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Earth's other 'moon' and its crazy orbit could reveal mysteries of the solar system
Phys.Org ^ | 02-25-2015 | by Duncan Forgan

Posted on 02/26/2015 6:29:41 AM PST by Red Badger

We all know and love the moon. We're so assured that we only have one that we don't even give it a specific name. It is the brightest object in the night sky, and amateur astronomers take great delight in mapping its craters and seas. To date, it is the only other heavenly body with human footprints.

What you might not know is that the moon is not the Earth's only natural satellite. As recently as 1997, we discovered that another body, 3753 Cruithne, is what's called a quasi-orbital satellite of Earth. This simply means that Cruithne doesn't loop around the Earth in a nice ellipse in the same way as the moon, or indeed the artificial satellites we loft into orbit. Instead, Cruithne scuttles around the inner solar system in what's called a "horseshoe" orbit.

Cruithne's orbit

To help understand why it's called a horseshoe orbit, let's imagine we're looking down at the solar system, rotating at the same rate as the Earth goes round the sun. From our viewpoint, the Earth looks stationary. A body on a simple horseshoe orbit around the Earth moves toward it, then turns round and moves away. Once it's moved so far away it's approaching Earth from the other side, it turns around and moves away again.

Cruithne from a stationary Earth position

Horseshoe orbits are actually quite common for moons in the solar system. Saturn has a couple of moons in this configuration, for instance.

What's unique about Cruithne is how it wobbles and sways along its horseshoe. If you look at Cruithne's motion in the solar system, it makes a messy ring around Earth's orbit, swinging so wide that it comes into the neighbourhood of both Venus and Mars. Cruithne orbits the sun about once a year, but it takes nearly 800 years to complete this messy ring shape around the Earth's orbit.

Cruithne close up

So Cruithne is our second moon. What's it like there? Well, we don't really know. It's only about five kilometres across, which is not dissimilar to the dimensions of the comet 67P/Churyumov-Gerasimenko, which is currently playing host to the Rosetta orbiter and the Philae lander.

The surface gravity of 67P is very weak – walking at a spirited pace is probably enough to send you strolling into the wider cosmos. This is why it was so crucial that Philae was able to use its harpoons to tether itself to the surface, and why their failure meant that the lander bounced so far away from its landing site.

Given that Cruithne isn't much more to us at this point than a few blurry pixels on an image, it's safe to say that it sits firmly in the middling size range for non-planetary bodies in the solar system, and any human or machine explorers would face similar challenges as Rosetta and Philae did on 67P.

If Cruithne struck the Earth, though, that would be an extinction-level event, similar to what is believed to have occurred at the end of the Cretaceous period. Luckily it's not going to hit us anytime soon – its orbit is tilted out of the plane of the solar system, and astrophysicists have shown using simulations that while it can come quite close, it is extremely unlikely to hit us. The point where it is predicted to get closest is about 2,750 years away.

Cruithne is expected to undergo a rather close encounter with Venus in about 8,000 years, however. There's a good chance that that will put paid to our erstwhile spare moon, flinging it out of harm's way, and out of the Terran family.

It's not just Cruithne

The story doesn't end there. Like a good foster home, the Earth plays host to many wayward lumps of rock looking for a gravitational well to hang around near. Astronomers have actually detected several other quasi-orbital satellites that belong to the Earth, all here for a little while before caroming on to pastures new.

So what can we learn about the solar system from Cruithne? Quite a lot. Like the many other asteroids and comets, it contains forensic evidence about how the planets were assembled. Its kooky orbit is an ideal testingground for our understanding of how the solar system evolves under gravity.

As I said before, it wasn't until the end of the 20th century that we even realised that bodies would enter such weird horseshoe orbits and stay there for such a long time. The fact they do shows us that such interactions will have occurred while the solar system was forming. Because we think terrestrial planets grow via collisions of bodies of Cruithne-size and above, this is a big new variable.

One day, Cruithne could be a practice site for landing humans on asteroids, and perhaps even mining them for the rare-earth metals our new technologies desperately crave. Most importantly of all, Cruithne teaches us that the solar system isn't eternal – and by extension, neither are we.


TOPICS: Astronomy; Education; Science; UFO's
KEYWORDS: 3753cruithne; asteroid; astronomy; catastrophism; cruithne; earth; earthcrossers; minimoon; minimoons; minormoon; moon; nearearthobject; orbit; quasisatellite; quasisatellites; space; xplanets
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To: WayneS

After 8000 years you may get to see it!........................

http://www.freerepublic.com/focus/f-news/3261803/posts


21 posted on 02/26/2015 7:09:55 AM PST by Red Badger (If you compromise with evil, you just get more evil..........................)
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To: Kenny Bunk

THEY are rolling around looking for a clue....................


22 posted on 02/26/2015 7:13:24 AM PST by Red Badger (If you compromise with evil, you just get more evil..........................)
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To: Red Badger

Thanks for posting. I had no idea about this.


23 posted on 02/26/2015 7:32:29 AM PST by JimSEA
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To: JimSEA

Neither did I!..............................


24 posted on 02/26/2015 7:38:15 AM PST by Red Badger (If you compromise with evil, you just get more evil..........................)
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To: KevinDavis; annie laurie; Knitting A Conundrum; Viking2002; Ernest_at_the_Beach; Mmogamer; ...
Thanks .
 
X-Planets
· join · view topics · view or post blog · bookmark · post new topic · subscribe ·
Google news searches: exoplanet · exosolar · extrasolar ·

25 posted on 02/26/2015 7:40:08 AM PST by SunkenCiv (What do we want? REGIME CHANGE! When do we want it? NOW!)
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To: brytlea; cripplecreek; decimon; bigheadfred; KoRn; Grammy; steelyourfaith; Mmogamer; dayglored; ...

Extra to APoD.


26 posted on 02/26/2015 7:40:18 AM PST by SunkenCiv (What do we want? REGIME CHANGE! When do we want it? NOW!)
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To: Red Badger; Robert A. Cook, PE; 75thOVI; agrace; aimhigh; Alice in Wonderland; AndrewC; aragorn; ...
Thanks Red Badger and Robert A. Cook, PE, be sure to check the other topics under the keywords, all.

27 posted on 02/26/2015 7:40:36 AM PST by SunkenCiv (What do we want? REGIME CHANGE! When do we want it? NOW!)
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To: Red Badger

When we planted the flag on Mars, we surely left footprints.


28 posted on 02/26/2015 8:01:43 AM PST by bgill (CDC site, "we still do not know exactly how people are infected with Ebola")
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To: Bloody Sam Roberts
I have had a very small (white) planet circling a large star since 10:00am Tuesday of this week. It still hasn't completed a full circle around it but it appears to be about 12 hours from doing so.

Here is a screen shot:


29 posted on 02/26/2015 8:04:29 AM PST by Eaker (You are really amazing Eaker. - Swordmaker 02/14/15)
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To: bgill

Tread tracks................


30 posted on 02/26/2015 8:16:43 AM PST by Red Badger (If you compromise with evil, you just get more evil..........................)
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To: Diana in Wisconsin

Diana,

See Post# 29.


31 posted on 02/26/2015 8:17:15 AM PST by Eaker (You are really amazing Eaker. - Swordmaker 02/14/15)
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To: Red Badger

“Earth’s other ‘moon’ and its crazy orbit could ...”

But it will require more federal funding.


32 posted on 02/26/2015 8:18:15 AM PST by SgtHooper (Anyone who remembers the 60's, wasn't there!)
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To: Eaker
Way. Cool.

I love that website. It's like Spirograph for grownups.

The only thing that would be better is if it were 3D and the mouse could be used to rotate it without disturbing the path lines.


33 posted on 02/26/2015 8:19:38 AM PST by Bloody Sam Roberts (Where am I to go now that I've gone too far?)
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To: Bloody Sam Roberts

Yeah, I hate it when I have to recenter and it erases all of the path lines.

This is the first time I have ever gotten one to last this long. There are three other tiny planets that escaped orbit. I am waiting for one of them to circle back and mess it up but after two days I suspect that they found a black hole on someone else’s computer.

I have to reboot Friday prior to backing my system up so it will end then.


34 posted on 02/26/2015 8:26:01 AM PST by Eaker (You are really amazing Eaker. - Swordmaker 02/14/15)
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To: Bloody Sam Roberts
Pam' Purple Spyrograph
35 posted on 02/26/2015 8:28:07 AM PST by null and void (No crime, real or imagined, is too small to not be declared a felony.)
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To: Don Corleone
rather close encounter with Venus

Didn't Bacchus already hit it?

36 posted on 02/26/2015 8:33:08 AM PST by central_va (I won't be reconstructed and I do not give a damn.)
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To: Red Badger
We Like The Moon
37 posted on 02/26/2015 8:42:22 AM PST by Don W (When blacks riot, neighborhoods and cities burn. When whites riot, nations and continents burn.)
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To: Red Badger

Should have stopped reading at “We all know and love the moon”. But I didn’t.

Any amateur astronomer (except the lunatics who look at the Moon [lunatics....Moon...get it]) would FAR rather the Moon be painted flat black or something. It totally interferes with seeing 13th mag galaxies.


38 posted on 02/26/2015 8:43:01 AM PST by Conan the Librarian (The Best in Life is to crush my enemies, see them driven before me, and the Dewey Decimal System)
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To: Red Badger
"...even mining them for the rare-earth rare-moon metals"

Fixed it.

39 posted on 02/26/2015 8:52:38 AM PST by Boogieman
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To: Tenacious 1

it is an illegal alien transport ship........

(hopefully it will remember to pick up Obama at the end of 2016 and take him back home)


40 posted on 02/26/2015 9:23:58 AM PST by faithhopecharity ((Brilliant, Profound Tag Line Goes Here, just as soon as I can think of one..).)
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