Jet Propulsion Laboratory

About: Jet Propulsion Laboratory is a facility organization based out in La Cañada Flintridge, California, United States. It is known for research contribution in the topics: Mars Exploration Program & Telescope. The organization has 8801 authors who have published 14333 publications receiving 548163 citations. The organization is also known as: JPL & NASA JPL.

Mercury's moment of inertia from spin and gravity data

Abstract: JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 117, E00L09, doi:10.1029/2012JE004161, 2012 Mercury’s moment of inertia from spin and gravity data Jean-Luc Margot, 1,2 Stanton J. Peale, 3 Sean C. Solomon, 4,5 Steven A. Hauck II, 6 Frank D. Ghigo, 7 Raymond F. Jurgens, 8 Marie Yseboodt, 9 Jon D. Giorgini, 8 Sebastiano Padovan, 1 and Donald B. Campbell 10 Received 15 June 2012; revised 31 August 2012; accepted 5 September 2012; published 27 October 2012. [ 1 ] Earth-based radar observations of the spin state of Mercury at 35 epochs between 2002 and 2012 reveal that its spin axis is tilted by (2.04 AE 0.08) arc min with respect to the orbit normal. The direction of the tilt suggests that Mercury is in or near a Cassini state. Observed rotation rate variations clearly exhibit an 88-day libration pattern which is due to solar gravitational torques acting on the asymmetrically shaped planet. The amplitude of the forced libration, (38.5 AE 1.6) arc sec, corresponds to a longitudinal displacement of $450 m at the equator. Combining these measurements of the spin properties with second-degree gravitational harmonics (Smith et al., 2012) provides an estimate of the polar moment of inertia of Mercury C/MR 2 = 0.346 AE 0.014, where M and R are Mercury’s mass and radius. The fraction of the moment that corresponds to the outer librating shell, which can be used to estimate the size of the core, is C m /C = 0.431 AE 0.025. Citation: Margot, J.-L., S. J. Peale, S. C. Solomon, S. A. Hauck II, F. D. Ghigo, R. F. Jurgens, M. Yseboodt, J. D. Giorgini, S. Padovan, and D. B. Campbell (2012), Mercury’s moment of inertia from spin and gravity data, J. Geophys. Res., 117, E00L09, doi:10.1029/2012JE004161. 1. Introduction [ 2 ] Bulk mass density r = M/V is the primary indicator of the interior composition of a planetary body of mass M and volume V. To quantify the structure of the interior, the most useful quantity is the polar moment of inertia Z r ð x; y; z Þ x 2 þ y 2 dV : C ¼ V In this volume integral expressed in a cartesian coordinate system with principal axes {x, y, z}, the local density is multiplied by the square of the distance to the axis of rotation, which is assumed to be aligned with the z axis. Moments of Department of Earth and Space Sciences, University of California, Los Angeles, California, USA. Department of Physics and Astronomy, University of California, Los Angeles, California, USA. Department of Physics, University of California, Santa Barbara, California, USA. Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, D. C., USA. Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, USA. Department of Earth, Environmental, and Planetary Sciences, Case Western Reserve University, Cleveland, Ohio, USA. National Radio Astronomy Laboratory, Green Bank, West Virginia, USA. Jet Propulsion Laboratory, Pasadena, California, USA. Royal Observatory of Belgium, Uccle, Belgium. Department of Astronomy, Cornell University, Ithaca, New York, USA. Corresponding author: J.-L. Margot, Department of Earth and Space Sciences, University of California, 595 Charles Young Dr. E., Los Angeles, CA 90095, USA. ( jlm@ess.ucla.edu) ©2012. American Geophysical Union. All Rights Reserved. 0148-0227/12/2012JE004161 inertia computed about the equatorial axes x and y are denoted by A and B, with A < B < C. The moment of inertia (MoI) of a sphere of uniform density and radius R is 0.4 MR 2 . Earth’s polar MoI value is 0.3307 MR 2 [Yoder, 1995], indicating a concentration of denser material toward the center, which is recognized on the basis of seismological and geochemical evidence to be a primarily iron-nickel core extending $55% of the planetary radius. The value for Mars is 0.3644 MR 2 , suggesting a core radius of $50% of the planetary radius [Konopliv et al., 2011]. The value for Venus has never been measured. Here we describe our determina- tion of the MoI of Mercury and that of its outer rigid shell (C m ), both of which can be used to constrain models of the interior [Hauck et al., 2007; Riner et al., 2008; Rivoldini et al., 2009]. [ 3 ] Both the Earth and Mars polar MoI values were secured by combining measurements of the precession of the spin axis due to external torques (Sun and/or Moon), which depends on [C A (A + B)/2]/C, and of the second-degree harmonic coefficient of the gravity field C 20 = A [C A (A + B)/2]/(MR 2 ). Although this technique is not applicable at Mercury, Peale [1976] proposed an ingenious procedure to estimate the MoI of Mercury and that of its core based on only four quantities. The two quantities related to the gravity field, C 20 and C 22 = (B A A)/(4MR 2 ), have been determined to better than 1% precision by tracking of the MESSENGER spacecraft [Smith et al., 2012]. The two quantities related to the spin state are the obliquity q (tilt of the spin axis with respect to the orbit normal) and amplitude of forced libration in longitude g (small oscillation in the orientation of the long axis of Mercury relative to uniform spin). They have been measured by Earth-based radar observations at 18 epochs between 2002 and 2006. These data provided strong obser- vational evidence that the core of Mercury is molten, and that E00L09 1 of 11

The Stability of the Point-Spread Function of the Advanced Camera for Surveys on the Hubble Space Telescope and Implications for Weak Gravitational Lensing*

Abstract: (abridged) We examine the spatial and temporal stability of the HST ACS Wide Field Camera (WFC) point spread function (PSF) using the two square degree COSMOS survey We show that stochastic aliasing of the PSF necessarily occurs during `drizzling' This aliasing is maximal if the output pixel scale is equal to the input pixel scale of 005'' We show that this source of PSF variation can be significantly reduced by choosing a Gaussian drizzle kernel and by setting the output pixel size to 003'' We show that the PSF is temporally unstable, most likely due to thermal fluctuations in the telescope's focus We find that the primary manifestation of this thermal drift in COSMOS images is an overall slow periodic focus change Using a modified version of TinyTim, we create undistorted stars in a 30x30 grid across the ACS WFC CCDs These PSF models are created for telescope focus values in the range -10 microns to +5 microns, thus spanning the allowed range of telescope focus values We then use the approximately ten well measured stars in each COSMOS field to pick the best-fit focus value for each field The TinyTim model stars are then used to perform PSF corrections for weak lensing allowing systematics due to incorrectly modeled PSFs to be greatly reduced We have made the software for PSF modeling using our modified version of TinyTim available to the astronomical community We show the effects of Charge Transfer Efficiency (CTE) degradation, which distorts the object in the readout direction, mimicking a weak lensing signal We derive a parametric correction for the effect of CTE on the shapes of objects in the COSMOS field as a function of observation date, position within the ACS WFC field, and object flux

SBMLToolbox: an SBML toolbox for MATLAB users

Abstract: Summary: We present SBMLToolbox, a toolbox that facilitates importing and exporting models represented in the Systems Biology Markup Language (SBML) in and out of the MATLAB environment and provides functionality that enables an experienced user of either SBML or MATLAB to combine the computing power of MATLAB with the portability and exchangeability of an SBML model. SBMLToolbox supports all levels and versions of SBML. Availability: SBMLToolbox is freely available from http://sbml.org/software/sbmltoolbox Contact: s.m.keating@herts.ac.uk

Updated Smithsonian Astrophysical Observatory Ozone Monitoring Instrument (SAO OMI) formaldehyde retrieval

Abstract: We present and discuss the Smithsonian Astrophysical Observatory (SAO) formaldehyde (H2CO) retrieval algorithm for the Ozone Monitoring Instrument (OMI) which is the operational retrieval for NASA OMI H2CO The version of the algorithm described here includes relevant changes with respect to the operational one, including differences in the reference spectra for H2CO, the fit of O2–O2 collisional complex, updates in the high-resolution solar reference spectrum, the use of a model reference sector over the remote Pacific Ocean to normalize the retrievals, an updated air mass factor (AMF) calculation scheme, and the inclusion of scattering weights and vertical H2CO profile in the level 2 products The setup of the retrieval is discussed in detail We compare the results of the updated retrieval with the results from the previous SAO H2CO retrieval The improvement in the slant column fit increases the temporal stability of the retrieval and slightly reduces the noise The change in the AMF calculation has increased the AMFs by 20%, mainly due to the consideration of the radiative cloud fraction Typical values for retrieved vertical columns are between 4 × 1015 and 4 × 1016 molecules cm−2, with typical fitting uncertainties ranging between 45 and 100% In high-concentration regions the errors are usually reduced to 30% The detection limit is estimated at 1 × 1016 molecules cm−2

Circumstellar Disk Candidates Identified in NGC 2264

Abstract: We present an optical and near-infrared study of a 45' × 45' field in NGC 2264, which includes both S Mon and the Cone Nebula. We report photometry at optical (UBVRCIC) and near-infrared (JHK) wavelengths for ~5600 stars and spectroscopic classifications for ~400 of these stars. We identify circumstellar disk candidates using three techniques: excess ultraviolet (U-V) emission, excess near-IR (I-K and H-K) emission, and Hα emission-line equivalent widths for those stars with spectra. We find generally good correlation between disk indicators thought to originate from different physical processes. We find little if any evolution of disk fraction with stellar age or mass. However, when we derive mass accretion rates () from the excess emission at U, we find that decreases with age over the age range spanned by our data, ~0.1–5 Myr, and increases with mass over the range ~0.25–1 M⊙. These findings are comparable to results found previously by us in the Orion Nebula cluster flanking fields.