Physics Today Daily Edition
Los Angeles Times: For the last 17 years, the Cosmic Ray Isotope Spectrometer (CRIS) on NASA's Advanced Composition Explorer spacecraft has been detecting particles approaching Earth. In that time, it has identified more than 30 000 particles of ordinary iron-56 and just 15 particles of radioactive iron-60. But the radioactive isotopes provided enough information for researchers working with CRIS to determine a source. Heavy elements such as iron are created in supernova explosions, but it takes the shock wave of a second supernova to accelerate the atoms and turn them into cosmic rays. The 2.6-million-year half-life of iron-60 allowed researchers to determine that the supernovae that launched the iron particles toward Earth occurred within 2 million years of each other and were relatively nearby. The finding closely matches a separate study that recently suggested a nearby star went supernova roughly 2.3 million years ago.
New Scientist: Mars's atmosphere is currently 95% carbon dioxide, with only trace amounts of oxygen. Because the planet's red coloring is the result of oxidization of iron on the surface, many scientists believe that the atmosphere used to be more oxygen-rich. However, there was little direct evidence to support the theory. Now NASA's Curiosity rover has identified significant amounts of manganese oxide in rocks in Gale crater. According to Agnès Cousin of the Research Institute in Astrophysics and Planetology in Toulouse, France, the formation of that oxidized manganese would have required much more oxygen than is present in the current atmosphere.
BBC: Gravitational forces introduce tiny but measurable fluctuations in the length of the Large Hadron Collider's (LHC's) 27 km circumference. The changes can be seen when the particle beams are calibrated to ensure they pass through the center of the ring's vacuum chamber. Any shift in the beams' position can be measured with micrometer accuracy. Those length fluctuations occur both daily and seasonally. The daily fluctuations are caused by normal tidal forces. Now one group of researchers investigating the fluctuations believes that the seasonal changes are caused by water from rain and snow, which accumulates during the winter and evaporates during the summer. Rolf Hut of Delft University of Technology, the Netherlands, and his colleagues found a correlation between the seasonal beam changes and local gravitational variations due to groundwater, as measured by NASA's GRACE satellites. Because of the low resolution of the satellites and the short period of operation of the LHC, the correlation is not conclusive. But Hut says that if his team's work is correct, then researchers could use the LHC as the world's largest rain gauge.