Could a near-Earth asteroid be a piece of the moon? | Hacker News Reader

Could a near-Earth asteroid be a piece of the moon?

spacechatter.com

113 pointsBrajeshwar27 comments

That video animation is bizarre, because it seems like the asteroid changes the direction of its orbit around the sun.

But am I right in interpreting this from the perspective of the Earth being stationary, and actually the asteroid keeps on moving around the sun in the same direction but sometimes we were catching up to the asteroid, and sometimes it was catching up to us?

Yes, sometimes our velocity relative to the Sun is greater than the asteroid's depending on where in the orbit we are, and vice versa.

Yes, the orbit is visualised in relation to the Earth-Sun system.

Yes, the asteroid and Earth are catching up to each other and actually exchanging energy (although the effect on Earth is probably not measurable).

Wikipedia has more information: https://en.wikipedia.org/wiki/Horseshoe_orbit

Thanks for writing this question up ;)

Three body mechanics leads to some weird solutions.

> Throughout its history, the moon has endured countless asteroid impacts, leaving visible impact craters on its surface. These craters form when asteroids or meteorites collide with celestial bodies. Although most of the ejected lunar material falls back onto the moon, a fraction reaches Earth as meteorites. However, an even smaller fraction can escape both lunar and Earth’s gravitational pull, entering solar orbits akin to those of near-Earth asteroids.

So I interpret this to mean they think this came from an impact after the moon formed that broke a chunk off, not a fragment from the formation of the moon itself? If it was the latter I would think that it would be a great subject to study about the formation of the moon

That's my reading as well, that it's a knock-off rather than a sibling.

If it was formed from the hypothesized Earth/Theia impact, would it have been (more) molten, and would that have affected its cooled shape?

Wow. I had no idea a horseshoe orbit was possible.

Same! The animation is wild.

Apparently it will oscillate between being in orbit around earth to going back into a bouncy horseshoe orbit. Over and over throughout the millennia.

There are even more animations here, though the one in the article is great:

https://en.wikipedia.org/wiki/469219_Kamo%CA%BBoalewa

https://en.wikipedia.org/wiki/469219_Kamo%CA%BBoalewa#/media...

This is only animation from all of these I've seen that makes any sense to my brain, I still can't figure out what's going on in the others:

https://en.wikipedia.org/wiki/File:Asteroid2016HO3-SunEarthO...

Thank you. But I am having the hardest time understanding how this entirely reasonable-looking orbit "around the sun":

https://en.wikipedia.org/wiki/File:Animation_of_2016_HO3_orb...

Somehow turns into this loop-de-loop "relative to the sun and earth":

https://en.wikipedia.org/wiki/File:Animation_of_2016_HO3_orb...

Is this essentially the origin of epicycle model of the planets? Do all planets look like that loop-de-loop graphic, but for whatever reason we never plot them that way, but for some reason this article is plotting the asteroid this way? (Just to confuse us?)

The second plot fixes Earth and Sun in place, and so you see the position of the asteroid relative to Earth. What is happening is that the asteroid is in an orbit so similar to Earth that they do not usually pass each other, and alternatively speeds up and slows down very slightly related to us. (When it approaches Earth from "behind" on it's orbit, earth's gravity accelerates it forwards, which makes it's orbit slightly longer, which makes it take a longer time to go around it, causing it to start lagging us. When Earth catches up to it, Earth's gravity will accelerate it backwards, as in slow it down, which will shrink it's orbit, meaning it will go around faster than us.)

The tight loops are caused by orbital inclination: As the asteroid is not orbiting in the same plane as Earth, each orbit around the Sun it will travel slightly above us and slightly below, this causes the loop.

It must be noted that it's a horseshoe only relative to the Sun-Earth system. Relative to the Sun it's just a normal elliptical orbit that keeps changing shape.

3+ body orbits can be wild!

It doesn't make any sense in a 2-body orbit (those are all conic sections).

Horseshoe orbits come from the most counterintuitive behavior of orbits: if you thrust forward, you go slower. And if you thrust backward, you go faster. (The reason is that thrusting forward puts you in a higher orbit.)

In a horseshoe orbit, when the small body approaches the medium body "from behind" (that is, the small body is moving faster than the medium body), the medium body tugs the small body forward. That is an effective forward thrust for the small body, which rises into a higher orbit and slows down as a result. That means the small body starts to fall behind, losing ground relative to the medium body.

After it loses enough ground, it approaches the medium body from the front (or, if you prefer, the medium body catches up to it from behind). Then the medium body's gravity tugs it backward, dropping it into a lower and faster orbit, and the cycle repeats.

The most exceptional example of this is two of Saturn's moons, Janus and Epimetheus, which share an orbit and periodically trade places in it as a result of these dynamics.

Another fun one is the long term orbits of expended Apollo hardware. The below article shows the booster entering by way of L1 into something like a Molniya orbit until leaving again.

Yeung’s discovery, formally named J002E3, became the focus of an intense analysis with a unique result. The object was not an asteroid captured by Earth in a cosmic game of coincidence. This was a relic of humanity’s space race: an Apollo-era rocket that had been placed in orbit around the Sun — and then returned to Earth.

https://www.astronomy.com/space-exploration/how-a-long-gone-...

Weird that an asteroid is named "thank you" -- according to Google translate from Hawaiian. Learned what a "horseshoe orbit" is -- that is a strange relative orbit.

I wonder what proportion of asteroids have Hawaiian names. Probably a lot given the relatively little light pollution at their spotting sites.

Would it make sense to put a base on this satellite and maybe use it for a telescope or build platform?

More or less sense than doing the same on the moon?

If it was stable for only about 1 century, that's very short timescale... Why be confident it'll remain so?

In the transitions between quasi-satellite orbit and horseshoe orbit, why does it not hit Earth?

Per @herpyderp's comment below, the best animation that shows this features a 3D rotation to orient so you can see how the rock is actually moving. [1] The movement is actually closer to a distorted torus with the Earth moving as a line in the center. The rock just rotates over the surface of the torus (longterm).

[1] https://upload.wikimedia.org/wikipedia/commons/transcoded/5/...

Because both objects are too small.

Why do a lot of science writers feel the need to turn hypotheses into certainties? That really drives me nuts.

“We are now establishing that the moon is a more likely source of Kamo’oalewa”, says study senior author Renu Malhotra.

He did NOT say "This Near-Earth Asteroid Is Actually A Chunk Of The Moon".

I mean would it really drive traffic down if the title said "likely" or "probably" instead of "actually"?

Ok, we've replaced the title with the question the article actually contains.

Oh, nice, thanks

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