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selvaarchi
2015-Mar-01, 09:28 PM
I was surprised to come across this article that claims earth has a 2nd moon. It is small, about five kilometers across and takes 800 years to complete one "horseshoe orbit" around earth. We have known about it since 1997 but the best image we have of it is only is "a few blurry pixels on an image". I would have thought this would have warranted a few missions at least to get to know more about our neighbor?

http://phys.org/news/2015-02-earth-moon-crazy-orbit-reveal.html


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.


wikipedia says it "is an Aten asteroid in orbit around the Sun in 1:1 orbital resonance with Earth, making it a co-orbital object. It is a minor planet in solar orbit that, relative to Earth, orbits in a bean-shaped orbit that ultimately effectively describes a horseshoe, and which can transition into a quasi-satellite orbit.[4] It has been incorrectly called "Earth's second moon".[2][5] Cruithne does not orbit Earth and at times it is on the other side of the Sun.[6] Its orbit takes it inside the orbit of Mercury and outside the orbit of Mars.[6] Cruithne orbits the Sun in about 1 year but it takes 770 years for the series to complete a horseshoe-shaped movement around the Earth.[6]

The name Cruithne is from Old Irish and refers to the early Picts (Irish: Cruthin) in the Annals of Ulster[6] and their eponymous king ("Cruidne, son of Cinge") in the Pictish Chronicle."

http://en.wikipedia.org/wiki/3753_Cruithne

grapes
2015-Mar-01, 10:01 PM
That's why it's important to read every single post ever made to BABB/UT/BAUT/CQ!

http://cosmoquest.org/forum/showthread.php?5776-What-ever-cam-out-of-this-article

At the wiki, the two animations of the orbit make it clear what's going on with the orbit--one one would really call that an orbit around esrth, although they are synchronized.

NEOWatcher
2015-Mar-01, 11:45 PM
I don't consider it to be a "moon" nor a "satellite" since it doesn't orbit around the Earth.
But given there's no formal definition, I guess I have to let it slide. Otherwise, Earth would not be considered a planet according to the IAU since the Earth's orbit is no longer clear.

Hornblower
2015-Mar-02, 12:10 AM
I don't consider it to be a "moon" nor a "satellite" since it doesn't orbit around the Earth.
But given there's no formal definition, I guess I have to let it slide. Otherwise, Earth would not be considered a planet according to the IAU since the Earth's orbit is no longer clear.

My bold. No, no, a thousand times no! That "clearing" criterion continues to be misunderstood because of the poor job the IAU delegates did in choosing their words and communicating with the public at large. All it means is either accreting or ejecting all but a tiny mass of debris from non-resonant orbits close to the planet's own orbit over the mature lifetime of the solar system. There will always be some transient residual stuff as a result of perturbation of asteroids by other planets, and a body like Cruithne in a synchronous or otherwise resonant orbit does not violate the criterion.

NEOWatcher
2015-Mar-02, 01:15 AM
My bold. No, no, a thousand times no!
Actually it was a tongue in cheek statement. But; I was only going on the idea that the IAU knew about these kinds of objects. I didn't understand why, so thanks for the explaination.

selvaarchi
2015-Mar-02, 02:26 AM
The Asteroid Redirect Mission (ARM) now has another candidate to move to a stable orbit around the moon. Will not that be cool. Our Moon will have a moon. :whistle:

Ara Pacis
2015-Mar-02, 07:57 AM
Not a moon, more like a little sister.

KaiYeves
2015-Mar-02, 06:01 PM
The Asteroid Redirect Mission (ARM) now has another candidate to move to a stable orbit around the moon. Will not that be cool. Our Moon will have a moon. :whistle:

Moon-ception.

publiusr
2015-Mar-07, 09:12 PM
This object is hard to get to, what with it loving to dive up and down. Wait--that was TK7
http://en.wikipedia.org/wiki/2010_TK7

Maybe not such a chore then.