Tubes in space

Carbon nanotubes form in space but use a metal-free chemistry until now unavailable to chemists on Earth. The discovery is a surprising outcome of laboratory experiments designed by Joseph Nuth at NASA’s Goddard Space Flight Center, in Greenbelt, Maryland, and his colleagues. They were hoping to understand how carbon atoms are recycled in stellar nurseries, the regions of space where stars and planets are born, but the finding could have applications in nanotechnology, as well as help explain some characteristics of supernovae.

Writing in the journal Astrophys J Lett, Nuth and colleagues explain how astrochemistry makes carbon nanotubes without requiring a metal catalyst. Nanotubes are produced, they say, when graphite dust particles are exposed to a mixture of carbon monoxide and hydrogen gases, conditions that exist in interstellar space.

The finding corroborates the discovery of graphite whiskers, bigger than nano nanotubes, in three meteorites. The meteoric discovery hinted at why some supernovae appear dimmer and farther away than they ought to be based on calculations using current models. Nuth’s approach is a variation of a well-established way to produce gasoline or other liquid fuels from coal. It’s known as Fischer-Tropsch synthesis, and researchers suspect that it could have produced at least some of the simple carbon-based compounds in the early solar system. Nuth proposes that the nanotubes yielded by such reactions could be the key to the recycling of the carbon that gets released when carbon-rich grains are destroyed by supernova explosions.

Stellar Nursery
A stellar nursery could be home to carbon nanotube factories (Credit: NASA, http://apod.nasa.gov/apod/ap021102.html)

The structure of the carbon nanotubes produced by Nuth and colleagues was determined by materials scientist Yuki Kimura, of Tohoku University, Japan, using transmission electron microscopy. He observed particles on which the original smooth graphite gradually morphed into an unstructured region and finally to an area rich in tangled hair-like masses. A closer look with an even more powerful microscope showed that these tendrils were in fact cup-stacked carbon nanotubes, resembling a stack of disposable drinking cups with the bottoms removed. If further testing indicates that the new method is suitable for materials-science applications, it could supplement, or even replace, the familiar way of making nanotubes, explains Kimura.

Researchers might also now evaluate whether graphite whiskers absorb light. A positive result would lend credence to the proposition that the presence of these molecules in space affects the observations of some supernovae.

LINKS

Astrophys J Lett, 2010, 710, L98-L101

http://dx.doi.org/10.1088/2041-8205/710/1/L98

Magnetic wind

An analysis of observations from the Hinode satellite suggest that the solar wind generated by the sun is probably driven by a process involving powerful magnetic fields, according to researchers at University College London and their colleagues.

The study carried out by the UCL Mullard Space Science Laboratory, Observatoire de Paris, Konkoly Observatory in Hungary and Instituto de Astronomía y Física del Espacio in Argentina, could have implications for our understanding of our nearest star and its effects on Earth and our electronic systems including communications satellites and even devices on the ground.

Scientists have long speculated as to what gives rise to the solar wind, a constant stream of extremely high energy particles that pours out from the sun in all directions. The Extreme Ultraviolet Imaging Spectrometer (EIS), on board the Japanese-UK-US Hinode satellite has produced unprecedented data that is now enabling scientists to reveal the underlying forces that give rise to the solar wind. Data provided by the SOHO/MDI consortium, international collaboration between ESA and NASA suggest that a process referred to as “slipping reconnection” may drive the solar wind.

UCL’s Deb Baker explains: “Solar wind is an outflow of million-degree gas and magnetic field that engulfs the Earth and other planets. It fills the entire solar system and links with the magnetic fields of the Earth and other planets. Changes in the Sun’s million-mile-per-hour wind can induce disturbances within near-Earth space and our upper atmosphere and yet we still don’t know what drives these outflows.

Solar wind
Solar wind

“However, our latest study suggests that it is the release of energy stored in solar magnetic fields which provides the additional driver for the solar wind. This magnetic energy release is most efficient in the brightest regions of activity on the Sun’s surface, called active regions or sunspot groups, which are strong concentrations of magnetic field. We believe that this fundamental process happens everywhere on the Sun on virtually all scales.”

The team studied images taken in February 2007 from the EIS instrument, which show hot plasma outflows. At the edges of active regions where slipping reconnection might occur, according to computer models, the researchers explain that a slow, continuous restructuring of the magnetic field leads to the release of energy and acceleration of particles in the Sun’s hot outer atmosphere, its corona.

The locations proposed by the computer model correlated with gas moving outward at up to 160,000 kilometres per hour, a thousand times faster than a terrestrial hurricane.

Links:

Astrophys. J. 2009, 705, 926-935
Deb Baker homepage

Over and Oort on the comet’s tale

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An enormous asteroid or comet smashing into the Earth 65 million years ago killed off the dinosaurs. But, according to a new study by US scientists, published in the wake of an impact event on Jupiter, cometary collisions with Earth probably didn’t cause any more than one other extinction event during life’s history.

US researchers have looked to the Oort Cloud to help them work out just how many comets may have struck the earth during the time complex life has existed. The Oort Cloud is a remnant of the nebula from which the solar system formed 4.5 billion years ago. It starts about 93 billion miles from the sun (a thousand times as far from the sun as the Earth) and stretches to an incredible three light years away. It is thought that the Oort Cloud contains billions of comets but most are so small and distant that we will never see them.

Now, Thomas Quinn, Nathan Kaib and colleagues at the University of Washington, have used computer models to simulate the evolution of comet clouds in the solar system over the last 1.2 billion years. They found that even outside the periods of comet showers, the inner Oort Cloud was a major source of long-period comets. Some of these can cross Earth’s path but the simulations show that no more than two or three comets could have struck the Earth even during the most powerful comet shower of the last 500 million years.

Astronomers have known for some time that the inner solar system of rocky planets – Earth, Mars, Venus, and Mercury – is protected from comets by the gas giants Saturn and Jupiter. The enormous gravitational fields of these planets essentially eject comets into interstellar space or act as traps for them. This latter point was reinforced on 20th July when a huge scar appeared on Jupiter’s surface, likely evidence of a cometary impact.

There are about 3,200 known long-period comets of which Hale-Bopp is perhaps the most famous as it was visible with the naked eye for much of 1996 and 1997. Some long-period comets take thousands if not millions of years to make a single orbit of the sun. Comet Halley by contrast, which reappears every 75 years, is a short-period comet, which originate in a different part of the solar system known as the Kuiper Belt and are much more predictable. The computer simulation by Quinn and colleagues assumed that the inner Oort Cloud is the only source of potentially dangerous long-period comets.

The long-period comet 2001 RX14
The long-period comet 2001 RX14

“For the past 25 years, the inner Oort Cloud has been considered a mysterious, unobserved region of the solar system capable of providing bursts of bodies that occasionally wipe out life on Earth,” Quinn explains, “We have shown that comets already discovered can actually be used to estimate an upper limit on the number of bodies in this reservoir.”

With three major impacts taking place almost simultaneously, researchers had suggested that the minor extinction event of 40 million years ago resulted from a comet shower. Kaib and Quinn’s research implies that if that relatively minor extinction event was caused by a comet shower, then that was probably the most-intense comet shower since the fossil record began.

Further resources

Science Express, 2009, Jul 30, online

Tom Quinn’s home page

Comet shower movie from Nathan Kaib