284 research outputs found
The precipitation of energetic heavy ions into the upper atmosphere of Jupiter
Evidence for auroral particle precipitation at Jupiter was provided by the ultraviolet spectrometers onboard the Voyagers 1 and 2 spacecraft and by the International Ultraviolet Explorer (IUE). Magnetospheric measurements made by instruments onboard the Voyager spacecraft show that energetic sulfur and oxygen ions are precipitating into the upper atmosphere of Jupiter. A theoretical model has been constructed describing the interaction of precipitating oxygen with the Jovian atmosphere. The auroral energy is deposited in the atmosphere by means of ionization, excitation, and dissociation and heating of the atmospheric gas. Energetic ion and electron precipitation are shown to have similar effects on the atmosphere and ionosphere of Jupiter
Gas-grain energy transfer in solar nebula shock waves: Implications for the origin of chondrules
Meteoritic chondrules provide evidence for the occurrence of rapid transient heating events in the protoplanetary nebula. Astronomical evidence suggests that gas dynamic shock waves are likely to be excited in protostellar accretion disks by processes such as protosolar mass ejections, nonaxisymmetric structures in an evolving disk, and impact on the nebula surface of infalling 'clumps' of circumstellar gas. Previous detailed calculations of gas-grain energy and momentum transfer have supported the possibility that such shock waves could have melted pre-existing chondrule-sized grains. The main requirement for grains to reach melting temperatures in shock waves with plausibly low Mach numbers is that grains existed in dust-rich zones (optical depth greater than 1) where radiative cooling of a given grain can be nearly balanced by radiation from surrounding grains. Localized dust-rich zones also provide a means of explaining the apparent small spatial scale of heating events. For example, the scale size of at least some optically thick dust-rich zones must have been relatively small (less than 10 kilometers) to be consistent with petrologic evidence for accretion of hot material onto cold chondrules. The implied number density of mm-sized grains for these zones would be greater than 30 m(exp -3). In this paper, we make several improvements of our earlier calculations to include radiation self-consistently in the shock jump conditions, and we include heating of grains due to radiation from the shocked gas. In addition, we estimate the importance of momentum feedback of dust concentrations onto the shocked gas which would tend to reduce the efficiency of gas dynamic heating of grains in the center of the dust cloud
Solar Wind Electron Interaction with the Dayside Lunar Surface and Crustal Magnetic Fields: Evidence for Precursor Effects
Electron distributions measured by Lunar Prospector above the dayside lunar surface in the solar wind often have an energy dependent loss cone, inconsistent with adiabatic magnetic reflection. Energy dependent reflection suggests the presence of downward parallel electric fields below the spacecraft, possibly indicating the presence of a standing electrostatic structure. Many electron distributions contain apparent low energy (<100 eV) upwardgoing conics (58% of the time) and beams (12% of the time), primarily in regions with non-zero crustal magnetic fields, implying the presence of parallel electric fields and/or wave-particle interactions below the spacecraft. Some, but not all, of the observed energy dependence comes from the energy gained during reflection from a moving obstacle; correctly characterizing electron reflection requires the use of the proper reference frame. Nonadiabatic reflection may also play a role, but cannot fully explain observations. In cases with upward-going beams, we observe partial isotropization of incoming solar wind electrons, possibly indicating streaming and/or whistler instabilities. The Moon may therefore influence solar wind plasma well upstream from its surface. Magnetic anomaly interactions and/or non-monotonic near surface potentials provide the most likely candidates to produce the observed precursor effects, which may help ensure quasi-neutrality upstream from the Moon
Interplanetary and Interstellar Dust Observed by the Wind/WAVES Electric Field Instrument
Observations of hypervelocity dust particles impacting the Wind spacecraft are reported here for the first time using data from the WindWAVES electric field instrument. A unique combination of rotating spacecraft, amplitude-triggered high-cadence waveform collection, and electric field antenna configuration allow the first direct determination of dust impact direction by any spacecraft using electric field data. Dust flux and impact direction data indicate that the observed dust is approximately micron-sized with both interplanetary and interstellar populations. Nanometer radius dust is not detected by Wind during times when nanometer dust is observed on the STEREO spacecraft and both spacecraft are in close proximity. Determined impact directions suggest that interplanetary dust detected by electric field instruments at 1 AU is dominated by particles on bound trajectories crossing Earths orbit, rather than dust with hyperbolic orbits
Chandra's Close Encounter with the Disintegrating Comets 73P/2006 (Schwassmann--Wachmann--3) Fragment B and C/1999 S4 (LINEAR)
On May 23, 2006 we used the ACIS-S instrument on the Chandra X-ray
Observatory (CXO) to study the X-ray emission from the B fragment of comet
73P/2006 (Schwassmann-Wachmann 3) (73P/B). We obtained a total of 20 ks of CXO
observation time of Fragment B, and also investigated contemporaneous ACE and
SOHO solar wind physical data. The CXO data allow us to spatially resolve the
detailed structure of the interaction zone between the solar wind and the
fragment's coma at a resolution of ~ 1,000 km, and to observe the X-ray
emission due to multiple comet--like bodies. We detect a change in the spectral
signature with the ratio of the CV/OVII line increasing with increasing
collisional opacity as predicted by Bodewits \e (2007). The line fluxes arise
from a combination of solar wind speed, the species that populate the wind and
the gas density of the comet. We are able to understand some of the observed
X-ray morphology in terms of non-gravitational forces that act upon an actively
outgassing comet's debris field. We have used the results of the Chandra
observations on the highly fragmented 73P/B debris field to re-analyze and
interpret the mysterious emission seen from comet C/1999 S4 (LINEAR) on August
1st, 2000, after the comet had completely disrupted. We find the physical
situations to be similar in both cases, with extended X-ray emission due to
multiple, small outgassing bodies in the field of view. Nevertheless, the two
comets interacted with completely different solar winds, resulting in
distinctly different spectra.Comment: accepted by ApJ, 44 Pages, including 4 tables and 14 figure
Collisional Evolution of Irregular Satellite Swarms: Detectable Dust around Solar System and Extrasolar Planets
Since the 1980's it has been becoming increasingly clear that the Solar
System's irregular satellites are collisionally evolved. We derive a general
model for the collisional evolution of an irregular satellite swarm and apply
it to the Solar System and extrasolar planets. Our model reproduces the Solar
System's complement of observed irregulars well, and suggests that the
competition between grain-grain collisions and Poynting-Robertson (PR) drag
helps set the fate of the dust. Because swarm collision rates decrease over
time the main dust sink can change with time, and may help unravel the
accretion history of synchronously rotating regular satellites that show
brightness asymmetries. Some level of dust must be present on AU scales around
the Solar System's giant planets, which we predict may be at detectable levels.
We also predict whether dust produced by extrasolar circumplanetary swarms can
be detected. The coronagraphic instruments on JWST will have the ability to
detect the dust generated by these swarms, which are most detectable around
planets that orbit at tens of AU from the youngest stars. Because the
collisional decay of swarms is relatively insensitive to planet mass, swarms
can be much brighter than their host planets and allow discovery of
Neptune-mass planets that would otherwise remain invisible. This dust may have
already been detected. The observations of the planet Fomalhaut b can be
explained as scattered light from dust produced by the collisional decay of an
irregular satellite swarm around a 10 Earth-mass planet. Such a swarm comprises
about 5 Lunar masses worth of irregular satellites. Finally, we consider what
happens if Fomalhaut b passes through Fomalhaut's main debris ring, which
allows the circumplanetary swarm to be replenished through collisions with ring
planetesimals. (abridged)Comment: accepted to MNRA
LADEE Science Results and Implications for Exploration
NASA's Lunar Atmosphere and Dust Environment Explorer, LADEE, concluded a fully successful investigation of the Moon's tenuous gas and dust atmosphere on April 18, 2014. LADEE hosted three science instruments to address atmospheric and dust objectives, and a technology demonstration of deep-space optical communication. The three science instruments were an ultraviolet-visible spectrometer (UVS), a neutral mass spectrometer (NMS), and a lunar dust experiment (LDEX). All data acquired by these instruments have been submitted to the Planetary Data System. A mission overview and science instrument descriptions are readily available. LADEE inserted into a low-altitude, retrograde lunar orbit optimized for observations at the sunrise terminator, where surface temperatures rise abruptly. LADEE also carried out observations over a wide range of local times and altitudes. Here we describe some of the initial results
Overview of the New Horizons Science Payload
The New Horizons mission was launched on 2006 January 19, and the spacecraft
is heading for a flyby encounter with the Pluto system in the summer of 2015.
The challenges associated with sending a spacecraft to Pluto in less than 10
years and performing an ambitious suite of scientific investigations at such
large heliocentric distances (> 32 AU) are formidable and required the
development of lightweight, low power, and highly sensitive instruments. This
paper provides an overview of the New Horizons science payload, which is
comprised of seven instruments. Alice provides spatially resolved ultraviolet
spectroscopy. The Ralph instrument has two components: the Multicolor Visible
Imaging Camera (MVIC), which performs panchromatic and color imaging, and the
Linear Etalon Imaging Spectral Array (LEISA), which provides near-infrared
spectroscopic mapping capabilities. The Radio Experiment (REX) is a component
of the New Horizons telecommunications system that provides both occultation
and radiometry capabilities. The Long Range Reconnaissance Imager (LORRI)
provides high sensitivity, high spatial resolution optical imaging
capabilities. The Solar Wind at Pluto (SWAP) instrument measures the density
and speed of solar wind particles. The Pluto Energetic Particle Spectrometer
Science Investigation (PEPSSI) measures energetic protons and CNO ions. The
Venetia Burney Student Dust Counter (VB-SDC) is used to record dust particle
impacts during the cruise phases of the mission.Comment: 17 pages, 4 figures, 1 table; To appear in a special volume of Space
Science Reviews on the New Horizons missio
Using Dust Shed from Asteroids as Microsamples to Link Remote Measurements with Meteorite Classes
Given the diversity of asteroids, it is impossible to consider returning samples from each one Dust particles are abundant around asteroids Primary minerals and organic materials can be measured by in situ dust detectorinstruments These particles can be used to classify the parent body as an ordinary chondrite,basaltic achondrite, or other class of meteorite Such instruments could provide direct links to known meteorite groups withoutreturning the samples to terrestrial laboratorie
Toxicity of lunar dust
The formation, composition and physical properties of lunar dust are
incompletely characterised with regard to human health. While the physical and
chemical determinants of dust toxicity for materials such as asbestos, quartz,
volcanic ashes and urban particulate matter have been the focus of substantial
research efforts, lunar dust properties, and therefore lunar dust toxicity may
differ substantially. In this contribution, past and ongoing work on dust
toxicity is reviewed, and major knowledge gaps that prevent an accurate
assessment of lunar dust toxicity are identified. Finally, a range of studies
using ground-based, low-gravity, and in situ measurements is recommended to
address the identified knowledge gaps. Because none of the curated lunar
samples exist in a pristine state that preserves the surface reactive chemical
aspects thought to be present on the lunar surface, studies using this material
carry with them considerable uncertainty in terms of fidelity. As a
consequence, in situ data on lunar dust properties will be required to provide
ground truth for ground-based studies quantifying the toxicity of dust exposure
and the associated health risks during future manned lunar missions.Comment: 62 pages, 9 figures, 2 tables, accepted for publication in Planetary
and Space Scienc
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