Michael H. Wong

A COMPARISON OF THE ATMOSPHERES OF JUPITER AND SATURN : DEEP ATMOSPHERIC COMPOSITION, CLOUD STRUCTURE, VERTICAL MIXING, AND ORIGIN

We present our current understanding of the composition, vertical mixing, cloud structure and the origin of the atmospheres of Jupiter and Saturn. Available observations point to a much more vigorous vertical mixing in Saturns middle-upper atmosphere than in Jupiters. The nearly cloud-free nature of the Galileo probe entry site, a 5-micron hotspot, is consistent with the depletion of condensable volatiles to great depths, which is attributed to local meteorology. Somewhat similar depletion of water may be present in the 5-micron bright regions of Saturn also. The supersolar abundances of heavy elements, particularly C and S in Jupiters atmosphere and C in Saturns, as well as the progressive increase of C from Jupiter to Saturn and beyond, tend to support the icy planetesimal model of the formation of the giant planets and their atmospheres. However, much work remains to be done, especially in the area of laboratory studies, including identification of possible new microwave absorbers, and modelling, in order to resolve the controversy surrounding the large discrepancy between Jupiters global ammonia abundance, hence the nitrogen elemental ratio, derived from the earth-based microwave observations and that inferred from the analysis of the Galileo probe-orbiter radio attenuation data for the hotspot. We look forward to the observations from Cassini-Huygens spacecraft which are expected to result not only in a rich harvest of information for Saturn, but a better understanding of the formation of the giant planets and their atmospheres when these data are combined with those that exist for Jupiter.

Composition and origin of the atmosphere of Jupiter—an update, and implications for the extrasolar giant planets

Abstract New developments have led to this update of the composition and origin of Jupiters atmosphere that were originally discussed in our Planet. Space Sci. 47 (1999) 1243 paper. Since Jupiter can provide important insight into the atmospheres of extrasolar giant planets (EGP), we also discuss here the possible implications of the first detection of an atmosphere on an EGP. The ammonia mixing ratio on Jupiter has now been determined directly from the Galileo probe mass spectrometer (GPMS) data, and its value relative to H 2 (7.1±3.2)×10 −4 in the 9– 12 bar region, is found to be similar to the previously reported result inferred from the radio attenuation technique on Galileo. The Jovian 15 N / 14 N ratio is found to be much lower than the terrestrial value at (2.3±0.3)×10−3. A complete analysis of the various uncertainties in the GPMS data yields an H2O mixing ratio of 6.0(+3.9,−2.8)×10−4 at 19 bar in the hotspot, and a trend of increase with depth; all other mixing ratios and error bars remain unchanged. CH3, previously detected on Saturn and Neptune, has now also been detected in the atmosphere of Jupiter recently by Cassini. Benzene is the heaviest hydrocarbon detected to date in the atmospheres of Jupiter and Saturn. Abundances inferred from Infrared Space Observatory measurements are 9(+4.5,−7.5)×1014 and 4.7(+2.1,−1.1)×10 13 cm −2 for pressures less than 50 and 10 mbar on Jupiter and Saturn, respectively. Finally, we propose that the recently detected sodium in the atmosphere of the EGP orbiting HD 209458 may have mainly a post-accretionary extraplanetary origin, rather than being primordial.

A low density of 0.8 g cm-3 for the Trojan binary asteroid 617 Patroclus

The Trojan population consists of two swarms of asteroids following the same orbit as Jupiter and located at the L4 and L5 stable Lagrange points of the Jupiter–Sun system (leading and following Jupiter by 60°). The asteroid 617 Patroclus is the only known binary Trojan. The orbit of this double system was hitherto unknown. Here we report that the components, separated by 680 km, move around the systems centre of mass, describing a roughly circular orbit. Using this orbital information, combined with thermal measurements to estimate the size of the components, we derive a very low density of 0.8 - 0.1 + 0.2 g cm-3. The components of 617 Patroclus are therefore very porous or composed mostly of water ice, suggesting that they could have been formed in the outer part of the Solar System.

Depth of a strong Jovian jet from a planetary-scale disturbance driven by storms

The atmospheres of the gas giant planets (Jupiter and Saturn) contain jets that dominate the circulation at visible levels. The power source for these jets (solar radiation, internal heat, or both) and their vertical structure below the upper cloud are major open questions in the atmospheric circulation and meteorology of giant planets. Several observations and in situ measurements found intense winds at a depth of 24 bar, and have been interpreted as supporting an internal heat source. This issue remains controversial, in part because of effects from the local meteorology. Here we report observations and modelling of two plumes in Jupiter’s atmosphere that erupted at the same latitude as the strongest jet (23° N). The plumes reached a height of 30 km above the surrounding clouds, moved faster than any other feature (169 m s-1), and left in their wake a turbulent planetary-scale disturbance containing red aerosols. On the basis of dynamical modelling, we conclude that the data are consistent only with a wind that extends well below the level where solar radiation is deposited.

New determination of the size and bulk density of the binary Asteroid 22 Kalliope from observations of mutual eclipses

Abstract In 2007, the M-type binary Asteroid 22 Kalliope reached one of its annual equinoxes. As a consequence, the orbit plane of its small moon, Linus, was aligned closely to the Suns line of sight, giving rise to a mutual eclipse season. A dedicated international campaign of photometric observations, based on amateur–professional collaboration, was organized and coordinated by the IMCCE in order to catch several of these events. The set of the compiled observations is released in this work. We developed a relevant model of these events, including a topographic shape model of Kalliope refined in the present work, the orbit solution of Linus as well as the photometric effect of the shadow of one component falling on the other. By fitting this model to the only two full recorded events, we derived a new estimation of the equivalent diameter of Kalliope of 166.2 ± 2.8 km , 8% smaller than its IRAS diameter. As to the diameter of Linus, considered as purely spherical, it is estimated to 28 ± 2 km . This substantial “shortening” of Kalliope, gives a bulk density of 3.35 ± 0.33 g / cm 3 , significantly higher than past determinations but more consistent with its taxonomic type. Some constraints can be inferred on the composition.

Primordial argon isotope fractionation in the atmosphere of Mars measured by the SAM instrument on Curiosity and implications for atmospheric loss.

[1] The quadrupole mass spectrometer of the Sample Analysis at Mars (SAM) instrument on Curiosity rover has made the first high-precision measurement of the nonradiogenic argon isotope ratio in the atmosphere of Mars. The resulting value of 36Ar/38Ar = 4.2 ± 0.1 is highly significant for it provides excellent evidence that “Mars” meteorites are indeed of Martian origin, and it points to a significant loss of argon of at least 50% and perhaps as high as 85–95% from the atmosphere of Mars in the past 4 billion years. Taken together with the isotopic fractionations in N, C, H, and O measured by SAM, these results imply a substantial loss of atmosphere from Mars in the posthydrodynamic escape phase.

The Puzzling Mutual Orbit of the Binary Trojan Asteroid (624) Hektor

Asteroids with satellites are natural laboratories to constrain the formation and evolution of our solar system. The binary Trojan asteroid (624) Hektor is the only known Trojan asteroid to possess a small satellite. Based on W. M. Keck adaptive optics observations, we found a unique and stable orbital solution, which is uncommon in comparison to the orbits of other large multiple asteroid systems studied so far. From lightcurve observations recorded since 1957, we showed that because the large Req = 125 km primary may be made of two joint lobes, the moon could be ejecta of the low-velocity encounter, which formed the system. The inferred density of Hektors system is comparable to the L5 Trojan doublet (617) Patroclus but due to their difference in physical properties and in reflectance spectra, both captured Trojan asteroids could have a different composition and origin. Key words: instrumentation: adaptive optics – minor planets, asteroids: general – minor planets, asteroids: individual (624 Hektor) – planets and satellites: detection – planets and satellites: dynamical evolution and stability

Peering through Jupiter's clouds with radio spectral imaging.

A radio view into Jupiters atmosphere Jupiters atmosphere is a complex system of belts, layers, storms, and cloud systems. de Pater et al. used Earth-bound radio observations to peer beneath its surface. Previous radio studies have been limited to average properties at each latitude, but the new observations allow a full two-dimensional view. This can be related to features (such as storms) seen in visible or infrared images. The results aid our understanding of gas giant atmospheres and will provide important context for the Juno spacecraft that arrives at Jupiter in July 2016. Science, this issue p. 1198 Radio observations probe beneath the clouds of Jupiter’s atmosphere. Radio wavelengths can probe altitudes in Jupiter’s atmosphere below its visible cloud layers. We used the Very Large Array to map this unexplored region down to ~8 bar, ~100 kilometers below the visible clouds. Our maps reveal a dynamically active planet at pressures less than 2 to 3 bar. A radio-hot belt exists, consisting of relatively transparent regions (a low ammonia concentration, NH3 being the dominant source of opacity) probing depths to over ~8 bar; these regions probably coincide with 5-micrometer hot spots. Just to the south we distinguish an equatorial wave, bringing up ammonia gas from Jupiter’s deep atmosphere. This wave has been theorized to produce the 5-micrometer hot spots; we observed the predicted radio counterpart of such hot spots.

Jupiter After the 2009 Impact: Hubble Space Telescope Imaging of the Impact-generated Debris and its Temporal Evolution

We report Hubble Space Telescope images of Jupiter during the aftermath of an impact by an unknown object in 2009 July. The 2009 impact-created debris field evolved more slowly than those created in 1994 by the collision of the tidally disrupted comet D/Shoemaker-Levy 9 (SL9). The slower evolution, in conjunction with the isolated nature of this single impact, permits a more detailed assessment of the altitudes and meridional motion of the debris than was possible with SL9. The color of the 2009 debris was markedly similar to that seen in 1994, thus this dark debris is likely to be Jovian material that is highly thermally processed. The 2009 impact site differed from the 1994 SL9 sites in UV morphology and contrast lifetime; both are suggestive of the impacting body being asteroidal rather than cometary. Transport of the 2009 Jovian debris as imaged by Hubble shared similarities with transport of volcanic aerosols in Earths atmosphere after major eruptions.

FIRST RESULTS FROM THE HUBBLE OPAL PROGRAM: JUPITER IN 2015

The Hubble 2020: Outer Planet Atmospheres Legacy program is generating new yearly global maps for each of the outer planets. This report focuses on Jupiter results from the first year of the campaign. The zonal wind profile was measured and is in the same family as the Voyager and Cassini era profiles, showing some variation in mid- to high-latitude wind jet magnitudes, particularly at +40° and −35° planetographic latitude. The Great Red Spot continues to maintain an intense orange coloration, but also shows new internal structures, including a reduced core and new filamentary features. Finally, a wave that was not previously seen in Hubble images was also observed and is interpreted as a baroclinic instability with associated cyclone formation near 16° N latitude. A similar feature was observed faintly in Voyager 2 images, and is consistent with the Hubble feature in location and scale.