[ForGod'sSake]

Could An Asteroid Hit Planet Earth, Again?

So these guys want to play tag with an asteroid? So we can more accurately follow its path? I'm sure it all depends on how much grant monies they're able to squeeze out of various govt's and NGO's; otherwise they'll just have to make do with present technology. The horror.

blam, I know you've done quite a bit of reading/research on catastrophism; I've done a little myself. What puzzles me at this point in my "studies" is there seems to be some theories bandied about that at various times our solar system or our part of the galaxy only occasionally goes through periods of disruption. That is, we are not at the same risk level at all times. That something causes a tremor in the force from time to time. Thoughts?

[Sudetenland]

Sith Lords, obviously.

[allmendream]

I have heard various catastrophism theories about the angle of the galaxy, orbits of a mega object (Nemesis star or something) that throws celestial debris our way, etc. But nothing substantial.

“Nemesis is a hypothetical red dwarf or brown dwarf star, orbiting the Sun at a distance of about 50,000 to 100,000 AU, somewhat beyond the Oort cloud. The existence of this star was postulated in an attempt to explain an inferred periodicity in the rate of biological extinction in the geological record.”

From Wiki.

[allmendream]

Also this....

Matese and Whitman have suggested that the supposed extinction periodicity might be caused by the solar system oscillating across the galactic plane of the Milky Way. These oscillations may lead to gravitational disturbances in the Oort cloud with the same proposed consequences as the orbit of “Nemesis”. However, the period of oscillation is not well-constrained observationally, and may differ from the needed 26 million years by as much as 40%.

[blam]

"Thoughts?"

See posts #34 & 35. I believe there are some cycles.

Try reading the book, "Cosmic Winter", Clube & Napier and the one below

[SunkenCiv]

Periodicity of bombardment has been suggested (as noted above by allmendream), but each time "Nemesis" has been looked for it has not been found, which has caused its hypothetical parameters to be revised. Matese et al rely on comet focussing, that is, a common point of origin of many long period comets, as well as the hypothetical Oort Cloud. At least one other researcher regards comet focussing to be an artifact of having most of the observatories in the northern hemisphere of the Earth.

Impacts happen all the time, but serious ones only once in a while. IMHO the fact is, periodicity is just a dodge to keep impacts from happening at all, an intellectual (rather, quasi-intellectual) method of keeping the Earth, and quite a number of careers, nice and safe from catastrophism.

Impacts happen at random. Far and away the bulk of the impacting objects come from objects also in orbit around the Sun, rather than from interlopers from outside the Solar System. The objects themselves may have common origins here and there (there was a calculation of the origin of the Chicxulub object, which said that most of the rest of the original object remains in orbit around the Sun as space debris), but basically, there are so many objects known and unknown, that the problem becomes too complex for periodicity to work. This explains, I think, the reason for the enormous margins of error in the so-called periods.

Nemesis: Does the Sun Have a 'Companion'?
by Robert Roy Britt
03 April 2001

Richard A. Muller... a physicist at University of California at Berkeley... [has] ideas... generally rooted in solid science and genius extrapolation... But Muller's biggest idea is a real Nemesis. Or so he claims. Like a thorn in the side of mainstream researchers, Muller's Nemesis theory -- that our Sun has a companion star responsible for recurring episodes of wholesale death and destruction here on Earth -- seems to reemerge periodically like microbes after a mass extinction. It's a theory that has many detractors. And it's a theory that has been beaten down and left for dead in the minds of most scientists... Muller's idea for Nemesis came to him 1983. Luis Alvarez, then an emeritus professor of physics at the University of California at Berkeley, and his son Walter had recently put forth the theory that a giant impact had wiped out the dinosaurs... Around the same time, two other researchers had suggested yet another controversial idea, that mass extinctions occurred at regular intervals -- every 26 million years or so. Scientists immediately folded the ideas into a new and breathtaking possibility: Impacts by space rocks were causing massive global species destruction every 26 million years.

Theory of Periodic Mass Extinctions
Frank R. Ettensohn

Why has interest in this hypothesis subsided? There are two reasons. First, there are statistical questions about extinction rates that just cannot be answered. It is not clear whether other hypotheses can fit the empirical data as well as does the hypothesis of periodicity. The distribution of extinction events in time is certainly not random, but there is more than one way to analyze the data. Does the fact that the data appear to fit well to a model of periodicity mean that the events truly are periodic? This question was debated throughout the late 1980s without reaching a resolution.

The second reason for the loss of interest is one not uncommon to science: Here is an intriguing observation that no one knows how to explain. Researchers formulated a number of very interesting astronomical hypotheses to account for the 26-million-year periodicity of extinction. The most famous of these was the Nemesis, or 'death star,' hypothesis, which stated that the sun has a distant companion whose highly elliptical orbit brings it into the Oort Cloud (a swarm of frozen comets orbiting far from the sun) once every 26 million years. During each pass through the Oort Cloud, the companion's gravity would scatter huge numbers of comets, some of which would crash into Earth. The environmental damage caused by these impacts would lead to an elevated rate of extinctions.