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PubMedDate not supplied

Discovery of Jupiter's 'gossamer' ring.

Jupiter's ring system has previously been described as being composed of a 'bright' narrow ring and an interior, vertically-extended halo. The one image which reveals this morphology most clearly is Voyager 2's parting shot of the Jupiter system, a wide-angle (WA) view of the ring ansa in forward-scattered light (FDS 20693.02). The bright ring is plainly visible, and the halo appears after slight contrast enhancement. By further enhancement of this image we have discovered an additional ring, which is far fainter than either of the (already faint) components previously identified, extending to a radius of 210,000 km.

Astronomical Phenomena↗
PubMed2000

Proximate humid and dry regions in Jupiter's atmosphere indicate complex local meteorology.

Models of Jupiter's formation and structure predict that its atmosphere is enriched in oxygen, relative to the Sun, and that consequently water clouds should be present globally near the 5-bar pressure level. Past attempts to confirm these predictions have led to contradictory results; in particular, the Galileo probe revealed a very dry atmosphere at the entry site, with no significant clouds at depths exceeding the 2-bar level. Although the entry site was known to be relatively cloud-free, the contrast between the observed local dryness and the expected global wetness was surprising. Here we analyse near-infrared (around 5 microm) observations of Jupiter, a spectral region that can reveal the water vapour abundance and vertical cloud structure in the troposphere. We find that humid and extremely dry regions exist in close proximity, and that some humid regions are spatially correlated with bright convective clouds extending from the deep water clouds to the visible atmosphere.

Atmosphere↗
PubMed1995

Chemical and thermal response of Jupiter's atmosphere following the impact of comet Shoemaker-Levy 9.

In July 1994, the collisions of the fragments of comet Shoemaker-Levy 9 with Jupiter resulted in dramatic changes in the planet's atmosphere. Observations of the events suggest that the composition and thermal properties of the atmosphere were considerably modified at the impact sites, with the changes persisting for times lasting from minutes to weeks (see, for example, refs 1-4). Here we report observations of the impact sites at millimetre wave-lengths, which reveal strong emission lines associated with carbon monoxide, carbonyl sulphide and carbon monosulphide. The abundance of carbon monoxide in the jovian atmosphere is normally very low; carbonyl sulphide and carbon monosulphide, on the other hand, have not hitherto been detected. We find that the largest fragments (G and K) each produced approximately 10(14) g of carbon monoxide, 3 x 10(12) g of carbonyl sulphide and 3 x 10(11) g of carbon monosulphide, most probably by shock-induced chemical reactions. Our observations also place firm constraints on the thermal response of Jupiter's stratosphere to the impacts.

Atmosphere↗
PubMed1995

Detection of an oxygen atmosphere on Jupiter's moon Europa.

Europa, the second large satellite out from Jupiter, is roughly the size of Earth's Moon, but unlike the Moon, it has water ice on its surface. There have been suggestions that an oxygen atmosphere should accumulate around such a body, through reactions which break up the water molecules and form molecular hydrogen and oxygen. The lighter H2 molecules would escape from Europa relatively easily, leaving behind an atmosphere rich in oxygen. Here we report the detection of atomic oxygen emission from Europa, which we interpret as being produced by the simultaneous dissociation and excitation of atmospheric O2 by electrons from Jupiter's magnetosphere. Europa's molecular oxygen atmosphere is very tenuous, with a surface pressure about 10(-11) that of the Earth's atmosphere at sea level.

Atmosphere↗
PubMed1995

Waves from the collisions of comet Shoemaker-Levy 9 with Jupiter.

Observations of the collisions of the fragments of comet Shoemaker-Levy 9 with Jupiter provided an unprecedented opportunity to probe the depths of the planet's atmosphere. Images taken by the Hubble Space Telescope revealed circular rings surrounding five of the impact sites. The rings were observed for up to 2.5 hours after the impacts and spread at a constant velocity of 450 m s-1. There are three types of disturbance that might explain these observations: acoustic waves trapped at the tropopause temperature minimum, gravity waves propagating vertically and horizontally in the stratosphere, and gravity waves trapped in a stable layer which acts as a horizontal waveguide and is located within the hypothesized tropospheric water cloud. Here we show that only the last of these phenomena can match the speed and relative amplitude of the observed waves, with the requirement that the impacts were deep and the stability of the trapping layer is large. The origin of the stable layer is still uncertain, but if it is produced by moist convection in the water cloud, then the ratio of oxygen to hydrogen on Jupiter must be surprisingly large--approximately ten times that on the Sun.

Atmosphere↗
PubMed2005

A reassessment of Galileo radiation exposures in the Jupiter magnetosphere.

Earlier particle experiments in the 1970s on Pioneer-10 and -11 and Voyager-1 and -2 provided Jupiter flyby particle data, which were used by Divine and Garrett to develop the first Jupiter trapped radiation environment model. This model was used to establish a baseline radiation effects design limit for the Galileo onboard electronics. Recently, Garrett et al. have developed an updated Galileo Interim Radiation Environment (GIRE) model based on Galileo electron data. In this paper, we have used the GIRE model to reassess the computed radiation exposures and dose effects for Galileo. The 34-orbit 'as flown' Galileo trajectory data and the updated GIRE model were used to compute the electron and proton spectra for each of the 34 orbits. The total ionisation doses of electrons and protons have been computed based on a parametric shielding configuration, and these results are compared with previously published results.

Atmosphere↗
PubMed1996

The helium mass fraction in Jupiter's atmosphere.

On 7 December 1995, the NASA Galileo probe provided in situ measurements of the helium abundance in the atmosphere of Jupiter. A Jamin interferometer measured the refractive index of the jovian atmosphere in the pressure region from 2 to 14 bars. These measurements indicate that the atmospheric helium mole fraction is 0.136 +/- 0.004. The corresponding helium mass fraction is slightly below the presolar value, which suggests that separation of helium from hydrogen in Jupiter's interior is only in its early stages.

Atmosphere↗
PubMed1996

Near-infrared spectroscopy and spectral mapping of Jupiter and the Galilean satellites: results from Galileo's initial orbit.

The Near Infrared Mapping Spectrometer performed spectral studies of Jupiter and the Galilean satellites during the June 1996 perijove pass of the Galileo spacecraft. Spectra for a 5-micrometer hot spot on Jupiter are consistent with the absence of a significant water cloud above 8 bars and with a depletion of water compared to that predicted for solar composition, corroborating results from the Galileo probe. Great Red Spot (GRS) spectral images show that parts of this feature extend upward to 240 millibars, although considerable altitude-dependent structure is found within it. A ring of dense clouds surrounds the GRS and is lower than it by 3 to 7 kilometers. Spectra of Callisto and Ganymede reveal a feature at 4. 25 micrometers, attributed to the presence of hydrated minerals or possibly carbon dioxide on their surfaces. Spectra of Europa's high latitudes imply that fine-grained water frost overlies larger grains. Several active volcanic regions were found on Io, with temperatures of 420 to 620 kelvin and projected areas of 5 to 70 square kilometers.

Ammonia↗
PubMed1995

Temperature measurements of shock-compressed liquid hydrogen: implications for the interior of Jupiter.

Shock temperatures of hydrogen up to 5200 kelvin were measured optically at pressures up to 83 gigapascals (830 kilobars). At highest pressures, the measured temperatures are substantially lower than predicted. These lower temperatures are caused by a continuous dissociative phase transition above 20 gigapascals. Because hydrogen is in thermal equilibrium in shock-compression experiments, the theory derived from the shock data can be applied to Jupiter. The planet's molecular envelope is cooler and has much less temperature variation than previously believed. The continuous dissociative phase transition suggests that there is no sharp boundary between Jupiter's molecular mantle and its metallic core. A possible convectively quiescent boundary layer might induce an additional layer in the molecular region, as has been predicted.

Chemical Phenomena↗
PubMed1995

HST spectroscopic observations of Jupiter after the collision of comet Shoemaker-Levy 9.

Ultraviolet spectra obtained with the Hubble Space Telescope identified at least 10 molecules and atoms in the perturbed stratosphere near the G impact site, most never before observed in Jupiter. The large mass of sulfur-containing material, more than 10(14) grams in S2 alone, indicates that many of the sulfur-containing molecules S2, CS2, CS, H2S, and S+ may be derived from a sulfur-bearing parent molecule native to Jupiter. If so, the fragment must have penetrated at least as deep as the predicted NH4SH cloud at a pressure of approximately 1 to 2 bars. Stratospheric NH3 was also observed, which is consistent with fragment penetration below the cloud tops. Approximately 10(7) grams of neutral and ionized metals were observed in emission, including Mg II, Mg I, Si I, Fe I, and Fe II. Oxygen-containing molecules were conspicuous by their absence; upper limits for SO2, SO, CO, SiO, and H2O are derived.

Ammonia↗
PubMed1964

The atmospheres of Mars, Venus and Jupiter.

The general properties of the atmospheres of Mars, Venus and Jupiter are reviewed. The evolutionary processes of planetary atmospheres are outlined as an introduction to a detailed discussion of the structure of the atmospheres of other planets. The most recent observational results indicate that the surface pressure on Mars could be as low as 20 mb, and the amount of CO2 may have a mixing ratio as high as 25% by volume. For Venus, the Mariner II results suggest that the surface temperature may actually be of the order of 600 degrees K. Also there are indications that the surface pressure on Venus could be approximately 100 atm., with the atmosphere mainly composed of N2. In the case of Jupiter, recent theoretical investigations of the atmosphere below the clouds suggest, that there may be regions in the atmosphere of very high density and pressure but at relatively low temperature, creating conditions possibly favorable to the occurrence of complex organic reactions.

Atmosphere↗
PubMed2005

Justification for the Use of Statins in Primary Prevention: an Intervention Trial Evaluating Rosuvastatin (JUPITER)--can C-reactive protein be used to target statin therapy in primary prevention?

The most important action of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) is their ability to lower levels of low-density lipoprotein (LDL) cholesterol. Statins have proved highly effective in reducing the risk of cardiovascular events in both primary and secondary prevention studies. However, the magnitude of risk reduction associated with statins is greater than that predicted on the basis of LDL cholesterol lowering alone. A likely explanation for this effect is the anti-inflammatory action of statins. Following the observation that high-sensitivity C-reactive protein (hs-CRP) is a powerful predictor of cardiovascular events, investigators in the Cholesterol and Recurrent Events (CARE) and Air Force/Texas Coronary Atherosclerosis Prevention Study (AFCAPS/TexCAPS) trials demonstrated that the magnitude of risk reduction associated with statin therapy was higher among those with elevated hs-CRP levels. In addition, there is accumulating evidence that statins lower plasma levels of hs-CRP in a manner largely independent of LDL cholesterol lowering. In contrast, little benefit has been demonstrated for statin therapy in the absence of both hyperlipidemia and inflammation. Justification for the Use of Statins in Primary Prevention: an Intervention Trial Evaluating Rosuvastatin (JUPITER) is a large multinational, long-term, double-blind, placebo-controlled, randomized clinical trial designed to assess directly whether statin therapy (rosuvastatin 20 mg/day) should be given to apparently healthy individuals with low LDL cholesterol levels but elevated hs-CRP levels--a critical issue for the prevention of cardiovascular disease. Support for the concept behind the JUPITER trial is also now available from several recent trials comparing different intensities of statin therapy on disease progression as well as clinical end points. These studies indicate that the hs-CRP level achieved after initiation of statin therapy may be as important as the LDL cholesterol level achieved. All of these data raise the possibility that hs-CRP could be used to target high-risk patients who may benefit from early statin use. Ongoing work will determine whether hs-CRP reduction, independent of LDL cholesterol reduction, results in a net clinical benefit.

Biomarkers↗
PubMed2000

Observation of moist convection in Jupiter's atmosphere. Galileo Imaging Team

The energy source driving Jupiter's active meteorology is not understood. There are two main candidates: a poorly understood internal heat source and sunlight. Here we report observations of an active storm system possessing both lightning and condensation of water. The storm has a vertical extent of at least 50 km and a length of about 4,000 km. Previous observations of lightning on Jupiter have revealed both its frequency of occurrence and its spatial distribution, but they did not permit analysis of the detailed cloud structure and its dynamics. The present observations reveal the storm (on the day side of the planet) at the same location and within just a few hours of a lightning detection (on the night side). We estimate that the total vertical transport of heat by storms like the one observed here is of the same order as the planet's internal heat source. We therefore conclude that moist convection-similar to large clusters of thunderstorm cells on the Earth-is a dominant factor in converting heat flow into kinetic energy in the jovian atmosphere.

Journal Article↗
PubMed2000

Moist convection as an energy source for the large-scale motions in Jupiter's atmosphere. Galileo Imaging Team

Jupiter's dominant large-scale weather patterns (dimensions approximately 10,000 km) are zonal jets and long-lived ovals. The jets have been flowing east and west at constant speeds of up to 180 m s(-1) for over 100 years. These jets receive energy from small-scale eddies, which pump eastward momentum into the eastward jets and westward momentum into the westward jets. This momentum transfer was predicted by numerical models before it was observed on Jupiter. The large ovals roll between the jets in an anticyclonic direction-clockwise in the northern hemisphere and counterclockwise in the southern hemisphere--where they regularly assimilate small anticyclonic eddies. But from where the eddies receive their energy has been an open question. Here we argue that the eddies, which ultimately drive both the jets and the ovals, receive their energy from moist convection. This hypothesis is consistent with observations of jovian lightning, which is an indicator of moist convection. It also explains the anticyclonic rotation and poleward drift of the eddies, and suggests patterns of upwelling and downwelling that resemble the patterns of large-scale axisymmetric overturning in the Earth's atmosphere.

Journal Article↗
PubMed2002

The dusk flank of Jupiter's magnetosphere.

Limited single-spacecraft observations of Jupiter's magnetopause have been used to infer that the boundary moves inward or outward in response to variations in the dynamic pressure of the solar wind. At Earth, multiple-spacecraft observations have been implemented to understand the physics of how this motion occurs, because they can provide a snapshot of a transient event in progress. Here we present a set of nearly simultaneous two-point measurements of the jovian magnetopause at a time when the jovian magnetopause was in a state of transition from a relatively larger to a relatively smaller size in response to an increase in solar-wind pressure. The response of Jupiter's magnetopause is very similar to that of the Earth, confirming that the understanding built on studies of the Earth's magnetosphere is valid. The data also reveal evidence for a well-developed boundary layer just inside the magnetopause.

Journal Article↗
PubMed2004

Prediction of a global climate change on Jupiter.

Jupiter's atmosphere, as observed in the 1979 Voyager space craft images, is characterized by 12 zonal jet streams and about 80 vortices, the largest of which are the Great Red Spot and three White Ovals that had formed in the 1930s. The Great Red Spot has been observed continuously since 1665 and, given the dynamical similarities between the Great Red Spot and the White Ovals, the disappearance of two White Ovals in 1997-2000 was unexpected. Their longevity and sudden demise has been explained however, by the trapping of anticyclonic vortices in the troughs of Rossby waves, forcing them to merge. Here I propose that the disappearance of the White Ovals was not an isolated event, but part of a recurring climate cycle which will cause most of Jupiter's vortices to disappear within the next decade. In my numerical simulations, the loss of the vortices results in a global temperature change of about 10 K, which destabilizes the atmosphere and thereby leads to the formation of new vortices. After formation, the large vortices are eroded by turbulence over a time of approximately 60 years--consistent with observations of the White Ovals-until they disappear and the cycle begins again.

Journal Article↗
PubMed1994

Jupiter's Great Red Spot and zonal winds as a self-consistent, one-layer, quasigeostrophic flow.

We present the point of view that both the vortices and the east-west zonal winds of Jupiter are confined to the planet's shallow weather layer and that their dynamics is completely described by the weakly dissipated, weakly forced quasigeostrophic (QG) equation. The weather layer is the region just below the tropopause and contains the visible clouds. The forcing mimics the overshoot of fluid from an underlying convection zone. The late-time solutions of the weakly forced and dissipated QG equations appear to be a small subset of the unforced and undissipated equations and are robust attractors. We illustrate QG vortex dynamics and attempt to explain the important features of Jupiter's Great Red Spot and other vortices: their shapes, locations with respect to the extrema of the east-west winds, stagnation points, numbers as a function of latitude, mergers, break-ups, cloud morphologies, internal distributions of vorticity, and signs of rotation with respect to both the planet's rotation and the shear of their surrounding east-west winds. Initial-value calculations in which the weather layer starts at rest produce oscillatory east-west winds. Like the Jovian winds, the winds are east-west asymmetric and have Karman vortex streets located only at the west-going jets. From numerical calculations we present an empirically derived energy criterion that determines whether QG vortices survive in oscillatory zonal flows with nonzero potential vorticity gradients. We show that a recent proof that claims that all QG vortices decay when embedded in oscillatory zonal flows is too restrictive in its assumptions. We show that the asymmetries in the cloud morphologies and numbers of cyclones and anticyclones can be accounted for by a QG model of the Jovian atmosphere, and we compare the QG model with competing models.

Journal Article↗
PubMed2006

Spectro-imaging observations of H3+ on Jupiter.

Narrow-band filter, high-spectral-resolution (0.2 cm(-1)) spectro-imaging infrared observations of Jupiter's auroral zones, acquired in October 1999 and October 2000 with the FTS/BEAR instrument at the Canada-France-Hawaii Telescope, have provided maps of the emission from the H2 S1(1) quadrupole line and several H3+ lines. H2 and H3+ emissions appear to be morphologically different, especially in the north, where the latter notably exhibits a 'hot spot' near lambdaIII = 150-170 degrees System III longitude. The spectra include a total of 14 H3+ lines, including two hot lines from the 3v2-v2 band, detected on Jupiter for the first time. They can be used to determine H3+ column densities, rotational (Trot) and vibrational (Tvib) temperatures. We find the mean Tvib of the v2 = 3 state to be lower (960 +/- 50 K) than the mean Trot in v2 = 2 (1170 +/- 75 K), indicating an underpopulation of the v2 = 3 level with respect to local thermodynamical equilibrium. Rotational temperatures and associated column densities are generally higher and lower, respectively, than inferred previously from v2 observations. These features can be explained by the combination of both a large positive temperature gradient in the sub-microbar auroral atmosphere and non-local thermal equilibrium effects affecting preferentially hot and combination bands. Spatial variations in line intensities are mostly owing to correlated variations in the H3+ column densities. The thermostatic role played by H3+ at ionospheric levels may provide an explanation. The exception is the northern 'hot spot', which exhibits a Tvib about 250 K higher than other regions.

Journal Article↗