I. de Pater

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

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Publications (392)674.88 Total impact

  • K. Kumar, I. de Pater, M.R. Showalter
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    ABSTRACT: We explored the hypothesis that Mab’s anomalous orbital motion, as deduced from Hubble Space Telescope (HST) data (Showalter, M.R., Lissauer, J.J. [2006]. Science (New York, NY) 311, 973–977), is the result of gravitational interactions with a putative suite of large bodies in the μ-ring. We conducted simulations to compute the gravitational effect of Mab (a recently discovered Uranian moon) on a cloud of test particles. Subsequently, by employing the data extracted from the test particle simulations, we executed random walk simulations to compute the back-reaction of nearby perturbers on Mab. By generating simulated observation metrics, we compared our results to the data retrieved from the HST. Our results indicate that the longitude residual change noted in the HST data ( deg) is well matched by our simulations. The eccentricity variations ( ) are however typically two orders of magnitude too small. We present a variety of reasons that could account for this discrepancy. The nominal scenario that we investigated assumes a perturber ring mass of 1 (Mab’s mass) and a perturber ring number density of 10 perturbers per 3 (Mab’s Hill radius). This effectively translates to a few tens of perturbers with radii of approximately 2–3 km, depending on the albedo assumed. The results obtained also include an interesting litmus test: variations of Mab’s inclination on the order of the eccentricity changes should be observable. Our work provides clues for further investigation into the tantalizing prospect that the Mab/μ-ring system is undergoing re-accretion after a recent catastrophic disruption.
    Icarus 07/2015; 254. DOI:10.1016/j.icarus.2015.03.002 · 2.84 Impact Factor
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    ABSTRACT: We imaged Uranus in the near infrared from 2012 into 2014, using the Keck/NIRC2 camera and Gemini/NIRI camera, both with adaptive optics. We obtained exceptional signal to noise ratios by averaging 8-16 individual exposures in a planet-fixed coordinate system. These noise-reduced images revealed many low-contrast discrete features and large scale cloud patterns not seen before, including scalloped waveforms just south of the equator, and an associated transverse ribbon wave near 6° S. In all three years numerous small (600-700 km wide) and mainly bright discrete features were seen within the north polar region (north of about 55° N). Two small dark spots with bright companions were seen at middle latitudes. Over 850 wind measurements were made, the vast majority of which were in the northern hemisphere. Winds at high latitudes were measured with great precision, revealing an extended region of solid body rotation between 62° N and at least 83° N, at a rate of 4.08 °/h westward relative to the planet’s interior (radio) rotation of 20.88°/h westward. Near-equatorial speeds measured with high accuracy give different results for waves and small discrete features, with eastward drift rates of 0.4° /h and 0.1° /h respectively. The region of polar solid body rotation is a close match to the region of small-scale polar cloud features, suggesting a dynamical relationship. The winds from prior years and those from 2012-2014 are consistent with a mainly symmetric wind profile up to middle latitudes, with a small asymmetric component of 0.09° /h peaking near 30°, and about 60% greater amplitude if only prior years are included, suggesting a declining mid-latitude asymmetry. While winds at high southern latitudes (50° S - 90° S) are unconstrained by groundbased observations, a recent reanalysis of 1986 Voyager 2 observations by Karkoschka (2015, Icarus 250, 294-307) has revealed an extremely large north-south asymmetry in this region, which might be seasonal. Greatly increased activity was seen in 2014, including the brightest ever feature seen in K′ images (de Pater et al. 2015, Icarus 252, 121-128), as well as other significant features, some of which had long lives. Over the 2012-2014 period we identified six persistent discrete features. Three were tracked for more than two years, two more for more than one year, and one for at least 5 months and continuing. Several drifted in latitude towards the equator, and others appeared to exhibit latitudinal oscillations with long periods. We found two pairs of long-lived features that survived multiple passages within their own diameters of each other. Zonally averaged cloud patterns were found to persist over 2012-2014. When averaged over longitude, there is a brightness variation with latitude from 55° N to the pole that is similar to effective methane mixing ratio variations with latitude derived from 2012 STIS observations (Sromovsky et al. 2014, Icarus 238, 137-155).
    Icarus 06/2015; 258. DOI:10.1016/j.icarus.2015.05.029 · 2.84 Impact Factor
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    ABSTRACT: The Large Binocular Telescope Interferometer mid-infrared camera, LMIRcam, imaged Io on the night of 2013 December 24 UT and detected strong M-band (4.8 μ m) thermal emission arising from Loki Patera. The 22.8 m baseline of the Large Binocular Telescope provides an angular resolution of ∼32 mas (∼100 km at Io) resolving the Loki Patera emission into two distinct maxima originating from different regions within Loki’s horseshoe lava lake. This observation is consistent with the presence of a high-temperature source observed in previous studies combined with an independent peak arising from cooling crust from recent resurfacing. The deconvolved images also reveal 15 other emission sites on the visible hemisphere of Io including two previously unidentified hot spots.
    The Astronomical Journal 04/2015; 149(5-5):175. DOI:10.1088/0004-6256/149/5/175 · 4.05 Impact Factor
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    ABSTRACT: From STIS observations of Uranus in 2012, we found that the methane volume mixing ratio declined from about 4% at low latitudes to about 2% at 60 deg N and beyond. This is similar to that found in the south polar regions in 2002, in spite of what appears to be strikingly different convective activity in the two regions. Keck and HST imaging observations close to equinox imply that the depletions were simultaneously present in 2007, suggesting they are persistent features. The depletions appear to be mainly restricted to the upper troposphere, with depth increasing poleward from about 30 deg N, reaching ~4 bars at 45 deg N and perhaps much deeper at 70 deg N. 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 modelling, it suggests that sparse localized convective events may be important in cloud formation. The small-scale latitudinal variations we found in the effective methane mixing ratio between 55 deg N and 82 deg 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.
    Icarus 08/2014; 238:137–155. DOI:10.1016/j.icarus.2014.05.016 · 2.84 Impact Factor
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    ABSTRACT: The Large Binocular Telescope (LBT) houses two 8.4-meter mirrors separated by 14.4 meters on a common mount. Coherent combination of these two AO-corrected apertures via the LBT Interferometer (LBTI) produces Fizeau interferometric images with a spatial resolution equivalent to that of a 22.8-meter telescope and the light- gathering power of single 11.8-meter mirror. Capitalizing on these unique capabilities, we used LBTI/LMIRcam to image thermal radiation from volcanic activity on the surface of Io at M-Band (4.8 μm) over a range of parallactic angles. At the distance of Io, the M-Band resolution of the interferometric baseline corresponds to a physical distance of ~135 km, enabling high-resolution monitoring of Io volcanism such as ares and outbursts inaccessible from other ground-based telescopes operating in this wavelength regime. Two deconvolution routines are used to recover the full spatial resolution of the combined images, resolving at least sixteen known volcanic hot spots. Coupling these observations with advanced image reconstruction algorithms demonstrates the versatility of Fizeau interferometry and realizes the LBT as the first in a series of extremely large telescopes.
    SPIE Astronomical Telescopes + Instrumentation; 07/2014
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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; 560:228-. DOI:10.1051/0004-6361/201322216 · 4.48 Impact Factor
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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.
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    ABSTRACT: CBET 3586 available at Central Bureau for Astronomical Telegrams.
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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). DOI:10.1016/j.icarus.2013.05.019 · 2.84 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). DOI:10.1088/0004-6256/146/1/14 · 4.05 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). DOI:10.1016/j.icarus.2012.11.002 · 2.84 Impact Factor
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    ABSTRACT: The impact of a body of unknown origin with Jupiter in July 2009 (Sánchez-Lavega et al., Astrophys. J. Lett, Vol. 715, L155. 2010) produced an intense perturbation of the planet's atmosphere at the visible levels. The perturbation was caused by dense aerosol material; this strongly absorbing material expanded steadily as it was advected by the local winds. This phenomenon was observed at high spatial resolution by the Hubble Space Telescope in July, August, September and November 2009 with recently installed Wide Field Camera 3. In this work, we present radiative transfer modeling of the observed reflectivity in the near UV (200nm) to near IR (950nm) range. The geometrical and spectral variations of reflectivity elucidate the main particle properties (optical thickness, size, imaginary refractive index) and their temporal evolution. The aerosol particles that formed during the impact have a mean radius of about 1 micron and are located high in the atmosphere (above 10 mbar), in good agreement ith ground-based observations in deep methane absorption bands in the near infrared. The density of this particle layer decreases with time until it approaches that of the pre-impact atmosphere. These results are also discussed in terms of what we know from other impacts in Jupiter (1994's SL9 event and 2010's bolide). Acknowledgements: SPH, ASL and RH are supported by the Spanish MICIIN AYA2009-10701 with FEDER and Grupos Gobierno Vasco IT-464-07.
    Icarus 11/2012; 221(2). DOI:10.1016/j.icarus.2012.10.012 · 2.84 Impact Factor
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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.

Publication Stats

3k Citations
674.88 Total Impact Points


  • 1985–2014
    • University of California, Berkeley
      • • Department of Astronomy
      • • Department of Statistics
      Berkeley, California, United States
  • 2008–2013
    • Delft University of Technology
      • Faculty of Aerospace Engineering (AE)
      Delft, South Holland, Netherlands
  • 2011
    • University College London
      • Department of Physics and Astronomy
      London, ENG, United Kingdom
  • 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
  • 2006
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
  • 2005–2006
    • SETI Institute
      Mountain View, California, United States
  • 2004
    • Stanford University
      • Graduate School of Business
      Palo Alto, California, United States
    • W. M. Keck Observatory
      Hilo, Hawaii, United States
    • University of California, Santa Cruz
      • Center for Adaptive Optics
      Santa Cruz, California, United States
    • Lowell Observatory
      Lowell, Massachusetts, United States
  • 2003
    • Academia Sinica
      • Institute of Astronomy and Astrophysics
      T’ai-pei, Taipei, Taiwan
  • 2002
    • The French Aeropace Lab ONERA
      Paliseau, Île-de-France, France
  • 2000
    • NASA
      Вашингтон, West Virginia, United States
  • 1980–1995
    • Leiden University
      Leyden, South Holland, Netherlands
  • 1991
    • University of Maryland, College Park
      Maryland, United States
  • 1990
    • University of Iowa
      • Department of Physics and Astronomy
      Iowa City, Iowa, United States
  • 1983–1984
    • The University of Arizona
      • Department of Chemistry and Biochemistry (College of Science)
      Tucson, Arizona, United States
    • National Radio Astronomy Observatory
      Charlottesville, Virginia, United States
    • NSF
      Ann Arbor, Michigan, United States
  • 1982–1984
    • University of Illinois, Urbana-Champaign
      • Department of Astronomy
      Urbana, IL, United States
    • University of Cambridge
      Cambridge, England, United Kingdom