20 | NewScientist | 22 October 2011

Pluto’s rival is tiny but shiny

POOR Pluto. It got kicked out of the planet club in 2006 after an even larger world, Eris, was found in the outer solar system. Now it seems Eris is no larger than Pluto – it simply looks bigger because its surface is blindingly bright.

Observations by the Hubble Space Telescope in 2005 suggested Eris is at least 2400 kilometres wide, a few per cent wider than Pluto, which spans 2338 km. But the data left room for doubt.

Last November, astronomers got their best chance yet to pin down Eris’s size when it passed directly in front of a distant star and cast a small shadow on Earth. Bruno Sicardy of the Paris Observatory, France, and his team compared the shadow’s size from two different sites in Chile and found that Eris is just 2326 km wide – about the same size as Pluto, if not smaller. He reported the results this month at the Division of Planetary Sciences meeting in Nantes, France.

The observations suggest Eris is brighter than fresh snow, and may be the solar system’s second brightest object after Saturn’s moon Enceladus. Nitrogen or methane frost on its surface may be the cause.

DNA-bonded crystals herald a new chemistryARTIFICIAL crystals based on an alternative chemistry of DNA-bonded nanoparticles, rather than chemically bonded atoms, can now be created on demand.

In nature, the sizes and properties of the atoms that make up a crystal – a regular array of bonded atoms – determine its structure. That’s why each sodium atom in sodium chloride is surrounded by six chlorines and vice versa, whereas in gallium arsenide, each atom has only four nearest neighbours.

To create crystal structures that

do not depend on the size and nature of the component atoms, Chad Mirkin of Northwestern University in Evanston, Illinois, and colleagues used gold nanoparticles instead of atoms. To these, they attached dozens of DNA molecules that stuck out like hairs. Their ends were single-stranded DNA and so could form a bond to a complementary section of DNA attached to another gold particle. As more connections developed, a crystal formed.

The researchers then devised rules relating the structure of the

THINK of solar arrays and you’ll probably picture panels under blistering desert heat – but we may be able to get more energy from solar panels on snow-capped mountains.

Kotaro Kawajiri at the Massachusetts Institute of Technology mapped solar irradiance across the globe in collaboration with colleagues in Japan. They found that some of the highest levels of sunlight can be found in the Himalayas and the Andes: at altitude, less light is lost to the atmosphere.

There’s another reason why high-altitude solar power makes

sense. At temperatures of around 40 °C, 13 per cent of the energy solar panels would normally produce is lost to heat. The cold air at high-altitude keeps the panels cool and efficient, says Kawajiri (Environmental Science and Technology, DOI: 10.1021/es200635x).

Keith Barnham, a photovoltaics researcher at Imperial College London, says cold climates may be the new frontier in solar. “There are a lot of underdeveloped regions and communities living high up in the foothills of the Himalayas that could benefit from solar energy,” he says.

Himalayas: the Saudi Arabia of solar

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resulting crystals to factors that are independent of the composition of the particles, such as the overall size of the nanoparticle, including its DNA coating. This size can be tailored by using either different lengths of DNA or different-sized nanoparticles (Science, DOI: 10.1126/science.1210493).

The rules could lead to artificial crystals with combinations of properties that would never arise in nature. These might have novel applications, says Mirkin, such as improving solar cell efficiency.

World’s oldest artist’s workshop

GRIND up ochre, melt bone-marrow fat, mix the lot with a splash of urine and paint the resulting gloop over your body. It sounds like an avant-garde performance, but something similar may have happened some 100,000 years ago in the oldest known artist’s workshop – a cave in South Africa.

Inside the cave, Christopher Henshilwood of the University of the Witwatersrand in Johannesburg, South Africa, found two abalone shells that were used for storing paint (see picture). There were also stones used to grind ochre to a powder and animal bones that served as stirrers.

Henshilwood’s team discovered evidence that some of the bones had been heated, probably to melt fat from the marrow that would then have bound the pigment. “There were also quartzite fragments to cement it, mixed with a liquid, probably urine,” says Henshilwood.

The workshop was preserved because the cave filled with wind-blown sand shortly after it was abandoned, he says (Science, DOI: 10.1126/science.1211535).

No ancient cave painting has been found nearby, suggesting the paint may have been used for body art.

“It’s quite simply stunning,” says Paul Pettitt, an archaeologist at the University of Sheffield, UK.

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