The microbes lurking in saliva and more — September’s best science images

Spit spot. Zooming in on a sample of human saliva reveals a cluster of microorganisms, including the yeast Candida albicans (blue) and the bacterium Streptococcus mutans (green), which secrete polymers called α-glucans (red). Scientists have shown that in samples from children with severe tooth decay, clusters such as this thrive on sugar, and are capable of ‘walking’ along tooth-like surfaces using the yeast’s long filaments as ‘legs’.

Catching the Sun. A last-minute modification to a camera on the European Space Agency’s Solar Orbiter probe has enabled scientists to capture unprecedented images of part of the Sun’s atmosphere at ultraviolet wavelengths. Adding a small, protruding ‘thumb’ to the safety door on the front of the instrument allowed the camera to see deeper into its target region than originally specified. When the door slides out of the way to let the light into the camera, the thumb covers the Sun’s bright disc, allowing the detection of much-fainter ultraviolet light from the Sun’s atmosphere. This video shows an ultraviolet image of the Sun’s atmosphere taken using this technique. An image of the Sun’s disc (from NASA’s STEREO mission) has been superimposed in the middle, in the area left blank by the thumb.

Elusive stem cells. Researchers have identified stem cells in the human thymus — a gland in the chest that produces immune cells. In this microscopy image of a slice through the thymus, the green areas show where specialized stem cells are clustered. These cells have the potential to develop into muscle or epithelium (cyan), a tissue that forms a mesh throughout the thymus and surrounds cells called thymocytes (red), which mature into disease-fighting T cells. The findings suggest that although it shrinks throughout adulthood, the thymus has some regenerative properties that could be exploited to boost the immune system.

Deadly quake. Morocco is still grappling with the aftermath of its most devastating earthquake for decades, which struck on 8 September in the High Atlas mountains, around 70 kilometres southwest of Marrakesh. The magnitude-6.8 quake resulted in thousands of deaths and injuries, partly because it struck an area where most buildings are not earthquake-resilient. The region is moderately seismically active — tremors are caused by the continuous collision of the African and Eurasian tectonic plates — but really big earthquakes are rare, happening only once every few hundred years.

Delicate operation. NASA’s OSIRIS-REx sample-return capsule, which contains pieces of the asteroid Bennu, landed safely in the Utah desert on 24 September, after a years-long journey through space. In this photo, curation teams are processing the capsule in a clean room at the US Department of Defense’s Utah Test and Training Range. Scientists are eager to analyse the chemistry and mineralogy of the pristine samples — which might hold clues to the origins of the Solar System.

Running up that hill. Using a rotating magnet and particles coated with iron oxide, engineers have made sand that flows uphill. A combination of torque and magnetic attraction causes each particle to rotate. When there are lots of the grains in a pile, their collective motion and ability to stick to each other cause a kind of ‘swarm’ that can do counter-intuitive things, including flowing upwards and climbing up stairs and over obstacles. The technique could have several applications. “We’re studying these particles to death,” said James Gilchrist, a biomolecular engineer at Lehigh University in Bethlehem, Pennsylvania. “Experimenting with different rotation rates, and different amounts of magnetic force to better understand their collective motion. I basically know the titles of the next 14 papers we’re going to publish.”