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Earth Must Have Another Moon, Say Astronomers
MIT Technology Review Physics Blog ^ | 12/20/2011 | kfc

Posted on 12/22/2011 7:05:56 AM PST by Lonesome in Massachussets

Back in 2006, the Catalina Sky Survey in Arizona noticed that a mysterious body had begun orbiting the Earth. This object had a spectrum that was remarkably similar to the titanium white paint used on Saturn V rocket stages and, indeed, a number of rocket stages are known to orbit the Sun close to Earth.

But this was not an object of ours. Instead, 2006 RH120, as it became known, turned out to be a tiny asteroid just a few metres across--a natural satellite like the Moon. It was captured by Earth's gravity in September 2006 and orbited us until June 2007 when it wandered off into the Solar System in search of a more interesting neighbour.

(Excerpt) Read more at technologyreview.com ...


TOPICS: Astronomy; Chit/Chat; Miscellaneous; Science
KEYWORDS: 2006rh120; catastrophism; cruithne; lunacy; moon; rh120
I don't understand the plot in inertial coordinates, or why it moves in that more or less triangular orbit. I assume the LD is [mean] lunar distance, about 248,000 miles and that the X-Y inertial plane is the plane containing the earth's equator, with positive X in the direction of the Vernal Equinox point. (The intersection of the ecliptic plane and equatorial plane, with positive X pointing in the direction of the sun in March.) They also do not give any time ticks, which is somewhat fustrating.

I downloaded the linked article in PDF. Maybe when I get done chewing on that I'll report back.

1 posted on 12/22/2011 7:05:59 AM PST by Lonesome in Massachussets
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To: Lonesome in Massachussets
... this was not an object of ours. Instead, 2006 RH120, as it became known, turned out to be a tiny asteroid just a few metres across--a natural satellite like the Moon. It was captured by Earth's gravity in September 2006 and orbited us until June 2007 when it wandered off into the Solar System in search of a more interesting neighbour.

Captured and released? How exactly did it get "released" to wander off in search of a more interesting neighbor?

2 posted on 12/22/2011 7:15:09 AM PST by JohnG45
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To: Lonesome in Massachussets

bump for later.


3 posted on 12/22/2011 7:22:21 AM PST by Tallguy (It's all 'Fun and Games' until somebody loses an eye!)
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To: JohnG45

It didn’t exactly get released. It just left in disgust.


4 posted on 12/22/2011 7:22:26 AM PST by bigheadfred (MERRY CHRISTMAS)
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To: Lonesome in Massachussets

I think I see it now. It only completed two orbits before moving on - yes?


5 posted on 12/22/2011 7:22:43 AM PST by JohnG45
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To: Lonesome in Massachussets

Did it “wander” off or was it slingshotted? Sounds like it was out for a Sunday stroll and then just moseyed off.


6 posted on 12/22/2011 7:25:58 AM PST by Larry Lucido
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To: Lonesome in Massachussets
orbited us until June 2007 when it wandered off

FR's resident Rapturists are slapping their foreheads asking "How could we have missed THAT sign of the imminent End-Of-The-World?"

7 posted on 12/22/2011 7:29:19 AM PST by Larry Lucido
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To: JohnG45

It’s all the moon’s fault. Without the moon, something not already in Earth orbit can only come by parabolically or hyperbolically (some which crash into the Earth). But a deflection by the moon can put it into a stable orbit, at least until the moon kicks it out again. Which it is likely to do, given how many other moons we have besides the main one, accumulated over billions of years of moon collection time.


8 posted on 12/22/2011 7:37:34 AM PST by coloradan (The US has become a banana republic, except without the bananas - or the republic.)
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To: Lonesome in Massachussets

http://www.freerepublic.com/focus/f-chat/2823802/posts


9 posted on 12/22/2011 7:42:41 AM PST by US Navy Vet (Go Packers! Go Rockies! Go Boston Bruins! See, I'm "Diverse"!)
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To: JohnG45
It was only ever weakly gravitationally bound to earth. An asteroid orbiting the sun in the same direction as the earth and the other planets can be captured by a planet when it's orbit crosses near the orbit of the planet in front of the direction in which the planet is orbiting the sun. The gravitational attraction drags the asteroid towards the planet (and the planet slightly towards the asteroid). The orbital velocity of the asteroid decreases and it can be kept in orbit around the planet. The amount of deceleration experienced by the asteroid determines how tightly it is bound to the planet.

The any object orbiting a planet is perturbed by the gravity of every other particle in the solar system. For objects orbiting the earth, the significant perturbing bodies are, more or less in order: the moon, the sun, Venus and Jupiter. Depending on their relative locations, they can provide just enough of a push to free a weakly bound object from the grasp of earth's gravity and continue in orbit around the sun.

Jupiter, of course is the king of capture, remember Shoemaker-Levy? It was captured in 1968, but not observed until 1994, shortly before its perturbed orbit caused it to collide with Jupiter.

The opposite of capture occurs, too. An asteroid approaching a planet's orbit from behind can be given a boost that increases its velocity enough to hurl it out of the solar system. Numerous solar system missions take advantage of the gravitational boost available from Jupiter and the other planets.

10 posted on 12/22/2011 7:43:38 AM PST by Lonesome in Massachussets (Ceterum autem censeo, Obama delenda est.)
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To: Lonesome in Massachussets

Thanks for the nice, succinct explanation.


11 posted on 12/22/2011 7:53:33 AM PST by JohnG45
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To: Lonesome in Massachussets

Damn.....even the asteroids want our welfare money. Go over to Mars! They have free healthcare!


12 posted on 12/22/2011 7:54:14 AM PST by blueunicorn6 ("A crack shot and a good dancer")
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To: JohnG45

PS: That also explains why the earth and the inner planets do not have significant ring structures and all the outter gas giants do. The relative strength of the perturbing forces, especially the sun, are so much stronger.

Both of Mars’ moons are believed to have been recently (like the past few million years) captured. Phobos is in retrograde orbit, opposite the direction of Mars’ rotation. The effect of tidal drag continually reduces the radius of its orbit and it is expected to collide with mars in a few million more years. (Tides actually increase the radius of our moon’s orbit by about one centimeter per year increase the length of the earth’s day by about 0.0015 seconds per century. The transfer of energy from earth’s rotation to the moon’s orbit is about one gigawatt.)


13 posted on 12/22/2011 8:13:28 AM PST by Lonesome in Massachussets (Ceterum autem censeo, Obama delenda est.)
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To: bigheadfred

Too bad it didnt beam up Hussein before it left...


14 posted on 12/22/2011 8:19:03 AM PST by blasater1960 (Deut 30, Psalm 111...the Torah and the Law, is attainable past, present and forever.)
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To: JohnG45
Captured and released? How exactly did it get "released" to wander off in search of a more interesting neighbor?

My thoughts exactly. Does it have it's own source of power, if not how did it move out of our gravity field. If it does, how did it get that source of power and is it man made?

15 posted on 12/22/2011 8:29:33 AM PST by calex59
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To: coloradan

Planets can capture objects that cross their orbits. This thing, obviously, was orbiting the earth-moon system, but it came within one lunar distance of something, either the earth or the baricenter. The most likely perturbation that released it from orbit around the earth-moon barycenter was probably due to the moon.


16 posted on 12/22/2011 8:30:33 AM PST by Lonesome in Massachussets (Ceterum autem censeo, Obama delenda est.)
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To: JohnG45
Captured and released? How exactly did it get "released" to wander off in search of a more interesting neighbor?

It must have crossed the border from Mexico.

17 posted on 12/22/2011 8:35:00 AM PST by COBOL2Java (Obama is the least qualified guy in whatever room he walks into.)
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To: Lonesome in Massachussets

Okay, now that we have all of that orbital eccentricity stuff explained, how about explaining that face on Mars!?


18 posted on 12/22/2011 8:41:57 AM PST by JohnG45
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To: JohnG45; Lonesome in Massachussets
how about explaining that face on Mars!?

Intelligent Design?

19 posted on 12/22/2011 8:48:42 AM PST by HiJinx (I can hardly wait; Christmas is almost here!!!!!!!)
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To: Lonesome in Massachussets
any object orbiting a planet is perturbed by the gravity of every other particle in the solar system. For objects orbiting the earth, the significant perturbing bodies are, more or less in order: the moon, the sun, Venus and Jupiter.

If you look for accurate ephemerides on the web, you will find instead of earth, a mysterious object called EMB. This is the earth-moon barycenter, which must be regarded as the object orbiting the sun as a single mass.

To speak of 2006 RH120 as being "perturbed by the moon" is like saying that Apollo 8, e.g., was orbiting the earth and "perturbed by the moon". I notice that the cited article is ambivalent on this point, which is amusing in light of the flap over the planetary status of Pluto. The embarrassing fact is that the earth-moon system is a double planet.

20 posted on 12/22/2011 9:05:12 AM PST by dr_lew
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To: dr_lew

I was keeping it simple. The EMB is always below the surface of the earth, in any case, saying that an object orbiting the EMB is an object in orbit around the Earth, perturbed by the moon is just another way of looking at it. For that matter, planets orbit the barycenter of the solar system, which can be more than two solar diameters from the center of the sun.

For earth satellites, GPS for instance, the second harmonic of the earth’s gravity field, J2, is about 127 times more significant that the moon. The J2 perturbation is on the order of 0.00024 times the J0 component, the effect a point mass equal to the mass of the earht, located at the center of the earth. The effect of the moon is only about 0.0000019 times the J2 component, on average.


21 posted on 12/22/2011 9:55:10 AM PST by Lonesome in Massachussets (Ceterum autem censeo, Obama delenda est.)
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To: HiJinx; JohnG45
how about explaining that face on Mars!?

Two effects: the human brain is hardwired to perceive faces and confirmation bias.

22 posted on 12/22/2011 9:58:37 AM PST by Lonesome in Massachussets (Ceterum autem censeo, Obama delenda est.)
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To: Lonesome in Massachussets

OK, I was doing fine until the “second harmonic of earth’s gravity field”. I don’t get it and would like to. You clearly have a clue. Care to share?


23 posted on 12/22/2011 10:15:40 AM PST by Mycroft Holmes (Returned for regrooving...)
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To: Larry Lucido

LOL!!


24 posted on 12/22/2011 10:27:40 AM PST by Bernard Marx
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To: Lonesome in Massachussets
I was keeping it simple.

Too simple, I would say, for a case where an object is "captured" by the earth-moon system, executes a chaotic trajectory within its sphere of influence, and is then "ejected". I don't think the moon can be considered a perturbing influence in such a case, when it is a full partner with earth in the festivities.

25 posted on 12/22/2011 10:51:52 AM PST by dr_lew
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To: Mycroft Holmes

http://en.wikipedia.org/wiki/Spherical_harmonics

The representation of the earth’s gravitational field you learned in high school, as being spherically symmetrical is not quite true.

In Newtonian mechanics the graviational field resulting from a spherical object of uniform density can be replaced for points outside the object by a point mass located at its center. You may realize, that the actual earth is not a homogenous sphere. If it were (and it didn’t rotate) a plumb bob would always point to the center of the earth. In fact, the earth, or the sea level surface, can be well approximated by an ellipsoid of rotation, with the polar radius about 56 kilometers less than the equatorial radius. (A cross section of the ellipsiod passing through the line joining the North and South pole, will be an ellipse.)

The actual direction that a plumb bob points, ignoring rotation, is always perpendicular to the equipotential surface. This means that away from the poles and the equator the plumb bob does not point at the center of the earth, in the northern hemisphere it points slightly to the south of the center, in southern hemisphere to the north. The effect is greatest at 45 degrees latitude, and the deflection is about a tenth of a degree.

If you were a satellite in a low orbit around the earth, and you happened to be at 45 degrees north latitude you would experience a gravititational acceleration, not towards the center of the earth, but about a tenth of a degree to the south of it. The effect can be resolved into two components, one toward the center of the earth, the J0 component and one at an angle, due to the earth’s equatorial bulge (that extra 56 kilometers around the equator). We call that the J2 component, or Second Zonal Harmonic. (There is no first Zonal Harmonic, the zeroth harmonic is due to the sphercial component of the field.) The effect of the zeroth harmonic decreases as R-squared, the J2 Harmonic as R-cubed. At the surface of the earth it is already only about one one-thousandth as strong as the zeroth component and for objects far enough away it can be ignored.

The latest earth gravity model, EMG96 has over 250,000 harmonics! The first good estimate of the the Earth’s J2 component was not available until we started tracking Sputnik in 1957. There are proposed models with over two million components. Good luck with that.


26 posted on 12/22/2011 11:08:56 AM PST by Lonesome in Massachussets (Ceterum autem censeo, Obama delenda est.)
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To: Mycroft Holmes

J2 is an expression of the gravitational quadrupole moment of the earth, due to its oblateness. It alters the shape of a spherical equipotential surface by a few miles out of the 4000 miles of the earth’s radius. The tidal effect of the moon raises and lowers these surfaces by a few feet.

But this is near the surface of the earth. We’re considering an object wandering extensively around the earth-moon sphere of influence.


27 posted on 12/22/2011 11:09:47 AM PST by dr_lew
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To: Bernard Marx

Well, comet Elenin didn’t work out as planned. :-)

What I don’t get it is, how is this a “second moon”? Doesn’t a body have to at least hang around and orbit a few times to qualify as a moon, or even as a satellite?

But then that’s why I’m not an astronomer.....


28 posted on 12/22/2011 11:13:10 AM PST by Larry Lucido
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To: Mycroft Holmes

Check out this video for a very kewl illustration of the effect of the J2 Harmonic on a satellite orbit:

http://www.youtube.com/watch?v=uZc0YJjyWGM

Mike Gruntman has a whole slew of kewl videos on his website:

http://astronauticsnow.com/vp/index.html

or check out his actual website:

http://astronauticsnow.com/


29 posted on 12/22/2011 11:33:26 AM PST by Lonesome in Massachussets (Ceterum autem censeo, Obama delenda est.)
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To: Larry Lucido
What I don’t get it is, how is this a “second moon”?

This is just hype to pique the interest of the unwashed masses. Everything has to be some kind of mind blow.

30 posted on 12/22/2011 11:34:40 AM PST by dr_lew
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To: Lonesome in Massachussets; dr_lew

Thanks much.


31 posted on 12/22/2011 11:35:22 AM PST by Mycroft Holmes (Returned for regrooving...)
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To: dr_lew
Give me a break please, the first thing to keep in mind when writing is audience. No one likes pedantry.
32 posted on 12/22/2011 11:37:32 AM PST by Lonesome in Massachussets (Ceterum autem censeo, Obama delenda est.)
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To: Larry Lucido
Standing by for the obligatory random Bible quote in 3...2...1
33 posted on 12/22/2011 2:35:42 PM PST by starlifter (Pullum sapit)
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To: brytlea; cripplecreek; decimon; bigheadfred; KoRn; Grammy; married21; steelyourfaith; Mmogamer; ...

Thanks Lonesome in Massachussets.

An “extra, extra” ping to the APoD list members.


34 posted on 01/05/2012 7:47:07 PM PST by SunkenCiv (Merry Christmas, Happy New Year! May 2013 be even Happier!)
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To: Larry Lucido

:’D


35 posted on 01/05/2012 7:50:24 PM PST by SunkenCiv (Merry Christmas, Happy New Year! May 2013 be even Happier!)
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To: Lonesome in Massachussets

Thanks!


36 posted on 01/05/2012 7:51:58 PM PST by SunkenCiv (Merry Christmas, Happy New Year! May 2013 be even Happier!)
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To: 75thOVI; agrace; aimhigh; Alice in Wonderland; AndrewC; aragorn; aristotleman; Avoiding_Sulla; ...

Thanks Lonesome in Massachussets.

Bon voyage, 2006 RH120.




37 posted on 01/05/2012 7:54:42 PM PST by SunkenCiv (Merry Christmas, Happy New Year! May 2013 be even Happier!)
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To: Lonesome in Massachussets; SunkenCiv
"Earth Must Have Another Moon, Say Astronomers"

Must we?

38 posted on 01/06/2012 3:00:37 AM PST by TheOldLady (FReepmail me to get ON or OFF the ZOT LIGHTNING ping list)
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To: TheOldLady

Yes, I insist. Have as many as you like, we’ll make more.


39 posted on 01/06/2012 4:24:14 AM PST by Lonesome in Massachussets (Ceterum autem censeo, Obama delenda est.)
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To: Lonesome in Massachussets

You are too kind. :-)


40 posted on 01/06/2012 5:38:12 AM PST by TheOldLady (FReepmail me to get ON or OFF the ZOT LIGHTNING ping list)
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To: TheOldLady; Lonesome in Massachussets

Otherwise we’d have to do the one-cheek sneak, and no one wants that. ;’)

http://www.freerepublic.com/tag/cruithne/index


41 posted on 01/07/2012 9:26:04 AM PST by SunkenCiv (Merry Christmas, Happy New Year! May 2013 be even Happier!)
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To: SunkenCiv; Lonesome in Massachussets; cruithne

Well, at least it didn’t post a vanity to attempt establishing its conservative credentials before it became a sleeper troll.

Gee, it should be waking up any day now...

Better linkie thingy:
http://www.freerepublic.com/tag/by:cruithne/index?brevity=full;tab=comments


42 posted on 01/07/2012 11:55:57 AM PST by TheOldLady (FReepmail me to get ON or OFF the ZOT LIGHTNING ping list)
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To: TheOldLady

Hey, that gives me an idea... if there’s ever an asteroid headed for Earth impact, one of your Zot messages may just do the trick...


43 posted on 01/07/2012 1:29:37 PM PST by SunkenCiv (Merry Christmas, Happy New Year! May 2013 be even Happier!)
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To: SunkenCiv

Sure! Anything I can do to help.


44 posted on 01/07/2012 7:57:49 PM PST by TheOldLady (FReepmail me to get ON or OFF the ZOT LIGHTNING ping list)
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