604 research outputs found
Revisiting the cosmic-ray induced Venusian radiation dose in the context of habitability
The Atmospheric Radiation Interaction Simulator (AtRIS) was used to model the
altitude-dependent Venusian absorbed dose and the Venusian dose equivalent. For
the first time, we modeled the dose rates for different shape-, size-, and
composition-mimicking detectors (phantoms): a CO-based phantom, a
water-based microbial cell, and a phantom mimicking human tissue. Based on a
new model approach, we give a reliable estimate of the altitude-dependent
Venusian radiation dose in water-based microorganisms here for the first time.
These microorganisms are representative of known terrestrial life. We also
present a detailed analysis of the influence of the strongest ground-level
enhancements measured at the Earth's surface, and of the impact of two historic
extreme solar events on the Venusian radiation dose. Our study shows that
because a phantom based on Venusian air was used, and because furthermore, the
quality factors of different radiation types were not taken into account,
previous model efforts have underestimated the radiation hazard for any
putative Venusian cloud-based life by up to a factor of five. However, because
we furthermore show that even the strongest events would not have had a
hazardous effect on putative microorganisms within the potentially habitable
zone (51 km - 62 km), these differences may play only a minor role
Detection of HCN and diverse redox chemistry in the plume of Enceladus
The Cassini spacecraft observed that Saturn's moon Enceladus possesses a
series of jets erupting from its South Polar Terrain. Previous studies of in
situ data collected by Cassini's Ion and Neutral Mass Spectrometer (INMS) have
identified HO, CO, CH, NH, and H within the plume of
ejected material. Identification of minor species in the plume remains an
ongoing challenge, owing to the large number of possible combinations that can
be used to fit the INMS data. Here, we present the detection of several new
compounds of strong importance to the habitability of Enceladus, including HCN,
CH, CH, and CH. Our analyses of the low velocity INMS
data, coupled with our detailed statistical framework, enable discrimination
between previously ambiguous species in the plume by alleviating the effects of
high dimensional model fitting. Together with plausible mineralogical catalysts
and redox gradients derived from surface radiolysis, these compounds could
potentially support extant microbial communities or drive complex organic
synthesis leading to the origin of life.Comment: revised manuscrip
Modified two-potential approach to tunneling problems
One-body quantum tunneling to continuum is treated via the two-potential
approach, dividing the tunneling potential into external and internal parts. We
show that corrections to this approach can be minimized by taking the
separation radius inside the interval determined by simple expressions. The
resulting two-potential approach reproduces the resonance energy and its width,
both for narrow and wide resonances. We also demonstrate that, without losing
its accuracy, the two-potential approach can be modified to a form resembling
the R-matrix theory, yet without any uncertainties of the latter related to the
choice of the matching radius.Comment: 7 two-column pages, 3 figures, extra-explanation added, Phys. Rev. A,
in pres
In search of subsurface oceans within the Uranian moons
The Galileo mission to Jupiter discovered magnetic signatures associated with hidden sub-surface oceans at the moons Europa and Callisto using the phenomenon of magnetic induction. These induced magnetic fields originate from electrically conductive layers within the moons and are driven by Jupiter’s strong time-varying magnetic field. The ice giants and their moons are also ideal laboratories for magnetic induction studies. Both Uranus and Neptune have a strongly tilted magnetic axis with respect to their spin axis, creating a dynamic and strongly variable magnetic field environment at the orbits of their major moons. Although Voyager-2 visited the ice giants in the 1980s, it did not pass close enough to any of the moons to detect magnetic induction signatures. However, Voyager-2 revealed that some of these moons exhibit surface features that hint at recent geologically activity, possibly associated with sub-surface oceans. Future missions to the ice giants may therefore be capable of discovering sub-surface oceans, thereby adding to the family of known “ocean worlds” in our solar system. Here, we assess magnetic induction as a technique for investigating sub-surface oceans within the major moons of Uranus. Furthermore, we establish the ability to distinguish induction responses created by different interior characteristics that tie into the induction response: ocean thickness, conductivity, and depth, and ionospheric conductance. The results reported here demonstrate the possibility of single-pass ocean detection and constrained characterization within the moons of Miranda, Ariel, and Umbriel, and provide guidance for magnetometer selection and trajectory design for future missions to Uranus
Detection of negative pickup ions at Saturn's moon Dione
We investigate a possible negative ion feature observed by the Cassini Plasma Spectrometer (CAPS) during a flyby of Saturn's moon Dione that occurred on April 7, 2010. By examining possible particle trajectories, we find that the observed particles are consistent with negative pick‐up ions originating near the moon's surface. We find that the mass of the negative pick‐up ions is in the range of 15 – 25 u and tentatively identify this species as O‐, likely resulting from ionization and subsequent pick‐up from Dione's O2‐CO2 exosphere. Our estimates show that the negative ion density is ~3 x 10‐3 cm‐3. This is comparable to, but slightly smaller than, that previously reported for the density of O2+ pick‐up ions for the same flyby, indicating that negative pick‐up ions may represent a major loss channel for Dione's exosphere
Radiation Tolerance of Low-Cost Magnetometer for Space Applications
Knowing the three-dimensional magnetic field configuration and dynamics in space environments is key to understand the physical processes taking place. Plasma dynamics depend on the local orientation of the magnetic field, and key quantities such as pitch angle and dynamical processes such as waves and reconnection cannot be studied without in-situ measurements of the fields. For this reason, magnetometers are one of the most important instruments for space physics-focused missions. This is true both for spacecraft and also for landed missions, particularly on atmosphere-less bodies, where the space environment interacts directly with the surface. To enable the next generation of small spacecraft and landers, sensors need to be low-cost and withstand the harsh radiation environment present in space. Here we present the latest advances in the characterization of a commercial-off-the-shelf three-dimensional magnetometer,summarizing previous and newresults from radiation tests. The sensor shows tolerance up to a total ionization dose (TID) of 300 krad, levels well beyond those typical for a low-Earth orbit mission, and compliant with those expected during a landed mission on the Jovian moon Europa
- …