4,479 research outputs found
Occultation Light Curves of Io's Hot Spots in 2014
We present ground-based observations of Io during Spring 2014, contributing to decadal timelines of individual hot spots' volcanic activity
Potential for Solar System Science with the ngVLA
Radio wavelength observations of solar system bodies are a powerful method of
probing many characteristics of those bodies. From surface and subsurface, to
atmospheres (including deep atmospheres of the giant planets), to rings, to the
magnetosphere of Jupiter, these observations provide unique information on
current state, and sometimes history, of the bodies. The ngVLA will enable the
highest sensitivity and resolution observations of this kind, with the
potential to revolutionize our understanding of some of these bodies. In this
article, we present a review of state-of-the-art radio wavelength observations
of a variety of bodies in our solar system, varying in size from ring particles
and small near-Earth asteroids to the giant planets. Throughout the review we
mention improvements for each body (or class of bodies) to be expected with the
ngVLA. A simulation of a Neptune-sized object is presented in Section 6.
Section 7 provides a brief summary for each type of object, together with the
type of measurements needed for all objects throughout the Solar System
Heavy particle concentration in turbulence at dissipative and inertial scales
Spatial distributions of heavy particles suspended in an incompressible
isotropic and homogeneous turbulent flow are investigated by means of high
resolution direct numerical simulations. In the dissipative range, it is shown
that particles form fractal clusters with properties independent of the
Reynolds number. Clustering is there optimal when the particle response time is
of the order of the Kolmogorov time scale . In the inertial range,
the particle distribution is no longer scale-invariant. It is however shown
that deviations from uniformity depend on a rescaled contraction rate, which is
different from the local Stokes number given by dimensional analysis. Particle
distribution is characterized by voids spanning all scales of the turbulent
flow; their signature in the coarse-grained mass probability distribution is an
algebraic behavior at small densities.Comment: 4 RevTeX pgs + 4 color Figures included, 1 figure eliminated second
part of the paper completely revise
Superdiffusion of massive particles induced by multi-scale velocity fields
We study drag-induced diffusion of massive particles in scale-free velocity
fields, where superdiffusive behavior emerges due to the scale-free size
distribution of the vortices of the underlying velocity field. The results show
qualitative resemblance to what is observed in fluid systems, namely the
diffusive exponent for the mean square separation of pairs of particles and the
preferential concentration of the particles, both as a function of the response
time.Comment: 5 pages, 5 figures. Accepted for publication in EP
Neptune at Summer Solstice: Zonal Mean Temperatures from Ground-Based Observations 2003-2007
Imaging and spectroscopy of Neptune's thermal infrared emission is used to
assess seasonal changes in Neptune's zonal mean temperatures between Voyager-2
observations (1989, heliocentric longitude Ls=236) and southern summer solstice
(2005, Ls=270). Our aim was to analyse imaging and spectroscopy from multiple
different sources using a single self-consistent radiative-transfer model to
assess the magnitude of seasonal variability. Globally-averaged stratospheric
temperatures measured from methane emission tend towards a quasi-isothermal
structure (158-164 K) above the 0.1-mbar level, and are found to be consistent
with spacecraft observations of AKARI. This remarkable consistency, despite
very different observing conditions, suggests that stratospheric temporal
variability, if present, is 5 K at 1 mbar and 3 K at 0.1 mbar during
this solstice period. Conversely, ethane emission is highly variable, with
abundance determinations varying by more than a factor of two. The retrieved
C2H6 abundances are extremely sensitive to the details of the T(p) derivation.
Stratospheric temperatures and ethane are found to be latitudinally uniform
away from the south pole (assuming a latitudinally-uniform distribution of
stratospheric methane). At low and midlatitudes, comparisons of synthetic
Voyager-era images with solstice-era observations suggest that tropospheric
zonal temperatures are unchanged since the Voyager 2 encounter, with cool
mid-latitudes and a warm equator and pole. A re-analysis of Voyager/IRIS 25-50
{\mu}m mapping of tropospheric temperatures and para-hydrogen disequilibrium
suggests a symmetric meridional circulation with cold air rising at
mid-latitudes (sub-equilibrium para-H2 conditions) and warm air sinking at the
equator and poles (super-equilibrium para-H2 conditions). The most significant
atmospheric changes are associated with the polar vortex (absent in 1989).Comment: 35 pages, 19 figures. Accepted for publication in Icaru
Simultaneous Observations of Comet C/2002 T7 (LINEAR) with the Berkeley-Illinois-Maryland Association and Owens Valley Radio Observatory Interferometers: HCN and CH_3OH
We present observations of HCN J = 1-0 and CH_3OH J(K_a, K_c) = 3(1, 3)-4(0, 4) A+ emission from comet C/2002 T7 (LINEAR) obtained simultaneously with the Owens Valley Radio Observatory (OVRO) and Berkeley-Illinois-Maryland Association (BIMA) millimeter interferometers. We combined the data from both arrays to increase the (u, v) sampling and signal to noise of the detected line emission. We also report the detection of CH_3OH J(K_a, K_c) = 8(0, 8)-7(1, 7) A^+ with OVRO data alone. Using a molecular excitation code that includes the effects of collisions with water and electrons, as well as pumping by the Solar infrared photons (for HCN alone), we find a production rate of HCN of 2.9 × 10^(26) s^(–1) and for CH_3OH of 2.2 × 10^(27) s^(–1). Compared to the adopted water production rate of 3 × 10^(29) s^(–1), this corresponds to an HCN/H_2O ratio of 0.1% and a CH_3OH/H_2O ratio of 0.7%. We critically assess the uncertainty of these values due to the noise (~10%), the uncertainties in the adopted comet model (~50%), and the uncertainties in the adopted collisional excitation rates (up to a factor of 2). Pumping by Solar infrared photons is found to be a minor effect for HCN, because our 15" synthesized beam is dominated by the region in the coma where collisions dominate. Since the uncertainties in the derived production rates are at least as large as one-third of the differences found between comets, we conclude that reliable collision rates and an accurate comet model are essential. Because the collisionally dominated region critically depends on the water production rate, using the same approximate method for different comets may introduce biases in the derived production rates. Multiline observations that directly constrain the molecular excitation provide much more reliable production rates
Triplicity and Physical Characteristics of Asteroid (216) Kleopatra
To take full advantage of the September 2008 opposition passage of the M-type
asteroid (216) Kleopatra, we have used near-infrared adaptive optics (AO)
imaging with the W.M. Keck II telescope to capture unprecedented high
resolution images of this unusual asteroid. Our AO observations with the W.M.
Keck II telescope, combined with Spitzer/IRS spectroscopic observations and
past stellar occultations, confirm the value of its IRAS radiometric radius of
67.5 km as well as its dog-bone shape suggested by earlier radar observations.
Our Keck AO observations revealed the presence of two small satellites in orbit
about Kleopatra (see Marchis et al., 2008). Accurate measurements of the
satellite orbits over a full month enabled us to determine the total mass of
the system to be 4.64+/-0.02 10^18 Kg. This translates into a bulk density of
3.6 +/-0.4 g/cm3, which implies a macroscopic porosity for Kleopatra of ~
30-50%, typical of a rubble-pile asteroid. From these physical characteristics
we measured its specific angular momentum, very close to that of a spinning
equilibrium dumbbell.Comment: 35 pages, 3 Tables, 9 Figures. In press to Icaru
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