and theoretical evidence for electronic state–selective production of O2 from SO2, a chemical constituent of many planetary atmospheres and one that played an important part on Earth in the Great Oxidation Event. The O2 production involves dissociative double ionization of SO2 leading to efficient formation of the ion, which can be converted to abiotic O2 by electron neutralization or by charge exchange. This formation process may contribute substantially to the abundance of O2 and related ions in planetary atmospheres, such as the Jovian moons Io, Europa, and Ganymede. We suggest that this sort of ionic pathway for the formation of abiotic O2 involving multiply charged molecular ion decomposition may also exist for other atmospheric and planetary molecules.

Field Line Resonances and Cavity Modes at Earth and Jupiter

Ultra-Low-Frequency (ULF) waves provide a means for the rapid propagation of energy and field-aligned current in planetary magnetospheres. At Earth, the ULF frequency range is usually defined as including waves with periods of 0.2–600 s; however, at Jupiter these waves can extend to periods of tens of minutes. In both magnetospheres, shear mode Alfvén waves can form field line resonances that exist between the ionospheres, with periods of a few minutes at Earth and a few tens of minutes at Jupiter. A major distinction between these two magnetospheres is in the density distribution. Earth has a dense ionosphere full of heavy ions, an extended, cold plasmasphere and a relatively low-density plasma sheet. In contrast, at Jupiter, the ionosphere is largely hydrogen (both in atomic form and in the H3+molecular ion), there is no appreciable plasmasphere and the plasma disk is dense and populated with heavy ions (largely sulfur and oxygen) originating at the moon Io and to some extent from other moons. As at Earth, the sharp Alfvén speed gradient above the ionosphere forms an ionospheric Alfvén resonator at Jupiter with periods of seconds. Furthermore, the high-latitude lobes at Jupiter have very low density and a resonant structure can be formed by waves bouncing between the ionosphere and the dense plasma disk. This structure leads to periods of tens of seconds. Finally, the dense Io plasma torus and plasma sheet provide conditions for compressional cavity modes to form in this region. Thus, the structure of the field line resonance modes is quite different at the two planets. Implications of these resonances on auroral particle acceleration will be discussed.

Loss of Energetic Ions Comprising the Ring Current Populations of Jupiter's Middle and Inner Magnetosphere

AbstractThe low‐altitude, polar orbit of the Juno mission allows the Jupiter Energetic Particle Detector Instrument to view into, and resolve, the loss cone of energetic ions comprising the low‐altitude extension of Jupiter's ring current ions. For regions mapping from just inside Ganymede's orbit to well beyond Ganymede's orbit, energetic ions (>50 keV H+ and >130 keV Oxygen and Sulfur ions) are strongly scattered into the loss cone and lost to the magnetosphere at the “strong diffusion limit” at essentially all times. We conclude, by arguing against magnetic curvature scattering, that the cause is waves, perhaps associated with Alfvénic variations previously documented in this equatorial region. Scattering is generally weak or nonexistent near the orbits of the moons Europa and Io, except for the regions just downstream of the corotating plasmas. For Io, we sometimes observe moderate, but not saturated, scattering within roughly 60° downstream. Significantly, scattering is weak or nonexistent just upstream of Io's position, an asymmetry echoed in some previous wave observations. A preliminary accounting of the total (longitude‐averaged) scattering losses near Io's orbit yields loss rates of order 4%–5% of the strong diffusion limit for H+ and 5%–7% for heavy ions (O + S). We conclude that near Io's orbit, charge exchange losses likely dominate over scattering losses for heavy ions and for the lower energy H+ ions (roughly <200 keV).

Occultation Mapping of Io’s Surface in the Near-infrared. I. Inferring Static Maps

Abstract With hundreds of active volcanoes varying in intensity on different timescales, Jupiter’s moon Io is the most volcanically active body in the solar system. Io has been observed from Earth using high-cadence near-infrared photometry during occultations by Jupiter and other Galilean moons since the 1980s. These observations encode a wealth of information about the volcanic features on its surface. We built a generative model for the observed occultation light curves using the code starry, which enables fast, analytic, and differentiable computation of occultation light curves in emitted and reflected light. Using this model, we are able to recover surface thermal emission maps of Io containing known volcanic hot spots without having to make assumptions about the locations, shapes, or number of hot spots. Our model is also directly applicable to the problem of mapping the surfaces of stars and exoplanets.

Successful Detection of a Preferred Frame Using Eclipses of Jupiter’s Moon Io

In this paper tests by Maxwell and Gift that search for a preferred frame or ether arising from movement through that frame using Jupiter’s moon Io are reviewed and discussed. Unlike the Michelson-Morley second-order experiment which unsuccessfully attempted to detect the orbital motion of the Earth relative to the ether, these tests are both first-order and therefore are unaffected by the second-order effects of length contraction and clock retardation. The test by Maxwell utilizes the delay in the eclipse of Io as the Earth orbits the Sun in an attempt to detect ether drift resulting from the galactic movement of the Sun. This test requires a 6-year duration for its full execution and was never performed because of practical difficulties. The test first presented by Gift can be conducted over a few days and employs the observed variation of the period of Io as the Earth moves toward or away from Jupiter. The result is a positive detection of ether drift arising from the orbital motion of the Earth. The detected ether drift is evidence of a preferred frame which we argue corresponds to the solar system barycentric or sun-centered inertial (SCI) frame.