Jones wrote: > But Michel, the fact that in crossing the galactic plane recently (in > cosmological time), there has been no apparent increase in what could be > considered 'danger' or hazardous debris impacting earth - doesn't that > argue against your conclusion?
I don't think so, crossing the galactic plane only increases the _probability_ of a collision, it doesn't make it a certainty. Also the asteroid impact which eradicated the dinosaurs 65 Myr ago did occur precisely at a galactic plane crossing: not the one 1Myr ago, nor the previous one 1+32=33 Myr ago, but the one before 33+32 = 65 Myr ago. In any case, whether it can explain all mass extinctions or not, and whether it is favored by galactic plane crossings or not, there is no arguing that asteroid impact is a real danger: it has occurred before and it will occur again. The next time it wants to occur it would be nice to have a countermeasure ready, e.g. what I suggested in my previous post. My guess is that focussing the reflected sunlight beams from a swarm of space mirrors large enough for GW mitigation (i.e. able to reflect off 1% of incident sunlight, i.e. collectively of a total area of 0.01*Pi*(6.4E6)^2=1.3E12 m^2) would be quite enough to deviate a hefty asteroid from a collision course if it's detected early enough. Horace wrote: > I think most of the oscillation is due to the sun's galactic orbit. > We have a 200 My galactic orbital period, so, given no matter at all > in the galactic plane, we should be in the galactic plane every 100 My. This would be right if there was no matter in the GP: the circular orbit would cross the plane at two points. With the matter there is, the sun bobs up and down with a 64 Myr periodicity so it crosses the plane roughly 8 times per 250 Myr orbit. Michel ----- Original Message ----- From: "Jones Beene" <[EMAIL PROTECTED]> To: "Michel Jullian" <[EMAIL PROTECTED]>; "vortex" <vortex-l@eskimo.com> Sent: Sunday, May 06, 2007 3:46 PM Subject: Re:The Ecliptic and Mass Extinctions > Michel Jullian wrote: > >> No Jones, the 62My period "vertical" oscillation superimposed on the >> "horizontal" circular orbit of the sun round the galactic center has nothing >> to do with the inclination of the solar system plane wrt the galactic plane. >> It is a purely gravitational effect due to the galactic plane being denser. >> The "real nemesis" is more likely to be the galactic plane itself, around >> which our solar system is more likely to undergo collisions. Such collisions >> explain why rotating clouds of matter always end up as planes BTW. > >> Actually I believe we are still in the danger zone presently, having crossed >> the plane only 1My ago or so. It seems to me this is in favor of using solar >> sail reflectors to mitigate global warming BTW: such reflectors could also >> be used occasionally to deviate from very far away any asteroids detected to >> be on collision course, using photon pressure as was discussed here some >> time ago. > > > But Michel, the fact that in crossing the galactic plane recently (in > cosmological time), there has been no apparent increase in what could be > considered 'danger' or hazardous debris impacting earth - doesn't that > argue against your conclusion? > > Also I think that the Menvedev idea might work with some variation of > Horace's 'nemesis cloud' idea in that we already have an Oort cloud > which can serve as a model, and both the cloud and the sun's radiance > would be affected by the "northern exposure" ... > > ... which BTW - and this is the most convincing detail of all to me in > the 'big picture' - as the so-called northernmost exposure out of the > Milky Way galactic plane puts the solar system facing directly towards > the "great attractor," which is probably the source of the most intense > cosmic rays ... plus one can assume (at least I can), since we are > strongly attracted to this feature in space - that it was probably the > very source from which our entire local group was expelled 13-15 billion > years ago - which - as it turns out, fits into the argument for a > succession of 'little bangs' (supercluster size) in a non-expanding but > pulsating universe - and not a single big bang in an expanding universe.. > > Jones
