Juno Plasma Wave Observations at Ganymede.

The Juno Waves instrument measured plasma waves associated with Ganymede's magnetosphere during its flyby on 7 June, day 158, 2021. Three distinct regions were identified including a wake, and nightside and dayside regions in the magnetosphere distinguished by their electron densities and associated variability. The magnetosphere includes electron cyclotron harmonic emissions including a band at the upper hybrid frequency, as well as whistler-mode chorus and hiss. These waves likely interact with energetic electrons in Ganymede's magnetosphere by pitch angle scattering and/or accelerating the electrons. The wake is accentuated by low-frequency turbulence and electrostatic solitary waves. Radio emissions observed before and after the flyby likely have their source in Ganymede's magnetosphere.

Abundant molecular oxygen in the coma of comet 67P/Churyumov-Gerasimenko.

The composition of the neutral gas comas of most comets is dominated by H2O, CO and CO2, typically comprising as much as 95 per cent of the total gas density. In addition, cometary comas have been found to contain a rich array of other molecules, including sulfuric compounds and complex hydrocarbons. Molecular oxygen (O2), however, despite its detection on other icy bodies such as the moons of Jupiter and Saturn, has remained undetected in cometary comas. Here we report in situ measurement of O2 in the coma of comet 67P/Churyumov-Gerasimenko, with local abundances ranging from one per cent to ten per cent relative to H2O and with a mean value of 3.80 ± 0.85 per cent. Our observations indicate that the O2/H2O ratio is isotropic in the coma and does not change systematically with heliocentric distance. This suggests that primordial O2 was incorporated into the nucleus during the comet's formation, which is unexpected given the low upper limits from remote sensing observations. Current Solar System formation models do not predict conditions that would allow this to occur.

Detection of a strongly negative surface potential at Saturn's moon Hyperion.

On 26 September 2005, Cassini conducted its only close targeted flyby of Saturn's small, irregularly shaped moon Hyperion. Approximately 6 min before the closest approach, the electron spectrometer (ELS), part of the Cassini Plasma Spectrometer (CAPS) detected a field-aligned electron population originating from the direction of the moon's surface. Plasma wave activity detected by the Radio and Plasma Wave instrument suggests electron beam activity. A dropout in energetic electrons was observed by both CAPS-ELS and the Magnetospheric Imaging Instrument Low-Energy Magnetospheric Measurement System, indicating that the moon and the spacecraft were magnetically connected when the field-aligned electron population was observed. We show that this constitutes a remote detection of a strongly negative (∼ -200 V) surface potential on Hyperion, consistent with the predicted surface potential in regions near the solar terminator.

Cusp observation at Saturn's high-latitude magnetosphere by the Cassini spacecraft.

We report on the first analysis of magnetospheric cusp observations at Saturn by multiple in situ instruments onboard the Cassini spacecraft. Using this we infer the process of reconnection was occurring at Saturn's magnetopause. This agrees with remote observations that showed the associated auroral signatures of reconnection. Cassini crossed the northern cusp around noon local time along a poleward trajectory. The spacecraft observed ion energy-latitude dispersions-a characteristic signature of the terrestrial cusp. This ion dispersion is "stepped," which shows that the reconnection is pulsed. The ion energy-pitch angle dispersions suggest that the field-aligned distance from the cusp to the reconnection site varies between ∼27 and 51 RS . An intensification of lower frequencies of the Saturn kilometric radiation emissions suggests the prior arrival of a solar wind shock front, compressing the magnetosphere and providing more favorable conditions for magnetopause reconnection. KEY POINTS: We observe evidence for reconnection in the cusp plasma at SaturnWe present evidence that the reconnection process can be pulsed at SaturnSaturn's cusp shows similar characteristics to the terrestrial cusp.

Microwave observations reveal the deep extent and structure of Jupiter's atmospheric vortices.

Jupiter's atmosphere has a system of zones and belts punctuated by small and large vortices, the largest being the Great Red Spot. How these features change with depth is unknown, with theories of their structure ranging from shallow meteorological features to surface expressions of deep-seated convection. We present observations of atmospheric vortices using the Juno spacecraft's Microwave Radiometer. We found vortex roots that extend deeper than the altitude at which water is expected to condense, and we identified density inversion layers. Our results constrain the three-dimensional structure of Jupiter's vortices and their extension below the clouds.

Saturn's near-equatorial ionospheric conductivities from in situ measurements.

Cassini's Grand Finale orbits provided for the first time in-situ measurements of Saturn's topside ionosphere. We present the Pedersen and Hall conductivities of the top near-equatorial dayside ionosphere, derived from the in-situ measurements by the Cassini Radio and Wave Plasma Science Langmuir Probe, the Ion and Neutral Mass Spectrometer and the fluxgate magnetometer. The Pedersen and Hall conductivities are constrained to at least 10-5-10-4 S/m at (or close to) the ionospheric peak, a factor 10-100 higher than estimated previously. We show that this is due to the presence of dusty plasma in the near-equatorial ionosphere. We also show the conductive ionospheric region to be extensive, with thickness of 300-800 km. Furthermore, our results suggest a temporal variation (decrease) of the plasma densities, mean ion masses and consequently the conductivities from orbit 288 to 292.

Polyphenolic Substance of Mytilus edulis: Novel Adhesive Containing L-Dopa and Hydroxyproline.

The fouling marine mussel Mytilus edulis attaches itself to various substrates by spinning byssal threads, the adhesive discs of which are rich in the amino acid 3,4-dihydroxyphenylalanine (dopa). An acid-soluble protein was extracted and purified from the phenol gland located in the byssus-secreting foot of the animal. This protein is highly basic and contains large amounts of lysine, dopa, and 3- and 4-hydroxyproline. The composition of this protein and its sticky tendencies in vitro strongly suggest that it contributes to byssal adhesion.

Extensible collagen in mussel byssus: a natural block copolymer.

To adhere to solid surfaces, marine mussels produce byssal threads, each of which is a stiff tether at one end and a shock absorber with 160 percent extensibility at the other end. The elastic extensibility of proximal byssus is extraordinary given its construction of collagen and the limited extension (less than 10 percent) of most collagenous materials. From the complementary DNA, we deduced that the primary structure of a collagenous protein (preCol-P) predominating in the extensible proximal portion of the threads encodes an unprecedented natural block copolymer with three major domain types: a central collagen domain, flanking elastic domains, and histidine-rich terminal domains. The elastic domains have sequence motifs that strongly resemble those of elastin and the amorphous glycine-rich regions of spider silk fibroins. Byssal thread extensibility may be imparted by the elastic domains of preCol-P.

EUVE Observations of Jupiter During the Impact of Comet Shoemaker-Levy 9.

The Extreme Ultraviolet Explorer (EUVE) satellite conducted extensive observations of the jovian system before, during, and after the impact of the fragments of comet Shoemaker-Levy 9 in July 1994. About 2 to 4 hours after the impacts of several of the larger fragments, the brightness of the neutral helium (He I) resonance line at 58.4 nanometers temporarily increased by a factor of about 10. The transient 58.4-nanometer brightenings are most simply explained by resonant scattering of sunlight from the widespread high-altitude remnants of the larger impact plumes. Other possible sources of emission, such as electron impact excitation of He or radiative recombination of He(+), may contribute to the observed signal.

A remarkable auroral event on jupiter observed in the ultraviolet with the hubble space telescope.

Two sets of ultraviolet images of the Jovian north aurora were obtained with the Faint Object Camera on board the Hubble Space Telescope. The first series shows an intense discrete arc in near corotation with the planet. The maximum apparent molecular hydrogen emission rate corresponds to an electron precipitation of approximately 1 watt per square meter, which is about 30,000 times larger than the solar heating by extreme ultraviolet radiation. Such a particle heating rate of the auroral upper atmosphere of Jupiter should cause a large transient temperature increase and generate strong thermospheric winds. Twenty hours after initial observation, the discrete arc had decreased in brightness by more than one order of magnitude. The time scale and magnitude of the change in the ultraviolet aurora leads us to suggest that the discrete Jovian auroral precipitation is related to large-scale variations in the current system, as is the case for Earth's discrete aurorae.

ROSAT Observations of X-ray Emissions from Jupiter During the Impact of Comet Shoemaker-Levy 9.

Röntgensatellit (ROSAT) observations made shortly before and during the collision of comet Shoemaker-Levy 9 with Jupiter show enhanced x-ray emissions from the planet's northern high latitudes. These emissions, which occur at System III longitudes where intensity enhancements have previously been observed in Jupiter's ultraviolet aurora, appear to be associated with the comet fragment impacts in Jupiter's southern hemisphere and may represent brightenings of the jovian x-ray aurora caused either by the fragment impacts themselves or by the passage of the fragments and associated dust clouds through Jupiter's inner magnetosphere.

Mussel-designed protective coatings for compliant substrates.

The byssus of marine mussels has attracted attention as a paradigm of strong and versatile underwater adhesion. As the first of the 3,4-dihydroxyphenylalanine (Dopa)-containing byssal precursors to be purified, Mytilus edulis foot protein-1 (mefp-1) has been much investigated with respect to its molecular structure, physical properties, and adsorption to surfaces. Although mefp-1 undoubtedly contributes to the durability of byssus, it is not directly involved in adhesion. Rather, it provides a robust coating that is 4-5 times stiffer and harder than the byssal collagens that it covers. Protective coatings for compliant tissues and materials are highly appealing to technology, notwithstanding the conventional wisdom that coating extensibility can be increased only at the expense of hardness and stiffness. The byssal cuticle is the only known coating in which high compliance and hardness co-exist without mutual detriment; thus, the role of mefp-1 in accommodating both parameters deserves further study.

Dust grains fall from Saturn's D-ring into its equatorial upper atmosphere.

The sizes of Saturn's ring particles range from meters (boulders) to nanometers (dust). Determination of the rings' ages depends on loss processes, including the transport of dust into Saturn's atmosphere. During the Grand Finale orbits of the Cassini spacecraft, its instruments measured tiny dust grains that compose the innermost D-ring of Saturn. The nanometer-sized dust experiences collisions with exospheric (upper atmosphere) hydrogen and molecular hydrogen, which forces it to fall from the ring into the ionosphere and lower atmosphere. We used the Magnetospheric Imaging Instrument to detect and characterize this dust transport and also found that diffusion dominates above and near the altitude of peak ionospheric density. This mechanism results in a mass deposition into the equatorial atmosphere of ~5 kilograms per second, constraining the age of the D-ring.

Chemical interactions between Saturn's atmosphere and its rings.

The Pioneer and Voyager spacecraft made close-up measurements of Saturn's ionosphere and upper atmosphere in the 1970s and 1980s that suggested a chemical interaction between the rings and atmosphere. Exploring this interaction provides information on ring composition and the influence on Saturn's atmosphere from infalling material. The Cassini Ion Neutral Mass Spectrometer sampled in situ the region between the D ring and Saturn during the spacecraft's Grand Finale phase. We used these measurements to characterize the atmospheric structure and material influx from the rings. The atmospheric He/H2 ratio is 10 to 16%. Volatile compounds from the rings (methane; carbon monoxide and/or molecular nitrogen), as well as larger organic-bearing grains, are flowing inward at a rate of 4800 to 45,000 kilograms per second.

Juno observations of spot structures and a split tail in Io-induced aurorae on Jupiter.

Jupiter's aurorae are produced in its upper atmosphere when incoming high-energy electrons precipitate along the planet's magnetic field lines. A northern and a southern main auroral oval are visible, surrounded by small emission features associated with the Galilean moons. We present infrared observations, obtained with the Juno spacecraft, showing that in the case of Io, this emission exhibits a swirling pattern that is similar in appearance to a von Kármán vortex street. Well downstream of the main auroral spots, the extended tail is split in two. Both of Ganymede's footprints also appear as a pair of emission features, which may provide a remote measure of Ganymede's magnetosphere. These features suggest that the magnetohydrodynamic interaction between Jupiter and its moon is more complex than previously anticipated.

Photoionization Modeling of Titan's Dayside Ionosphere.

Previous modeling studies of Titan's dayside ionosphere predict electron number densities that are roughly a factor of 2 higher than those observed by the RPWS/Langmuir probe. The issue can equivalently be described as the ratio between the calculated electron production rates and the square of the observed electron number densities resulting in roughly a factor of 4 higher effective recombination coefficient than expected from the ion composition and the electron temperature. Here we make an extended reassessment of Titan's dayside ionization balance, focusing on 34 flybys between TA and T120. Using a recalibrated data set and by taking the presence of negative ions into account, we arrive at lower effective recombination coefficients compared with earlier studies. The values are still higher than expected from the ion composition and the electron temperature, but by a factor of ~2-3 instead of a factor of ~4. We have also investigated whether the derived effective recombination coefficients display dependencies on the solar zenith angle (SZA), the integrated solar EUV intensity (<80 nm), and the corotational plasma ram direction (RAM), and found statistically significant trends, which may be explained by a declining photoionization against the background ionization by magnetospheric particles (trends in SZA and RAM) and altered photochemistry (trend in EUV). We find that a series of flybys that occurred during solar minimum (2008) and with similar flyby geometries are associated with enhanced values of the effective recombination coefficient compared with the remaining data set, which also suggests a chemistry dependence on the sunlight conditions.

Titan's ionosphere: A survey of solar EUV influences.

Effects of solar EUV on positive ions and heavy negative charge carriers (molecular ions, aerosol, and/or dust) in Titan's ionosphere are studied over the course of almost 12 years, including 78 flybys below 1400 km altitude between TA (October 2004) and T120 (June 2016). The Radio and Plasma Wave Science/Langmuir Probe-measured ion charge densities (normalized by the solar zenith angle) show statistically significant variations with respect to the solar EUV flux. Dayside charge densities increase by a factor of ≈2 from solar minimum to maximum, while nightside charge densities are found to anticorrelate with the EUV flux and decrease by a factor of ≈3-4. The overall EUV dependence of the ion charge densities suggest inapplicability of the idealized Chapman theory below 1200 km in Titan's ionosphere. Nightside charge densities are also found to vary along Titan's orbit, with higher values in the sunward magnetosphere of Saturn compared to the magnetotail.

Xenon isotopes in 67P/Churyumov-Gerasimenko show that comets contributed to Earth's atmosphere.

The origin of cometary matter and the potential contribution of comets to inner-planet atmospheres are long-standing problems. During a series of dedicated low-altitude orbits, the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) on the Rosetta spacecraft analyzed the isotopes of xenon in the coma of comet 67P/Churyumov-Gerasimenko. The xenon isotopic composition shows deficits in heavy xenon isotopes and matches that of a primordial atmospheric component. The present-day Earth atmosphere contains 22 ± 5% cometary xenon, in addition to chondritic (or solar) xenon.

Role of melanin in mechanical properties of Glycera jaws.

The remarkable mechanical prowess of the jaws of the bloodworm Glycera dibranchiata appears to be a consequence of a robust cross-linked network of organic molecules, notably melanin and proteins, as well as small amounts of unmineralized Cu and a Cu-based mineral. The present study focuses on the role of melanin. Mechanical properties of untreated jaws and the constituent melanin are probed through nanoindentation, both in air and underwater. Complementary information is obtained from density and porosity measurements and attempts at Cu removal from the jaws using EDTA, an effective metal chelator in most biological systems. In near-tip regions of the jaws, mechanical properties attain the highest values and diminish only slightly when wet (by 15-25%), in contrast to the behavior of other organic biomaterials. The melanin constituent contributes significantly to the mechanical integrity of the jaw; its hardness and elastic modulus are about half those of untreated jaws. Although melanin may be the dominant shape-determining component of the structure, it remains to be shown whether jaw assembly is mediated by protein deposition on a melanin scaffold or, conversely, by melanin deposition on a protein scaffold. The inability of EDTA to chelate Cu from the jaws and the relatively high density of the jaws and the melanin support the notion of a highly cross-linked molecular structure. Finally, based on the metric H(3)/E(2) (H being hardness and E the Young's modulus), the results suggest that the abrasion resistance of the jaws is superior to all engineering polymers and competitive with the hardest metallic alloys.

Ion and aerosol precursor densities in Titan's ionosphere: A multi-instrument case study.

The importance of the heavy ions and dust grains for the chemistry and aerosol formation in Titan's ionosphere has been well established in the recent years of the Cassini mission. In this study we combine independent in situ plasma (Radio Plasma and Wave Science Langmuir Probe (RPWS/LP)) and particle (Cassini Plasma Science Electron Spectrometer, Cassini Plasma Science Ion Beam Spectrometer, and Ion and Neutral Mass Spectrometer) measurements of Titan's ionosphere for selected flybys (T16, T29, T40, and T56) to produce altitude profiles of mean ion masses including heavy ions and develop a Titan-specific method for detailed analysis of the RPWS/LP measurements (applicable to all flybys) to further constrain ion charge densities and produce the first empirical estimate of the average charge of negative ions and/or dust grains. Our results reveal the presence of an ion-ion (dusty) plasma below ~1100 km altitude, with charge densities exceeding the primary ionization peak densities by a factor ≥2 in the terminator and nightside ionosphere (n e /n i ≤ 0.1). We suggest that ion-ion (dusty) plasma may also be present in the dayside ionosphere below 900 km (n e /n i < 0.5 at 1000 km altitude). The average charge of the dust grains (≥1000 amu) is estimated to be between -2.5 and -1.5 elementary charges, increasing toward lower altitudes.