[HN Gopher] Could a near-Earth asteroid be a piece of the moon?
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Could a near-Earth asteroid be a piece of the moon?
Author : Brajeshwar
Score : 79 points
Date : 2023-10-26 16:04 UTC (6 hours ago)
(HTM) web link (www.spacechatter.com)
(TXT) w3m dump (www.spacechatter.com)
| SamBam wrote:
| 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?
| datameta wrote:
| 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.
| onetimeuse92304 wrote:
| 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).
| piecerough wrote:
| Thanks for writing this question up ;)
| netcraft wrote:
| > 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
| Terr_ wrote:
| 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?
| aceazzameen wrote:
| Wow. I had no idea a horseshoe orbit was possible.
| echelon wrote:
| 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...
| herpdyderp wrote:
| 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.
| ..
| crazygringo wrote:
| 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?)
| fluoridation wrote:
| 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.
| aaaronic wrote:
| 3+ body orbits can be wild!
|
| It doesn't make any sense in a 2-body orbit (those are all
| conic sections).
| finite_depth wrote:
| 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.
| adolph wrote:
| 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-...
| te wrote:
| In the transitions between quasi-satellite orbit and horseshoe
| orbit, why does it not hit Earth?
| araes wrote:
| 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/...
| readyplayernull wrote:
| Because both objects are too small.
| d--b wrote:
| 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"?
| dang wrote:
| Ok, we've replaced the title with the question the article
| actually contains.
| d--b wrote:
| Oh, nice, thanks
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