Earth Location Research Articles

Stellar basins of gravitationally bound particles

A new physical phenomenon is identified: volumetric stellar emission into gravitationally bound orbits of weakly coupled particles such as axions, moduli, hidden photons, and neutrinos. While only a tiny fraction of the instantaneous luminosity of a star (the vast majority of the emission is into relativistic modes), the continual injection of these particles into a small part of phase space causes them to accumulate over astrophysically long time scales, forming what I call a "stellar basin", in analogy with the geologic kind. The energy density of the Solar basin will surpass that of the relativistic Solar flux at Earth's location after only a million years, for any sufficiently long-lived particle produced through an emission process whose matrix elements are unsuppressed at low momentum. This observation has immediate and striking consequences for direct detection experiments---including new limits on axion parameter space independent of dark matter assumptions---and may also increase the prospects for indirect detection of weakly interacting particles around compact stars.

The need of an ethics of planetary sustainability

AbstractThe concept of sustainability is widely acknowledged as a political guideline. Economic, ecological, social and cultural aspects of sustainability are already under discussion. Current space mining efforts demand that the discussion become a broader one about ‘planetary sustainability’, including the space surrounding Earth. To date, planetary sustainability has mainly been used with reference to Earth only and I will extend it here, elaborating on a similar NASA initiative. This article (1) sketches the contemporary economic–political initiatives which call for a special reflection of Earth's location in space, and then (2) discusses the meaning of the concept of sustainability in this context. Next, (3) I relate the discussion to the issue of planetary and environmental protection, before, (4) finally, presenting a philosophical and theological perspective that seems particularly able to broach the issue of the multiple dimensions of sustainability in this context. This is the concept of constructive-critical realism. My overview of the topic concludes with (5) a summarizing outlook.

Star Masses and Star-Planet Distances for Earth-like Habitability.

This paper presents statistical estimates for the location and duration of habitable zones (HZs) around stars of different mass. The approach is based upon the assumption that Earth's location, and the Sun's mass, should not be highly atypical of inhabited planets. The results support climate-model-based estimates for the location of the Sun's HZ except models giving a present-day outer-edge beyond 1.64 AU. The statistical approach also demonstrates that there is a habitability issue for stars smaller than 0.65 solar masses since, otherwise, Earth would be an extremely atypical inhabited world. It is difficult to remove this anomaly using the assumption that poor habitability of planets orbiting low-mass stars results from unfavorable radiation regimes either before, or after, their stars enter the main sequence. However, the anomaly is well explained if poor habitability results from tidal locking of planets in the HZs of small stars. The expected host-star mass for planets with intelligent life then has a 95% confidence range of 0.78 M⊙ < M < 1.04 M⊙, and the range for planets with at least simple life is 0.57 M⊙ < M < 1.64 M⊙. Key Words: Habitability—Habitable zone—Anthropic—Red dwarfs—Initial mass function. Astrobiology 17, 61–77.

Shock Propagation Model version 2 and its application in predicting the arrivals at Earth of interplanetary shocks during Solar Cycle 23

The Shock Propagation Model (SPM) based on an analytic solution of blast waves has been proposed to predict shock arrival times at Earth. Here to reduce the limitations of the SPM theoretical model in real applications and optimize its input parameters, a new version (called SPM2) is presented in order to enhance prediction performance. First, an empirical relationship is established to adjust the initial shock speed, which, as computed from the Type II burst drift rate, often contains observational uncertainties. Second, an additional acceleration/deceleration relation is added to the model to eliminate inherent prediction bias. Third, the propagation direction is derived in order to mitigate the isotropy limitation of blast wave theory in real predictions. Finally, an equivalent shock strength index at the Earth's location to judge whether or not an interplanetary shock will encounter the Earth is implemented in SPM2. The prediction results of SPM2 for 551 solar disturbance events of Solar Cycle 23 demonstrate that the success rate of SPM2 for both shock (W‐shock) and nonshock (W/O‐shock) events at Earth is ∼ 60%. The prediction error for the W‐shock events is less than 12 h (root‐mean‐square) and 10 h (mean‐absolute). Comparisons between the predicted results of SPM2 and those of Shock Time of Arrival (STOA), Interplanetary Shock Propagation (ISPM), and Hakamada‐Akasofu‐Fry version 2 (HAFv.2) based on similar data samples reveal that the SPM2 model offers generally equivalent prediction accuracy and reliability compared to the existing Fearless Forecast models (STOA, ISPM, and HAFv.2).

Direct detection of dark matter debris flows

Tidal stripping of dark matter from subhalos falling into the Milky Way produces narrow, cold tidal streams as well as more spatially extended ``debris flows'' in the form of shells, sheets, and plumes. Here we focus on the debris flow in the Via Lactea II simulation, and show that this incompletely phase-mixed material exhibits distinctive high velocity behavior. Unlike tidal streams, which may not necessarily intersect the Earth's location, debris flow is spatially uniform at 8 kpc and thus guaranteed to be present in the dark matter flux incident on direct detection experiments. At Earth-frame speeds greater than 450 km/s, debris flow comprises more than half of the dark matter at the Sun's location, and up to 80% at even higher speeds. Therefore, debris flow is most important for experiments that are particularly sensitive to the high speed tail of the dark matter distribution, such as searches for light or inelastic dark matter or experiments with directional sensitivity. We show that debris flow yields a distinctive recoil energy spectrum and a broadening of the distribution of incidence direction.

Dark matter direct detection signals inferred from a cosmological N-body simulation with baryons

We extract at redshift z = 0 a Milky Way sized object including gas, stars and dark matter (DM) from a recent, high-resolution cosmological N-body simulation with baryons. Its resolution is sufficient to witness the formation of a rotating disk and bulge at the center of the halo potential,therefore providing a realistic description of the birth and the evolution of galactic structures in the ΛCDM cosmology paradigm.The phase-space structure of the central galaxy reveals that, throughout a thick region, the dark halo is co-rotating on average with the stellar disk.At the Earth's location, the rotating component, sometimes called dark disk in the literature,is characterized by a minimum lag velocity vlag ≃ 75 km/s,in which case it contributes to around 25% of the total DM local density, whose value is ρDM ≃ 0.37GeV/cm3.The velocity distributions also show strong deviations from pure Gaussian and Maxwellian distributions, with a sharper drop of the high velocity tail.We give a detailed study of the impact of these features on the predictions for DM signals in direct detection experiments.In particular, the question of whether the modulation signal observed by DAMA is or is not excluded by limits set by otherexperiments (CDMS, XENON and CRESST…) is re-analyzed and compared to the case of a standard Maxwellian halo.We consider spin-independent interactions for both the elastic and the inelastic scattering scenarios.For the first time, we calculate the allowed regions for DAMA and the exclusion limits of other null experimentsdirectly from the velocity distributions found in the simulation. We then compare these results with the predictions of various analytical distributions.We find that the compatibility between DAMA and the other experiments is improved.In the elastic scenario, the DAMA modulation signal is slightly enhanced in the so-called channeling region,as a result of several effects that include a departure from a Maxwellian distribution and anisotropiesin the velocity dispersions due to the dark disk.For the inelastic scenario, the improvement of the fit is mainly attributable to the departure from a Maxwellian distribution at high velocity.It is correctly modeled by a generalized Maxwellian distribution with a parameter α ≃ 1.95, or by a Tsallis distributionwith q ≃ 0.75.

Bound on the dark matter density in the Solar System from planetary motions

High precision planet orbital data extracted from direct observation, spacecraft explorations, and laser ranging techniques enable to constrain the maximal dark matter density of a spherical halo centered around the Sun. If we assume a halo profile with a power-law dependence in the heliocentric distance, the maximal density at Earth's location is of the order ${10}^{5}\text{ }\text{ }\mathrm{GeV}/{\mathrm{cm}}^{3}$. Moreover, this value shows only a mild dependence on the slope of the halo profile, taken between 0 and $\ensuremath{-}2$. This bound competes with that obtained from the perihelion precession limits.

USE OF COSMIC RAY MEASUREMENTS TO IDENTIFY THE SECTOR POLARITIES OF THE INTERPLANETARY MAGNETIC FIELD

The knowledge of the interplanetary magnetic field sector polarity at the Earth's location is relevant to study many phenomena related to the Space Climatology. We filled the gaps in the daily polarities of the interplanetary magnetic field derived from spacecraft observations by using two sets of ground-based measurements: i) the cosmic ray muon component intensities supplied by the multidirectional Nagoya telescope; ii) the geomagnetic field from the Antarctic Vostok Observatory. We discuss the time variability of the sector polarities inferred from the wavelet technique in the period 1971–1992.

Interplanetary magnetic field polarities inferred from the north–south cosmic ray anisotropy

The interplanetary magnetic field sector polarity at the Earth's location can be inferred from ground measurements of the cosmic ray north‐south anisotropy. We present here the results of a systematic comparison between inferred and directly measured polarities in the period from January 1971 through December 1997. The overall success rate of the prediction method is 72%, in rather good agreement with previous findings. On the other hand, our analysis shows for the first time the limits of the method and calls for warning in its use. In fact, it turns out that the inferred polarities are affected by a bias, which becomes more relevant around the sunspot minimum. Even though the bias cannot be removed, it is possible to select conditions, occurring for 30% of the time, under which the inferred polarities are very reliable (the success rate being 95%).

Potential weakly interacting massive particle signature for the caustic ring halo model

Weakly interacting massive particle (WIMP) direct detection event rate calculations usually rely on fairly simple, essentially static, analytic halo models. This is largely since the resolution of numerical simulations is not yet large enough to allow the full numerical calculation of the WIMP density and velocity distribution. In this paper we study the direct detection rate, in particular its energy dependence and annual modulation, for the caustic ring halo model. In this model, which uses simple assumptions to model the infall of dark matter onto the halo, the distribution of the cold dark matter particles at the Earth's location has a series of peaks in velocity space. We find that the recoil energy spectrum contains distinctive steps and the sign of the annual modulation in the event rate changes as a function of recoil energy. These effects provide a potentially distinctive experimental signal.

A global 3-D simulation of interplanetary dynamics in June 1991

The global dynamics of the solar wind and interplanetary magnetic field in June 1991 is simulated based on a fully three-dimensional, time-dependent numerical MHD model. The numerical simulation includes eight transient disturbances associated with the major solar flares of June 1991. The unique features of the present simulation are: (i) the disturbances are originated at the coronal base (1Rs) and their propagation through inhomogeneous ambient solar wind is simulated out to 1.5 AU; (ii) as a background for the transients, the global steady-state solar wind structure inferred from the 3-D steady-state model (Usmanov, 1993c) is used. The parameters of the initial pulses are prescribed in terms of the near-Sun shock velocities (as inferred from the metric Type II radio burst observations) relative to the preshock steady-state flow parameters at the flare sites. The computed parameters at the Earth's location for the period 1–18 June, 1991 are compared with the available observations of the interplanetary magnetic field, solar wind velocity, density, and with variation of the geomagnetic activityKpindex.