Number 86, June 26, 1992 by Phillip F. Schewe and Ben Stein THE YOKHOH X-RAY SATELLITE has by now recorded more detailed images (including motion pictures) of the Sun's x-ray activity than any previous solar mission. The Japanese satellite, launched 8 months ago, has studied, for example, the nature of x-ray emitting flares, observing that some powerful flares eject huge amounts of material, comparable in mass to that of the charged particles thrown out as solar wind. (Science News, 20 June 1992.) THE SUDBURY NEUTRINO LABORATORY in northern Canada, to be commissioned in early 1995, will be the first facility that can detect muon and tau neutrinos as well as the electron neutrinos measured recently by the Gallex detector in Italy. Although Gallex detected fully two-thirds of the solar electron neutrinos predicted by theory, it nonetheless leaves open the possibility that electron neutrinos may be converted to other types of neutrinos on their way to earth via the proposed Mikheyev-Smirnov-Wolfenstein (MSW) mechanism. One of the first objectives of the Sudbury experiment will be to look for evidence of the MSW mechanism at work. Another next-generation neutrino detector is Super-Kamiokande, to be finished in Japan in 1996. (Science, 12 June 1992.) PLUTO'S ATMOSPHERE may be dominated by nitrogen, according to recent observations by Tobias Owen of the University of Hawaii and his colleagues. Using the UK Infrared Telescope in Mauna Kea they detected spectral lines indicating for the first time the presence of nitrogen and carbon monoxide ice on Pluto's surface. Because these two substances, along with methane (previously discovered on Pluto), are some of the essential constituents of interstellar clouds, astronomers believe that studying the composition of Pluto may be useful in understanding the chemical processes which formed the solar system. (New Scientist, 20 June 1992.) SUPERSTRING THEORY has hit some snags. The notion that the universe consists of tiny one-dimensional strings vibrating and interacting to produce particles and forces was an attractive one, because, when combined with several mathematical postulates such as "supersymmetry," it showed promise of combining the laws of quantum mechanics and those of general relativity within a single framework, a feat that would unify all four known forces in physics. However, theorists now believe a more fundamental understanding of the nature of particles and forces--and a better grasp of the mathematical implications of superstrings--will be necessary before a successful theory can be constructed. One troubling aspect of the theory is that it tolerates many solutions, some of which are nonsensical, and others which, although approximating the real world, require the existence of extra dimensions and exotic particles presently unsubstantiated by experiment. Nevertheless, theorists are not abandoning the concept of superstrings because, for example, the theory can directly produce the equations of general relativity and more recently has yielded simplified sets of equations describing black holes. (Science, 12 June 1992)