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Earth's Little Brother Found
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To invent, you need a good imagination and a pile of junk. -- Thomas Edison
To invent, you need a good imagination and a pile of junk. -- Thomas Edison
See the orbital motion for yourself (Score:5, Informative)
JPL has a very nice tool for looking at the orbits of asteroids. Go to
http://neo.jpl.nasa.gov/orbits/ [nasa.gov]
for the general case. For 2002AA29 in particular, you can use
http://neo.jpl.nasa.gov/cgi-bin/db?name=2002AA29&g roup=all&search=Search [nasa.gov]
Keep in mind that the orbital solution is based on only a short arc: only 28 days, about one twelfth of a complete revolution. Our estimates of the orbital parameters -- and behavior -- could change quite a bit over the next few months.
Re:Not quite a planet, eh? (Score:5, Informative)
The squares of the periods of the planets are proportional to the cubes of their semimajor axes
(http://home.cvc.org/science/kepler.htm).
So the mass of a planet has nothing to do with its orbital period (well, assuming it is small enough that it doesn't make the sun orbit it). So anything placed at Earth's distance from the sun and moving at the same speed would orbit the sun in the same path the Earth does regaurdless of its mass.
Re:Not quite a planet, eh? (Score:5, Informative)
Wtf? Orbital velocity is a constant that depends only on the mass of the parent body, as long as the orbiting body is significantly lighter.
After all, geosynchronous satellites are all at approximately same height, although they have the same speed (to maintain synch), but different mass.
The formula for calculating orbits is:
T=2*pi*(a+h)/v
where T = period, a = radius of the parent body, h = orbit height, and v = satellite velocity, which can be calculated from:
v = sqrt(g/(a+h)),
where g is gravitational acceleration of the parent body.
You don't see the mass of the satellite anywhere here.
Re:Not quite a planet, eh? (Score:5, Informative)
It is also intriguing since no 'trojans' have been discovered for the Earth and this could signal that we do in fact have some. Trojans are asteroids that occupy the 4th and 5th Lagrangian points about a larger body (Jupiter has the most, due to its large mass). Because of the physics involved in a 2 body system where any additional bodies have negligible mass compared to the original 2, there are a few 'stable' points where the gravitational forces cancel out...these are known as Lagrangian points. L4 and L5 are co-orbital to the less-massive object (Jupiter, Earth, whatever).
Although this object is not a trojan, since it has a horseshoe orbit and temporarily gets caught up in Earth's orbit, it suggests that there are bodies out there that could be trojans. Perhaps as our detection abilities progress, we will discover some Earth-trojans.
Re:Not quite a planet, eh? (Score:1, Informative)
Basically, at a given orbital energy, or velocity, and object can orbit at a certain distance from the central mass (the Sun in this case). If it speeds up, it has to move to a smaller orbital radius. If it slows down, it moves to a larger orbital radius. In this case, it sounds like the following may be happening:
(1) The asteroid is moving faster than the Earth, and so travels in a slightly lower orbit. When it gets to one Lagrange point, it will slightly overrun it, and the Earth's pull will send it to a higher orbit, stealing some of its kinetic energy. It then slows down and the Earth speeds away from it.
(2) The now slower-moving, higher-orbiting asteroid moves backward with respect to the Earth, until the Earth catches up to it until it overruns the other Lagrange point. When that happens, the Earth pulls it into a lower, more energetic orbit, and it proceeds to speed away from the Earth.
(3) go back to #1 and repeat.
During the brief time that the Earth's influence on the asteroid is greater than that of the Sun, the asteroid technically becomes a satellite of the Earth.
I could be wrong about all this, but at first read, this was how I interpreted things...
BBC, News for Nerds & stuff that REALLY matter (Score:3, Informative)
Re:Horseshoe orbit? (Score:5, Informative)
This picture [paias.com] illustrates it pretty well.
Re:Not quite a planet, eh? (Score:4, Informative)
I don't have the equation for the gravitational attraction between two bodies. But I know it is a function of the SUM of the masses of the two objects. So, how much do you think the sum of the masses of the sun and the Earth differs from the sum of the masses of the sun and 2002 AA29?
There are lots of explanations of horseshoe orbits on the web. Basically, if two objects share the same, or very similar, orbits, they are attracted to one another. That gravitational attraction drains kinetic energy from the leading object, and slightly adds kinetic energy to the trailing object.
The leading object, having lost energy, moves closer to the primary. Its year gets slightly shorter, and its actual velocity relative to the primary speeds up. Similarly, the trailing object moves farther away, and its year grows slightly longer.
So the leading objects closer orbit has it revolve around the Primary more quickly, and it will slowly move away from the trailing object. Eventually the leading object is exactly opposite from the trailing object. According to the BBC article, this takes 95 years.
Once the object that was leading is more than 180 degrees ahead in it orbit from the object that was trailing, their mutual attraction starts to add energy to its orbit, and raise it to a higher orbit. Similarly, the mutual attraction drains energy from the other object.
What we have just seen is the two objects trade places. The object that was the trailing object is now the trailing object.
It seems paradoxical that mutual attraction should tear the two object apart. Until you remember that the Sun's influence on the object's trajectories is much more important than their attraction to one another.
At least that is my understanding of the BBC's article.
How does this mechanism allow 2002 AA29 to be briefly captured by the Earth? I'd welcome an explanation of this.
Re:BBC, News for Nerds & stuff that REALLY mat (Score:1, Informative)
Re:Second Moon (Score:2, Informative)
Re:Horseshoe orbit? (Score:2, Informative)
Re:BBC, News for Nerds & stuff that REALLY mat (Score:2, Informative)
uh... 'scuse me? (Score:5, Informative)
Size Matters (Score:3, Informative)
The thing is 100 meters wide. Imagine a 100 meter (300 foot) wide ball. If we just grabbed it and brought it to earth's surface (gently), it still wouldn't affect our tides at all. It's small enough to fit in a stadium. It's the size of a big hill. The point is that it wouldn't affect us at all.
Also, the reason it wasn't seen that long ago was that it was too far away and too small to see with the naked eye. (we could barely see it with a scope).
Re:Not quite a planet, eh? (Score:3, Informative)
Follow along in your copy of Principia Mathematica and repeat after me:
An object maintains linear velocity unless acted upon by an outside force.
Force of sun on asteroid: outside force
Force of asteroid on sun: not involved
It doesn't matter whether the mass in question is you, a '57 buick or the Death Star. An object 1 AU away (on the average) from something with the mass of the sun orbits once every 365.2429 days, give or take.
Galileo figured out in the 17th cenutry that all objects reguardless of mass fall at the same acceleration. Where have you been in the past 350 years or so?
Re:Confused... (Score:3, Informative)
That's all. A companion describes a similar orbit as another body. The Earth's moons have, necessarily, a slightly different orbit from the Earth if you plot them.
Re:Interesting... but wrong (Score:1, Informative)
Re:Why the US will never switch to metric (Score:3, Informative)
Please; just subtract 273:
>298K: t-shirt, shorts
293K-298K:t-shirt, jeans
etc...
Re:Forgetting our history? (Score:2, Informative)
A Trojan asteroid is "any planetoidal body at the triangular Lagrangian point of any two bodies" named thus because the Trojan asteroids of the Sun - Jupiter system are named according to the Illiad.(Wikipedia [wikipedia.org]). There's an interesting webpage on the Trojan asteroids in the Sun - Earth system here [queensu.ca]
Comment removed (Score:3, Informative)