November 29, 2013 6:54 pm

Science: astronomy’s new ice age

US-led observatory detects cosmic neutrinos, which stream across the universe in unimaginable quantities
The IceCube neutrino observatory©Sven Lidstrom, Icecube/NSF

The IceCube neutrino observatory at the South Pole

One of the world’s strangest astronomical observatories, based on a cubic kilometre of Antarctic ice, has opened a new window on the universe. The $270m IceCube facility at the South Pole has started to detect high-energy cosmic neutrinos – subatomic particles that reach Earth from deep space.

Ordinary telescopes look at incoming photons (light particles) at various wavelengths, from radio through visible to X-rays and gamma rays. IceCube, however, sees neutrinos, which stream across the universe in unimaginable quantities but are extremely hard to detect because, unlike photons, they hardly ever interact with ordinary matter. They carry no electric charge and very little mass.

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The US-led IceCube consortium chose the inhospitable polar location to maximise the chance of observing cosmic neutrinos. They melted holes in the ice cap and lowered 5,160 light detectors to depths of between 1,500m and 2,000m beneath the surface.

Although trillions of neutrinos travel unscathed through the observatory every second, a precious few arrive at exactly the right angle to hit an atom in the ice. This collision generates electrically charged particles which radiate light that is picked up by the detectors. Then computers calculate the energy and incoming direction of the neutrino from the pattern and intensity of the light emitted.

(A similar method, with detectors buried in deep mines rather than Antarctic ice, is being used – so far without success – to identify the more elusive particles of “dark matter” that pervade the universe, according to cosmologists’ confident predictions.)

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A Finnish study has found that “telomeres”, DNA sequences whose length is a marker for ageing, erode faster in men who are out of work for more than two years.

In a paper in Science last week, the IceCube team said that they had detected 28 high-energy neutrinos coming from beyond the solar system over two years. Lower-energy neutrinos reach us in vast numbers from the sun and also from the interaction between cosmic rays and Earth’s upper atmosphere.

These 28 neutrinos are too small a sample to derive any conclusions about what produced them, but whatever it is must generate staggeringly high energies. Two of the detected neutrinos had more energy than a fly in flight, packed into a single subatomic particle.Likely sources include supernovae – exploding stars – and material being sucked into huge black holes.

The great advantage of neutrinos as astronomers’ probes is that they travel in absolutely straight lines from their source without being deflected by magnetic fields or absorbed by matter. They escape more readily than photons from, say, the core of a supernova.

“It is gratifying to finally see what we have been looking for,” says Francis Halzen of the University of Wisconsin and IceCube principal investigator. “This is the dawn of a new age of astronomy.”

. . .

Resurrection plants: designed to survive

Resurrection plant

The plant-breeding industry is making a big effort to develop crop varieties that are more tolerant of drought – through both conventional techniques and genetic manipulation. Few modifications would do more to extend world agriculture than enabling crops to grow in really dry conditions.

For Jill Farrant, professor of plant physiology at the University of Cape Town, the answer lies in “resurrection plants”. Most plants die when they lose 10 to 45 per cent of the water in their tissues; resurrection plants can survive for years with 95 per cent water loss and then spring back to life within a day or two of rehydration.

“Only about 350 plants – 0.1 per cent of the total number of species in the world – can tolerate extreme water loss and then revive on rehydration, and 90 per cent of them occur in southern Africa,” says Farrant.

Resurrection plants are not edible, however. “Their leaves are very bitter,” says Farrant. “No animals will eat them.” So she is investigating the molecular and systems biology of resurrection plants with a view to using them as a source of genes to transfer to staple crops such as maize.

Resurrection plants switch on a series of specific genes to protect their tissues as they dry out. Normal plants have some similar genes but these are only active in their seeds, which can often survive desiccation for many years.

“Resurrection plants shut down photosynthesis and curl up their leaves to minimise exposure to light,” Farrant says. “They also make sunblocking pigments to protect themselves. With maize, I want to increase the amount of sunblock pigments in the leaves, but it would not be feasible to make maize fold its leaves in drought.”

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New light on Michelangelo

Sistine Chapel ceiling©Foto Servizio Fotografico Musei Vaticani

The Sistine Chapel ceiling

The five million tourists who crowd into the Sistine Chapel every year to see Michelangelo’s ceiling will have a far better view from next February – the 450th anniversary of the artist’s death – when the Vatican switches on a new lighting system to match the illumination to the paintings.

The current lighting system, based on 1980s technology, has conventional spotlights and halogen projectors fitted with plastic covers to absorb ultraviolet light that might damage the paint. This bathes much of the ceiling in a low-contrast twilight that fails to bring out the colours in Michelangelo’s masterpiece.

The replacement LED (light emitting diode) system will enable visitors “to experience the art in a completely new diversity of colour”, says Osram, the German lighting company that developed it in collaboration with European universities and with EU research funding. Light levels will be 10 times higher than today – 50-100 lux rather than 5-10 lux – while both energy consumption and ultraviolet radiation levels will be cut.

The 7,000 individual LEDs have a spectrum that is tuned to suit Michelangelo’s paint pigments, which were analysed by colour experts at Pannonian University in Hungary. The artist is believed to have mixed his colours in daylight rather than by candlelight or torchlight.

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Predicting height through DNA

Forensic scientists are gradually gathering data to help determine the physical appearance of unknown criminals from genetic material left behind at a crime scene. A study in the Netherlands shows that scientists can now predict with reasonable accuracy whether someone is tall on the basis of DNA alone.

The researchers looked at 180 DNA variants associated with height in a Dutch population sample including 770 very tall people and 9,000 normal controls. Predicting height on the basis of these genes gave an accuracy of 0.75 on a scale from 0.5 (random prediction) to 1.0 (complete accuracy).

“The achieved accuracy is approaching practical relevance … in paediatrics and forensics,” the scientists conclude in a paper in the journal Human Genetics. Although forensics may be the main application of the work, paediatricians would also benefit from a genetic test that would predict the adult height of infants with parents of abnormal stature, to help decide whether to administer hormone treatment.

Manfred Kayser of Erasmus University Medical Centre in Rotterdam, the study leader, says: “Although the achieved DNA-based prediction accuracy for tall stature is still somewhat lower than we previously established for eye colour, hair colour and age, I expect that upcoming new knowledge on height genetics will further increase the accuracy in predicting tall stature, and eventually the full range of body height, from DNA.”

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