Engineering topics

de Pater, I.

Publications and source records attributed to de Pater, I..

10 records

NASA NTRS2018

The Gas Composition and Deep Cloud Structure of Jupiter's Great Red Spot

We have obtained high-resolution spectra of Jupiter's Great Red Spot (GRS) between 4.6-5.4 microns using telescopes on Mauna Kea to derive gas abundances and to constrain its cloud structure between 0.5-5 bars. We used line profiles of deuterated methane (CH3D) at 4.66 microns to infer the presence of an opaque cloud at 5 plus or minus 1 bars. From thermochemical models, this is almost certainly a water cloud. We also used the strength of Fraunhofer lines in the GRS to obtain the ratio of reflected sunlight to thermal emission. The level of the reflecting layer was constrained to be at 570 plus or minus 30 millibars based on fitting strong NH3 lines at 5.32 microns. We identify this layer as an ammonia cloud based on the temperature where gaseous NH3 condenses. We found evidence for a strongly absorbing but not totally opaque cloud layer at pressures deeper than 1.3 bars by combining Cassini/CIRS (Composite Infrared Spectrometer) spectra of the GRS at 7.18 microns with ground-based spectra at 5 microns. This is consistent with the predicted level of an NH4SH cloud. We also constrained the vertical profile of H2O and NH3. The GRS spectrum is matched by a saturated H2O profile above an opaque water cloud at 5 bars. The pressure of the water cloud constrains Jupiter's O/H ratio to be at least 1.1 times solar. The NH3 mole fraction is 200 plus or minus 50 ppm (parts per million) for pressures between 0.7-5 bars. Its abundance is 40 ppm at the estimated pressure of the reflecting layer. We obtained 0.8 plus or minus 0.2 ppm for PH3, which is a factor of 2 higher than in the warm collar surrounding the GRS. We detected all five naturally occurring isotopes ofgermanium in GeH4 in the GRS. We obtained an average value of 0.35 plus or minus 0.05 ppb (parts per billion) for GeH4. Finally, we measured 0.8 plus or minus 0.2 ppb for CO in the deep atmosphere.

Bjoraker, G. L.↗

NASA NTRS2017

Neptune Long-Lived Atmospheric Features in 2013 - 2015 from Small (28-cm) to Large (10-m) Telescopes

Since 2013, observations of Neptune with small telescopes (28-50 cm) have resulted in several detections of long-lived bright atmospheric features that have also been observed by large telescopes such as Keck II or Hubble. The combination of both types of images allows the study of the long-term evolution of major cloud systems in the planet. In 2013 and 2014 two bright features were present on the planet at southern mid-latitudes. These may have merged in late 2014, possibly leading to the formation of a single bright feature observed during 2015 at the same latitude. This cloud system was first observed in January 2015 and nearly continuously from July to December 2015 in observations with telescopes in the 2-10-m class and in images from amateur astronomers. These images show the bright spot as a compact feature at −40.1 +/- 1.6 deg planetographic latitude well resolved from a nearby bright zonal band that extended from −42 deg to −20 deg. The size of this system depends on wavelength and varies from a longitudinal extension of 8000 +/- 900 km and latitudinal extension of 6500 +/- 900 km in Keck II images in H and Ks bands to 5100 +/- 1400 km in longitude and 4500 +/- 1400 km in latitude in HST images in 657 nm. Over July to September 2015 the structure drifted westward in longitude at a rate of 24.48 +/- 0.03 deg/day or −94 +/- 3 m/s. This is about 30 m/s slower than the zonal winds measured at the time of the Voyager 2 flyby. Tracking its motion from July to November 2015 suggests a longitudinal oscillation of 16 deg in amplitude with a 90-day period, typical of dark spots on Neptune and similar to the Great Red Spot oscillation in Jupiter. The limited time covered by high-resolution observations only covers one full oscillation and other interpretations of the changing motions could be possible. HST images in September 2015 show the presence of a dark spot at short wavelengths located in the southern flank (planetographic latitude −47.0 deg) of the bright compact cloud observed throughout 2015. The drift rate of the bright cloud and dark spot translates to a zonal speed of −87.0 +/- 2.0 m/s, which matches the Voyager 2 zonal speeds at the latitude of the dark spot. Identification of a few other features in 2015 enabled the extraction of some limited wind information over this period. This work demonstrates the need of frequently monitoring Neptune to understand its atmospheric dynamics and shows excellent opportunities for professional and amateur collaborations.

dynamics↗

NASA NTRS2016

An Enduring Rapidly Moving Storm as a Guide to Saturn's Equatorial Jet's Complex Structure

Saturn has an intense and broad eastward equatorial jet with a complex three-dimensional structure mixed with time variability. The equatorial region experiences strong seasonal insolation variations enhanced by ring shadowing, and three of the six known giant planetary-scale storms have developed in it. These factors make Saturn's equator a natural laboratory to test models of jets in giant planets. Here we report on a bright equatorial atmospheric feature imaged in 2015 that moved steadily at a high speed of 450/ms not measured since 1980-1981 with other equatorial clouds moving within an ample range of velocities. Radiative transfer models show that these motions occur at three altitude levels within the upper haze and clouds. We find that the peak of the jet (latitudes 10degN to 10degS) suffers intense vertical shears reaching + 2.5/ms/km, two orders of magnitude higher than meridional shears, and temporal variability above 1 bar altitude level.

Saturn↗

NASA NTRS2015

Dramatic Change in Jupiter's Great Red Spot

Jupiter's Great Red Spot (GRS) is one of its most distinct and enduring features, having been continuously observed since the 1800's. It currently spans the smallest latitude and longitude size ever recorded. Here we show analyses of 2014 Hubble spectral imaging data to study the color, structure and internal dynamics of this long-live storm.

Red Spot↗

NASA NTRS2014

Comet C2012 S1 (ISON)s Carbon-rich and Micron-size-dominated Coma Dust

Comet C/2012 S1 (ISON) was unique in that it was a dynamically new comet derived from the Nearly Isotropic Oort cloud reservoir of comets with a sun-grazing orbit. We present thermal models for comet ISON (rh approx.1.15 AU, 2013-Oct-25 11:30 UT) that reveal comet ISON's dust was carbon-rich and dominated by a narrow size distribution dominated by approx. micron-sized grains. We constrained the models by our SOFIA FORCAST photometry at 11.1, 19.7 and 31.5 microns and by a silicate feature strength of approx.1.1 and an 8-13microns continuum greybody color temperature of approx. 275-280 K (using Tbb ∝ r−0.5 h and Tbb approx. 260-265 K from Subaru COMICS, 2013-Oct-19 UT)[1,2]. N-band spectra of comet ISON with the BASS instrument on the NASA IRTF (2013-Nov-11-12 UT) show a silicate feature strength of approx. 1.1 and an 11.2microns forsterite peak.[3] Our thermal models yield constraints the dust composition as well as grain size distribution parameters: slope, peak grain size, porosity. Specifically, ISON's dust has a low silicate-to- amorphous carbon ratio (approx. 1:9), and the coma size distribution has a steep slope (N4.5) such that the coma is dominated by micron-sized, moderately porous, carbon-rich dust grains. The N-band continuum color temperature implies submicronto micron-size grains and the steep fall off of the SOFIA far-IR photometry requires the size distribution to have fewer relative numbers of larger and cooler grains compared to smaller and hotter grains. A proxy for the dust production rate is fρ approx.1500 cm, akin to Afρ. ISON has a moderate-to-low dust-to-gas ratio. Comet ISON's dust grain size distribution does not appear similar to the few well-studied long-period Nearly Isotropic Comets (NICs), namely C/1995 O1 (Hale-Bopp) and C/2001 Q4 (NEAT) that had smaller and/or more highly porous grains and larger sizes, or C/2007 N4 (Lulin) and C/2006 P1 (McNaught) that had large and/or compact grains. Radial transport to comet-forming disk distances (≥ 20 AU) is easier for smaller grains (≤1 micron) than for larger grains (approx. 20 microns like Stardust terminal particles). The presence of predominantly micron-sized and smaller grains suggests comet ISON may have formed either earlier in disk evolution whereby larger grains did not have the time to be transported to distances beyond Neptune, or the comet formed so far out in the disk that larger grains did not traverse such large radial distances. The high carbon-content of ISON's refractory dust appears to be complimented by the presence of limitedlifetime organic (CHON-like) grain materials: preliminary analyses of near-IR and high-resolution optical spectra indicate that gas-phase daughter molecules C2, CN, and CH were more abundant than their parent molecules (C2H2, C2H6, measured in the near- IR). Dust composition as well as grain size distribution parameters (slope, peak grain size, and porosity) give clues to comet origins.

NASA/DLR Stratospheric Observatory↗

NASA NTRS2011

The 2010-2011 Revival of Jupiter's South Equatorial Belt: Perturbations of Temperatures, Clouds and Composition from Infrared Observations

On 2010 November 9, a perturbation appeared in Jupiter's South Equatorial Belt (SEB), which began a classical "revival" of the SEB, returning the entire axisymmetric region to its normal dark color from its anomalous, light, "faded" state. The early revival is marked by strong upwelling gas at the outbreak location, to the west of which appear alternating clear and cloudy regions. Clear regions are correlated with dark clouds near the outbreak and in a southern retrograding branch but less so in a northern prograding branch. A 5-micrometer image from 2010 March 1 shows much of the SEB closer to a pre-faded state.

atmosphere↗

NASA NTRS2011

Long-Term Evolution of the Aerosol Debris Cloud Produced by the 2009 Impact on Jupiter

We present a study of the long-term evolution of the cloud of aerosols produced in the atmosphere of Jupiter by the impact of an object on 19 July 2009. The work is based on images obtained during 5 months from the impact to 31 December 2009 taken in visible continuum wavelengths and from 20 July 2009 to 28 May 2010 taken in near-infrared deep hydrogen-methane absorption bands at 2.1-2.3 micron. The impact cloud expanded zonally from approximately 5000 km (July 19) to 225,000 km (29 October, about 180 deg in longitude), remaining meridionally localized within a latitude band from 53.5 deg S to 61.5 deg S planetographic latitude. During the first two months after its formation the site showed heterogeneous structure with 500-1000 km sized embedded spots. Later the reflectivity of the debris field became more homogeneous due to clump mergers. The cloud was mainly dispersed in longitude by the dominant zonal winds and their meridional shear, during the initial stages, localized motions may have been induced by thermal perturbation caused by the impact's energy deposition. The tracking of individual spots within the impact cloud shows that the westward jet at 56.5 deg S latitude increases its eastward velocity with altitude above the tropopause by 5- 10 m/s. The corresponding vertical wind shear is low, about 1 m/s per scale height in agreement with previous thermal wind estimations. We found evidence for discrete localized meridional motions with speeds of 1-2 m/s. Two numerical models are used to simulate the observed cloud dispersion. One is a pure advection of the aerosols by the winds and their shears. The other uses the EPIC code, a nonlinear calculation of the evolution of the potential vorticity field generated by a heat pulse that simulates the impact. Both models reproduce the observed global structure of the cloud and the dominant zonal dispersion of the aerosols, but not the details of the cloud morphology. The reflectivity of the impact cloud decreased exponentially with a characteristic timescale of 15 days; we can explain this behavior with a radiative transfer model of the cloud optical depth coupled to an advection model of the cloud dispersion by the wind shears. The expected sedimentation time in the stratosphere (altitude levels 5-100 mbar) for the small aerosol particles forming the cloud is 45-200 days, thus aerosols were removed vertically over the long term following their zonal dispersion. No evidence of the cloud was detected 10 months after the impact.

Sanchez-Lavega, A.↗

NASA NTRS2010

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 Earth's atmosphere after major eruptions.

Hammel, H. B.↗

NASA NTRS2010

The Impact of a Large Object on Jupiter in 2009 July

On 2009 July 19, we observed a single, large impact on Jupiter at a planetocentric latitude of 55 S. This and the Shoemaker-Levy 9 (SL9) impacts on Jupiter in 1994 are the only planetary-scale impacts ever observed. The 2009 impact had an entry trajectory in the opposite direction and with a Tower incidence angle than that of SL9. Comparison of the initial aerosol cloud debris properties, spanning 4800 km east west and 2500 km north south, with those produced by the SL9 fragments and dynamical calculations of pre-impact orbit indicates that the impactor was most probably an icy body with a size of 0.5-1 km. The collision rate of events of this magnitude may be five to ten times more frequent than previously thought. The search for unpredicted impacts, such as the current one, could be best performed in 890 nm and K (2.03--2.36 micrometer) filters in strong gaseous absorption, where the high-altitude aerosols are more reflective than Jupiter's primary clouds.

Sanchez-Lavega, A.↗

NASA NTRS1995

Outburst of Jupiter's synchrotron radiation after the impact of comet Shoemaker-Levy 9

Jupiter's nonthermal microwave emission, as measured by a global network of 11 radio telescopes, increased dramatically during the Shoemaker-Levy 9 impacts. The increase was wavelength-dependent, varying from approximately 10 percent at 70 to 90 centimeters to approximately 45 percent at 6 and 36 centimeters. The radio spectrum hardened (flattened toward shorter wavelengths) considerably during the week of impacts and continued to harden afterward. After the week of cometary impacts, the flux density began to subside at all wavelengths and was still declining 3 months later. Very Large Array and Australia Telescope images of the brightness distribution showed the enhancement to be localized in longitude and concentrated near the magnetic equator. The evidence therefore suggests that the increase in flux density was caused by a change in the resident particle population, for example, through an energization or spatial redistribution of the emitting particles.

Jupiter↗