Interception of comet Hyakutake's ion tail at a distance of 500 million kilometres

Remote sensing observations and the direct sampling of material from a few comets have established the characteristic composition of cometary gas. This gas is ionized by solar ultraviolet radiation and the solar wind to form 'pick-up' ions, ions in a low ionization state that retain the same compositional signatures as the original gas. The pick-up ions are carried outward by the solar wind, and they could in principle be detected far from the coma (Sampling of pick-up ions has also been used to study interplanetary dust, Venus' tail and the interstellar medium.) Here we report the serendipitous detection of cometary pick-up ions, most probably associated with the tail of comet Hyakutake, at a distance of 3.4 AU from the nucleus. Previous observations have provided a wealth of physical and chemical information about a small sample of comets, but this detection suggests that remote sampling of comet compositions, and the discovery of otherwise invisible comets, may be possible.     

Discovery of a comet by its Lyman-alpha emission

Several searches for near-Earth objects have recently been initiated, as a result of increased awareness of the hazard of impacts on the Earth. These programs mainly search for asteroids, so amateur astronomers can still contribute to the discovery of comets, especially out of the orbital plane of the Solar System. An ideal way to search for comets would be to use a spaceborne instrument capable of imaging the whole sky on a daily basis in a systematic and repeatable way. Such an instrument already exists on the solar observatory SOHO; it operates at the Lyman-alpha wavelength of neutral hydrogen, which is the main component of the emission cloud of a comet. Here we report the discovery, using archival data from this satellite, of a hitherto unnoticed comet which reached a perihelion of 1.546 a.u. on 26 June 1997. We derive the water production rate of the comet as a function of time and find that it increases after perihelion, like that of comet Halley.     

Rapid prototyping of patterned functional nanostructures

Living systems exhibit form and function on multiple length scales and at multiple locations. In order to mimic such natural structures, it is necessary to develop efficient strategies for assembling hierarchical materials. Conventional photolithography, although ubiquitous in the fabrication of microelectronics and microelectromechanical systems, is impractical for defining feature sizes below 0.1 micrometres and poorly suited to pattern chemical functionality. Recently, so-called 'soft' lithographic approaches have been combined with surfactant and particulate templating procedures to create materials with multiple levels of structural order. But the materials thus formed have been limited primarily to oxides with no specific functionality, and the associated processing times have ranged from hours to days. Here, using a self-assembling 'ink' we combine silica-surfactant self-assembly with three rapid printing procedures--pen lithography, ink-jet printing, and dip-coating of patterned self-assembled monolayers--to form functional, hierarchically organized structures in seconds. The rapid-prototyping procedures we describe are simple, employ readily available equipment, and provide a link between computer-aided design and self-assembled nanostructures. We expect that the ability to form arbitrary functional designs on arbitrary surfaces will be of practical importance for directly writing sensor arrays and fluidic or photonic systems.     

Geodetic evidence for a low slip rate in the Altyn Tagh fault system

The collision between India and Asia has been simulated with a variety of computational models that describe or predict the motions of the main faults of east Asia. Geological slip-rate estimates of 20-30 mm yr(-1) suggest that the largest of these faults, the 2,000-km-long Altyn Tagh fault system on the northern edge of the Tibetan plateau, absorbs as much of the Indo-Asian convergence signal as do the Himalayas--partly by oblique slip and partly by contraction and mountain growth. However, the predictions of dynamic models for Asian deformation and the lower bounds of some geological slip-rates estimates (3-9 mm yr(-1); refs 7, 8) suggest that the Altyn Tagh system is less active. Here, we report geodetic data from 89-91 degrees E that indicate left-lateral shear of 9 +/- 5 mm yr(-1) and contraction of 3 +/- 1 mm yr(-1) across the Altyn Tagh system. This result--combined with our finding that, at 90 degrees E, Tibet contracts north-south at 9 +/- 1 mm yr(-1)--supports the predictions of dynamic models of Asian deformation.