NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Not exactly Navigation, but close...
From: Frank Reed
Date: 2008 Apr 23, 23:48 -0400
From: Frank Reed
Date: 2008 Apr 23, 23:48 -0400
Alex wrote: "Shortly speaking, scientists DO monitor these bodies. The bodies that are on the "possible collision course". They are able to detect any such body many years in advance. If a really dangerous one is detected this will be known, and we DO have means to deflect it. The main problem is how much in advance we know. Modern technology (and moderate expenses) permit to detect really dangerous bodies about 20 years in advance." There's no 'a priori' guarantee that such objects will be detected twenty years in advance. The big unknown is long-period comets which are frequently discovered as little as one year before they reach the vicinity of the Earth's orbit. It's not clear what fraction of the impact risk comes from long-period comets. It may be as little as 5%. It might be as much as 30%. And you wrote: "There are technologies with permit us to deal with this danger in 20 years period (including research and development)." Yes. And one of the best solutions, which many people find surprising, is "paint it white". Dust a dangerous asteroid with white powder and it will reflect much more light increasing the sunlight pressure on it and deflecting the asteroid over the course of a few years. And you wrote: "Anyway, my personal conclusion from this lecture was that "there is nothing to worry about" in comparison to the REAL dangers facing us. Roughly speaking, the risk of a serious collision (in terms of the number of victims and the chance that this happens) is comparable to the risk of a major earthquake). All this is negligible in comparison with the real dangers we face:-(" You should look into it yourself. The risk is certainly not negligible --but it has, of course, been exaggerated frequently in the media. The really nice thing about this particular source of mass destruction is that the risk can be SIGNIFICANTLY reduced, and indeed has already been significantly reduced (in the past dozen years or so), by spending a relatively small amount of money. All we have to do is compile an almanac --an almanac of all of the exceedingly faint asteroids that happen to be in orbits near the Earth's orbit. Twenty years ago, the risk of an asteroid impact had to be treated as a purely statistical risk, very similar to the risk of an earthquake. But asteroids are different. We can predict their motion once they are catalogued. It's as good as having a train schedule. During the 1990s and continuing today, the United States, in particular, has spent a little money funding these cataloguing projects. The number of known asteroids with well-determined orbits has exploded in recent years (see attached graphic). The statistical risk has thus been reduced by a factor of five or better. There are still uncertainties regarding impact risk. There's the long-period comet problem that I mentioned above. And even among the ordinary asteroids, no one is even considering the enormous task of tracking "city-buster" objects (like the one believed to be responsible for the Tunguska event in 1908). There are far too many. In the case of those objects, we simply have to count on the fact that the population of the Earth, as well as our valuable assets, are highly concentrated geographically so, even though we may get one impact every century or two, the expected casualties and costs are "acceptable". Attachment shows the count of "numbered asteroids" versus time. The numbered asteroids are objects with well-determined orbits. The number of asteroids with partially determined orbits is around a million. The majority have been discovered in the past ten years. Almost all of these were discovered by projects intended to reduce the impact risk. -FER --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---