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Nature has a way of getting arounds things...
Topic Started: Aug 4 2009, 11:13 PM (1,115 Views)
Mike
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http://www.popularmechanics.com/science/air_space/4326395.html

An large object entered our solar system, and slammed into Jupiter. Despite the fact that we have arrays of telescopes aimed at the stars, space is bigger than our detection efforts will ever be.
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ngc1514
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Mike
Aug 4 2009, 11:13 PM
http://www.popularmechanics.com/science/air_space/4326395.html

An large object entered our solar system, and slammed into Jupiter. Despite the fact that we have arrays of telescopes aimed at the stars, space is bigger than our detection efforts will ever be.
Objects slamming into Jupiter do not represent a threat to the earth.

Orbital dynamics and the proportions of sizes of planets and the distances between planets (planets are very small and the distances very great) mean the odds of something hitting the earth on its first pass through the Solar System are microscopic. Not quite zero, but getting close. Imagine the earth represented by a BB. The Jupiter impactor (based on the size of the mark compared to the marks left by Comet Shoemaker-Levy 9 back in 1994) would be about the size of a small bacterium. Now, stand back and throw the bacteria at the BB from a distance of about 100 feet (scale distance from sun to Pluto - most cometary objects come from the Oort belt which is MUCH further away!) and let me know how many times you hit the BB.

Objects collide after they have become enmeshed gravitationally. Shoemaker-Levy 9 was watched as it spiraled into Jupiter; it did not come flying in from the depths of space to hit the planet.

The present efforts to detect potential earth colliding objects is limited to those whose orbit crosses the earth's. Far smaller objects than the Jupiter impactor can be seen when you are looking closer to the earth. Objects which pass close to the earth will eventually have their orbits perturbed by the earth's gravitational field. Depending on the geometry of the encounter, we can expect 50% will be thrown further into space (gravitational boost used in most planetary exploration satellites) and 50% will orbit in closer and become a bigger threat.

As of December 31, 2008, something like 5,800 near earth asteroids and 82 near earth comets are being tracked by Spacewatch, NEAT and other projects.

So, because we can't see them all... we should not bother keeping an eye on the ones we do?
Edited by ngc1514, Aug 5 2009, 01:18 AM.
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Mike
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I think we should keep an eye on objects that pose a threat. There might be a chance of saving lives and property, were such an observation able to predict where on earth the object might hit.

We can't prevent a collision but we can warn folks of the pending disaster.
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ngc1514
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It's not all that easy, Mike. Orbits of objects are constantly changing tiny amounts, mainly by gravitational perturbations as the smaller objects react to the pull from larger objects in the Solar System. Tiny perturbations today can have a large impact on the object's orbit down the road.

The end result is that the crash point of an incoming object will not be fully known until the object is on its way to the earth's surface and possibly not accurately known then due to the effect of the earth's atmosphere. The Great Daylight Fireball of 1972 actually hit the top of the earth's atmosphere and bounced back into space. Sure wish I'd seen it!

Posted Image
http://apod.nasa.gov/apod/ap090302.html
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Mike
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Great picture!

I was unaware of the gravitational issues you brought up. Then in reality, there isn't much value at all in know which objects might come our way. We are sitting ducks.
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ngc1514
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Right now, yes. But in the future? Perhaps not. As I mentioned, a small change in an impactor's orbit can lead to a big change in its future location. If we know something is coming in and has a high probability of impacting the planet, there are possible plans on how to change the orbit.

Nothing that can be accomplished today, but in a few years? All depends upon the wants and will of the human race because I think it's too big a project for any one nation to take on by itself.
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Mike
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Maybe that is the eventual use for the star wars research. Right now, attempting to knock down an enemies rocket is beyond our scope, but eventually being able to re-direct a civilization ending space object merits consideration.

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ngc1514
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Not sure how it will be done... assuming it ever is. Star wars is not a long distance project and the technology is supposed to function during the brief interval between the launch of an ICBM and its impact.

Moving asteroids out of the way won't be nearly as dramatic. Small impulses applied over a period of years isn't the sort of stuff out of which we make movies.
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Mike
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What do you think would be the right force? Sound waves?
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ngc1514
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A nuclear powered mass driver would possibly work. Utilizing Newton's Third Law of Motion - for every action, there is an equal and opposite reaction.

Just like the kick from firing a rifle, a mass driver and it's supporting mechanism would take the asteroidal material and throw it away from the asteroid at high speed and in the direction necessary to effect the orbital change required.

Throwing away megatons of material at high velocities over a long period of time would change the body's orbit.

Breaking up an incoming body using nuclear weapons or sound waves just turns a single bullet into the equivalence of a shotgun blast. Rather than a small localized event, you turn it into a smaller, but widespread event. The conversion of energy from potential to kinetic as the body hits would be the same.

Even if you managed to blast the incoming object to microscopic pieces, the energy conversion is the same. The effects might be different, however. With a big single chunk we might blow a crater into the earth. With a microscopic swarm of the same mass hitting us, it might just heat up and boil off a measurable percentage of the earth's atmosphere.
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