Superfluid Helium: Hunt for an 'unidentified electron object'

This image shows vortex rings as the result of vortex multiplication in a quantum fluid. Some electrons are free, some got trapped by one or more vortices. 

Credit: Gleb and Sofia Berloff, ISM

New research sheds light on the nature of 'unidentified electron objects'—a mysterious class of objects that exists in superfluid helium at low temperature.

Researchers have developed a new mathematical framework capable of describing motions in superfluids – low temperature fluids that exhibit classical as well as quantum behaviour.

The framework was used to lift the veil of mystery surrounding strange objects in superfluid helium (detected ten years ago at Brown University).

The study, conducted by an international collaboration of researchers from the UK, Russia and France is published today in the journal Proceedings of National Academy of Sciences (PNAS).

The quantum nature of superfluids manifests itself in the form of quantized vortices, tiny twisters, with the core sizes of the order of an Angstrom (0.1nm – approximately the diameter of an atom) that move through fluid severing and coalescing, forming bundles and tangles.

To make these processes even more intricate and distinct from motions in usual classical fluids, these tiny twisters live on the background consisting of a mixture of viscous and inviscid fluid components that constitute superfluid.

The mathematical modelling of such complex systems that involve a range of scales is a notoriously difficult problem.

Natalia Berloff

The international team of researchers; Natalia Berloff of the University of Cambridge and the Russian Skolkovo Institute of Science and Technology, Marc Brachet of Université Pierre-et-Marie-Curie and Nick Proukakis of Joint Quantum Centre Durham came up with a novel framework for achieving this task.

The team applied their method to elucidate an intriguing phenomenon in liquid helium research.

Electrons immersed in superfluid helium are useful experimental probes. As they move through superfluid they form soft bubbles of about 2 nm in diameter that get trapped by quantized vortices quite similar to how houses and cars become trapped and transported by a tornado.

A research team from Brown University led by Professor Humphrey Maris has studied the effect of oscillating pressures on electron bubbles.

As pressure decreases below the criticality, the bubble expands and explodes, reaching micron sizes, with the bubble trapped by a vortex exploding at a pressure larger than that for the free bubble.

Maris' team also discovered another class of object that existed at very low temperatures only and exploded at even larger pressures. They termed these "unidentified electron objects".

More information: The paper 'Modeling quantum fluid dynamics at nonzero temperatures' was published today, 24 March 2014, in the journal Proceedings of the National Academy of Sciences (PNAS). www.pnas.org/cgi/doi/10.1073/pnas.1312549111

B612 Sentinel Space Telescope to Hunt Dangerous Asteroids

Artist's Illustration of the B612 Foundation's Sentinel mission, which will search for potentially dangerous near-Earth asteroids.

CREDIT: B612

With the dangers of rogue asteroids made clear by the surprise explosion of a meteor over Russia in February, a non-profit organization is ramping up its effort to search for potentially hazardous space rocks near Earth.

The B612 Foundation was started in 2002 by former NASA astronauts Ed Lu and Rusty Schweickart with colleagues. The organization aims to launch a space telescope called Sentinel in 2017 to catalog near-Earth asteroids, including those that may pose a danger to Earth.

To date, about 90 percent of near-Earth asteroids large enough to destroy the entire planet (about 1 kilometer, or 0.6 miles wide) have been discovered, but far fewer of the smaller, city-killing size (roughly 140 meters, or 460 feet, in diameter) have been found.

"We are essentially flying blind in a cosmic shooting gallery," Scott Hubbard, B612 program architect, told reporters on Tuesday (April 9) at the 29th annual National Space Symposium in Colorado Springs, Colo.

This reality was starkly illustrated on Feb. 15, when a 55-foot-wide (17 meters) meteor exploded over Chelyabinsk, Russia, just hours before an asteroid almost three times its size called 2012 DA14 flew uncomfortably close to Earth.

Sentinel's goal is to detect about 90 percent of this city-killing class of asteroids over a period of 6.5 years.

The $450 million mission is to be privately funded, though the foundation has partnered with NASA to share its data and use the agency's Deep Space Network of satellites to facilitate communications between Sentinel and the ground. NASA and lawmakers have said they enthusiastically support the mission and the B612 Foundation's efforts.

"We must better recognize what the private sector can do to aid our efforts to protect the world," Rep. Lamar Smith, R-Texas, chairman of the House Committee on Science, Space and Technology, said during a Congressional hearing on the asteroid issue Wednesday (April 10).

Subaru Optics Image: Spiral structure of disk may reveal planets

An image of the disk around SAO 206462 captured with Subaru's  HiCIAO. A coronagraph blocks the direct light of the central star, which appears as the black, circular area in the image. Arrows show the two arms of the spiral structure around the star. Credit: NAOJ 

An international team of astronomers has used HiCIAO (High Contrast Instrument for the Subaru Next Generation Optics) to observe a disk around the young star SAO 206462.

They succeeded in capturing clear, detailed images of its disk, which they discovered has a spiral structure with two discernable arms.

On the basis of their observations and modeling according to spiral density wave theory, the team suspects that dynamic processes, possibly resulting from planets in the disk, may be responsible for its spiral shape.

This research may provide the basis for another indirect method of detecting planets. Scientists have known that planets form in a broad disk of dust and gas surrounding a star, a so-called "protoplanetary disk."

However, the composition of these special disks as well as the process by which they give rise to planets have remained a mystery.

The bright light of a central star makes it difficult to detect fainter objects around it or to capture a detailed image of the composition of the disk itself.

Recent research with HiCIAO, Subaru Telecope's "planet-hunter", has overcome some of those obstacles.

By masking the bright light from the central star, the instrument can then detect more detailed features of the star's disk and the objects that it contains. 

Hunting the Moon

Hunting the Moon by Jean-Baptiste Feldmann (France). 

A playful silhouette places an Earth-bound Moon-catcher in pursuit of the waxing crescent Moon in the early evening sky on 6 April 2011.

The bright crescent is the part of the Moon lit directly by the Sun which is visible from Earth.

The rest of the face of the Moon is also visible, although much fainter owing to reflected light from the Earth, known as earthshine.

To actually reach the Moon the net would need to be 380,000 km long.

Picture: Jean-Baptiste Feldmann

Hunting For Fossils On Jupiter's Europa

Hunting For Fossils On Europa

If extraterrestrial life exists on Jupiter's moon Europa, instead of deploying probes to drill past its ice shell to look for aliens in the ocean below, one might just go fossil-hunting on the icy surface.

"A prospector sent there could possibly find extraterrestrial life within our lifetimes," suggested planetary scientist Richard Greenberg at the University of Arizona's Lunar and Planetary Laboratory at Tucson.

Europa, which is roughly the size of Earth's moon, is enveloped by a global ocean that may be about 100 miles deep (160 km). This ocean is overlain by an icy crust of unknown thickness, although some estimates are that it could be only a few miles thick.

Since wherever there is water on Earth there is a chance of life, for many years scientists have entertained the notion that this Jovian moon could support extraterrestrials. Recent findings even suggest its ocean could be loaded with oxygen, enough to support millions of tons worth of marine life like the type that exists on Earth.

To see if any kind of life actually evolved on Europa, scientists have proposed missions to drill through its outer shell, perhaps using heat to melt through the ice, whirring blades to clear away rocks and robot subs to explore the ocean.

"With that vision in mind, NASA has a multi-staged plan, first with a Europa orbiter scheduled for 18 years from now, and 10 or 20 years after that, a lander to see what the surface is like, and then maybe a generation later, hopefully we can figure out how to drill all the way down through the ice," Greenberg noted.

He recently wrote a book, "Unmasking Europa," which touched upon how one might search for life on the Jovian moon.

Borna Virus: Hunting Fossil Viruses in Human DNA

The borna virus is at once, obscure and grotesque. It can infect mammals and birds, but scientists know little about its effects on its victims.

In some species it seems to be harmless, but it can drive horses into wild fits. The horses sometimes kill themselves by smashing in their skulls.

In other cases, they starve themselves to death. Some scientists have even claimed that borna viruses alter human behavior, playing a role in schizophrenia and bipolar disorder, although others say there is no solid evidence of a link.

The virus now turns out to have an intimate bond with every person on Earth. In the latest issue of Nature, a team of Japanese and American scientists report that the human genome contains borna virus genes. The virus infected our monkey-like ancestors 40 million years ago, and its genes have been passed down ever since.

Borna viruses are not the only viruses lurking in our genome. Scientists have found about 100,000 elements of human DNA that probably came from viruses. But the borna virus belongs to a kind of virus that has never been found in the human genome before. Its discovery raises the possibility that many more viruses are left to be found.

Scientists who hunt for these viruses think of themselves as paleontologists searching for fossils. Just as animals get buried in rock, these viruses become trapped in the genomes of their hosts. While their free-living relatives continue to evolve, fossil viruses are effectively frozen in time.

“We can really dig fossils out of the genome and literally put them back together,” said Cédric Feschotte, a genome biologist at the University of Texas, Arlington. “It’s like putting a hominid back together and asking it if it can walk upright.”

When scientists sequenced the human genome in 2001, they noticed many segments that bore a striking resemblance to genes in retroviruses, a class of viruses that includes H.I.V.

Retroviruses carry their genetic material in a single-stranded version of DNA, called RNA. To make new viruses, they make DNA versions of their genes, which are inserted into a host cell’s genome. The cell then reads the retrovirus’s genes as if they were its own, and manufactures new retroviruses.

Scientists speculated that every now and then a retrovirus inserted itself into a host cell and then failed to turn it into a virus factory. If the trapped retrovirus happened to be in sperm or egg cells, its DNA might be passed down to the host’s descendants. From generation to generation, the virus’s DNA would mutate. It would lose its ability to produce normal viruses. For a while it might be able to make new viruses that could re-infect the same cell, but over enough time, the viruses would become disabled.

In recent years, scientists have found several lines of evidence to support this idea. . Koala retroviruses, for example, appear to be in the middle of the journey. The viruses can move from one koala to another. But in some populations of koalas, the virus’s DNA is permanently lodged in their genomes.

Thierry Heidmann of the Gustave Roussy Institute in France and his colleagues put the fossil virus hypothesis to a spectacular test: they tried to resurrect a dead retrovirus. They first identified a number of copies of the same virus-like stretch of DNA in the human genome. Each version had its own set of mutations that it acquired after the virus had invaded our ancestors.

By comparing the copies, Dr. Heidmann and his colleagues were able to figure out what the original sequence of the virus’s genes had been. When they synthesized the genes from scratch and injected the genetic material into cells, the cells produced new viruses.

“It was a tour-de-force of an experiment,” said John Coffin, an expert on fossil viruses at Tufts University.

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Hunting Moon Rocks in your Backyard!

YOU don't have to visit the moon to hold a chunk of it in your hand. Every day around 160 tonnes of rubble from space rains down on Earth, and some of it comes from the moon.

All you need to find a piece of moon rock is keen eyesight, patience and an expanse of ice or desert against which a dark little chunk of our neighbour will stand out.

French collector Luc Labenne, who has been scouring deserts for meteorites since 1997.

Meteorite hunters like Labenne follow an approach pioneered in the 1930s by the American collector Harvey Nininger, working on the Great Plains that stretch west from the Mississippi river to the Rocky mountains. Nininger taught local people to seek out black stones on the pale ground, and thanks to their efforts he bagged more than 200 meteorites over three decades.

Another rich source was identified in 1969 by the Japanese Antarctic Research Expedition, which found meteorites on a blue ice field near the Yamato mountains in East Antarctica. Other deserts became a focus of interest in the early 1990s, including the one that yielded our moon rock.

Lunar meteorites are exceedingly rare: only around 60 have been identified. And they don't just interest collectors. Space scientists are also keen to get hold of them, because they hold clues to what the rock is like on parts of the moon beyond the areas explored by the Apollo and robotic landers.