Posted on by Mark Mortimer

Book Review: The Tunguska Fireball

The Tunguska fireball occured in 1908 in the further reaches of Russia. Bright lights, loud sounds and searing heat signalled this event. Cutting edge measuring devices detected anomalies as far away as Britian, while most people of Europe had the pleasure of seeing a fairy tale like night time sky. Years later, some ground explorers loped into action to find a remarkably wide- spread landscape of shattered trees and burnt surfaces. Further, the tress fell in a pattern as to suggest being blown down by an extremely powerful force. However, given the inhospitable climate of the region, the assessment was brief and decades separated subsequent investigators. Further, given the political climate of the times, almost 50 years passed before international researchers arrived. Nonetheless, with the fertile imagination with which humans are blessed, we have taken what information was available, together with our growing cadre of knowledge in astrophysics, to raise a plethora of rationale for this fireball.

Surendra Verma presents his compilation of the events and possible causes in a smoothly flowing and succintly detailed rendition. He begins by repeating the known facts and figures. People, times, and places fill out the background for the reader and stress the challenges in solving this mystery. Much seems to stem from the brevity of facts and the inaccesibility of the region. In a loosely chronological sequence, Verma pins together the details in a fashion more reminiscent of note taking than of novel writing. He appears to stay to the facts and takes little literary excess with hyperbole of either facts or reactions. However, the reader can easily make their own decuctions. For instance, I was fascinated to learn of the small amount of interest shown by the locals. Instead of acknowledging the fireball and learning from it, their response was to treat it as a sort of mythical situation that was better left alone. Nevertheless, given that there always seems to be some overly curious types, people did consider this event and Verma does bring their observations to the fore.

Once he has established this basis, Verma than treats us to the smorgasbord of hypotheses that arose. He doesn’t solve it himself, as suggested by the sub-title. Rather, he seems to have two other purposes. One is to demonstrate that many natural processes give rise to similar effects. People saw lights, heard explosions and felt heat. The source might have been asteroids, comets, nuclear explosions, anti-matter, mirror matter, black holes, aliens, and so on. The other purpose he provides is to discuss the natural processes themselves. These tidbits will keep the up and coming scientiest curious for many pages. Verma usually isolates each process in individual chapters. As an example, the chapter on asteroids discusses their typical composition, locations within in our solar system and frequency of striking planets. Occassional asides mention the possibility of a companion star for our sun that occasionaly redirects asteroids toward Earth. At the book’s end, Verma does sum up the data and selects his most likely suspect, just like the second last chapter in a mystery novel.

With the combination of scientific and historical background, Verma presents an easy to read treatise on both the fireball and on physical phenomena that could cause such a huge effect upon the flora and fauna on the Earth. Sometimes the description of the science seems to overshadow the event. For instance, a large section describes the extinction of dinosaurs. True, this extinction event, in ways, is just as mysterious as the fireball. However, asteroids and comets were already discussed. The discovery of the Chicxculub crater and its implications seems superlative to the main theme. Given the scarceness of data, there is no surprise on this relative emphasis on the science.

The fireball that blew into Russia’s north may be due to an understood physical event. However, as Surendra Verama shows us in his book Tunguska Fireball we are not exactly sure which event. Much in its history remains obscure, while each of many popular hypotheses rely on contradictory points. Nevertheless, as with any good mystery, there are lots of suspects and enough questions to keep contemplating and enjoy perusing within.

Review by Mark Mortimer

Read more reviews online, or purchase a copy from Amazon.com.

Posted on by Fraser Cain

Saturn’s Moon Pan

Moon Pan behind ring A. Image credit: NASA/JPL/SSI Click to enlarge
Cassini turns its gaze toward Saturn’s outer A ring to find the moon Pan coasting behind one of the thin ringlets which it shares with the Encke Gap. Pan is 26 kilometers (16 miles) across.
Understanding the influence of Saturn’s moons on its immense ring system is one of the goals of the Cassini mission. The study of the icy rings includes the delicate and smoky-looking F ring, seen here toward the upper right. The F ring exhibits bright kinks and multiple strands here.

Arching across the center of the scene, the outermost section of the A ring is notably brighter than the ring material interior to it.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Aug. 13, 2005, at a distance of approximately 2.3 million kilometers (1.5 million miles) from Saturn. The image scale is 14 kilometers (9 miles) per pixel on Pan.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

Venus, Jupiter and the Moon Reunited Again

Similar close encounter last November. Image credit: Babak A. Tafreshi Click to enlarge
Something nice is happening in the sunset sky. Venus and Jupiter, the two brightest planets, are converging, and they’re going to be beautifully close together for the next two weeks.

Step outside tonight when the sun goes down and look west. If there are no trees or buildings in the way, you can’t miss Jupiter and Venus. They look like airplanes, hovering near the horizon with their lights on full blast. (Venus is the brighter of the two.) You can see them even from brightly-lit cities.

Try catching the pair just after sundown and just before the first stars appear. Venus and Jupiter pop into view while the sky is still twilight-blue. The scene has a special beauty.

When the sky darkens completely, look to the left of Jupiter for Spica, the brightest star in the constellation Virgo. Although it’s a bright star, Spica is completely outclassed by the two planets.

Venus and Jupiter are converging at the noticeable rate of 1o per day, with closest approach coming on September 1st when the two will be a little more than 1o apart. (How much is 1o? Hold your pinky finger at arm’s length. The tip is about 1o wide.)

When planets are so close together, not only do you notice them, you’ll have a hard time taking your eyes off them. They’re spellbinding.

There’s a biological reason for this phenomenon: In the back of your eye, near the center of the retina, lies a small patch of tissue called “the fovea” where cones are extra-densely packed. “Whatever you see with the fovea, you see in high-definition,” explains Stuart Hiroyasu, O.D., of Bishop, California. “The fovea is critical to reading, driving, watching television; it has the brain’s attention.” The field of view of the fovea is 5o. When two objects converge to, say, 1o as Venus and Jupiter will do, they can beam into your fovea simultaneously, signaling your brain?attention, please!

After September 1st, the two planets separate, but the show’s not over. On September 6th, with Jupiter and Venus still pleasingly close together, the slender crescent Moon will leap up from the sun’s glare and join the two planets. Together, they’ll form a compact triangle that will simply knock your socks off.

Feel like staring? Do.

Original Source: NASA News Release

Posted on by Fraser Cain

Earth’s Core Rotates Faster Than Its Crust

Earth. Image credit: NASA Click to enlarge
Scientists have ended a long debate by proving that Earth’s core rotates faster than its surface.

Their research measured differences in the time it took seismic waves generated by nearly identical earthquakes to travel through Earth’s inner core.

According to geologists Jian Zhang of the Lamont-Doherty Earth Observatory (LDEO), Xiaodong Song of the University of Illinois at Urbana-Champaign and other co-authors of a paper in the Aug. 26 issue of the journal Science, Earth’s iron core is rotating approximately 1 degree per year faster than the rest of the planet.

“Whether the Earth’s core spins faster than its surface has been a hotly debated topic,” says Robin Reichlin, program director in the National Science Foundation (NSF)’s Division of Earth Sciences, which funded the research. “These new observations provide compelling support that it does.”

The scientists studied waveform doublets–earthquakes that are detected at the same seismic recording station in two different places, at two different times. A Sept. 2003, earthquake in the Atlantic Ocean near the South Sandwich Islands that was also detected in Ala., provided a near-exact match with one that had occurred in Dec.1993.

The seismograms were almost identical for shocks that had traveled only in the mantle and outer core. But seismic waves that had traveled through the inner core looked slightly different: they had made the trip through the Earth faster in 2003 than in 1993.

“The similar seismic waves that passed through the inner core show changes in travel times,” says Song. “The only plausible explanation is the faster rotation of the inner core.”

In all, the geologists analyzed 18 “doublets” from the South Sandwich Islands that were detected at Ala. seismic stations between 1961 and 2004.

“For decades, people thought of the Earth’s interior as changing very slowly over millions of years,” said scientist Paul Richards of LDEO, a co-author of the paper. “These results show that we live on a remarkably dynamic planet. They also underscore the fact that we know more about the moon than we know about what’s beneath our feet. Now we need to understand what is driving this difference.”

In addition to Zhang, Song and Richards, co-authors of the paper are Illinois graduate students Yingchun Li and Xinlei Sun and research scientist Felix Waldhauser. The work was also funded by the Natural Science Foundation of China.

Original Source: NSF News Release

Posted on by Fraser Cain

Spaceships Made from Plastic?

Artist’s concept of humans set off to Mars. Image credit: NASA Click to enlarge
After reading this article, you might never look at trash bags the same way again.

We all use plastic trash bags; they’re so common that we hardly give them a second thought. So who would have guessed that a lowly trash bag might hold the key to sending humans to Mars?

Most household trash bags are made of a polymer called polyethylene. Variants of that molecule turn out to be excellent at shielding the most dangerous forms of space radiation. Scientists have long known this. The trouble has been trying to build a spaceship out of the flimsy stuff.

But now NASA scientists have invented a groundbreaking, polyethylene-based material called RXF1 that’s even stronger and lighter than aluminum. “This new material is a first in the sense that it combines superior structural properties with superior shielding properties,” says Nasser Barghouty, Project Scientist for NASA’s Space Radiation Shielding Project at the Marshall Space Flight Center.

To Mars in a plastic spaceship? As daft as it may sound, it could be the safest way to go.

Less is more

Protecting astronauts from deep-space radiation is a major unsolved problem. Consider a manned mission to Mars: The round-trip could last as long as 30 months, and would require leaving the protective bubble of Earth’s magnetic field. Some scientists believe that materials such as aluminum, which provide adequate shielding in Earth orbit or for short trips to the Moon, would be inadequate for the trip to Mars.

Barghouty is one of the skeptics: “Going to Mars now with an aluminum spaceship is undoable,” he believes.

Plastic is an appealing alternative: Compared to aluminum, polyethylene is 50% better at shielding solar flares and 15% better for cosmic rays.

The advantage of plastic-like materials is that they produce far less “secondary radiation” than heavier materials like aluminum or lead. Secondary radiation comes from the shielding material itself. When particles of space radiation smash into atoms within the shield, they trigger tiny nuclear reactions. Those reactions produce a shower of nuclear byproducts — neutrons and other particles — that enter the spacecraft. It’s a bit like trying to protect yourself from a flying bowling ball by erecting a wall of pins. You avoid the ball but get pelted by pins. “Secondaries” can be worse for astronauts’ health than the original space radiation!

Ironically, heavier elements like lead, which people often assume to be the best radiation shielding, produce much more secondary radiation than lighter elements like carbon and hydrogen. That’s why polyethylene makes good shielding: it is composed entirely of lightweight carbon and hydrogen atoms, which minimizes secondaries.

These lighter elements can’t completely stop space radiation. But they can fragment the incoming radiation particles, greatly reducing the harmful effects. Imagine hiding behind a chain-link fence to protect yourself in a snowball fight: You’ll still get some snow on you as tiny bits of snowball burst through the fence, but you won’t feel the sting of a direct hit from a hard-packed whopper. Polyethylene is like that chain link fence.

“That’s what we can do. Fragmenting — without producing a lot of secondary radiation — is actually where the battle is won or lost,” Barghouty says.

Made to order

Despite their shielding power, ordinary trash bags obviously won’t do for building a spaceship. So Barghouty and his colleagues have been trying to beef-up polyethylene for aerospace work.

That’s how Shielding Project researcher Raj Kaul, working together with Barghouty, came to invent RXF1. RXF1 is remarkably strong and light: it has 3 times the tensile strength of aluminum, yet is 2.6 times lighter — impressive even by aerospace standards.

“Since it is a ballistic shield, it also deflects micrometeorites,” says Kaul, who had previously worked with similar materials in developing helicopter armor. “Since it’s a fabric, it can be draped around molds and shaped into specific spacecraft components.” And because it’s derived from polyethylene, it’s an excellent radiation shield as well.

The specifics of how RXF1 is made are secret because a patent on the material is pending.

Strength is only one of the traits that the walls of a spaceship must have, Barghouty notes. Flammability and temperature tolerance are also important: It doesn’t matter how strong a spaceship’s walls are if they melt in direct sunlight or catch fire easily. Pure polyethylene is very flammable. More work is needed to customize RXF1 even further to make it flame and temperature resistant as well, Barghouty says.

The Bottom Line

The big question, of course, is the bottom line: Can RXF1 carry humans safely to Mars? At this point, no one knows for sure.

Some “galactic cosmic rays are so energetic that no reasonable amount of shielding can stop them,” cautions Frank Cucinotta, NASA’s Chief Radiation Health Officer. “All materials have this problem, including polyethylene.”

Cucinotta and colleagues have done computer simulations to compare the cancer risk of going to Mars in an aluminum ship vs. a polyethylene ship. Surprisingly, “there was no significant difference,” he says. This conclusion depends on a biological model which estimates how human tissue is affected by space radiation–and therein lies the rub. After decades of spaceflight, scientists still don’t fully understand how the human body reacts to cosmic rays. If their model is correct, however, there could be little practical benefit to the extra shielding polyethylene provides. This is a matter of ongoing research.

Because of the many uncertainties, dose limits for astronauts on a Mars mission have not been set, notes Barghouty. But assuming that those dose limits are similar to limits set for Shuttle and Space Station flights, he believes RXF1 could hypothetically provide adequate shielding for a 30 month mission to Mars.

Today, to the dump. Tomorrow, to the stars? Polyethylene might take you farther than you ever imagined.

Original Source: NASA News Release

Posted on by Fraser Cain

Astronomers Looking for Help with Cataclysmic Variable Star

GALEX , one of the telescopes that will study AE Aqr. Image credit: NASA Click to enlarge
Amateur astronomers are being asked to help a constellation of observatories unravel the mysteries of a puzzling binary star system.

On August 30-August 31, 2005 two space-based and four professional ground-based observatories are scheduled to observe the cataclysmic variable star AE Aqr. Each of the observatories covers a different wavelength of light and amateur astronomers have been asked to help cover the visible-light portion.

“This observing campaign will take place over nearly a full day, and since no single ground-based observatory can observe AE Aqr for that long due to Earth’s rotation, amateur astronomers can make a unique and invaluable contribution to this campaign,” said Dr. Christopher Mauche of Lawrence Livermore National Laboratory, the principal investigator of the project.

Because they are spaced all across the globe, amateur astronomers can observe this star and other celestial objects unhindered by nightfall or weather.

The Chandra and GALEX space telescopes will be working with the HESS, MAGIC, VLT, and VLA ground-based telescopes. Combined, they will provide coverage of AE Aqr from high-energy gamma-rays to low-energy radio waves. Such simultaneous multiwavelength coverage is required to provide the clearest picture of the locations, mass motions, energetics, and inter-relationships of the various emission regions in the star.

AE Aqr is an intermediate polar, a type of cataclysmic variable star. It actually consists of two stars – a red dwarf and rapidly spinning magnetic white dwarf. Material drawn off the red dwarf falls toward the white dwarf, but instead of landing on the white dwarf surface, it is flung out of the system by the white dwarf’s rapidly spinning magnetic field. This mechanism, which is uncommon but not unique to AE Aqr, is referred to as a magnetic propeller.

“Amateurs astronomers have been observing AE Aqr since 1944. Since then, they have recorded over 28,815 measurements of the star, most of them made with just a telescope and their eyes. This type of historical data is immensely valuable in studying variable stars and only amateurs can provide it,” Dr. Arne Henden, Director of the American Association of Variable Star Observers (AAVSO), said.

Amateur astronomers are being asked to observe AE Aqr every night possible until September 3. Those with CCD cameras on their telescopes are requested to make scientific brightness measurements, known as photometry, of the system as well. For information on how to measure the brightness of AE Aqr and submit results to professionals, visit the AAVSO web site at http://www.aavso.org/alertnotice .

The AAVSO is the world’s preeminent professional-amateur astronomical association. Specializing in the study of variable stars, the AAVSO’s International Database has over 11 million observations of variable stars dating back over 100 years. Founded in 1911 as part of the Harvard College Observatory, the AAVSO became independent in 1954 and currently has over 3,000 members and observers in over 40 countries.

Original Source: AAVSO News Release