The depth to which Jupiter's observed east-west jet streams extend has been a long-standing question. Resolving this puzzle has been a primary goal for the Juno spacecraft, which has been in orbit ...around the gas giant since July 2016. Juno's gravitational measurements have revealed that Jupiter's gravitational field is north-south asymmetric, which is a signature of the planet's atmospheric and interior flows. Here we report that the measured odd gravitational harmonics J
, J
, J
and J
indicate that the observed jet streams, as they appear at the cloud level, extend down to depths of thousands of kilometres beneath the cloud level, probably to the region of magnetic dissipation at a depth of about 3,000 kilometres. By inverting the measured gravity values into a wind field, we calculate the most likely vertical profile of the deep atmospheric and interior flow, and the latitudinal dependence of its depth. Furthermore, the even gravity harmonics J
and J
resulting from this flow profile also match the measurements, when taking into account the contribution of the interior structure. These results indicate that the mass of the dynamical atmosphere is about one per cent of Jupiter's total mass.
We hypothesize that trace amounts of phosphides formed in the mantle are a plausible abiotic source of the Venusian phosphine observed by Greaves et al.
, https://doi.org/10.1038/s41550-020-1174-4 ...(2020). In this hypothesis, small amounts of phosphides (P
bound in metals such as iron), sourced from a deep mantle, are brought to the surface by volcanism. They are then ejected into the atmosphere in the form of volcanic dust by explosive volcanic eruptions, which were invoked by others to explain the episodic changes of sulfur dioxide seen in the atmosphere Esposito,
223, 1072-1074 (1984). There they react with sulfuric acid in the aerosol layer to form phosphine (2 P
+ 3H
SO
= 2PH
+ 3SO
). We take issue with the conclusion of Bains et al. arXiv:2009.06499 (2020) that the volcanic rates for such a mechanism would have to be implausibly high. We consider a mantle with the redox state similar to the Earth, magma originating deep in the mantle-a likely scenario for the origin of plume volcanism on Venus-and episodically high but plausible rates of volcanism on a Venus bereft of plate tectonics. We conclude that volcanism could supply an adequate amount of phosphide to produce phosphine. Our conclusion is supported by remote sensing observations of the Venusian atmosphere and surface that have been interpreted as indicative of currently active volcanism.
Jupiter's atmosphere is rotating differentially, with zones and belts rotating at speeds that differ by up to 100 metres per second. Whether this is also true of the gas giant's interior has been ...unknown, limiting our ability to probe the structure and composition of the planet. The discovery by the Juno spacecraft that Jupiter's gravity field is north-south asymmetric and the determination of its non-zero odd gravitational harmonics J
, J
, J
and J
demonstrates that the observed zonal cloud flow must persist to a depth of about 3,000 kilometres from the cloud tops. Here we report an analysis of Jupiter's even gravitational harmonics J
, J
, J
and J
as observed by Juno and compared to the predictions of interior models. We find that the deep interior of the planet rotates nearly as a rigid body, with differential rotation decreasing by at least an order of magnitude compared to the atmosphere. Moreover, we find that the atmospheric zonal flow extends to more than 2,000 kilometres and to less than 3,500 kilometres, making it fully consistent with the constraints obtained independently from the odd gravitational harmonics. This depth corresponds to the point at which the electric conductivity becomes large and magnetic drag should suppress differential rotation. Given that electric conductivity is dependent on planetary mass, we expect the outer, differentially rotating region to be at least three times deeper in Saturn and to be shallower in massive giant planets and brown dwarfs.
Although there is evidence that liquids have flowed on the surface at Titan's equator in the past, to date, liquids have only been confirmed on the surface at polar latitudes, and the vast expanses ...of dunes that dominate Titan's equatorial regions require a predominantly arid climate. We report the detection by Cassini's Imaging Science Subsystem of a large low-latitude cloud system early in Titan's northern spring and extensive surface changes (spanning more than 500,000 square kilometers) in the wake of this storm. The changes are most consistent with widespread methane rainfall reaching the surface, which suggests that the dry channels observed at Titan's low latitudes are carved by seasonal precipitation.
The four massive Galilean satellites are believed to have formed within a circumplanetary disk during the last stages of Jupiter's formation. While the existence of a circum-Jovian disk is supported ...by hydrodynamic simulations, no consensus exists regarding the origin and delivery mechanisms of the building blocks of the forming satellites. The opening of a gap in the circumsolar disk would have efficiently isolated Jupiter from the main sources of solid material. However, a reservoir of planetesimals should have existed at the outer edge of Jupiter's gap, where solids were trapped and accumulated over time. Here we show that the formation of Saturn's core within this reservoir, or its prompt inward migration, allows planetesimals to be redistributed from this reservoir toward Jupiter and the inner Solar System, thereby providing enough material to form the Galilean satellites and to populate the Main Belt with primitive asteroids. We find that the orbit of planetesimals captured within the circum-Jovian disk are circularized through friction with gas in a compact system comparable to the current radial extent of the Galilean satellites. The decisive role of Saturn in the delivery mechanism has strong implications for the occurrence of massive moons around extrasolar giant planets as they would preferentially form around planets within multiple planet systems.
The existence of cryovolcanic features on Titan has been the subject of some controversy. Here we use observations from the Cassini RADAR, including Synthetic Aperture Radar (SAR) imaging, ...radiometry, and topographic data as well as compositional data from the Visible and Infrared Mapping Spectrometer (VIMS) to reexamine several putative cryovolcanic features on Titan in terms of likely processes of origin (fluvial, cryovolcanic, or other). We present evidence to support the cryovolcanic origin of features in the region formerly known as Sotra Facula, which includes the deepest pit so far found on Titan (now known as Sotra Patera), flow‐like features (Mohini Fluctus), and some of the highest mountains on Titan (Doom and Erebor Montes). We interpret this region to be a cryovolcanic complex of multiple cones, craters, and flows. However, we find that some other previously supposed cryovolcanic features were likely formed by other processes. Cryovolcanism is still a possible formation mechanism for several features, including the flow‐like units in Hotei Regio. We discuss implications for eruption style and composition of cryovolcanism on Titan. Our analysis shows the great value of combining data sets when interpreting Titan's geology and in particular stresses the value of RADAR stereogrammetry when combined with SAR imaging and VIMS.
Key PointsEvidence to support volcanic origin of features on TitanSeveral Cassini data sets used to support the argumentSotra patera and associated features provide strongest evidence of cryovolcanism
The Cassini‐Huygens probe gas chromatograph mass spectrometer (GCMS) determined the composition of the Titan atmosphere from ∼140 km altitude to the surface. After landing, it returned composition ...data of gases evaporated from the surface. Height profiles of molecular nitrogen (N2), methane (CH4), and molecular hydrogen (H2) were determined. Traces were detected on the surface of evaporating methane, ethane (C2H6), acetylene (C2H2), cyanogen (C2N2), and carbon dioxide (CO2). The methane data showed evidence that methane precipitation occurred recently. The methane mole fraction was (1.48 ± 0.09) × 10−2 in the lower stratosphere (139.8–75.5 km) and (5.65 ± 0.18) × 10−2 near the surface (6.7 km to the surface). The molecular hydrogen mole fraction was (1.01 ± 0.16) × 10−3 in the atmosphere and (9.90 ± 0.17) × 10−4 on the surface. Isotope ratios were 167.7 ± 0.6 for 14N/15N in molecular nitrogen, 91.1 ± 1.4 for 12C/13C in methane, and (1.35 ± 0.30) × 10−4 for D/H in molecular hydrogen. The mole fractions of 36Ar and radiogenic 40Ar are (2.1 ± 0.8) × 10−7 and (3.39 ± 0.12) × 10−5, respectively. 22Ne has been tentatively identified at a mole fraction of (2.8 ± 2.1) × 10−7. Krypton and xenon were below the detection threshold of 1 × 10−8 mole fraction. Science data were not retrieved from the gas chromatograph subsystem as the abundance of the organic trace gases in the atmosphere and on the ground did not reach the detection threshold. Results previously published from the GCMS experiment are superseded by this publication.
The Gravity Field and Interior Structure of Enceladus Iess, L.; Stevenson, D. J.; Parisi, M. ...
Science (American Association for the Advancement of Science),
04/2014, Letnik:
344, Številka:
6179
Journal Article
Recenzirano
Odprti dostop
The small and active Saturnian moon Enceladus is one of the primary targets of the Cassini mission. We determined the quadrupole gravity field of Enceladus and its hemispherical asymmetry using ...Doppler data from three spacecraft flybys. Our results indicate the presence of a negative mass anomaly in the south-polar region, largely compensated by a positive subsurface anomaly compatible with the presence of a regional subsurface sea at depths of 30 to 40 kilometers and extending up to south latitudes of about 50°. The estimated values for the largest quadrupole harmonic coefficients (106J2 = 5435.2 ± 34.9, 106C22 = 1549.8 ± 15.6, 1σ) and their ratio (J2/C22 = 3.51 ± 0.05) indicate that the body deviates mildly from hydrostatic equilibrium. The moment of inertia is around 0.335MR2, where M is the mass and R is the radius, suggesting a differentiated body with a low-density core.
The lakes of Titan Stofan, E. R; Elachi, C; Lunine, J. I ...
Nature,
01/2007, Letnik:
445, Številka:
7123
Journal Article
Recenzirano
The surface of Saturn's haze-shrouded moon Titan has long been proposed to have oceans or lakes, on the basis of the stability of liquid methane at the surface. Initial visible and radar imaging ...failed to find any evidence of an ocean, although abundant evidence was found that flowing liquids have existed on the surface. Here we provide definitive evidence for the presence of lakes on the surface of Titan, obtained during the Cassini Radar flyby of Titan on 22 July 2006 (T16). The radar imaging polewards of 70° north shows more than 75 circular to irregular radar-dark patches, in a region where liquid methane and ethane are expected to be abundant and stable on the surface. The radar-dark patches are interpreted as lakes on the basis of their very low radar reflectivity and morphological similarities to lakes, including associated channels and location in topographic depressions. Some of the lakes do not completely fill the depressions in which they lie, and apparently dry depressions are present. We interpret this to indicate that lakes are present in a number of states, including partly dry and liquid-filled. These northern-hemisphere lakes constitute the strongest evidence yet that a condensable-liquid hydrological cycle is active in Titan's surface and atmosphere, in which the lakes are filled through rainfall and/or intersection with the subsurface 'liquid methane' table.
PDF
