CERN experiment confirms antimatter falls down, not up

Antimatter experiences the same force of gravity as regular matter. Observing this simple phenomenon had eluded physicists for decades. Scientists at CERN made a thin gas of antihydrogen and dropped it from the top of a 3-metre-tall vertical shaft — a delicate task, because if the antiatoms come into contact with any regular matter, they both cease to exist.

Brainless box jellies learn from experience

Jellyfish have demonstrated that you don’t need a centralised nervous system to learn by association. Tiny Caribbean box jellyfish (Tripedalia cystophora) can be trained to associate the feeling of bumping into an obstacle with a visual cue, and to use the information to avoid future collisions. Learning happens in the jellies’ rhopalia — structures containing rudimentary eyes plus nerve centres that control swimming pulses.

How worlds are born: JWST reveals exotic chemistry of planetary nurseries

The James Webb Space Telescope (JWST) has turned its gaze to several planet-forming swirls of gas and dust surrounding young stars. Two of these ‘protoplanetary’ disks had large amounts of liquid water that can serve as a raw ingredient for planets forming. Another contained a surprisingly large amount of carbon, which could allow newly born planets to sweep up diverse ingredients. In the debris disc around the star Beta Pictoris, scientists discovered a ‘cat’s tail’ of dust that is probably the aftermath of a massive collision.

These ancient whittled logs could be the earliest known wooden structure

The remains of what might have been a wooden structure built by hominins roughly half a million years ago have been uncovered in Zambia. Researchers can’t definitively identify the possible structure — it might have been a raised platform, a shelter or something else entirely. Whatever it was, it pre-dates the evolution of Homo sapiens by more than 100,000 years.

Jawbone hints at new human species

A 300,000-year-old jawbone discovered in a cave in eastern China could represent a new branch of the human family tree. The bone bears a curious mix of modern and archaic features: it’s thick along the jawline, a feature shared with early human species, and lacks the true chin of Homo sapiens. But the side of the mandible is more reminiscent of that of modern humans. The finding deepens the mystery of which ancient human species inhabited East Asia during the Pleistocene, and whether any of them could be ancestors of modern humans.

‘Weird’ dinosaur prompts rethink of bird evolution

The fossil of a bird-like dinosaur that lived around the same time as Archaeopteryx — considered by many palæontologists to be the first bird — has been found in what is now southeastern China. Fujianvenator prodigiosus adds to mounting evidence that there were plenty of different birds living in the Late Jurassic period. Dinosaurs might have diversified into different kinds of bird to occupy different ecological niches, says palæontologist Hailu You. Fujianvenator’s particularly elongated hindlimbs suggest that it was all about running or wading, instead of flying.

Were these stone balls made by ancient human relatives?

Mysterious, spherical bashed-up rocks litter the archaeological record, popping up at many early human sites. Researchers analysed 150 baseball-sized limestone spheroids from what is now northern Israel and say that the balls were crafted on purpose — rather than by natural processes or being formed over time by being used as hammers, for example.

Black holes keep 'burping up' stars they destroyed years earlier, and astronomers don't know why

Many black holes that consume a star seem to ‘burp up’ energy long after the fact. When the star is ripped apart, some the stellar material forms a swirling accretion disk that orbits the hole. Sometimes, material is flung out from this disk, which is detectable as a wash of radio waves. Astronomers observed 24 star-destroying black holes and were surprised to find radio signals indicating that 10 of them emitted these outflows years after the initial event — although we don’t yet know why.

AI predicts chemicals’ smells from their structures

An artificial-intelligence system can describe how compounds smell simply by analysing their chemical structures. The neural network can provide descriptions, such as ‘grassy’, for hundreds of molecules, including some that don’t exist in nature. Smell is the only sensory input that goes directly from the sensory organ to the brain’s memory and emotional centres without passing through other brain regions — which is why scents can evoke specific, intense memories.

Human ancestors nearly went extinct 900,000 years ago

Roughly 900,000 years ago, climate changes sweeping the globe might have pushed our distant ancestors to the brink of extinction. The unknown human-like species was reduced to just 1,280 breeding individuals, creating a genetic bottleneck that is still detectable in the DNA of modern-day humans. The population didn’t expand for more than 100,000 years, after which it bloomed again and the progenitors of our species and of our extinct relatives, the Denisovans and the Neanderthals, emerged.

Rare oxygen isotope detected at last — and it defies expectations

Physicists have for the first time detected oxygen-28 — an isotope of oxygen that has 12 extra neutrons packed into its nucleus. Scientists have long predicted that this isotope is unusually stable. But initial observations of the ²⁸O nucleus suggest that this isn’t the case: it disintegrates rapidly after creation. If the results can be replicated, physicists might need to update theories of how atomic nuclei are structured.