I. de Pater

University of California, Berkeley, Berkeley, California, United States

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Publications (392)663.26 Total impact

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    ABSTRACT: We use transient within low nightside ARTEMIS magnetic field measurements with forward modeling to constrain the electrical conductivity of the lunar interior.
    02/2014;
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    ABSTRACT: Thermal models to FORCAST observations of Comet ISON (r_h = 1.2 AU) at 11, 19 and 32 µm show the coma has a steep size distribution of carbon-rich 0.7-1-µm grains.
    02/2014;
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    ABSTRACT: From Space Telescope Imaging Spectrograph (STIS) observations of Uranus in 2012, when good views of its north polar regions were available, we found that the methane volume mixing ratio declined from about 4% at low latitudes to about 2% at 60–80°N. This depletion in the north polar region of Uranus in 2012 is similar in magnitude and depth to that found in the south polar regions in 2002. This similarity is remarkable because of the strikingly different appearance of clouds in the two polar regions: we have never seen any obvious signs of convective activity in the south polar region, while the north has been peppered with numerous small clouds thought to be of convective origin. Keck and Hubble Space Telescope imaging observations close to equinox at wavelengths of 1080 nm and 1290 nm, with different sensitivities to methane and hydrogen absorption but similar vertical contribution functions, imply that the depletions were simultaneously present in 2007, and at least their gross character is probably a persistent feature of the Uranus atmosphere. The depletion appears to be mainly restricted to the upper troposphere, with the depth increasing poleward from about 30°N, reaching ∼4 bars at 45°N and perhaps much deeper at 70°N, where it is not well constrained by our observations. The latitudinal variations in degree and depth of the depletions are important constraints on models of meridional circulation. Our observations are qualitatively consistent with previously suggested circulation cells in which rising methane-rich gas at low latitudes is dried out by condensation and sedimentation of methane ice particles as the gas ascends to altitudes above the methane condensation level, then is transported to high latitudes, where it descends and brings down methane depleted gas. Since this cell would seem to inhibit formation of condensation clouds in regions where clouds are actually inferred from spectral modeling, it suggests that sparse localized convective events may be important in cloud formation. A more complex meridional circulation pattern may be necessary to reproduce the observed cloud distribution, but microwave observations appear to be most compatible with a single deep circulation cell. The small-scale latitudinal variations we found in the effective methane mixing ratio between 55°N and 82°N have significant inverse correlations with zonal mean latitudinal variations in cloud reflectivity in near-IR Keck images taken before and after the HST observations. If the CH4/H2 absorption ratio variations are interpreted as local variations in para fraction instead of methane mixing ratio, we find that downwelling correlates with reduced cloud reflectivity. While there has been no significant secular change in the brightness of Uranus at continuum wavelengths between 2002 and 2012, there have been significant changes at wavelengths sensing methane and/or hydrogen absorption, with the southern hemisphere darkening considerably between 2002 and 2012, by ∼25% at mid latitudes near 827 nm, for example, while the northern hemisphere has brightened by ∼25% at mid latitudes at the same wavelength.
    Icarus 01/2014; 238:137–155. · 3.16 Impact Factor
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    ABSTRACT: On 28 September 2012, Hubble's Space Telescope Imaging Spectrograph (STIS) observed Uranus (GO 12894, L. Sromovsky PI). The result is a hyperspectral data cube of one half of the planet with spectral coverage of 300-1000 nm. The observations were designed to characterize latitudinally (from about 50 deg S to the north pole) the vertical structure of aerosols and global distribution of methane after the planet's 2007 equinox. These observations form a unique counterpart to similar observations made in 2002 (GO 9035, E. Karkoschka PI) when Uranus' south pole was in view. In 2002, Uranus was found to have a depletion of methane in southern mid-to-high latitudes (Karkoschka and Tomasko 2009, Icarus 202, 287-309; Sromovsky et al. 2011, Icarus 215, 292-312). Characterizing this distribution is possible by the simultaneous sounding of both hydrogen and methane spectral absorption regions (hydrogen CIA peaks near 825 nm). As Uranus' northern hemisphere came into view, it became apparent from near-IR observations of the troposphere (sensing to about 10 bars), that the north and south hemispheres were asymmetric in brightness, and that unexpectedly rapid seasonal changes were taking place (Sromovsky et al. 2009, Icarus 203, 265-286). The north polar region also has what appear to be many small convective features poleward of 60 deg N, in stark contrast to the south polar region (Sromovsky et al. 2012, Icarus 220, 694-712). Sromovsky et al. 2012 speculated this difference could be due to a seasonally-forced methane abundance asymmetry. However, 2007 NICMOS F108N and Keck NIRC2 PaBeta (1271 nm) equinox imagery suggest that the north polar region is also depleted in methane, as do 2009 IRTF SpeX observations (Tice et al. 2013, Icarus 223, 684-698). We can now confirm this northern hemispheric methane depletion appears symmetric rather than a seasonal phenomenon, thanks to the new STIS observations with an excellent view of Uranus northern latitudes. We will also present preliminary results of radiative transfer modeling of the current vertical structure of aerosols, and compare the current state to that of 2002. This work was supported by STScI and the NASA Planetary Astronomy program.
    10/2013;
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    ABSTRACT: Images of Jupiter at 5 microns reveal a dynamic range of about 20 in thermal emission between the hottest Hot Spots and the lowest flux regions on the planet. The Great Red Spot is dark at 5 microns due to thick clouds, but imaging alone does not reveal which cloud layers are responsible for attenuating this radiation. Initial expectations were that upper level clouds were sufficiently opaque that structure at the water cloud level would be completely hidden. Fortunately, this is not the case. We used NIRSPEC on the Keck telescope and CSHELL on the Infrared Telescope Facility to spectrally resolve line profiles of CH3D and other molecules on Jupiter in order to derive the pressure of the line formation region in the 5-micron window. Deuterated methane is a good choice for studying cloud structure because methane and its isotopologues do not condense on Jupiter. Variations in CH3D line shape with position on Jupiter are therefore ONLY due to cloud structure rather than due to changes in gas mole fraction. By aligning the slit east/west on Jupiter, we sampled the Great Red Spot and a Hot Spot 7 arcsec to the west. The profile of the CH3D lines is very broad in the Hot Spot due to collisions with up to 8 bars of H2, where unit optical depth due to collision induced H2 opacity occurs. The extreme width of these CH3D features implies that Hot Spots do not have significant cloud opacity where water is expected to condense. This is consistent with the Galileo probe results. Within the Great Red Spot, the line profiles are substantially narrower than in the Hot Spot, but they are broader than would be expected if they were formed in a column above an opaque cloud at 0.7 bars (NH3) or 2 bars (NH4SH). The best fit to the line shape of CH3D requires an opaque cloud at 5 bars, which we identify as being a water cloud. Gaseous H2O is clearly evident in the Great Red Spot, which provides independent evidence that we are sounding deep in Jupiter’s atmosphere. A combination of Keck and IRTF data will allow us to retrieve NH3, PH3, and gaseous H2O inside the Hot Spot and within the Great Red Spot. This technique can be applied to study the deep cloud structure anywhere on Jupiter whether or not upper level clouds are present.
    10/2013;
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    ABSTRACT: We present models of the Uranian atmosphere and rings based on near-infrared (H- and K-band) observations of Uranus taken with the OSIRIS integral field spectrograph at the W.M. Keck Observatory in 2010 and 2011. In July 2010 we observed the Uranian atmosphere with spatial and spectral resolution at latitudes ranging from the north polar region to mid southern latitudes. We demonstrate radiative transfer models used to characterize the properties and vertical & latitudinal distribution of clouds and hazes. We also present spectra of a discrete cloud feature observed in July 2011, alongside radiative transfer models used to constrain the cloud altitude and properties. Finally, we present near-infrared spectra of the Uranian ring system, which we find to be gray. We determined ring particle reflectivities for each ring group based on this data, and find reflectivities consistent with previous results with the exception of the 456 ring group, which we find to be slightly fainter.
    10/2013;
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    ABSTRACT: Previous studies using data from Pioneer Venus suggested that oxygen ion escape flux may be enhanced by orders of magnitude during Interplanetary Coronal Mass Ejections. However, this large enhancement has been ambiguous in Venus Express ion data - with some analyses showing no flux enhancement or a small enhancement (within 2 times undisturbed cases). One possible explanation is that high escape flux may be due to high dynamic pressure in the solar wind, and the dynamic pressure has been lower during the VEX time period. So, we focus on ICMEs with the largest dynamic pressure and with VEX sampling of the escaping ions during the sheath of the ICMEs (during which the highest dynamic pressures in the solar wind occur). We will show the characteristics of these large events measured by VEX, and compare them to the largest ICMEs measured by PVO. We will then discuss estimates of the oxygen ion escape flux during these events.
    10/2013;
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    ABSTRACT: We report on observations of Neptune's rings, arcs and inner moons as obtained by the Hubble Space Telescope during 2004-2009. These are the only Earth-based observations of the ring system obtained at visual wavelengths, permitting direct photometric comparison with the Voyager images. This allows us to determine quantitatively how the arcs have evolved from the time they were first imaged. Of the four arcs identified in 1989, the leading two have vanished, but the trailing two appear to have remained quite stable. New analysis of the images has also revealed a small moon, S/2004 N 1, orbiting between Proteus and Larissa. The body has a mean motion of 378.907 +/- 0.001 degrees per day, corresponding to semimajor axis 105,283 km. Its V magnitude is 26.5 +/- 0.3, suggesting a radius of ~ 10 km if its albedo is ~ 10%, comparable to that of the other inner moons. Tentative detections of Naiad, the smallest moon discovered by Voyager, will also be discussed.
    10/2013;
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    ABSTRACT: The Planetary Radio Interferometry and Doppler Experiment (PRIDE) is a multi-disciplinary enhancement of the scientific suite of the Jupiter Icy Moons Explorer (JUICE). PRIDE will exploit the technique of Very Long Baseline Interferometry (VLBI) observations of spacecraft and natural celestial radio sources by a network of Earth-based radio telescopes (Fig. 1, see [1,2]). The main "measured deliverables" of PRIDE are lateral coordinates of spacecraft in the celestial reference frame. In addition to the lateral coordinates, a by-product of PRIDE is the measurement of the line-ofsight velocity of spacecraft. It is worth to notice the synergistic nature of PRIDE measurements to other key experiments of the JUICE mission, in particular addressing the quest of Icy Moons interior and Jovian system ephemerides. In addition of providing consistency checks of a number of experiments, PRIDE is highly synergistic to a number of other JUICE experiments, in particular radio science and laser ranging ones. Tracking of the spacecraft in the gravity field of Jupiter and its satellites will allow us to not only provide valuable inputs into the determination of the spacecraft trajectory, but also to improve the ephemerides of Jupiter and the Galilean Satellites. VLBI tracking of the spacecraft, in combination with routine observations of background radio sources of the celestial reference frame, will also allow us to firmly tie the Jupiter system into the celestial reference frame. This would represent a major contribution to the Solar System celestial mechanics and the definition of the Solar System reference system. Furthermore, PRIDE will contribute to various aspects of Ganymede's, Callisto's and Europa's science. VLBI positioning and radio occultation data may represent an important and independent reference for the GALA laser altimeter data. The trajectory data during the multiple satellite flybys will help to further constrain the low order gravity field parameters. In addition to the science topics, PRIDE can provide support to the mission operations by engaging, as necessary, an extended network of Earth-based radio telescopes. A separate and potentially beneficial application of PRIDE is its ability to provide limited Direct-to-Earth delivery of data from JUICE spacecraft. PRIDE offers a high degree of synergy with JUICE's on-board instrumentation and does not include components requiring mission-critical technology developments. The on-board instrumentation required by PRIDE (transmitters, ultra-stable oscillators, antennas) will be developed and used by other JUICE experiments and mission service module systems. PRIDE observations of the spacecraft can be carried out simultaneously to radio science observations to provide consistency checks and complementary lateral position of the spacecraft. Furthermore, PRIDE measurements can also run while the spacecraft is communicating with Earth. PRIDE will not require additional load on the mass budget and is expected to require minimal experiment specific power budget of the JUICE mission. It is important to underline that PRIDE-JUICE does not require any specific on-board instrumentation beyond those devices which will be available on board the mission spacecraft independently of PRIDE. The Earth-based segment of PRIDE includes a network of radio telescopes and specialised data processing centre. These components of PRIDE constitute a backbone of the European and global VLBI networks. Their current state is already consistent with the PRIDE requirements. The work in progress at JIVE, other organisations of the PRIDEJUICE consortium as well as members of the European VLBI Network (EVN) will extend the broad-band capability of the European radio telescopes and data processing facility (correlator) from its current 1 Gbs per station to 4 Gbs and higher data rates. This will further advance the capability of PRIDE by enabling high-accuracy observations with weaker celestial background reference radio sources. The timeframe of this EVN development is well within the timeline of the JUICE implementation.
    09/2013;
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    ABSTRACT: Observations of Jupiter by a large number of amateurs have resulted in the discovery of three fireballs in its atmosphere produced by the impacts of small objects. The fireballs were detected on June 3, 2010, August 20, 2010 and September 10, 2012. The light-curves of these atmospheric airbursts provide a measure of the masses and sizes of the impacting objects and the statistical significance of the three events can be examined from knowledge of the large pool of Jupiter observations by the global community of amateur astronomers. These objects are in the category of 5-20 m sizes depending on their density and release energies comparable to the recent Chelyabinsk airburst. Current biases in observations of Jupiter suggest a rate of similar impacts of 18-160 per year.
    Astronomy and Astrophysics 09/2013; · 5.08 Impact Factor
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    ABSTRACT: CBET 3586 available at Central Bureau for Astronomical Telegrams.
    Central Bureau Electronic Telegrams. 07/2013;
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    ABSTRACT: We present maps of Neptune in and near the CO (2-1) rotation line at 230.538 GHz. These data, taken with the Combined Array for Research in Millimeter-wave Astronomy (CARMA) represent the first published spatially-resolved maps in the millimeter. At large (~5 GHz) offsets from the CO line center, the majority of the emission originates from depths of 1.1-4.7 bar. We observe a latitudinal gradient in the brightness temperature at these frequencies, increasing by 2-3 K from 40 degrees N to the south pole. This corresponds to a decrease in the gas opacity of about 30% near the south pole at altitudes below 1 bar, or a decrease of order a factor of 50 in the gas opacity at pressures greater than 4 bar. We look at three potential causes of the observed gradient: variations in the tropospheric methane abundance, variations in the H2S abundance, and deviations from equilibrium in the ortho/para ratio of hydrogen. At smaller offsets (0-213 MHz) from the center of the CO line, lower atmospheric pressures are probed, with contributions from mbar levels down to several bars. We find evidence of latitudinal variations at the 2-3% level in the CO line, which are consistent with the variations in zonal-mean temperature near the tropopause found by Conrath et al. (1998) and Orton et al. (2007).
    Icarus 06/2013; 226(1). · 3.16 Impact Factor
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    ABSTRACT: The Taiwanese-American Occultation Survey (TAOS) aims to detect serendipitous occultations of stars by small (about 1 km diameter) objects in the Kuiper Belt and beyond. Such events are very rare (<0.001 events per star per year) and short in duration (about 200 ms), so many stars must be monitored at a high readout cadence. TAOS monitors typically around 500 stars simultaneously at a 5 Hz readout cadence with four telescopes located at Lulin Observatory in central Taiwan. In this paper, we report the results of the search for small Kuiper Belt Objects (KBOs) in seven years of data. No occultation events were found, resulting in a 95% c.l. upper limit on the slope of the faint end of the KBO size distribution of q = 3.34 to 3.82, depending on the surface density at the break in the size distribution at a diameter of about 90 km.
    The Astronomical Journal 01/2013; 146(1). · 4.97 Impact Factor
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    Statia H. Luszcz-Cook, Imke de Pater
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    ABSTRACT: We present observations of Neptune's 1- and 3-mm spectrum from the Combined Array for Research in Millimeter-wave Astronomy (CARMA). Radiative transfer analysis of the CO (2-1) and (1-0) rotation lines was performed to constrain the CO vertical abundance profile. We find that the data are well matched by a CO mole fraction of 0.1^+0.2_-0.1 parts per million (ppm) in the troposphere, and 1.1^+0.2_-0.3 ppm in the stratosphere. A flux of 0.5-20 times 10^8 CO molecules cm-2 s-1 to the upper stratosphere is implied. Using the Zahnle et al. (2003) estimate for cometary impact rates at Neptune, we calculate the CO flux that could be formed from (sub)kilometer-sized comets; we find that if the diffusion rate near the tropopause is small (200 cm2 s-1), these impacts could produce a flux as high as 0.5^+0.8_-0.4 times 10^8 CO molecules cm-2 s-1. We also revisit the calculation of Neptune's internal CO contribution using revised calculations for the CO ->CH4 conversion timescale in the deep atmosphere (Visscher et al. 2011). We find that an upwelled CO mole fraction of 0.1 ppm implies a global O/H enrichment of at least 400, and likely more than 650, times the protosolar value.
    Icarus 01/2013; 222(1). · 3.16 Impact Factor
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    ABSTRACT: Post-equinox high S/N imaging of Uranus, by HST in 2009-10 and by Keck and Gemini telescopes in 2011, provide the first detailed views of its high northern latitudes. These images reveal numerous small cloud features from which we were able to extend the zonal wind profile of Uranus into its north polar region and accurately characterize its 60° N 250-m/s prograde jet. We also found a large N-S asymmetry in the morphology of polar cloud features (Sromovsky et al. 2012, Icarus 220, 694-712). The variation of wind speed with latitude in the north polar region is consistent with solid body rotation at a rate of 4.3°/h relative to the interior. When new measurements are combined with measurements from 1997 onward, there remains a small but significant asymmetry at middle latitudes, peaking near 35°, where southern hemisphere winds are 20 m/s more westward than corresponding northern hemisphere winds. The discovery of polar discrete cloud features is significant because of their possible connection to large scale meridional mass flows. Analysis of 2002 HST STIS spectra shows that the southern high latitudes are depleted of methane in the upper troposphere (Karkoschka & Tomasko 2009 Icarus 202 287-309; Sromovsky et al. 2011, Icarus 215, 292-312), suggesting an upper tropospheric downwelling in the south polar region that would tend to depress convective cloud formation there. Indeed, no comparable features have ever been seen in high southern latitudes. On the other hand, the existence of numerous small, possibly convective, features at high northern latitudes suggests that the predominant meridional flow there is not downwelling and that CH4 may not yet be depleted there. New HST STIS observations are expected to resolve this issue. This research was supported by grants from NASA Planetary Atmospheres and Astronomy programs, and from the Space Telescope Science Institute.
    10/2012;
  • Mate Adamkovics, I. de Pater
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    ABSTRACT: We present spatially-resolved observations of Titan in the near-infrared obtained with the field integral spectrograph, OSIRIS, at the W. M. Keck Observatory. Datacubes were acquired in H (1.5 μm) and K (2 μm) bands from April 2006 to January 2012. Broadband spectra reveal the aerosol vertical structure from the surface through the stratosphere. We describe the temporal and spatial variation in aerosol distribution as constrained by our radiative transfer models, which include updates to methane opacity and aerosol scattering. This work is supported by NSF planetary astronomy grant AST-1008788.
    10/2012;
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    ABSTRACT: High signal-to-noise imaging of Uranus, using specially-designed observations and special image combination techniques (Fry, P. M., et al. 2012, Astron. J. 143, 150-161) has now been applied to H and Hcont filtered images from Keck II NIRC2 and Gemini-North NIRI instruments, and F845M images from the HST WFC3 camera. Uranus' zonal wind profile has been updated as the viewing of more northerly latitudes improves, and the presence of high-latitude northern clouds has raised the possibility of fundamentally different large-scale meridional circulation patterns in the north and south hemispheres (L. A. Sromovsky et al. 2012, Icarus 220, 694-712). Detection of the low-contrast polar clouds and their altitude determination (by H/Hcont contrast ratios) is only possible using high-SNR imaging techniques. Though high-SNR imaging is not required to detect extremely bright features on Uranus, such as the variable-brightness interacting systems observed in late 2011, it has proved valuable in allowing tracking of persistent features to aid in investigation of their genesis, evolution, and dissipation (L. A. Sromovsky et al. 2012, Icarus 220, 6-22). Characterization of fine details of the latitudinal band structure can also be improved by these observations. We will show how this band structure has recently evolved, using H-band imagery from 2003 to the present, and HST F845M images from 2009 to 2011. Our 2011 Keck II observations were productive, in spite of sub-par image quality. Assuming normal image quality, we expect our upcoming Keck II observations (24, 28 July 2012, 14-15 August 2012) to reveal exceptional detail in small low-contrast polar cloud features, to allow tracking of extremely low-contrast low latitude features, and to show the current fine structure of Uranus' bands. Sample results will be shown if observations are successful. This research was supported by the NASA Planetary Astronomy program, the W. M. Keck Observatory, and STScI.
    10/2012;
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    ABSTRACT: Understanding the effects of large solar wind disturbances on the ion escape rate at Venus is critical for bounding the history of water on the planet. Previous studies have suggested that solar wind disturbances can cause an enhancement in the the ion escape rate, but did not look specifically at the effect of the sheath region of Interplanetary Coronal Mass Ejections, when the highest dynamic pressures in the solar wind are encountered. The high dynamic pressure region is of specific interest because it pushes the ionopause to a lower altitude exposing more ions to the magnetic fields in the solar wind. We will present a case study from a large (fast and high magnetic field) ICME that hit Venus on November 5, 2011. This event had the highest piled up magnetic field yet encountered by VEX (>250 nT) and also is the best event for studying the effects of the high dynamic pressure sheath region on escape because VEX was near the planet measuring escaping ions during the time period when the ICME sheath passed Venus. During this time period MESSENGER and STEREO B were aligned with Venus, allowing additional measurements of this event. We will present details of this ICME with data from VEX, MESSENGER and STEREO B. The ion escape was enhanced during this event, which we will show by comparison with undisturbed days with similar Interplanetary Magnetic Field directions and orbit geometry.
    10/2012;
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    ABSTRACT: Showalter and Lissauer (2003) reported the discovery of two previously unknown inner satellites of Uranus (Mab and Cupid), using data from the Hubble Space Telescope (HST). Subsequently, they announced the discovery of an outer ring system composed of the ν-ring and the μ-ring (Showalter and Lissauer, 2006). They showed that the orbit of Mab, embedded in the μ-ring, is not well understood, after comparing its orbital position derived from Voyager flyby data (1986) to HST data (2003-2006). The observed positions were compared with a Keplerian orbital model that included the gravitational flattening of Uranus. Although this model works well for nine other Uranian moons, for Mab the fitting errors are six times larger. Mab is relatively bright in the data and well isolated from the other moons, suggesting that the measurement errors should not be large. Hence, the magnitude of the orbit fit residual seems to indicate that we are currently overlooking an essential part of the dynamics that determines the orbit of Mab. It is clear from these discoveries that Mab and the μ-ring are intriguing, constituting "a densely packed, rapidly varying, and possibly unstable dynamical system." We investigated the nature of Mab's anomalous orbital motion, which has thus far remained unexplained. The dynamical effects we simulated result from the interaction of Mab with a hypothetical ring of undetected moonlets in its neighborhood. We explored the effects of varying the characteristics of such a ring (mass and orbital-element distribution) on Mab's orbital motion. From these results we are able to highlight a number of interesting dynamical regimes. In particular, our simulations reveal the important role that perturbers occupying horseshoe orbits might play in determining the perturbations experienced by Mab. Further studies will be conducted to investigate the long-term stability of a possible perturber ring.
    10/2012;
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    ABSTRACT: Of all the planets in our solar system, the two ice giants Uranus and Neptune remain the least explored and poorly understood because of their great distance from Earth. And yet they occupy a unique position in the hierarchy of planetary types, being intermediate between gas giants with their enormous hydrogen-helium envelopes, and terrestrial-sized worlds and Super Earths. These ice giants, so-called because their bulk compositions are dominated by heavier elements, are a true frontier of our exploration of planetary atmospheres, having been visited only once by Voyager 2 in 1986 and 1989, and may be representative of a whole class of planetary objects throughout our galaxy. Even though Earth-based observations (ISO, Spitzer, Herschel, ground-based) have improved dramatically in the decades since Voyager 2, many questions about this unexplored region of our Solar System remain unanswered. Voyager revealed unexpected differences in the appearance, composition, dynamics and chemistry between these two worlds, which could ultimately help us to understand how planetary atmospheres form and evolve as a function of distance from their host stars. This talk will review our present understanding of ice giant atmospheres, and assess the key questions to be answered by future exploration.
    09/2012;

Publication Stats

2k Citations
663.26 Total Impact Points

Institutions

  • 1986–2014
    • University of California, Berkeley
      • Department of Astronomy
      Berkeley, California, United States
  • 2010
    • Boston University
      • Center for Space Physics
      Boston, Massachusetts, United States
  • 2009
    • Laboratoire d'Etudes en Géophysique et Óceanographie Spatiales
      Tolosa de Llenguadoc, Midi-Pyrénées, France
  • 2008
    • Sierra College
      Cornell, Wisconsin, United States
  • 2005–2007
    • SETI Institute
      Mountain View, California, United States
  • 2006
    • Harvard-Smithsonian Center for Astrophysics
      Cambridge, Massachusetts, United States
    • The Space Science Institute
      Boulder, Colorado, United States
  • 1985–2005
    • CSU Mentor
      Long Beach, California, United States
  • 1998–2004
    • Stanford University
      Palo Alto, California, United States
    • Cornell University
      • Department of Astronomy
      Ithaca, NY, United States
    • Lawrence Livermore National Laboratory
      Livermore, California, United States
  • 2003
    • University of California, Santa Cruz
      Santa Cruz, California, United States
  • 1982–2001
    • The University of Arizona
      Tucson, Arizona, United States
  • 1999
    • Honolulu University
      Honolulu, Hawaii, United States
  • 1997
    • University of Bonn
      Bonn, North Rhine-Westphalia, Germany
  • 1991
    • University of Maryland, College Park
      Maryland, United States
  • 1983–1984
    • University of Illinois, Urbana-Champaign
      • Department of Astronomy
      Urbana, IL, United States
    • NSF
      Ann Arbor, Michigan, United States
    • National Radio Astronomy Observatory
      Charlottesville, Virginia, United States
  • 1980
    • Max Planck Institute for Radio Astronomy
      Bonn, North Rhine-Westphalia, Germany