We report on spatial soliton formation and self/cross waveguiding in planar cells containing a nematic liquid crystal in the presence of an externally applied voltage. Self-confinement and cross-induced guidance are demonstrated with an Argon ion laser (514 nm) and a helium–neon probe (633 nm), respectively, over millimeter lengths and with milliwatt pump powers.

A comparison of the laboratory reflectance spectra of meteorites with observations of asteroids revealed that the latter are much 'redder', with the spectral difference explained by 'space weathering', though the actual processes and timescales involved have remained controversial. A recent study of young asteroid families concluded that they suffered only minimal space weathering. Here we report additional observations of those families, revealing that space weathering must be a very rapid process-the final colour of a silicate-rich asteroid is acquired shortly after its 'birth' (within 10(6) years of undergoing a catastrophic collision). This rapid timescale favours solar wind implantation as the main mechanism of space weathering, as laboratory experiments have shown that it is the most rapid of several competing processes. We further demonstrate the necessity to take account of composition when evaluating weathering effectiveness, as both laboratory and asteroid data show an apparent dependence of weathering on olivine abundance. The rapid colour change that we find implies that colour trends seen among asteroids are most probably due to compositional or surface-particle-size properties, rather than to different relative ages. Apparently fresh surfaces most frequently seen among small near-Earth asteroids may be the result of tidal shaking that rejuvenates their surfaces during planetary encounters.

The ESA mission BepiColombo will explore the planet Mercury with equipment allowing an extremely accurate tracking. While determining its orbit around Mercury, it will be possible to indirectly observe the motion of its center of mass, with an accuracy several orders of magnitude better than what is possible by radar ranging to the planet's surface. This is an opportunity to conduct a relativity experiment which will be a modern version of the traditional tests of general relativity, based upon Mercury's perihelion advance and the relativistic light propagation near the Sun. We define the mathematical methods to be used to extract from the data of the BepiColombo mission, as presently designed, the best constraints on the main post-Newtonian parameters, especially ␤,␥ and the Nordtvedt parameter , but also the dynamic oblateness of the Sun J 2᭪ and the preferred frame parameters ␣ 1 ,␣ 2 . We have performed a full cycle simulation of the BepiColombo radio science experiments, including this relativity experiment, with the purpose of assessing in a realistic ͑as opposed to formal͒ way the accuracy achievable on each parameter of interest. For ␥ the best constraint can be obtained by means of a dedicated superior conjunction experiment, with a realistic accuracy Ӎ2ϫ10 Ϫ6 . For ␤ the main problem is the very strong correlation with J 2᭪ ; if the Nordtvedt relationship ϭ4␤Ϫ␥Ϫ3 is used, as it is legitimate in the metric theories of gravitation, a realistic accuracy of Ӎ2ϫ10 Ϫ6 for ␤ and Ӎ2ϫ10 Ϫ9 for J 2᭪ can be achieved, while itself is constrained within Ӎ10 Ϫ5 . If the preferred frame parameters ␣ 1 ,␣ 2 are included in the analysis, they can be constrained within Ӎ8ϫ10 Ϫ6 and Ӎ10 Ϫ6 , respectively, at the price of some degradation in ␤, J 2᭪ and . It is also possible to test the change with time of the gravitational constant G, but the results are severely limited because of the problems of absolute calibration of the ranging transponder, to the point that the improvement as compared with other techniques ͑such as lunar laser ranging͒ is not so important.

Some active asteroids have been proposed to be formed as a result of impact events1. Because active asteroids are generally discovered by chance only after their tails have fully formed, the process of how impact ejecta evolve into a tail has, to our knowledge, not been directly observed. The Double Asteroid Redirection Test (DART) mission of NASA2, in addition to having successfully changed the orbital period of Dimorphos3, demonstrated the activation process of an asteroid resulting from an impact under precisely known conditions. Here we report the observations of the DART impact ejecta with the Hubble Space Telescope from impact time T + 15 min to T + 18.5 days at spatial resolutions of around 2.1 km per pixel. Our observations reveal the complex evolution of the ejecta, which are first dominated by the gravitational interaction between the Didymos binary system and the ejected dust and subsequently by solar radiation pressure. The lowest-speed ejecta dispersed through a sustained tail that had a consistent morphology with previously observed asteroid tails thought to be produced by an impact4,5. The evolution of the ejecta after the controlled impact experiment of DART thus provides a framework for understanding the fundamental mechanisms that act on asteroids disrupted by a natural impact1,6.