Interstellar atoms penetrate the heliosphere, are ionized by solar UV radiation or charge exchange with solar wind ions, and are "picked up" by the solar wind onto a ring distribution in velocity space. The ring distribution is unstable to the generation of hydromagnetic waves with growth time scales which are small compared with those of the continual pickup process and convection with the solar wind. First, the growth rates for parallel propagation are derived, presented, and compared with previous work. Then the spatially homogeneous quasi-linear equations describing the subsequent hydromagnetic wave excitation and pickup ion velocity diffusion in pitch angle and energy are presented under the assamption of wave propagation parallel to the ambient magnetic field. Neglecting ion energy changes, analytical expressions for the time-asymptotic wave spectra accompanying the time-asymptotic isotropic ion distribution are derived. The results indicate that pickup helium has a very small (unobservable) effect on the solar wind wave spectrum, but that pickup hydrogen results in substan_.tial modifications at cyclotron resonant frequencies (•, 10 -2 Hz at •,7 AU). Finally, based on the previous expressions, the radial evolution of the pickup-hydrogen-modified wave spectra for both polarizations and propagation directions is computed analytically including the degradation of the wave power in the divergent solar wind. The predicted modifications beyond •, 5 AU are substantial and could be observable at spacecraft frequencies greater than •-5 x 10 -3 Hz if not degraded by turbulent wave-wave interactions or stochastic ion acceleration. The predicted enhancement by a factor of order 10 at •, 7 AU involves •, 10% of the power in the ambient field, is left-polarized (Alfv•nic as opposed to magnetosonic) in the solar wind frame, is unpolarized in the spacecraft frame, and includes an equal admixture of propagation directions. -3 mines the local interstellar densities' n n = 0.065 ___ 0.01 cm and n.e = 0.01 _+ 0.0045 cm -3 [Chassefiere et al., 1986]. As soon as an interstellar neutral is ionized it is accelerated by the solar wind electric field, E = -c-•Vsw x B, where Vsw is the solar wind velocity and B is the ambient solar wind magnetic field, and "picked-up" onto a ring distribution about B in velocity v space. In the frame of the solar wind the ring is characterized by a speed Ivl-Vsw and a pitch angle equal to the angle between B and Vsw, such that the ions propagate sunward. The ring is initially broad due to variations in Vsw and, especially, B during the pickup process and is broadened further by ion scattering in the solar wind electric and magnetic field fluctuations. Since the phase speed of the irregularities which most effectively scatterer the ions is approximately the Alfv6n speed V A and VA << Vsw, the ions are initially scattered in pitch angle to form a thin spherical shell in velocity space. Adiabatic deceleration of the ions in the divergent solar wind combined with continual pickup of new ions yields a th...

The Rosetta probe, orbiting Jupiter-family comet 67P/Churyumov-Gerasimenko, has been detecting individual dust particles of mass larger than 10 −10 kg by means of the GIADA dust collector and the OSIRIS Wide Angle Camera and Narrow Angle Camera since 2014 August and will continue until 2016 September. Detections of single dust particles allow us to estimate the anisotropic dust flux from 67P, infer the dust loss rate and size distribution at the surface of the sunlit nucleus, and see whether the dust size distribution of 67P evolves in time. The velocity of the Rosetta orbiter, relative to 67P, is much lower than the dust velocity measured by GIADA, thus dust counts when GIADA is nadir-pointing will directly provide the dust flux. In OSIRIS observations, the dust flux is derived from the measurement of the dust space density close to the spacecraft. Under the assumption of 1 radial expansion of the dust, observations in the nadir direction provide the distance of the particles by measuring their trail length, with a parallax baseline determined by the motion of the spacecraft. The dust size distribution at sizes >1 mm observed by OSIRIS is consistent with a differential power index of −4, which was derived from models of 67P's trail. At sizes <1 mm, the size distribution observed by GIADA shows a strong time evolution, with a differential power index drifting from −2 beyond 2 au to −3.7 at perihelion, in agreement with the evolution derived from coma and tail models based on ground-based data. The refractory-to-water mass ratio of the nucleus is close to six during the entire inbound orbit and at perihelion.

On 4 July 2005, many observatories around the world and in space observed the collision of Deep Impact with comet 9P/Tempel 1 or its aftermath. This was an unprecedented coordinated observational campaign. These data show that (i) there was new material after impact that was compositionally different from that seen before impact; (ii) the ratio of dust mass to gas mass in the ejecta was much larger than before impact; (iii) the new activity did not last more than a few days, and by 9 July the comet's behavior was indistinguishable from its pre-impact behavior; and (iv) there were interesting transient phenomena that may be correlated with cratering physics.

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The role of cosmic rays (CRs) in the formation and evolution of clusters of galaxies has been much debated. It may well be related to other fundamental questions, such as the mechanism that heats and virializes the intracluster medium (ICM) and the frequency at which the ICM is shocked. There is now compelling evidence, both from the cluster soft excess (CSE) and the "hard-tail" emissions at energies above 10 keV, that many clusters are luminous sources of inverse Compton (IC) emission. This is the first direct measurement of cluster CRs: the technique is free from our uncertainties in the ICM magnetic field and is not limited to the small subset of clusters that exhibit radio halos. The CSE-emitting electrons fall within a crucial decade of energy where they have the least spectral evolution and where most of the CR pressure resides. However, their survival times do not date them back to the relic CR population. By using the CSE data of the Coma Cluster, we demonstrate that the CRs are energetically as important as the thermal ICM: the two components are in pressure equiparition. Thus, contrary to previous expectations, CRs are a dominant component of the ICM, and their origin and effects should be explored. The best-fit CR spectral index is in agreement with the Galactic value.Recent research on clusters of galaxies unveiled a number of independent and contemporaneous indications that nonthermal activities in the intracluster medium (ICM) are at a much higher level than previously thought. First came the Extreme Ultraviolet Explorer discovery of 69-190 eV radiation in excess of that expected from the thermal ICM, confirmed by the ROSAT and BeppoSAX detections of similar soft X-ray (0.1-0.4 keV) excesses (Lieu et al.

Aims. We study the link between gravitational slopes and the surface morphology on the nucleus of comet 67P/Churyumov-Gerasimenko and provide constraints on the mechanical properties of the cometary material (tensile, shear, and compressive strengths). Methods. We computed the gravitational slopes for five regions on the nucleus that are representative of the different morphologies observed on the surface (Imhotep, Ash, Seth, Hathor, and Agilkia), using two shape models computed from OSIRIS images by the stereo-photoclinometry (SPC) and stereo-photogrammetry (SPG) techniques. We estimated the tensile, shear, and compressive strengths using different surface morphologies (overhangs, collapsed structures, boulders, cliffs, and Philae's footprint) and mechanical considerations. The strength-to-gravity ratio is similar for 67P and weak rocks on Earth. As a result of the low compressive strength, the interior of the nucleus may have been compressed sufficiently to initiate diagenesis, which could have contributed to the formation of layers. Our value for the tensile strength is comparable to that of dust aggregates formed by gravitational instability and tends to favor a formation of comets by the accrection of pebbles at low velocities.

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