You may have missed… how giant water striders jump on the surface of water, mapping the cells of our intestines, DART knocked boulders off Dimorphos, and more!

DART knocked boulders off of asteroid Dimorphos

NASA’s DART (Double Asteroid Redirection Test) spacecraft intentionally crashed into the asteroid Dimorphos on 27 September 2022, successfully changing its orbit around the larger asteroid Didymos as a result.

Now, NASA’s Hubble Space Telescope has discovered a swarm of 37 boulders, drifting away at speeds of less than 1km/h, that were possibly shaken loose off of the surface of the asteroid in the process.

“This is a spectacular observation – much better than I expected. We see a cloud of boulders carrying mass and energy away from the impact target. The numbers, sizes, and shapes of the boulders are consistent with them having been knocked off the surface of Dimorphos by the impact,” says Professor David Jewitt, a planetary scientist from the University of California, Los Angeles, in the US.

“This tells us for the first time what happens when you hit an asteroid and see material coming out up to the largest sizes. The boulders are some of the faintest things ever imaged inside our solar system.”

Revealing the map of our intestinal neighbourhoods

Researchers have produced an ultra-high resolution map of the cell types that make up the digestive system, and published the findings in a new study in Nature.

“This is the first time anyone has made a spatial map of the intestine at the single-cell level,” says Michael Snyder, Professor and Chair of Genetics at Stanford Medicine in the US, and co-senior author of the research.

“Our maps are intended to be a reference for a healthy intestine, with which we can compare everything from irritable bowel disease to early-stage colon cancer.

“This will be foundational for our understanding of all kinds of digestive diseases.”

By pinpointing where each cell type is located, and which other cells they associate with, they were able to investigate how the organisation of healthy tissue changes throughout the digestive tract.

The study was carried out using samples from the small and large intestines of nine deceased adult donors – the majority of whom were white and male – so the next steps will be to increase the diversity of the samples. 

How do the world’s largest water striders jump on the water?

Water striders are a family of insects that have adapted to live on top of still water thanks to their long, hydrophobic legs. Their legs support their bodies on the surface without breaking it, with the water surface bending to create a dimple, or meniscus, underneath.

When small water strider species escape from attacks by underwater predators, they use each dimple as a mini trampoline to jump upward using just enough force to avoid breaking the surface.

Now, new research has revealed that the world’s largest water strider, the giant water strider (Gigantometra gigas), uses a different mechanism.

The clip shows an example of an upward jump by the giant water strider. The movements are slowed down (0.0375 normal speed). The second smaller water strider jumping belongs to the genus Ptilomera. Credit: Piotr G Jablonski, Woojoo Kim, and coauthors of Allometry of jumping on water by water striders. Some rights reserved (CC BY-SA 4.0)

High-speed videos revealed that this heftier species does in fact break the water surface when they jump; when the legs penetrate the water surface they move downward, surrounded by a layer of air caught around their long leg hairs. This causes drag, which propels them in the opposite direction (upward) in the second phase of the jump.

They developed a mathematical model that predicts all jumping spiders heavier than about 80 mg should use this method to reach the speed that can protect them from fish’s attack. 

“This discovery is interesting from both engineering and evolutionary viewpoints because it provides inspiration for water walking robots and establishes solid theoretical grounds for future comparative analyses across multiple species of water striders to understand coevolution between body size and jumping mechanism in water striders,” the authors write in their paper in PNAS.

The clip shows an example of an upward jump by the giant water strider filmed at a closer distance. The water strider leaves the field of view. The movements are slowed down (0.125 normal speed). Credit: Piotr G Jablonski, Woojoo Kim, and coauthors of Allometry of jumping on water by water striders. Some rights reserved (CC BY-SA 4.0)

Are bin chickens spreading Japanese encephalitis?

Australia experienced the largest recorded Japanese encephalitis virus outbreak in 2021 and 2022, with 45 human cases and seven deaths. The disease is a type of encephalitis, or inflammation of the brain, and is caused by an RNA virus spread by insects like ticks and mosquitoes.

Wild water birds act as reservoirs for the virus, because the virus replicates to levels high enough to infect a mosquito that bites it.

Native Australian ibises (Threskiornis Molucca), commonly known as bin chickens, were implicated in the outbreak among other birds. But because they are common in urban centres, they could play a role in spreading Japanese encephalitis and other important pathogens.

Researchers at CSIRO’s Australian Centre for Disease Preparedness are now using genomics to investigate whether this is the case.