22 research outputs found
Modeling Meteoroid Impacts on the Juno Spacecraft
Events which meet certain criteria from star-tracker images on board the Juno spacecraft have been proposed to be due to interplanetary dust particle impacts on its solar arrays. These events have been suggested to be caused by particles with diameters larger than 10 μm. Here, we compare the reported event rates to expected dust-impact rates using dynamical meteoroid models for the four most abundant meteoroid/dust populations in the inner solar system. We find that the dust-impact rates predicted by dynamical meteoroid models are not compatible with either the Juno observations in terms of the number of star-tracker events per day, or with the variations of dust flux on Juno's solar panels with time and position in the solar system. For example, the rate of star-tracker events on Juno's antisunward surfaces is the largest during a period in which Juno is expected to experience the peak impact fluxes on the opposite, sunward hemisphere. We also investigate the hypothesis of dust leaving the Martian Hill sphere originating either from the surface of Mars itself or from one of its moons. We do not find such a hypothetical source to be able to reproduce the star-tracker event-rate variations observed by Juno. We conclude that the star-tracker events observed by Juno are unlikely to be the result of instantaneous impacts from the zodiacal cloud.
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Probing Ganymede's atmosphere with HST Ly images in transit of Jupiter
We report results from far-ultraviolet observations by the Hubble Space
Telescope of Jupiter's largest moon Ganymede transiting across the planet's
dayside hemisphere. {Within} a targeted campaign on 9 September 2021 two
exposures were taken during one transit passage to probe for attenuation of
Jupiter's hydrogen Lyman- dayglow above the moon limb. The background
dayglow is slightly attenuated over an extended region around Ganymede, with
stronger attenuation in the second exposure when Ganymede was near the planet's
center. In the first exposure when the moon was closer to Jupiter's limb, the
effects from the Ganymede corona are hardly detectable, likely because the
Jovian Lyman- dayglow is spectrally broader and less intense at this
viewing geometry. The obtained vertical H column densities of around
~cm are consistent with previous results.
Constraining angular variability around Ganymede's disk, we derive an upper
limit on a local HO column density of ~cm, such
as could arise from outgassing plumes in regions near the observed moon limb
The Io, Europa and Ganymede auroral footprints at Jupiter in the ultraviolet: positions and equatorial lead angles
Jupiter's satellite auroral footprints are a consequence of the interaction
between the Jovian magnetic field with co-rotating iogenic plasma and the
Galilean moons. The disturbances created near the moons propagate as Alfv\'en
waves along the magnetic field lines. The position of the moons is therefore
"Alfv\'enically" connected to their respective auroral footprint. The angular
separation from the instantaneous magnetic footprint can be estimated by the
so-called lead angle. That lead angle varies periodically as a function of
orbital longitude, since the time for the Alfv\'en waves to reach the Jovian
ionosphere varies accordingly. Using spectral images of the Main Alfv\'en Wing
auroral spots collected by Juno-UVS during the first forty-three orbits, this
work provides the first empirical model of the Io, Europa and Ganymede
equatorial lead angles for the northern and southern hemispheres. Alfv\'en
travel times between the three innermost Galilean moons to Jupiter's northern
and southern hemispheres are estimated from the lead angle measurements. We
also demonstrate the accuracy of the mapping from the Juno magnetic field
reference model (JRM33) at the completion of the prime mission for M-shells
extending to at least 15RJ . Finally, we shows how the added knowledge of the
lead angle can improve the interpretation of the moon-induced decametric
emissions.Comment: 20 pages, 8 figures, Accepted for publication in Journal of
Geophysical Research: Space Physics on 20 April 202
The case for studying other planetary magnetospheres and atmospheres in Heliophysics
Heliophysics is the field that "studies the nature of the Sun, and how it
influences the very nature of space - and, in turn, the atmospheres of
planetary bodies and the technology that exists there." However, NASA's
Heliophysics Division tends to limit study of planetary magnetospheres and
atmospheres to only those of Earth. This leaves exploration and understanding
of space plasma physics at other worlds to the purview of the Planetary Science
and Astrophysics Divisions. This is detrimental to the study of space plasma
physics in general since, although some cross-divisional funding opportunities
do exist, vital elements of space plasma physics can be best addressed by
extending the expertise of Heliophysics scientists to other stellar and
planetary magnetospheres. However, the diverse worlds within the solar system
provide crucial environmental conditions that are not replicated at Earth but
can provide deep insight into fundamental space plasma physics processes.
Studying planetary systems with Heliophysics objectives, comprehensive
instrumentation, and new grant opportunities for analysis and modeling would
enable a novel understanding of fundamental and universal processes of space
plasma physics. As such, the Heliophysics community should be prepared to
consider, prioritize, and fund dedicated Heliophysics efforts to planetary
targets to specifically study space physics and aeronomy objectives
Synergies between interstellar dust and heliospheric science with an Interstellar Probe
We discuss the synergies between heliospheric and dust science, the open
science questions, the technological endeavors and programmatic aspects that
are important to maintain or develop in the decade to come. In particular, we
illustrate how we can use interstellar dust in the solar system as a tracer for
the (dynamic) heliosphere properties, and emphasize the fairly unexplored, but
potentially important science question of the role of cosmic dust in
heliospheric and astrospheric physics. We show that an Interstellar Probe
mission with a dedicated dust suite would bring unprecedented advances to
interstellar dust research, and can also contribute-through measuring dust - to
heliospheric science. This can, in particular, be done well if we work in
synergy with other missions inside the solar system, thereby using multiple
vantage points in space to measure the dust as it `rolls' into the heliosphere.
Such synergies between missions inside the solar system and far out are crucial
for disentangling the spatially and temporally varying dust flow. Finally, we
highlight the relevant instrumentation and its suitability for contributing to
finding answers to the research questions.Comment: 18 pages, 7 Figures, 5 Tables. Originally submitted as white paper
for the National Academies Decadal Survey for Solar and Space Physics
2024-203
Morphology of the Auroral Tail of Io, Europa, and Ganymede From JIRAM L-Band Imager
Jupiter hosts intense auroral activity associated with charged particles precipitating into the planet's atmosphere. The Galilean moons orbiting within the magnetosphere are swept by the magnetic field: the resulting perturbation travels along field lines as Alfven waves, which are able to accelerate electrons toward the planet, producing satellite-induced auroral emissions. These emissions due to the moons, known as footprints, can be detected in various wavelengths (UV, visible, IR) outside the main auroral emission as multiple bright spots followed by footprint tails. Since 2016 the Juno spacecraft orbiting Jupiter has surveyed the polar regions more than 30 times at close distances. Onboard the spacecraft, the Jovian InfraRed Auroral Mapper (JIRAM) is an imager and spectrometer with an L-band imaging filter suited to observe auroral features at unprecedented spatial resolution. JIRAM revealed a rich substructure in the footprint tails of Io, Europa, and Ganymede, which appear as a trail of quasi-regularly spaced bright sub-dots whose intensity fades away along the emission trail as the spatial separation from the footprint increases. The fine structure of the Europa and Ganymede footprint tails is reported in this work for the first time. We will also show that the typical distance between subsequent sub-dots is the same for all three moons at JIRAM resolution in both hemispheres. In addition, the sub-dots observed by JIRAM are static in a frame corotating with Jupiter. A feedback mechanism between the ionosphere and the magnetosphere is suggested as a potential candidate to explain the morphology of the footprint tails
Lunar Volatiles and Solar System Science
Understanding the origin and evolution of the lunar volatile system is not
only compelling lunar science, but also fundamental Solar System science. This
white paper (submitted to the US National Academies' Decadal Survey in
Planetary Science and Astrobiology 2023-2032) summarizes recent advances in our
understanding of lunar volatiles, identifies outstanding questions for the next
decade, and discusses key steps required to address these questions
Detecting meteoroid streams with an in-situ dust detector above an airless body
AbstractThe Lunar Dust Experiment (LDEX), aboard NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE) successfully mapped the dust density distribution over the lunar surface up to an altitude of ∼ 250 km. LDEX detected dust grains launched off the surface in ejecta plumes generated by impacts of cometary and asteroidal micrometeoroids striking the Moon. While on average LDEX detected particles at a rate of 1 min−1, periodically it measured bursts of particles at a rate exceeding the average value by up to two orders of magnitude. The timing and location of the most intense period of bursts is used here to independently determine the radiant for the Geminids meteoroid stream. The method is proposed to be of general interest to characterize meteoroid streams bombarding any of the airless bodies in the solar system using in-situ dust detectors
Analyzing LDEX's Current Measurements in Lunar Orbit
The Lunar Dust Experiment (LDEX) on board the Lunar Atmosphere and Dust Environment Explorer mission orbited the Moon from 2014 September to 2015 April and observed a dynamic, permanently present dust cloud produced by continual meteoroid bombardment. In addition to measuring individual ejecta with radii >0.3 μ m, LDEX also recorded an integrated current of the collective signal generated by the impacts of smaller ejecta particles. From this signal, we explore the potential for electrostatic dust lofting via twilight craters through correlation with changes in lunar topography. As the integrated current can contain numerous background contributions, we start by isolating regions of transient enhancements of this signal. A consistent lunar dayside enhancement is identified, with solar wind ions reflected as energetic neutral atoms shown to be a feasible source. We do not detect any enhanced integrated current correlated with the antihelion meteoroid bombardment or discernible enhancement due to electrostatic lofting via twilight craters, suggesting that electrostatic dust lofting does not contribute to the lunar dust environment at high altitudes (≫1 km)