Tuesday, 30 April 2013

Rare Meteorite Grains May be from Supernova

New research suggests that two surprising grains of sand in a pair of meteorites that landed on Earth suggest they were formed in a single supernova which occurred billions of years ago. These grains may even come from the same star explosion that sparked the formation of the solar system, scientists say.

Both meteorites were found in Antarctica, and appear to date from before the solar system was born 4.6 billion years ago. Each contains a single grain of silica (SiO2). The chemical signature of these grains is identical, and extremely rare. Scientists suspect both grains came from a single supernova. This type of supernova occurs when a massive star runs out of fuel for nuclear fusion and collapses in on itself in a giant explosion.

These are the first such grains found in primitive meteorites, and are distinct because of the type of oxygen contained in the silica. Previous research has uncovered a handful of space rocks containing silica grains enriched in oxygen-17, which is thought to be created by living stars. But a slightly heavier version of oxygen, called oxygen-18, was found in these two new grains. Oxygen-18 must be formed in a supernova. 

The silica grains are so small they are invisible to the naked eye. Using an instrument called a NanoSIMS 50 ion microprobe, which magnifies objects 20,000 times, graduate student Pierre Haenecour of Washington University in St. Louis uncovered the single grain in one of the meteorites. The other was found by Xuchao Zhao, now a scientist at the Institute of Geology and Geophysics in Beijing, China, inside a meteorite discovered by the Chinese Antarctic Research Expedition.

Haenecour investigated just how the silica grains might have come to be, and found that their formation would have required a complex process of mixing material from various different layers of the star as it exploded. Because the precise mixing required to create oxygen-18 is so specific, the researchers suspect that both silica grains originated in the same supernova. The supernova might even be the same explosion that gave rise to the solar system. Scientists think a shock wave from a supernova might have been the event that caused a rotating cloud of gas and dust to condense, eventually giving rise to the planets of our solar system. As it exploded, the supernova also would have seeded the cloud with material, and some of that material may have ended up in the meteorites.

New 'Fairy' Insect is really small

A new species of tiny fly named after the fairy in "Peter Pan" is mind-blowingly miniscule, with delicate wings trimmed in fringe. Tinkerbella nana is a newly discovered species of fairyfly from Costa Rica. Fairyflies are a type of chalcid wasp, and almost all are parasites, living on the eggs and larvae of other insects. It's a gruesome way to live, but it makes fairyflies useful for farmers, who sometimes import them to control nasty pests.

Many fairyflies are extraordinarily tiny, including Kikiki huna, a Hawaiian species that grows to be only 0.005 inches (0.13 millimeters) long. This makes them tough to find, but researchers led by John Huber of Natural Resources Canada conducted their search by seeking out insect eggs in leaf litter, soil and on plants in the Costa Rican province of Alajeula.

There, they found specimens of Tinkerbella nana, none of which were more than 250 micrometers in length. One micrometer is a thousandth of a millimeter. Under the microscope, these teeny-tiny insects reveal fine detail, particularly their long, skinny wings, which terminate in hairlike fringe. This wing shape may help ultra-small insects reduce turbulence and drag when they fly, a feat that requires beating their wings hundreds of times per second. Researchers don't know how small insects can get, Huber said. "If we have not already found them, we must surely be close to discovering the smallest insects," he said. 

First rocket test flight of Virgin's passenger spaceship

A six-passenger spaceship owned by an offshoot of Virgin Group fired its rocket engine in flight for the first time, a key step toward the start of commercial service in about a year, Virgin owner Richard Branson said. The powered test flight over California's Mojave Desert lasted 16 seconds and broke the sound barrier. "It was stunning," Branson said. "You could see it very, very clearly. Putting the rocket and the spaceship together and seeing it perform safely, it was a critical day."

The spaceship and its carrier aircraft, WhiteKnightTwo, took off from the Mojave Air and Space Port, heading to an altitude of about 46,000 feet, where SpaceShipTwo was released. Two pilots then ignited the ship's rocket engine and climbed another 10,000 feet, reaching Mach 1.2 in the process. Additional test flights are planned before the spaceship will fly even faster, eventually reaching altitudes that exceed 62 miles.

"Going from Mach 1 to Mach 4 is relatively easy, but obviously we've still got to do it. I think that the big, difficult milestones are all behind us," Branson said. Virgin Galactic is selling rides aboard SpaceShipTwo for $200,000 per person. More than 500 people have put down deposits. Branson and his grown children plan to be the first non-test pilots to ride in the spacecraft, about a year from now.

SpaceShipTwo is based on a three-person prototype called SpaceShipOne, which in October 2004 clinched the $10 million Ansari X Prize for the first privately funded human spaceflights. Microsoft co-founder Paul Allen bankrolled SpaceShipOne's development, estimated at $25 million. Virgin Galactic and partner Aabar Investments PJC of Abu Dhabi have spent about $500 million developing SpaceShipTwo, and expect to sink in another $100 million before commercial service starts.

The company plans to build four more spaceships and several WhiteKnight carrier jets, which also will be used for a satellite-launching business. In addition to flying passengers, Virgin Galactic is marketing SpaceShipTwo to research organizations, including NASA, to fly experiments, with or without scientists. Other companies planning to offer suborbital spaceflight service include privately owned XCOR Aerospace, which expects to begin test flights of its two-person Lynx rocket plane this year.

Experiment Shows that Earth's Center Is 1,000 Degrees Hotter Than Previously Thought

Scientists have determined the temperature near the Earth's centre to be 6000 degrees Celsius, 1000 degrees hotter than in a previous experiment run 20 years ago. These measurements confirm geophysical models that the temperature difference between the solid core and the mantle above, must be at least 1500 degrees to explain why the Earth has a magnetic field. The scientists were even able to establish why the earlier experiment had produced a lower temperature.

Above view depicts the different layers of the Earth and their representative temperatures: crust, upper and lower mantle, liquid outer core and solid inner core. The pressure at the border between the liquid and the solid core is 3.3 million atmospheres, with a temperature now confirmed as 6000 degrees Celsius. The research team was led by Agnès Dewaele from the French national technological research organization CEA, alongside members of the French National Center for Scientific Research CNRS and the European Synchrotron Radiation Facility ESRF in Grenoble, France.

The Earth's core consists mainly of a sphere of liquid iron at temperatures above 4000 degrees and pressures of more than 1.3 million atmospheres. Under these conditions, iron is as liquid as the water in the oceans. It is only at the very centre of the Earth, where pressure and temperature rise even higher, that the liquid iron solidifies. Analysis of earthquake-triggered seismic waves passing through the Earth, tells us the thickness of the solid and liquid cores, and even how the pressure in the Earth increases with depth. 

These waves do not provide information on temperature, which has an important influence on the movement of material within the liquid core and the solid mantle. Indeed the temperature difference between the mantle and the core is the main driver of large-scale thermal movements, which together with the Earth's rotation, act like a dynamo generating the Earth's magnetic field. The temperature profile through the Earth's interior also underpins geophysical models that explain the creation and intense activity of hot-spot volcanoes.

To generate an accurate picture of the temperature profile within the Earth's centre, scientists can look at the melting point of iron at different pressures in the laboratory, using a diamond anvil cell to compress speck-sized samples to pressures of several million atmospheres, and powerful laser beams to heat them to 4000 or even 5000 degrees Celsius."In practice, many experimental challenges have to be met," explains Agnès Dewaele from CEA, "as the iron sample has to be insulated thermally and also must not be allowed to chemically react with its environment. Even if a sample reaches the extreme temperatures and pressures at the centre of the Earth, it will only do so for a matter of seconds. In this short timeframe it is extremely difficult to determine whether it has started to melt or is still solid."

This is where X-rays come into play. "We have developed a new technique where an intense beam of X-rays from the synchrotron can probe a sample and deduce whether it is solid, liquid or partially molten within as little as a second, using a process known diffraction," says Mohamed Mezouar from the ESRF, "and this is short enough to keep temperature and pressure constant, and at the same time avoid any chemical reactions."

The scientists determined experimentally the melting point of iron up to 4800 degrees Celsius and 2.2 million atmospheres pressure, and then used an extrapolation method to determine that at 3.3 million atmospheres, the pressure at the border between liquid and solid core, the temperature would be 6000 +/- 500 degrees. This extrapolated value could slightly change if iron undergoes an unknown phase transition between the measured and the extrapolated values.

When the scientists scanned across the area of pressures and temperatures at the MPI for Chemistry in Mainz (Germany), had in 1993 published values about 1000 degrees lower. Starting at 2400 degrees, recrystallization effects appear on the surface of the iron samples, leading to dynamic changes of the solid iron's crystalline structure. The experiment twenty years ago used an optical technique to determine whether the samples were solid or molten, and it is highly probable that the observation of recrystallization at the surface was interpreted as melting.

"We are of course very satisfied that our experiment validated today's best theories on heat transfer from the Earth's core and the generation of the Earth's magnetic field. I am hopeful that in the not-so-distant future, we can reproduce in our laboratories, and investigate with synchrotron X-rays, every state of matter inside the Earth," concludes Agnès Dewaele.