[HN Gopher] What we know about Earth's new minimoon
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What we know about Earth's new minimoon
Author : CapitalistCartr
Score : 63 points
Date : 2020-11-28 14:39 UTC (8 hours ago)
(HTM) web link (www.universetoday.com)
(TXT) w3m dump (www.universetoday.com)
| tedunangst wrote:
| Buried lede: it's no longer in earth orbit.
| junon wrote:
| Then why is it considered a "mini moon" if it's not a moon at
| all?
| dwaltrip wrote:
| It's a former minimoon. It orbited earth for 2.7 years,
| making numerous revolutions in that time. There is a cool
| animation in the article that shows the path it took.
| ant6n wrote:
| It's odd they were able to reconstruct its flight path,
| which appears to be quite chaotic (in the scientific
| sense), given that the observations are only from after it
| left the earth-moon System.
| crazygringo wrote:
| What specifically seems so odd about it?
|
| If we know its trajectory with decent precision when it
| left, and we know the position and gravitational strength
| of the earth, moon and sun, and you just plug in the
| numbers and simulate and it should be quite
| straightforward.
|
| I suppose you're referring to "chaotic" meaning that tiny
| variations or mismeasurements in its later trajectory
| would be vastly amplified as its orbits were traced. But
| my understanding is that such chaotic/unpredictable
| orbital effects generally show up on the scale of many
| many thousands of orbits if not much more, not 2 years?
| jagger27 wrote:
| How cool would it be if we had probes like Hayabusa or Osiris-Rex
| ready to go for encounters like this?
|
| `Oumuamua would have been a long shot but this rock seems within
| reach.
| airstrike wrote:
| Also how about we leave some instrument on the rock even after
| it departs? Would be interesting to track where it went next
| TeMPOraL wrote:
| Generally there's little point in doing that, unless you want
| to study the body itself or otherwise care about its
| presence. That's because to rendezvous with something in
| space you need to get close to it and bring your velocity
| relative to it to zero - which puts you on the exact same
| orbit, so even without attaching to it, you'll go where it
| goes.
| black_puppydog wrote:
| Also, at 2m diameter, its gravity would be so low that
| "leaving" a probe on it would mean strapping the probe to
| it? That would be a funny tech demo for catching a small
| rock, but if you already do that, why not put it into a
| stable orbit for further study?
| amelius wrote:
| I think the problem is that the rock is at its highest speed
| whenever it is near Earth (see animation in the article).
| crazygringo wrote:
| Ugh. I hate this new supposed term "minimoon" -- it's
| sensationalistic and misleading.
|
| This object is 1 to 2 meters in diameter, was captured by Earth
| for just 2.7 years, and with an extremely irregular orbit.
|
| By contrast, a moon requires a "relatively stable orbit" [1],
| which this clearly did _not_ have.
|
| Can we just call it what it actually is? It's an _asteroid_. It
| revolves around the Sun, and it was very briefly a _temporary_
| satellite of the Earth.
|
| [1] https://en.wikipedia.org/wiki/Claimed_moons_of_Earth
| rdiddly wrote:
| The word "new" isn't exactly well placed either. Wanna go see
| my new car? I sold it to a guy last April.
| moralsupply wrote:
| Why did it take so long to figure out we have 2 moons?
| politelemon wrote:
| Here's a quick read of that one time Minor Planet Center
| cataloged the Rosetta Space Probe as an asteroid
|
| https://thenerdnextdoor.com/tag/2007-vn84/
| dave_4_bagels wrote:
| I've been curious why we don't start pushing de-commissioned
| satellites / space junk in earth orbit into a moon-like mass
| orbiting earth? It would take a swarm of maybe a few hundred
| powered "satellite movers" maybe a decade. But in time, seems
| like it could become a fantastic means of dealing with space
| debris surrounding earth especially space junk that can't easily
| be ditched to re-enter the earth's atmosphere and burn up.
| vosper wrote:
| Perhaps it would just move the problem from the earth to the
| moon? If we're going to the effort to build "satellite movers"
| to get unwanted/dead satellites to a moon orbit, then perhaps
| we would be better of just sending them into the sun, or on a
| path out into deep space?
| dogma1138 wrote:
| I would say having shit in lunar orbit might be a bigger
| problem since they will not burn on reentry. Sure it's not a
| problem now but by the time we can push junk into a lunar
| orbit the moon might be quite a bit more populated.
| kempbellt wrote:
| It would be better to glob them together for a space station
| to repurpose the materials.
|
| A lot of time, energy and money is spent getting material
| into orbit. No sense wasting it, unless it's completely
| useless. Then de-orbiting in the Earth's atmosphere is the
| cheapest solution.
| walrus01 wrote:
| > I've been curious why we don't start pushing de-commissioned
| satellites / space junk in earth orbit into a moon-like mass
| orbiting earth?
|
| if you randomly choose 20 dead satellites by their TLEs,
| they're all in different inclinations and orbits. plane change
| manoeuvres are very costly in delta-v.
|
| there is no economic incentive or need to build a lot of
| individual dead-satellite-grabbing ion/hall effect thruster
| powered satellites that would go up and grab things to shove
| them into a katamari-damacy like ball of dead satellites.
| jl6 wrote:
| Some possible reasons:
|
| * Lots of space junk is very small (e.g. paint flecks and metal
| chips) and we don't know exactly where it is (but even objects
| of this small size can still be hazardous travelling at 5km/s).
|
| * When we do know where it is, it's probably still uneconomic
| to spend delta-V getting to it and pushing it anywhere.
|
| * Potentially unknown payloads on old satellites, or uncertain
| ownership status. Russia might have opinions on someone else
| touching its junk.
|
| * Proliferation risk of developing technology that can easily
| interfere with satellites on-demand. If a satellite mover can
| move junk, it can move live units too.
|
| * Actual risk of error causing uncontrolled deorbiting, either
| with a mis-push, or by bouncing junk off the growing moon-like
| mass
|
| * That moon-like mass could easily become a liability -
| irregularly shaped with hard-to-model behaviour. Most space
| junk will burn up on reentry, but a giant agglomeration of
| metal might survive reentry and land on something it shouldn't.
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(page generated 2020-11-28 23:00 UTC)