Monday, February 19, 2007

Meteorite Madness 4

Stony Meteorites


Appropriately, stony meteorites without chondrules are termed "achondrites," except for the carbonaceous chondrites and some the enstatite chondrites. Only about 40 achondrites have been recovered and studied, and most of them are falls. These meteorites are terribly difficult for untrained observers to identify, except for the distinctive black fusion crusts on fresh falls. The achondrites do not contain abundant nickel-iron and tend to be more coarsely crystalline than other stony meteorites but not quite as crystalline as the iron meteorites. Some achrondites have the texture of regular old rocks, and many others contain angular clasts of different mineralogies and textures. Some achondrites contain angular fragments of chondrites.

Achondrites were divided by Prior into two groups based on calcium content: calcium-poor and calcium-rich. Within these two broad groups, Prior named a number of subdivisions. The calcium-poor achrondites include aubrites, diogenites, chassignites, and ureilites. The calcium-rich achrondites include eucrites and howardites, angrites, and nakhlites. These subdivisions were modified somewhat by others, but the system remains largely intact. But because the total amount of studied achondrites remains so small, each subsequent discovery has the potential to radically alter the world of meteoritology. Many individual descriptions and contributions treat only a single specimen or a few samples of achondrites. There has yet to be a comprehensive study of achondrites.

In numbers, the calcium-rich achondrites dominate the group, especially the eucrites and howardites of which more than 20 specimens are known. Some of the other classes are represented by only a single stone (angrites and chassignites), and only two nakhlites have been recognized. The aubrites and diogenites have eight specimens each. Some meteorites in these groups are interesting for the very large crystals they contain, as much as several centimenters long. One of the aubrites, Pena Blanca Springs (right), has a hilarious and interesting story behind it. In 1946, the meteorite fell into a swimming pool constructed by damming up a small creek near the headquarters of a large Texas ranch. More than 70kg of the stone were recovered, the phenomena accompanying the daylight fall was well documented. It may look like a piece of your driveway, but it most certainly is not!

Scientists have speculated about the origin of the achondrites and come up with a number of competing theories. M.B. Duke and L.T. Silver suggest that the basaltic achondrites may have originated from the Moon as secondary ejecta from meteoroid impacts. They speculated that the howardites might be fragments of the lunar highlands, and that the eucrites might have originated from the maria. This suggestion has been widely accepted by meteorite workers, but no lunar samples have confirmed this idea.

Whatever the origins of the achondrites, they constitute a group that, for the most part, are chemically and texturally distinct from the more common classes of stony meteorites. Further work on the achondrites may help to provide information on early Solar System Conditions and processes. This type of mystery should inspire young meteoriteers to join the field and unravel the riddles of these sky stones. At the very least, you should learn to identify these types of stones so that the scientists will have a larger body of data to work from. When you are on the cutting edge, every little bit helps!

Friday, February 16, 2007

Space Shuttle Atlantis

This afternoon, at around 3pm EST, the Space Shuttle Atlantis arrived at Kennedy Space Center Launch Pad 39A. Atlantis is one of three functional Space Shuttles in NASA's fleet after the destruction of Challenger and Columbia. The other two remaining shuttles are Discovery and Endeavor. After the shuttle completes this launch to repair the Hubble Space Telescope, it will be the first shuttle in its class to be retired.

It alarms me that of the five original Space Shuttles only three remain operational. It alarms me that NASA has continued to use Shuttles that were designed for ten years of operation for more than twenty years. Atlantis' first flight was in October 1985, this, ostensibly, will be its last. It alarms me that NASA has made no new discoveries to get Man into Space more quickly and more safely than Space Shuttles and Solid Fuel Booster Rockets. They're stuck, and they know it.

Atlantis will be the first Space Shuttle retired, but it won't be the last. Both of the other remaining Space Shuttles are supposed to be decommissioned by 2010. At that time, NASA hopes to introduce its Orion spacecraft as its primary Crew Exploration Vehicle (CEV) and Ares I as its primary Crew Launch Vehicle (CLV). NASA will have achieved the equivalent of changing the tires on your car, everything is the same (the technology, the operation, the agenda) except what actually touches the road (space travel) is a little bit better and hopefully a who lot less dangerous.

NASA is in a rut. If this sci-fi friendly rendering of space travel is the best that they can do to dynamically restore the program as paramount to the United States, then color me unimpressed.

Monday, February 12, 2007

Meteorite Madness 3

Stony Meteorites

The chondrites, stony meteorites containing chondrules, numerically dominate the falls, and may be the most abundant class of meteorite in the known Solar System at the present time. Chondrules are usually spherical to subspherical bodies, composed of primarily silicates, that range in size from less than 0.1 to more than 20 mm. Mineralogically, chondrules commonly are composed to olivine, pyroxene, plagioclase, glass, troilite, nickel-iron, and any combination of these minerals. Texturally, chondrules may be aggregates of crystals, single crystals, pure glass, or crystal and glass in a wide range of proportions and textures in seemingly endless variety. Many chrondrules appear to have been free fluid drops that assumed a spherical or nearly spherical shape due to surface tension and later solidified and crystallized. However, other chondrules clearly have not had this sort of history, but may be rounded clasts, or have had other more complex origins.

The classification of chondrites is based on their chemistry and mineralogy. The most widely accepted classification was first proposed in 1920 by G.T. Prior in Mineralogy Magazine and was later modified by Brian Mason (right) in his book Meteorites and includes the following classes: enstatite chondrites; bronzite chondrites; hypersthene chondrites; and carbonaceous chondrites. Chemical and mineralogical regularities in the chondrites were recognized early by Prior, and these observations led to the formulation in of Prior's Rules, which can be stated as follows:
1. The smaller the volume of nickel-iron in a chondrite, the greater must be the nickel to iron ratio in the metal.
2. The smaller the volume of nickel-iron in a chondrite, the greater must be the iron to magnesium ratio in ferromagnesian silicates.

These rules were landmark in the history of meteoritics and had a profound influence on the discipline from that time forward. But with their emphasis on just a few elements, Prior’s Rules also reflect the technological limitations of the early part of the 20th Century. Advances in meteoritics since that time have led some to treat Prior's Rules as having historical importance rather than contemporary relevance. It is important to remember however, that Prior's Rules recognize, mineralogically, the fundamental importance of oxidation states and by implication oxygen fugacity on the gross character of meteoritic samples.

Earlier work with chondrites and their classification was done notably by G. Rose, who first recognized the chondrites as a distinct group, Gustav Tschermak (left), who was a superb petrographer, and Aristides Brezina, who eventually divided the chondrites into more than 30 classes. The Rose-Tschermak-Brezina classification was widely used by students of meteorites until about 1960. The fallacies and superficial basis of much of the Rose-Tschermak-Brezina classification had been pointed out by Prior, but the system was not fully abandoned until the comprehensive review of meteorites by Mason. Students continue to use Mason's system of classification today, with few revisions.

Friday, February 9, 2007

The Rich Get Richer

Congress recently approved the federal budget for the fiscal year of 2007, and amidst all the hubbub about Homeland Security and the War in Iraq, a great tragedy was overlooked. As we all now know, freedom has its costs, but so does science. And the new budget completely ignores true scientific endeavors for the sake of gallant space pipe-dreams. I don't like to mix politics into my posts (around the Susbuck house we call that "postitics"), but both parties are to blame here. I'm an independent, I let each side have its say, but when you get right down to it, they're both a bunch of idiots.

NASA got all the money that it was asking for, pushing its budget up to $16.8 billion! When the country is experiencing such an enormous deficit, we should not be increasing any agency's budget! We've got to cut back and get back on top of this deficit thing. A quick perusal of NASA's budget request reveals exactly how they want to spend our money. Once you get through all the corporate-speak, you can really start to see where the money goes. More money for constellation exploration, less money for education, more money for the International Space Station, less money for human systems research and technology. It doesn't make any sense to me!!

If even a fraction of this money went towards space geology, we would be much better off as a country. Meteorites and asteroids fly by the planet everyday, only missing our planet by inches. We need to learn what they are made of so that we will be better prepared to spot and stop them. I know that the movie Armageddon is fiction, but it is also a heady warning about our future. If we wonder if there is life elsewhere in the universe, we should look at the rocks that the universe throws through our window (the atmosphere)! We can find the answers to these questions, we just need to learn more about the geology of space!

Monday, February 5, 2007

Meteorite Madness 2

Meteorite Composition

Traditionally, meteorites have been classified by the relative amounts of metal and silicate that they contain. The terms iron, stony-iron, and stone are widely used to categorize meteorites. Irons are composed primarily of metallic nickel-iron, but may contain silicate and other minerals. Stones are made up of mostly silicates, largely iron-magnesium silicates, but may contain more than 24% metallic nickel-iron. The stony-irons are a group of uncommon, ill-defined meteorites that have a large amount of nickel-iron and contain a variety of silicate minerals. The relative abundances of these three groups of meteorites are best represented by the simple statistics of observed falls and finds. Stones account for approximately 63% of meteorites, irons roughly 33%, and stony-irons the remaining 4%.

Of course, there are significant selection factors involved with the recognition of finds by untrained persons, who initially uncover the majority of finds. Irons are relatively easy to distinguish from ordinary terrestrial rocks. They are ferromagnetic, commonly rusty in surface appearance, have a high specific gravity, and have bright white to light gray metallic luster on a freshly filed surface. Another identifying feature of iron meteorites is their ruggedness. They seem to weather less rapidly than many other stones and will persist longer at surface conditions. Stones, on the other hand, require a more careful or trained observer for their recognition. They have many identifiable characteristics (fusion crust, presence of chondrules, minor amounts of metal, etc), but they are not so conspicuous among terrestrial rocks.

There are more than 80 types of minerals that have been found in meteorites, but the total number of meteorites that have been identified and studied is embarrasingly small. New and unstudied specimens are sorely need by all major universities and science laboratories. If you think you have found a meteorite, please go to this link. Eric Twelker (right) is a very helpful man and will be more than happy to positively identify a meteorite for you. He has helped me with many of my found meteorites (unfortunately, they weren't always meteorites!). Then you can proudly display your sky stones, or sell them to research institutions and universities for some big bucks! The knowledge gained is always priceless!

Tuesday, January 30, 2007

Everything Goes Wrong

Quickly, these are some important developments in space. This past week, two things have set back Man's presence in space.

First, the Hubble Telescope's main camera lost two thirds of its capacity when it short circuited. "We believe that the wide field channel and high resolution channel on the ACS instruments are no longer available to us," said Preston Burch, the Hubble program manager. It will take until 2008 for NASA to launch a repair mission and keep the telescope operational.

Second, the newest satellite from European satellite giant SES New Skies, the NSS-8, was destroyed in an explosion on the launch pad early on Tuesday. Of course, the hubristic company still has a site up extolling the virtues of their now defunct brainchild. Here's a photo of the satellite's fiery demise.The company plans to attempt another launch in 2009.

I don't want to make it seem as if I am celebrating these accidents, but my point is clear. Space is not the place for mankind. All our fancy machinery breaks down and fails us. Give me a telescope and a notebook and a clear night and I will read the stars for you.

Monday, January 29, 2007

Meteorite Madness 1

This post will begin a series of posts on meteorites. These posts will be more technical and less subjective than my others, and I hope that the jargon will not dilute the underlying message. I will attempt to make my writing as accessible as possible for everyone from veteran astrogeologists to a Boy Scout with his first telescope. Please join me and my meteorite (right)!

Meteorite Basics

All of our extraterrestrial samples, except for the Moon rocks returned by the Apollo Project, are meteorites. History has documented accounts of stones falling from the sky in every language from Chinese to Greek. Of course, these ancient peoples accounted for the phenomenon in a variety of ludicrous ways. Strong winds would supposedly blow the stones into the sky and from whence they fell back to the Earth. One of the most holy Muslim relics is the black stone (the Hadschar al Aswad) of the Kaaba (left), which is widely believed to be a fragment of a meteorite and may be the oldest preserved fragment from an observed fall. Such was the fate of a meteorite when it fall onto the ancient Earth.

But even after meteorites were recognized as genuine natural phenomena, debates raged over the places and processes of their origin. In 1879, it was seriously proposed that meteorites were terrestrial fragments that had been placed in near-Earth space by immense volcanic explosions. Since then, our understanding of meteorites has progressed slowly and is still in a rather primitive state compared with our current understanding of terrestrial rocks and even lunar samples. This is why we urgently need to divert energy and resources to the problem of meteorites. Although a vast descriptive and analytical literature of meteorites exists, the critical lack of certainty as to their places of origin has severely limited interpretations of modes of meteorite origin and possible genetic relations between different meteorite types.

More than 3600 different meteorites are preserved in collections throughout the world and that number is growing astronomically (pun intended). A meteorite fall may consist of thousands of of stone fragments or individual pieces of iron, but all of these pieces are considered part of the same meteorite. In virtually all cases, multiple falls are known to be the result of a larger individual piece into many more fragments under the immense aerodynamic pressure from the hypervelocity entry of the meteoroid into the dense portion of the Earth's atmosphere. Reported falls of meteorites are common.

If a recovered meteorite was not observed during its luminous passage through the atmosphere as a meteor or bolide, but is recognized as such by its texture, mineralogy, chemistry, surface features or unusual occurrence, it is termed a "find" (as opposed to a "fall"). By international convention, meteorites are named for the closest post office or community to the location of the fall or find that is easily located on a small scale map of the area.