16 | NewScientist | 5 October 2013

IS EARTH’S core playing cupid? It seems that xenon, a normally inert gas, can pair up with iron under the extreme conditions there. This could explain why our planet appears to lack xenon.

The atmosphere contains just 1/20th of Earth’s expected total xenon, as revealed by analyses of meteorites that should have a similar make-up to Earth.

To see if the missing xenon is

trapped in the planet’s core, Yanming Ma of Jilin University in Changchun, China, and colleagues used a supercomputer to model the element’s reactivity. Xenon would not normally react with iron – which makes up 85 per cent of the core – but at pressures of about 300 gigapascals and temperatures of about 6000 °C, found in Earth’s core, the two seemed attracted to one another.

The Red Planet’s supervolcanic past

MARS had a Yellowstone all of its own. And like the one lurking under the US national park, it went bang in a series of vast explosions that could have shaped the planet’s entire future.

The biggest known volcanoes on Mars, like Olympus Mons, coughed up lava slowly. But on Earth, supervolcanoes have been known to release 1000 cubic kilometres of lava and ash in a single explosive outburst.

When NASA’s Jacob Bleacher and his colleagues studied images of crater-like features in Mars’s Arabia Terra, they concluded that their size, depth and structure are good matches for supervolcano calderas. Each behemoth could have spat out between 4600 and 7200 cubic kilometres of lava and ash, they say (Nature, DOI: 10.1038/nature12482).

Such eruptions would have had a big impact on Mars’s climate and suitability for life, the team says.

Small islands are catastrophe for small mammals

NO ANIMAL is an island. Mammals marooned on small islands or in isolated forest fragments are more vulnerable than anyone knew. A case study in Thailand suggests they can go extinct in just 25 years. This is worrying because ecosystems around the world are being diced up as human activities encroach.

When Thailand flooded a rainforest to build a dam in 1986, it created an opportunity to study how isolation affects mammal populations. Poking above the waters of the new Chiew Larn reservoir were 100 islands of tropical rainforest. William Laurance from James Cook University

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Xenon and iron, a match made in the core A compound can form from one xenon and three iron atoms. Because it has lower energy than the sum of the pure elements’ energies under those conditions, it is the preferred state (arxiv.org/abs/1309.2169).

Ma’s team found that xenon could even react with nickel, a minor component of the core. “Earth’s core is a natural reservoir for xenon,” Ma says. So it could be that iron’s hot embrace is to blame for Earth’s missing xenon.

in Cairns, Australia, and colleagues identified 16 islands, varying in size from 0.3 to 56.3 hectares, and measured how quickly the small mammals there became extinct.

Five years after the flooding, the nine fragments under 10 hectares had lost almost all of their small mammals. Twenty years later, the larger islands had met the same fate. The only mammal left in any abundance was the Malayan field rat, an invasive species that had colonised the islands. The native species had declined so much – due to competition with the rats and inbreeding – that on many islands, researchers could only find a single individual (Science, doi.org/n2r).

“It’s a very striking and catastrophic decline of biodiversity,” says Laurance, and it emphasises the importance of linking habitats to create larger reserves.

BLACK holes famously trap everything in their path. Now it seems swirling eddies in the ocean are mathematically the same – and could help to slow climate change.

George Haller at the Swiss Federal Institute of Technology in Zurich and colleagues showed that eddies’ boundaries satisfy the same equations as the area surrounding black holes in general relativity. That helped them spot seven new whirlpools in the South Atlantic Ocean, off the coast of Africa (Journal of Fluid Mechanics, doi.org/n26). Previous studies suggest such eddies could carry warm water away from southern sea ice. That could help slow the ice’s melting, which affects global currents and weather.

Ocean’s black holes trap warm water