[HN Gopher] Earth has caught a 'second moon'
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Earth has caught a 'second moon'
Author : divbzero
Score : 38 points
Date : 2024-10-01 16:30 UTC (6 hours ago)
(HTM) web link (www.space.com)
(TXT) w3m dump (www.space.com)
| 7373737373 wrote:
| I wish spaceflight was sufficiently commoditized that sending a
| satellite there to get some pictures would be trivial
| RandomCitizen12 wrote:
| How can it be called a 'capture' when it's already known when and
| how it will leave. That's like calling a resort vacation stay a
| kidnapping.
| pengaru wrote:
| Technically The Moon is slowly leaving earth's orbit too, to
| the tune of 38mm per year[0]. Everything's temporary...
|
| [0] https://en.wikipedia.org/wiki/Orbit_of_the_Moon
| deafpolygon wrote:
| Any impact on tidal activity?
| nso wrote:
| Like measurable in our lifetime? The average distance to
| the moon will be 3.8 meters further away in a hundred
| years. That's insignificant as far as tides goes.
|
| Despite what another commenter says, the moon will not
| leave earths captive field. It will recede until it gets
| tidally locked with earth, and both the tide cycles and the
| moons recension will halt. That is, if there still is water
| in a few billion years and it hasn't been replaced with
| Brawndo
| flqn wrote:
| Is the moon not already tidally locked? The same
| hemisphere of it always faces the earth. Is there a
| different kind of tidal locking or orbital resonance it
| will settle into?
| alfiopuglisi wrote:
| It goes on until an Earth's day is as long as a month.
| Both will face each other in a fixed way. But it takes
| many billions of years and the Sun will burn both to a
| cinder much before that.
| mjevans wrote:
| That's like calling a lifetime lived within just one village
| 'temporary'. On the scale of human events it's nearly as
| permanent as anything else for which we commonly ascribe
| permanence and reliability within lifetime scales.
| runako wrote:
| It's fair to describe objects in relation to the lifespans
| of those objects, not of those who observe. "On the scale
| of human events" is not the only relevant timeframe for
| discussing celestial bodies.
| ck2 wrote:
| the way I remember that fact is it is also average fingernail
| growth per year
| jumploops wrote:
| Goodbye Moon would be a great name for a children's book
| focused on space and time!
| bongodongobob wrote:
| Because during that time from its frame of reference it will be
| falling around the earth until it reaches escape velocity and
| starts falling around the sun again.
| enragedcacti wrote:
| I had the same confusion so here's my layman's understanding.
| They are defining capture/orbit as having negative "geocentric
| energy" which is a term of art no one else seems to use but I
| think is just a mathematical representation of the following:
|
| > a temporary satellite is any body that enters the Hill sphere
| of a planet at a sufficiently low velocity such that it becomes
| gravitationally bound to the planet for some period of time.
| [1]
|
| again stretching my understanding too far, I think this
| basically means that in the absence of other celestial bodies
| the satellite would be in a stable orbit, but that in reality
| after some time it gets far enough away that the sun's
| gravitational pull dominates and stops it from making a full
| orbit.
|
| [1] https://en.wikipedia.org/wiki/Temporary_satellite
| timjver wrote:
| > in the absence of other celestial bodies the satellite
| would be in a stable orbit
|
| Presumably entering such an orbit is only possible due to
| forces from other celestial bodies in the first place, since
| otherwise if you reversed time it would spontaneously leave
| its orbit. In other words, the act of the earth "capturing"
| the object is ultimately performed by external forces?
| hansvm wrote:
| To be fair, it's still kidnapping in most states even if the
| duration is very short.
| ravenstine wrote:
| I'd hardly call a 37 foot object that wont even make a complete
| orbit a "second moon."
| lxgr wrote:
| Obi-Wan Kenobi couldn't have said it better!
| ndesaulniers wrote:
| That's no moon!
| arduanika wrote:
| https://www.youtube.com/watch?v=eT4shwU4Yc4
| BurningFrog wrote:
| Third at best!
| brutal_chaos_ wrote:
| FTA: "You may say that if a true satellite is like a customer
| buying goods inside a store, objects like 2024 PT5 are window
| shoppers."
|
| The article agrees with you. It's always those pesky headlines.
| tboyd47 wrote:
| > Marcos explained, "Asteroid 2024 PT5 will not describe a full
| orbit around Earth. You may say that if a true satellite is like
| a customer buying goods inside a store, objects like 2024 PT5 are
| window shoppers."
|
| Is it a NASA thing to deploy outrageously absurd analogies for no
| apparent reason? Is there a checkout desk for space objects?
| MisterTea wrote:
| It's not absurd, you're reading too far into it.
| ravenstine wrote:
| Yes, I'm not sure why they chose that analogy. It just sounds
| cutesy and doesn't really add anything.
| lxgr wrote:
| > While the moon is an estimated 2,159 miles (3,475 km) in
| diameter [...]
|
| Is the article implying that we don't know the Moon's (I assume
| they're referring to the capital-M one) diameter to at least
| kilometer-precision...?
| mattficke wrote:
| It's an irregularly shaped body so there's not one single
| radius. Mean radius is always going to be an approximation
| (even for Earth); the mean radius of the Moon is 1,737.4 km.
| lxgr wrote:
| But it's still an approximation, not an estimate, right? (The
| fact that you can list the mean radius with sub-decimal
| precision suggests as much.)
|
| To me, an estimate suggests that there's error bars; an
| approximation suggests that there's variance that we can
| quantify (or at least we're very confident about our error
| bars).
| feoren wrote:
| There are error bars on absolutely everything that we ever
| measure.
| lxgr wrote:
| Sorry, missed a "large". It would sound pretty strange to
| me to claim that the distance between New York and London
| is "an estimated x kilometers" (with single-kilometer
| precision), even though there is tectonic movement etc.
| aryan14 wrote:
| Didn't know we were referring to asteroids as moons now
| EarlKing wrote:
| The Jovian satellites would like to have a word with you.
|
| Also, Earth already has a second moon: 3753 Cruithne.
| qwertox wrote:
| Which website/software/app is good for tracking the location of
| 2024 PT5, so that it can be found in the local night sky?
| nomel wrote:
| Being 100ft across, it won't be visible except for long
| exposure [1].
|
| [1] https://theskylive.com/where-is-2024pt5
| ck2 wrote:
| so even the Green Bank telescope could only get two pixels?
|
| https://petapixel.com/2023/01/26/these-are-the-highest-resol...
| buildsjets wrote:
| "There's a Moon in the Sky (Called 2024 PT5)" just doesn't hit
| the same.
|
| https://genius.com/The-b-52s-theres-a-moon-in-the-sky-called...
| benjiweber wrote:
| https://www.youtube.com/watch?v=CIqOsM6_3Dw
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