Physics Today Daily Edition
The Economist: Predicting sea-level rise due to melting ice sheets is complicated because of the difficulty in measuring the changing masses of the ice. Currently the mass is measured with laser topography and gravitational fluctuations, but those methods are limited by cost and resolution. Now Aurélien Mordret of MIT and his colleagues have developed a technique that uses seismometers to measure the vibrations created by ocean waves striking near ice sheets. The vibrations travel at different speeds depending on the compression of the rocky crust from the ice above. Mordret and his team predicted that the vibration speeds they would measure during the winter, when Greenland's ice sheet is largest, would be different from those measured in the summer, when the sheet is smallest. Using seven monitoring stations throughout 2012 and 2013, the researchers found that their calculations were in line with measurements made using other techniques. Mordret says that expanding the network of seismometer stations in Greenland and elsewhere could give a much clearer picture of changes in ice-sheet mass.
New Scientist: A collection of 60 micrometeorites found in Australia reached Earth 2.7 billion years ago, which makes them the oldest known surviving meteorites. Andrew Tomkins of Monash University and his colleagues were surprised to find the micrometeorites to begin with; the fact that the rocks contain iron oxides is rewriting part of Earth's early history. The oxides most likely formed as the meteorites passed through Earth's upper atmosphere. The meteorites landed in a highly alkaline lake, which was completely anoxic at the bottom, and got preserved in layers of limestone. Scientists believe Earth's atmosphere at that time had very low levels of oxygen, but all the supporting evidence is limited to the lower atmosphere. Several theories suggest that the upper atmosphere may have been oxygen-rich due to solar radiation splitting molecules of water, carbon dioxide, and sulfur dioxide.
Science News: Particle colliders have been a standard part of the physicist's toolkit for around 100 years, with different kinds of colliders being created for different kinds of particles. Now, Rupert Huber of the University of Regensburg in Germany and his colleagues have developed a collider that smashes electrons into quasiparticles known as holes. A hole is a void that is formed by the absence of an electron in a sea of electrons and that behaves like a particle. Huber's group created pairs of electrons and holes in tungsten diselenide with a short pulse of light and then applied an oscillating electric field. The field pulled the electrons and holes apart and then slammed them back together at several thousand kilometers per second. The collision results in the emission of light, which Huber's team analyzed to measure the energy required to separate the electron–hole pair. Huber says the information could be useful for improving solar cells, which collect the energy from the separation of electron–hole pairs generated by sunlight.
Wired: Established as a site for scientists to share and discuss their work before publication in peer-reviewed journals, arXiv now stores more than 1 million scientific papers and supports more than 125 million downloads per year. But the site's front-facing design has not changed much over the past 25 years, and its back end is running on a lot of legacy code, so site operators are planning on some refurbishment. In April arXiv asked users for design and functionality requests. The survey also asked whether the site should change how it handles checking the quality of uploaded papers and whether it should allow users to directly comment on and annotate papers. Any of these changes could significantly alter how the site, often viewed as a bastion of open-access research, fits into the larger realm of scientific publishing.
Ars Technica: In the 1970s NASA's Viking lander found that Mars's atmosphere was 95% carbon dioxide, with only minuscule levels of the nitrogen and oxygen that are a significant part of Earth's atmosphere. Over the past 40 years, no subsequent measurements of those trace gases in the Martian atmosphere have been made. Now NASA's Stratospheric Observatory for Infrared Astronomy (SOFIA) has taken a look at Mars's upper atmosphere, where it measured levels of oxygen that were about half of what Viking measured. SOFIA is a Boeing 747 that is specially modified to fly at an altitude of 45 000 ft (13.7 km) and is equipped with a highly sensitive spectrometer that enables measurements in the far-IR. The SOFIA team says the lower-than expected oxygen levels are likely the result of an uneven distribution of the gas in the atmosphere caused by localized releases of oxygen from chemical reactions in the Martian soil.
BBC: The Solomon Archipelago is a lightly populated chain of islands in the South Pacific Ocean. A survey of aerial and satellite images collected between 1947 and 2014 has revealed that five of the islands have been swallowed by the ocean through a combination of rising sea levels and erosion. The islands were vegetated reefs that were unpopulated and relatively small—the largest was only 12 acres (0.05 km2). However, larger, populated islands are also being damaged. One of them, Nuatambu, has lost half its inhabitable area and 11 houses since 2011. The study notes that although the islands have seen sea levels rise as much as 10 mm/year over the last two decades, extreme weather events and inappropriate development are also responsible for some of the damage.
Los Angeles Times: On 10 May, the team running NASA's Kepler space telescope announced that the spacecraft had identified another 1284 extrasolar planets, which brings the total number to 2325. The majority of the newly discovered planets are super-Earths or mini-Neptunes—both defined as planets roughly 1.25 to 10 times the mass of Earth. Nine of the planets orbit in the habitable zone of their parent star. The new planet haul resulted not from more data but from a new algorithm that determined how likely a signal detected by Kepler was a planet rather than a false positive. The algorithm was applied to the full dataset of 4302 candidate planets identified by the telescope, including the 984 previously confirmed exoplanets. The algorithm correctly identified the previously confirmed planets and pulled out the 1284 other signals that the team presented.
CNN: India is experiencing its worst drought in decades. Exceptionally high temperatures some 3–5 °C above average over the past year and two years of below-average rainfall have severely reduced groundwater levels. According to India's Central Water Commission, the country's major water reservoirs are 79% empty, and three-quarters of the country's basins have less water than the 10-year average. They are so depleted that the next monsoon season, which begins in June, will likely not be enough to fully replenish them, says Nitya Jacob of WaterAid India.