A variety of new technologies, ranging from broad enabling technologies to specific weapon systems, may threaten or enhance strategic stability. In this essay, I analyze a technology’s potential to ...significantly affect stability along three axes: the pace of advances in, and diffusion of, this technology; the technology’s implications for deterrence and defense; and the technology’s potential for direct impact on crisis decisionmaking. I apply this framework to examples including hypersonic weapons, antisatellite weapons, artificial intelligence, and persistent overhead monitoring. Formal arms control to contain dangers posed by some of these seems technically possible, though currently politically difficult to achieve. Others, particularly enabling technologies, resist arms control based on effective verification. The major powers will therefore instead have to find other ways to cope with these technologies and their implications. These options should include exchanges with potential adversaries so that pathways to nuclear escalation, and possible mitigating steps, can be identified and discussed.
Induced electrical currents within Europa inferred from
Galileo spacecraft magnetometer instrument data have been interpreted as due to a salty europan ocean. Published compositional models for ...Europa's ocean, based on aqueous leaching of carbonaceous chondrites, range over five orders of magnitude in predicted magnesium sulfate concentrations. We combine the
Galileo spacecraft magnetometer-derived oceanic conductivities and radio Doppler data-derived interior models with laboratory conductivity vs concentration data for both magnesium sulfate solutions and terrestrial seawater to determine empirically the range of salt concentrations permitted for Europa's ocean. Solutions for both a three-layer spherical model, and a five-layer half-space model, that satisfy current preferred best fits to magnetometer data imply high, near-saturation salt concentrations and require a europan ice shell of less than 15 km thick, with a best fit at 4 km ice thickness. Adding a conductive core and mantle has a negligible effect on the amplitude when ocean conductivities are greater than a few Siemens per meter. Similarly, we find that including a realistic ionosphere has a negligible effect. We examine the implications of these results for the subsurface habitability of Europa.
Abstract
Two forms of ohmic heating of astrophysical secondaries have received particular attention: unipolar-generator heating with currents running between the primary and secondary, and magnetic ...induction heating due to the primary’s time-varying field. Neither appears to cause significant dissipation in the contemporary solar system. But these discussions have overlooked heating derived from the spatial variation of the primary’s field across the interior of the secondary. This leads to Lorentz-force-driven currents around paths entirely internal to the secondary, with resulting ohmic heating. We examine three ways to drive such currents, by the cross product of (1) the secondary’s azimuthal orbital velocity with the nonaxially symmetric field of the primary, (2) the radial velocity (due to nonzero eccentricity) of the secondary with the primary’s field, or (3) the out-of-plane velocity (due to nonzero inclination) with the primary’s field. The first of these operates even for a spin-locked secondary whose orbit has zero eccentricity, in strong contrast to tidal dissipation. We show that Jupiter’s moon Io today could dissipate about 600 GW (more than likely current radiogenic heating) in the outer 100 m of its metallic core by this mechanism. Had Io ever been at 3 Jovian radii instead of its current 5.9, it could have been dissipating 15,000 GW. Ohmic dissipation provides a mechanism that could operate in any solar system to drive inward migration of secondaries that then necessarily comes to a halt upon reaching a sufficiently close distance to the primary.
Chyba and Phillips examine Europa's suitability for life and consider candidate ecosystems that seem plausible in light of current knowledge. Life detection experiments that could then be conducted ...with a spacecraft lander are also discussed.
Create a COVID-19 commission Chyba, Christopher F; Cassel, Christine K; Graham, Susan L ...
Science (American Association for the Advancement of Science),
2021-Nov-19, 2021-11-19, 20211119, Letnik:
374, Številka:
6570
Journal Article
Recenzirano
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We need a definitive public reference for the history of events.
Abstract
Thermochemical modeling and shock-tube experiments show that shocks applied to N
2
/CH
4
gas mixtures can synthesize organic molecules. Sufficiently large, hypersonic meteoroids entering the ...atmosphere of Saturn’s moon Titan should therefore drive organic chemistry. To do so meteoroids must be sufficiently large compared to the atmospheric mean free path at a given altitude to generate shocks, and deposit enough energy per path length to produce temperatures high enough to excite and dissociate the relevant molecules. The Cassini spacecraft imaged multiple meteoroid impacts on Saturn’s rings, allowing for the first time an empirical estimate to be made of the flux and size–frequency distributions of meteoroids in the millimeter-to-meter size range. We combine these results with an atmospheric entry model and thermochemical and experimental shock production efficiencies for N
2
/CH
4
atmospheres and calculate the shock production rates for HCN, C
2
H
2
, and C
2
H
4
as well as the resulting H
2
generation. We find that meteoroids may be producing these molecules at as much as ∼1% the production rate of photochemistry driven by UV photons, and may be depositing more energy than magnetospheric ions and 90–100 nm UV photons. Moreover, these meteoroids produce these organic molecules hundreds of kilometers lower in Titan’s atmosphere than the relevant UV photons and magnetospheric ions penetrate, with peak production occurring between 200 and 500 km altitudes, i.e., at the observed haze layer. Meteoroid-driven shock generation of molecules may therefore be crucial to understanding Titan’s atmospheric chemistry.
Europa is a prime target for astrobiology. The presence of a global subsurface liquid water ocean and a composition likely to contain a suite of biogenic elements make it a compelling world in the ...search for a second origin of life. Critical to these factors, however, may be the availability of energy for biological processes on Europa. We have examined the production and availability of oxidants and carbon-containing reductants on Europa to better understand the habitability of the subsurface ocean. Data from the Galileo Near-Infrared Mapping Spectrometer were used to constrain the surface abundance of CO(2) to 0.036% by number relative to water. Laboratory results indicate that radiolytically processed CO(2)-rich ices yield CO and H(2)CO(3); the reductants H(2)CO, CH(3)OH, and CH(4) are at most minor species. We analyzed chemical sources and sinks and concluded that the radiolytically processed surface of Europa could serve to maintain an oxidized ocean even if the surface oxidants (O(2), H(2)O(2), CO(2), SO(2), and SO(4) (2)) are delivered only once every approximately 0.5 Gyr. If delivery periods are comparable to the observed surface age (30-70 Myr), then Europa's ocean could reach O(2) concentrations comparable to those found in terrestrial surface waters, even if approximately 10(9) moles yr(1) of hydrothermally delivered reductants consume most of the oxidant flux. Such an ocean would be energetically hospitable for terrestrial marine macrofauna. The availability of reductants could be the limiting factor for biologically useful chemical energy on Europa.
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