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Gravity changing trajectory/speed questions

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#1 KDizzle

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Posted 14 December 2012 - 12:02 PM

While reading about the recent 'near miss', I came across 2012DA14 which is supposed to come round Feb 15 or so. I was researching and came across the wikipedia orbit trajectory and noticed there is a definite bend in the trajectory as it goes near Earth. The obvious explanation seems like the same principle we use for speeding up our own spacecraft by slightshotting nearby.

First, is that indeed what the "extra bend" in the arc is here or is it from something else?

Second, when this happens, does that speed up the object just as our spacecraft would be sped up?

Thanks!

#2 Aldo Vitagliano

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Posted 16 December 2012 - 10:32 AM

First, is that indeed what the "extra bend" in the arc is here or is it from something else?

Yes

Second, when this happens, does that speed up the object just as our spacecraft would be sped up?

In this case, the object will pass “ahead” of Earth with respect to our planet’s motion around the Sun.
This means that it will be slowed down in its motion by the Earth’s attraction, which in turn means that its orbit will shrink and its period of revolution will become shorter. This is indeed the most important dynamical effect of the encounter. The semimajor axis of the orbit will be reduced from 1.002 AU to 0.909 AU and the period of revolution from 1.0030 y to 0.867 y.

It is not possible to tell now what will be the exact change of semimajor axis and revolution period, because of the present uncertainty in the exact distance of the closest approach. The “nominal” value is 33,400 km from the center of Earth, but the possible range is from about 27,000 km up to about 46,000 km.

Regards
Aldo Vitagliano

#3 Centaur

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Posted 16 December 2012 - 01:26 PM

Thanks for your expert explanation, Aldo. For those who do not know, Aldo is the creator of the free Solex astronomical numerical integration program: http://main.chemistr...alvitagl/solex/

#4 KDizzle

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Posted 16 December 2012 - 06:58 PM

The semimajor axis of the orbit will be reduced from 1.002 AU to 0.909 AU and the period of revolution from 1.0030 y to 0.867 y.

Wow, that seems like a pretty substantial change. I think now I'm beginning to appreciate more fully the challenges in tracking all these different objects out there -- they are all interacting with one another and changing course/speed all the time! Thanks for the insight.

#5 Centaur

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Posted 18 December 2012 - 03:10 AM

Aldo gave me some data on asteroid 2012 DA14 to put into my copy of his Solex program. With its output and my self-made graphics software, I've created a view of the orbits of the asteroid and Earth from far north of the ecliptic plane. Do understand that the data is preliminary and subject to adjustment. Nevertheless, it's obvious that the orbit switches from one with a longer major axis than Earth's to a shorter one after close passage. The diagram can be seen at: www.CurtRenz.com/asteroids

#6 GlennLeDrew

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Posted 31 December 2012 - 01:56 AM

Whether the orbital energy of a passing body increases (orbit enlarged) or decreases (orbit reduced) depends upon which side of the accelerating body it passes and the relative direction of motion of each with respect to the other.

#7 Achernar

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Posted 31 December 2012 - 10:04 AM

It sounds like this encounter with Earth may set it up for a collision with us in the future, now that it became an Aten class asteroid. These objects hide in the glare of the Sun most of the time, and that is how they can blindside us literally the way the asteroid that exploded over Siberia did in 1908. That was a stony object that approaced out of the glare of the Sun, and now this one has the potential of doing the same thing. One thing is certain, it's cannot stay for long in it's new orbit before it hits a planet, gets tossed outwards again, or plummets into the Sun. Time is now running out for it. It is about 130 feet across, more than enough to kill 10 or 20 million people if it airbursts over a large metropolitian area.

Taras

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