Flash Physics is our daily pick of the latest need-to-know developments from the global physics community selected by Physics World‘s team of editors and reporters
NASA catches Earth flashing the Sun
Tiny ice crystals in Earth’s atmosphere create unexpected flashes of light in images of the planet taken from space. The bright glints were caught by NASA’s Earth Polychromatic Imaging Camera (EPIC) on board the Deep Space Climate Observatory (DSCOVR). Positioned between the Earth and the Sun, EPIC takes almost-hourly images of the sunlit planet. When studying these images, Alexander Marshak, DSCOVR deputy project scientist at NASA’s Goddard Space Flight Center, noticed occasional light flashes appearing over oceans. A closer look revealed these also happened over land, meaning they couldn’t be simply caused by sunlight reflecting off smooth water. Marshak and colleagues turned their attention to another water system on Earth – the ice crystals high in the atmosphere. The researchers catalogued 866 flashes over land between DSCOVR’s launch in June 2015 to August 2016. By calculating angles of reflection and combining with EPIC’s measurements of cloud height, the team concluded that the flashes were caused by sunlight reflecting off horizontally orientated ice crystals in high cirrus clouds (5–8 km). Marshak is now investigating whether the ice crystals are common enough to impact the amount of sunlight passing through the atmosphere, so as to incorporate it into computer models of Earth’s temperature transfers. Detecting similar glints on exoplanets could also provide information about their atmospheres. The work is presented in Geophysical Research Letters.
Quantum drum amplifies microwaves
A new type of electromechanical circuit for microwaves has been created by physicists in Switzerland and the UK. The device comprises a resonant microwave cavity that is coupled to a tiny mechanical oscillator that resembles a drum. The “micro-drum” is 30 μm in diameter and just 100 nm thick. The system is initialized by cooling the micro-drum so that it vibrates in its quantum-mechanical ground state – which is done by scattering microwave photons from the drum, each of which carries away a tiny amount of energy. The drum is coupled to the cavity such that the position of the drum modulates the resonant frequency of the cavity. Conversely, the cavity can affect the motion of the drum by exerting a force on it. As a result of these interactions, energy can be transferred between the drum and cavity. The device has several modes of operation, including one in which the drum is able to absorb microwaves from the cavity – acting as a dissipative reservoir. By tuning the interaction parameters, the device can also be operated as a microwave amplifier that operates just above the quantum limit for noise. In a different regime, the device can be operated as a microwave laser – or maser. Created by László Tóth, Nathan Bernier, Alexey Feofanov and colleagues at École Polytechnique Fédérale de Lausanne and the University of Cambridge, the device is described in Nature Physics. “There has been a lot of research focus on bringing mechanical oscillators into the quantum regime in the past few years,” says Feofanov. “However, our experiment is one of the first which actually shows and harnesses their capabilities for future quantum technologies.”
Scientists map comet’s charged particles
A detailed 3D map of how the solar wind interacts with the 67P/Churyumov–Gerasimenko has been produced by an international team of scientists, who have explained puzzling observations made by the Rosetta mission to the comet. In the above image created by the team, the solar wind of hypersonic charged particles approaches the comet from the left and interacts with the watery halo of the comet. Jan Deca of the University of Colorado Boulder, and colleagues in Russia, Sweden, France and Belgium, used 3D particle-in-cell (PIC) kinetic simulations to study the interaction of four components – electrons and ions in the solar wind, and electrons and water ions in the halo. They found that the interaction between the magnetic-field lines of the solar wind and the comet cause the solar-wind electrons to be deflected around the nucleus of the comet. The heavier solar protons, however, are not deflected as much as the electrons and tend to penetrate the nucleus. Beyond the comet, these protons are neutralized by electrons flowing from the comet. Meanwhile, the solar-wind electrons neutralize some of the water ions that flow from the comet and make up its tail. These charge-exchange processes also transfer momentum from the solar wind to the tail of the comet. Writing in Physical Review Letters, the team describes how it was also able to explain the unexpected existence of two distinct populations of electrons in the halo – warm electrons and hotter suprathermal electrons – which were discovered by Rosetta.