Stephen Ornes

In 2008, Satoshi Nakamoto introduced the world to Bitcoin, a volatile digital currency that’s untethered to any specific institution or country (1). (Satoshi Nakamoto was quickly revealed to be a pseudonym; the true identity of the inventor or inventors remains unknown.) In the years that followed, the value of Bitcoin has soared, plummeted, and soared again while giving rise to a raft of new cryptocurrencies of varying stability and legitimacy. Bitcoin and the others have their boosters and their detractors (see Opinion: Valuation, liquidity price, and stability of cryptocurrencies, https://www.pnas.org/content/115/6/1131).

But Bitcoin wasn’t just revolutionary as a virtual currency innovation. It also introduced a novel way for investors and others to obtain, monitor, and trade that currency. Users record and secure financial transactions along with a timestamp using blockchain, a ledger system designed by Nakamoto that’s unlike any traditional accounting system used before. A blockchain isn’t stored on a central computer or controlled by a single boss; instead, it’s distributed, which means every user on a blockchain network has a copy of the entire ledger. Information is also protected by a consensus algorithm — a computer program that enables the network to validate transactions. …

Amy McDermott

More than a decade ago, amphibian microbial ecologist Reid Harris watched a mother salamander as she marched in a figure-eight pattern through her clutch of soft, jellylike eggs. He knew that her strange walk, rubbing up against her brood, transferred beneficial bacteria from her skin onto the eggs to fight off fungal infection. Then something clicked. Harris wondered if she might also be showing him the solution to a scourge threatening hundreds of other amphibian species around the world.

Then, as now, amphibians were dying in droves. At least one-third of species face extinction, with at least 90 confirmed gone and another 500 in decline (1, 2). The major culprit is the skin disease chytridiomycosis, caused by the waterborne fungus Batrachochytrium dendrobatidis, or Bd for short. Under a microscope, fungal bodies anchor themselves in the translucence of frog skin and often group together to form a collection of small spheres. …

Adam Mann

Late one night in October 2015, Andrew Wetzel was fretting. For 15 days, his cosmological models had been swirling virtual dark matter around cybernetic gas and dust and slowly generating a synthetic galaxy approximately the size of our own Milky Way, and Wetzel was about to receive the results. “I finally got the plot up to compare our simulation with the Milky Way,” recalls Wetzel, an assistant professor of physics at the University of California, Davis. “I went to bed very happy that night.”

That’s because, for the first time, a simulation had accurately reproduced a realistic population of dwarf galaxies near the Milky Way. These small companions orbit larger galaxies like planets around a star, and for a decade and a half, they had presented astronomers with a big problem. Simulations suggested that thousands of companion galaxies should surround the Milky Way, but telescopes had seen only a handful. …

Leah Shaffer

Just over 20 years ago, a Lyme disease vaccine called LYMErix was approved for sale in the United States. Researchers designed the vaccine to prevent the transmission of the tick-borne pathogen Borellia burgdorferi, which spurs a bacterial infection that can cause fever, headaches, and joint pain if left untreated.

LYMErix was on the market for just four years. Concerns over adverse reactions and a lukewarm reception from public health agencies led the vaccine’s manufacturer, SmithKline Beecham, to shelve the product in 2002. Since then, the need for a vaccine has grown. An estimated 300,000 people are diagnosed with Lyme disease in the United States annually, and reported cases of the disease have tripled since the 1990s. In some counties in the northeast United States, disease incidence has increased more than 300% over a 20-year period. …

Adam Mann

On September 3, 2018, an unpowered experimental sailplane made history by flying into the stratosphere. After leaving from El Calafate, a town near the Southern Patagonian Ice Field in Argentina, glider pilots Jim Payne and Tim Gardner surfed on enormous airborne waves emanating from the Andes Mountains. They achieved a world record height of 23,203 meters — higher than a Lockheed U-2 spy plane’s cruising altitude. No other unpowered aircraft has ever achieved such elevation. …

Nola Taylor Redd

The distant rock has offered clues about planet formation and the state of the early solar system.

Within the cloud of icy rocks at the edge of the solar system lie objects that have remained virtually untouched since their formation more than four billion years ago. Last January, NASA’s New Horizons spacecraft made the first flyby of one such primitive sample, an object known as 2014 MU69 and nicknamed “Ultima Thule” (although that label has proved controversial*). After New Horizons’ successful flyby of Pluto in 2015, researchers were keen to study a primordial body that was within the craft’s reach. With MU69, that dream became a reality. The tiny object, one of only three possible destinations discovered after the mission launched, turned out to be an incredible target. …

Benjamin S. Halpern, Richard S. Cottrell, Julia L. Blanchard, Lex Bouwman, Halley E. Froehlich, Jessica A. Gephart, Nis Sand Jacobsen, Caitlin D. Kuempel, Peter B. McIntyre, Marc Metian, Daniel D. Moran, Kirsty L. Nash, Johannes Többen, and David R. Williams

Improving global food systems is essential to addressing climate change, mitigating biodiversity loss, and meeting both sustainability and human development goals. International assessments from the Intergovernmental Panel on Climate Change and Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services and business and technology innovations such as lab-grown and plant-based meat, as well as many consumer diet trends, can all be traced to studies that identify undesirable impacts of certain food systems. …

Amber Dance

Neuroscientists believe that immediately after a mammal is born, brain cells called microglia spring into action, pruning away connections between neurons. This may be a way for the brain to refine its neural networks. Until recently, neurobiologists had assumed the microglia worked by phagocytosis, reaching out a cup-shaped tendril to swallow the neuron-to-neuron bridges whole. But in 2017 when Laetitia Weinhard, then a graduate student at EMBL Rome in Italy, observed pruning via a combination of light-sheet and electron microscopy, she saw something others had missed.

Weinhard, now a postdoc at New York University, discovered that the microglia were instead nibbling off bits of neural connections in a process called trogocytosis, as she reported in 2018 (1). Her group is one of many that have recently found trogocytosis happening in unexpected places and for unsuspected purposes. “I think trogocytosis is really underappreciated,” says Katy Ralston, a microbiologist at the University of California, Davis. “It’s exploding…where it’s happening, and also what it’s being used for.” …