Saturn’s moon Enceladus has an ice-covered ocean; a plume of material erupts from cracks in the ice. The plume contains chemical signatures of water-rock interaction between the ocean and a rocky ...core. We used the Ion Neutral Mass Spectrometer onboard the Cassini spacecraft to detect molecular hydrogen in the plume. By using the instrument’s open-source mode, background processes of hydrogen production in the instrument were minimized and quantified, enabling the identification of a statistically significant signal of hydrogen native to Enceladus. We find that the most plausible source of this hydrogen is ongoing hydrothermal reactions of rock containing reduced minerals and organic materials. The relatively high hydrogen abundance in the plume signals thermodynamic disequilibrium that favors the formation of methane from CO₂ in Enceladus’ ocean.
The nature and structure of the observed east-west flows on Jupiter and Saturn have been a long-standing mystery in planetary science. This mystery has been recently unraveled by the accurate gravity ...measurements provided by the Juno mission to Jupiter and the Grand Finale of the Cassini mission to Saturn. These two experiments, which coincidentally happened around the same time, allowed the determination of the overall vertical and meridional profiles of the zonal flows on both planets. This paper reviews the topic of zonal jets on the gas giants in light of the new data from these two experiments. The gravity measurements not only allow the depth of the jets to be constrained, yielding the inference that the jets extend to roughly 3000 and 9000 km below the observed clouds on Jupiter and Saturn, respectively, but also provide insights into the mechanisms controlling these zonal flows. Specifically, for both planets this depth corresponds to the depth where electrical conductivity is within an order of magnitude of 1 S m
−1
, implying that the magnetic field likely plays a key role in damping the zonal flows. An intrinsic characteristic of any gravity inversion, as discussed here, is that the solutions might not be unique. We analyze the robustness of the solutions and present several independent lines of evidence supporting the results presented here.
Magnetic Field Conditions Upstream of Ganymede Vogt, Marissa F.; Bagenal, Fran; Bolton, Scott J.
Journal of geophysical research. Space physics,
December 2022, 2022-12-00, 20221201, Letnik:
127, Številka:
12
Journal Article
Recenzirano
Odprti dostop
Jupiter's magnetic field is tilted by ∼10° with respect to the planet's spin axis, and as a result the Jovian plasma sheet passes over the Galilean satellites at the jovigraphic equator twice per ...planetary rotation period. The plasma and magnetic field conditions near Ganymede's magnetosphere therefore change dramatically every ∼5 hr, creating a unique magnetosphere‐magnetosphere interaction, and on longer time scales as evidenced by orbit‐to‐orbit variations. In this paper, we summarize the typical magnetic field conditions and their variability near Ganymede's orbit as observed by the Galileo and Juno spacecraft. We fit Juno data from orbit 34, which included the spacecraft's close Ganymede flyby in June 2021, to a current sheet model and show that the magnetospheric conditions during orbit 34 were very close to the historical average. Our results allow us to infer the upstream conditions at the time of the Juno Ganymede flyby.
Plain Language Summary
Ganymede is the only moon in the solar system with an intrinsic magnetic field. This field forms a bubble in space around the moon, called a magnetosphere, that is itself contained within Jupiter's magnetosphere. The magnetic field and plasma conditions within Ganymede's magnetosphere can be used to infer information about the satellite's atmosphere, ionosphere, and interior. It is therefore important to understand the interaction between Ganymede's magnetosphere and the Jovian environment in the same way that we study the effects of space weather on the Earth. Here we analyze Galileo magnetic field measurements from Jupiter's magnetosphere in the region near Ganymede's orbit to establish the typical magnetic field magnitude and direction. We discuss the average conditions as well as the nature of the variability that occurs due to dynamic processes occurring in Jupiter's magnetosphere. This information provides useful context for analyzing data from Juno's recent flyby of Ganymede, which we show occurred during typical magnetospheric conditions.
Key Points
The magnetic field magnitude and direction upstream of Ganymede vary strongly with longitude
Temporal variations in the magnetosphere also influence Ganymede's upstream field conditions
Juno's Ganymede flyby occurred during typical magnetospheric conditions
Abstract
Jupiter’s atmosphere interior is a coupled fluid dynamical system strongly influenced by the rapid background rotation. While the visible atmosphere features east–west zonal winds on the ...order of ∼100 m s
−1
, zonal flows in the dynamo region are significantly slower, on the order of ∼cm s
−1
or less, according to the latest magnetic secular variation analysis. The vertical profile of the zonal flows and the underlying mechanism remain elusive. The latest Juno radio tracking measurements afforded the derivation of Jupiter’s gravity field to spherical harmonic degree 40. Here, we use the latest gravity solution to reconstruct Jupiter’s deep zonal winds without a priori assumptions about their latitudinal profile. The pattern of our reconstructed deep zonal winds strongly resemble that of the surface wind within ±35° latitude from the equator, in particular the northern off-equatorial jet (NOEJ) and the southern off-equatorial jet. The reconstruction features larger uncertainties in the southern hemisphere due to the north–south asymmetric nature of Juno's trajectory. The amplitude of the reconstructed deep NOEJ matches that of the surface wind when the wind is truncated at a depth ∼2500 km, and becomes twice that of the surface wind if the truncation depth is reduced to ∼1500 km. Our analysis supports the physical picture in which a prominent part of the surface zonal winds extends into Jupiter’s interior significantly deeper than the water cloud layer.
Clonal hematopoiesis (CH) is defined by the presence of an expanded clonal hematopoietic cell population due to an acquired mutation conferring a selective growth advantage and is known to predispose ...to hematologic malignancy. In this review, we discuss sequencing methods for CH detection in bulk sequencing data and corresponding bioinformatic approaches for variant calling, filtering, and curation. We detail practical recommendations for CH calling. Finally, we discuss how improvements in CH sequencing and bioinformatic approaches will enable the characterization of CH trajectories, its impact on human health, and therapeutic approaches to mitigate its adverse effects.
Abstract
The Juno spacecraft has been collecting data to shed light on the planet’s origin and characterize its interior structure. The onboard gravity science experiment based on X-band and Ka-band ...dual-frequency Doppler tracking precisely measured Jupiter’s zonal gravitational field. Here, we analyze 22 Juno’s gravity passes to investigate the gravity field. Our analysis provides evidence of new gravity field features, which perturb its otherwise axially symmetric structure with a time-variable component. We show that normal modes of the planet could explain the anomalous signatures present in the Doppler data better than other alternative explanations, such as localized density anomalies and non-axisymmetric components of the static gravity field. We explain Juno data by p-modes having an amplitude spectrum with a peak radial velocity of 10–50 cm/s at 900–1200 μHz (compatible with ground-based observations) and provide upper bounds on lower frequency f-modes (radial velocity smaller than 1 cm/s). The new Juno results could open the possibility of exploring the interior structure of the gas giants through measurements of the time-variable gravity or with onboard instrumentation devoted to the observation of normal modes, which could drive spacecraft operations of future missions.
Abstract
Water and ammonia vapors are known to be the major sources of spectral absorption at pressure levels observed by the microwave radiometer (MWR) on Juno. However, the brightness temperatures ...and limb darkening observed by the MWR at its longest-wavelength channel of 50 cm (600 MHz) in the first nine perijove passes indicate the existence of an additional source of opacity in the deep atmosphere of Jupiter (pressures beyond 100 bar). The absorption properties of ammonia and water vapor, and their relative abundances in Jupiter’s atmosphere, do not provide sufficient opacity in the deep atmosphere to explain the 600 MHz channel observation. Here we show that free electrons due to the ionization of alkali metals, i.e., sodium and potassium, with subsolar metallicity, M/H (log-based 10 relative concentration to solar) in the range of M/H = −2 to M/H = −5, can provide the missing source of opacity in the deep atmosphere. If the alkali metals are not the source of additional opacity in the MWR data, then their metallicity at 1000 bars can only be even lower. This upper bound of −2 on the metallicity of the alkali metals contrasts with the other heavy elements—C, N, S, Ar, Kr, and Xe—that are all enriched relative to their solar abundances, having a metallicity of approximately +0.5.
Our knowledge about the fine structure of lightning processes at Jupiter was substantially limited by the time resolution of previous measurements. Recent observations of the Juno mission revealed ...electromagnetic signals of Jovian rapid whistlers at a cadence of a few lightning discharges per second, comparable to observations of return strokes at Earth. The duration of these discharges was below a few milliseconds and below one millisecond in the case of Jovian dispersed pulses, which were also discovered by Juno. However, it was still uncertain if Jovian lightning processes have the fine structure of steps corresponding to phenomena known from thunderstorms at Earth. Here we show results collected by the Juno Waves instrument during 5 years of measurements at 125-microsecond resolution. We identify radio pulses with typical time separations of one millisecond, which suggest step-like extensions of lightning channels and indicate that Jovian lightning initiation processes are similar to the initiation of intracloud lightning at Earth.
The Alfvén wave mode transmits field‐aligned currents and large‐scale turbulence throughout Jupiter's magnetosphere. Magnetometer data from the Juno spacecraft have provided the first observations of ...Alfvénic fluctuations along the polar magnetic flux tubes connected to Jupiter's main auroral oval and the Jovian satellites. Transverse magnetic field perturbations associated with Io are observed up to ~90° away from main Io footprint, supporting the presence of extended Alfvénic wave activity throughout the Io footprint tail. Additional broadband fluctuations measured equatorward of the statistical auroral oval are composed of incompressible magnetic turbulence that maps to Jupiter's equatorial plasma sheet at radial distances within ~20 RJ. These fluctuations exhibit a k|| power spectrum consistent with strong magnetohydrodynamic turbulence. This turbulence can generate up to ~100 mW/m2 of Poynting flux to power the Jovian aurora in regions connected to the inner magnetosphere's central plasma sheet.
Plain Language Summary
Here we provide the first direct observations of magnetic turbulence near Jupiter's poles. The locations and power of these turbulent fluctuations provide new constraints for modeling the particle acceleration that leads to the generation of Jupiter's aurora. We find that this turbulence provides sufficient energy to produce the aurora at Jupiter, as well as emission associated with Jupiter's moon Io. Constraints on turbulent auroral heating at Jupiter are relevant for analogous processes at other giant magnetospheres such as Saturn, Uranus, and Neptune.
Key Points
Alfvénic turbulence is observed in high‐latitude regions associated with Jupiter's auroral emission
Turbulent magnetic field fluctuations at high latitude map to the central plasma sheet in the inner magnetosphere
High-latitude fluctuations indicate the presence of significant Alfvénic wave activity at longitudes up to ~90° along the Io footprint tail
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