NEO News (02/24/09) Texas fireball & Nova show

NEO News (02/24/09): Texas fireball & Nova show [From Dave Morrison]:

TEXAS FIREBALL ON FEBRUARY 16

The recent daylight fireball in Texas received considerable press attention because it came shortly after the collision of US and Russian satellities. There was speculation that this might be a fragment from that collision rather than a natural meteor. That issue is apparently settled by the following message from Peter Brown of Western Ontario University in Canada. "I have been catching up with details of the Texas fireball -- it appears to be an L5 chondrite and seems to have produced numerous fragments on the ground. Clearly not related to the satellite collision of a few weeks back."

As background, there was no reason to assume that the fireball seen in Texas on February 16 was not a natural meteor. Objects this size collide with the Earth every few days. They vaporize or explode in the atmosphere, often (but not always) providing a few small solid fragments that fall to the ground as meteorites. Note that these meteorites fall at normal free-fall velocities (not cosmic speeds) and that they are usually cold by the time they reach the ground. Since the meteorites are cool when they reach the ground, we would not expect "scorched ground" or fires at the impact point.

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NOVA PROGRAM ON EXTINCTION OF NORTH AMERICAN MEGAFAUNA

NEO News has reported previously on the hypothesis that a massive comet explosion (or cloud of thousands of comets) was responsible for the megafauna extinction in North America about 13,000 years ago. We have been skeptical because of the difficulty of imagining a massive impact that left no craters, spread its effects over thousands of kilometers, but was focused just on North America. A new paper on the discovery of nano-diamonds at several Clovis sites dating from this time is in press in Science. In addition, this hypothesis is the subject of a Nova documentary to be shown on PBS a month from now (described below). One of the unusual aspects is the close collaboration between the science team and the film-makers, with one of the Nova staff appearing as a co-author on the Science paper. Perhaps this is a direction science will move in the future, with coordinated journal publication and release of a TV documentary to reach a broader public audience.

NOVA: Last Extinction (Airs Tuesday, March 31)

What killed the mastodons? Thirteen thousand years ago, these tusked beasts disappeared from North America, along with some 35 genera of oversized mammals, including woolly mammoths, saber-tooth cats and even camels. For four decades, debate has raged over the cause of this extinction. In LAST EXTINCTION, NOVA presents an exclusive investigation of a startling and controversial new hypothesis which suggests that a cosmic collision could be the culprit. If a comet exploded in the upper atmosphere over the Great Lakes, the blast would have vaporized everything within a 100-mile radius. From coast to coast, wildfires would have raged and turned forests into cinder. Now, at more than two dozen sites across the continent, a multidisciplinary team finds evidence that just such a fire once ravaged North America. But other scholars argue that ancient hunters armed with a distinctive, lethal stone weapon -- the Clovis spear point -- drove the giant beasts into oblivion. Still others believe the unstable climate at the end of the Ice Age was responsible. Now the dramatic new evidence of a cosmic explosion suggests a third possibility -- that mammoths and mastodons already stressed out by human 'overkill' and climate change may have received a fiery coup-de-grace as devastation swept across the continent.
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