[HN Gopher] Oumuamua may be a hydrogen iceberg
___________________________________________________________________
Oumuamua may be a hydrogen iceberg
Author : elorant
Score : 99 points
Date : 2020-06-02 12:17 UTC (1 days ago)
(HTM) web link (news.yale.edu)
(TXT) w3m dump (news.yale.edu)
| bovermyer wrote:
| I like the idea that these things could be potential star-seeds.
| It would be an interesting way for new solar systems to form.
| monadic2 wrote:
| Makes me wonder if you could slingshot around the sun towards
| relativistic speeds with thermal power. At the very least it
| could save fuel on the egress, if not the second half.
|
| Can you aerobrake around a star?
| isoprophlex wrote:
| Magneto-braking maybe?
| mhh__ wrote:
| Can't do the maths at the moment but you'd probably need a lead
| spacecraft to get close enough. Getting close to the sun also
| means you'll be going _ridiculously_ fast e.g. Parker Solar
| Probe will hit something like 200km /s and it's still millions
| of kilometres from the sun
| TeMPOraL wrote:
| > _Can you aerobrake around a star?_
|
| If you can keep your cool, why not? Matter is matter.
|
| What's better, you could technically radiation-brake around a
| star. I don't know how big of a solar sail you'd have to
| present to get a meaningful force from it.
| troymc wrote:
| Brown dwarf stars can be relatively cool and can have
| atmospheres, so you could aerobrake around those.
| ddxxdd wrote:
| Thermal power requires a reservoir of cold temperature; your
| car's engine would do nothing if the incoming air was just as
| hot as the post-ignited air.
| sq_ wrote:
| > Can you aerobrake around a star?
|
| Not a physicist, but it seems like you should be able to do
| something similar to aerobraking (not one-to-one since the
| Sun's "atmosphere" is different from a planet's). Maybe using a
| solar sail of some sort directed at the right angle?
| idreyn wrote:
| I went on a wiki-binge on this topic a few days ago and so I
| recognize this as a magsail[0]. It would be an attractive
| addition to an interstellar craft since it obviates the need
| to carry propellant for deceleration.
|
| [0] https://en.wikipedia.org/wiki/Magnetic_sail
| tectonic wrote:
| See also e-sail:
| https://orbitalindex.com/archive/2019-04-09-archive-
| Issue-7/
| sq_ wrote:
| That's really cool. Definitely helpful in order to drop
| deceleration fuel requirements if we ever manage to put
| together a relativistic interstellar spacecraft.
| phkahler wrote:
| In a bit over 1M years another star is expected to pass
| around 1000 AU from the sun. Chemical rockets should be
| able to get there in a decade or two. It's a huge
| stretch, but we have a million years to prepare.
| sq_ wrote:
| Oh wow. Had never heard about that. Wouldn't that pass
| within the range of the Oort Cloud? Seems like we might
| have some issues from the gravitational effects if so
| (although that's assuming humans manage to keep ourselves
| going for another million years).
| jamestimmins wrote:
| "It has now passed beyond Saturn's orbit and will travel another
| 10,000 years before exiting the system".
|
| How big is our solar system? I always assumed it referred to
| everything between the sun and Pluto, but 10,000 years suggests
| it's far larger.
| saberdancer wrote:
| I'm not sure of what definition they used here, but one that is
| common is heliosphere, or in other words sphere around the Sun
| where solar wind is dominant. This is about 120 AU.
| wahern wrote:
| 'Oumuamua's incoming and outgoing speed is ~5AU/year. In
| 10,000 years that's 50,000AU, which is approximately the
| distance to the outer most region of the Oort Cloud:
| https://en.wikipedia.org/wiki/Oort_cloud
| lgl wrote:
| I always thought the Oort cloud was a scientifically proven
| thing but apparently it's "a theoretical cloud of
| predominantly icy planetesimals proposed to surround the
| Sun at distances ranging from 2,000 to 200,000 au (0.03 to
| 3.2 light-years)"
| divbzero wrote:
| Thanks for correcting my similar impression that the Oort
| cloud was scientifically confirmed. It's curious to note
| that the proposed outer limit of the Oort cloud (3.2 ly)
| is more than halfway to the closest star system (4.4 ly)
| [1] though I'm unclear on whether the cloud would be
| roughly spherical or have some sort of asymmetry.
|
| [1]: https://en.wikipedia.org/wiki/Alpha_Centauri
| messe wrote:
| Too faint to be proven with our current instruments.
| Voloskaya wrote:
| But it would still take way less than 10000 years to cross
| the heliopshere boundary (it took 40 years for the Voyagers
| probes). It is probably referring to the gravitational sphere
| of influence of the solar system (marked by the Oort cloud) 1
| to 2 light years away.
| messe wrote:
| Could be the distance at which the sun's gravitational
| influence is comparable to that of the surrounding stars.
| This would vary over time, but as a rough estimate it's
| probably alright.
| fenwick67 wrote:
| This is great sci-fi fodder, imagine if you could land a tiny
| craft on that thing and then use the hydrogen as fuel without
| having to haul all that fuel into deep space (very unlikely to be
| practical but the idea is exciting).
| motoboi wrote:
| Imagine you just land a tiny craft on that thing and let the
| thing take you to interestelar space without you having to burn
| no more fuel.
|
| Unfortunately, if you can't catch it, you don't need it for
| that, as you'll be traveling faster that it to be able to
| intercept it and would just burn fuel trying to break enough to
| match its speed.
| TeMPOraL wrote:
| Rule 1 of orbital mechanics: if you're about to dock with
| something, you're already on the same trajectory as that
| thing.
|
| Might make a good radiation shield, though.
| phreeza wrote:
| Except this is not an orbit around any body. If you can do
| what the parent proposes, you can add the chemical energy
| of fusing the hydrogen to your kinetic energy and defeat
| the rocket equation
| TeMPOraL wrote:
| That's what my comment's GP proposed. I understand my
| comment's parent to be asking about just attaching
| yourself to an asteroid.
| ragebol wrote:
| I'm not into orbital mechanics at all, just an interested
| layman, but how does a space tug work in relation to your
| 'Rule 1 of orbital mechanics'?. What is the point of a
| space tug then?
| TeMPOraL wrote:
| Others have provided excellent answers explaining both
| regular tugs and gravity tractors. So let me add a
| justification of my "1st rule".
|
| It boils down to the fact that in space you can, with a
| very good degree of approximation, determine the
| trajectory of an object not under thrust, knowing only
| these two things: it's position at a given time, and it's
| velocity at that same time. These two vectors give you a
| single trajectory through space.
|
| It follows from two physical laws that you may remember
| from high school:
|
| - Newton's second law, or F=ma
|
| - Newton's law of universal gravitation, or F=GMm/r^2
|
| If you put them against each other, you get ma=GMm/r^2,
| or consequently a=GM/r^2. The acceleration (and thus,
| future position and velocity) of an inert object in space
| is independent of its mass. So all you need to tell where
| it will go is to know where it is, and what is it's
| current speed and direction of movement. And, of course,
| what other bodies influence it with their gravity.
|
| Of course, in practice, there are other considerations in
| which the mass may become relevant. For instance, solar
| radiation acts on the surface, impacting force that's
| scaled by object's mass. The same is true for collisions
| with various stray atoms, especially prevalent near
| planets with atmospheres.
|
| But discounting above factors (and, again, you can go
| pretty far just ignoring them), if you have two objects
| very close to each other and not moving relative to each
| other, they'll just go together along the same path for a
| long, long time.
| marcusverus wrote:
| The space tug and its load / target are on the same
| trajectory at the time of rendezvous. Once they're synced
| up, they're drawn toward each other, with the tiny
| gravity of each affecting the trajectory of the other.
| But while the load is passively traveling through space,
| the tug can reposition itself. This way, the tug
| determines the ultimate trajectory of the load while also
| having some control of its own trajectory, which it uses
| to continually bend the load's trajectory.
| hjb wrote:
| The space tug is there to change the trajectory of the
| other thing:
|
| 1. Tug gets in same position and velocity as its target,
| and docks.
|
| 2. Tug performs some kinda of burn to put both it and its
| target on the new trajectory.
|
| 3. Tug undocks and performs a burn to head off to where
| ever else it's needed.
|
| If I understand correctly, it's really just a way to
| avoid putting engines and fuel tanks on things that don't
| need to change trajectory much.
| walrus01 wrote:
| One of the purposes of a proposed 'space tug' is to use
| slow low thrust but high delta-v, high efficiency engines
| to do things such as:
|
| Raise the orbit of satellites in LEO which are affected
| by atmospheric drag. Or re-boost things like the
| international space station, proposed future Chinese
| space station, etc.
|
| Extend the lifetime of geostationary satellites which are
| still electrically functional, but out of station keeping
| propellant. One such thing docked for the very first time
| with a satellite earlier this year.
| https://en.wikipedia.org/wiki/Mission_Extension_Vehicle
|
| On unmanned missions, slowly move cargo from low earth
| orbit to destinations at the Moon or Mars. If you can use
| ion and hall effect type thrusters for your missions to
| move cargo around, you can establish a logistics supply
| chain for essential supplies consisting of unmanned
| craft.
|
| https://en.wikipedia.org/wiki/Delta-v_budget
|
| https://en.wikipedia.org/wiki/Specific_impulse
|
| An interesting example of using ion engines to maintain
| low earth orbit, through long continual thrust was this
| mission:
|
| https://en.wikipedia.org/wiki/Gravity_Field_and_Steady-
| State...
| TeMPOraL wrote:
| I try to follow interesting space missions, but I've
| never heard about either of the two you linked to here.
| Thank you!
| BurningFrog wrote:
| You can imagine intercepting a thing like this (Oumu has left
| the building), and hooking elastic rope to it to get dragged
| along.
|
| Seems like a real hard mechanical problem, but not
| fundamentally impossible.
| moron4hire wrote:
| Spacehook ala Skyhook https://www.cia.gov/news-
| information/featured-story-archive/...
| fenwick67 wrote:
| Pfft, you can just lasso it
| aj7 wrote:
| Or just follow it.
| Symmetry wrote:
| Yeah, though there's lots of water in the outer solar system
| you can get your propellant from. The term to google is In Situ
| Resource Utalization (ISRU).
|
| https://en.wikipedia.org/wiki/In_situ_resource_utilization
| LeifCarrotson wrote:
| But those are mostly just orbiting the sun.
|
| If you ever wanted to send a probe to Proxima Centauri, and
| stop when it got there, accelerating the fuel you'd want to
| have available to decelerate up to solar escape velocity
| would be a tremendous energy expenditure, even if you can
| mine it in the asteroid belt.
|
| If, instead, you got lucky and jumped your probe (fuel tanks
| dry) on an interstellar wanderer that happened to be going
| approximately in the direction you wanted, you could have
| hundreds of tons of rocket fuel moving at interstellar
| velocities.
| detritus wrote:
| True, but those interstellar velocities are mercilessly
| pitiful in respect to much of use there.
| diroussel wrote:
| Then the problem becomes getting oxygen. As a hydrogen won't
| burn in a vacuum.
| sawjet wrote:
| I could still be useful as a propellant for say, a nuclear
| thermal engine.
| ISL wrote:
| Unless you can fuse it into helium.
| throwaway2048 wrote:
| If you have the tech to fuse hydrogen the amount of fuel
| you would need for a nearly unlimited amount of energy is
| tiny, you would save very little by harvesting it off a
| comet/asteroid.
| jandrese wrote:
| Depends on how much energy you need. If you are talking
| about turning it into an interstellar spacecraft by
| hooking up some kind of fusion powered thruster (probably
| using H2 as the reaction mass) to the back you may need
| all of its mass.
|
| This is of course well beyond our current capabilities,
| but it's not something that's impossible to consider in
| the medium-distant future. Plus, even if you expend a
| colossal amount of energy accelerating you're still
| talking about thousands of years for the journey where
| you'll need to keep those reactors running for the entire
| trip (there is no useful solar collection in deep space)
| having a literal mountain of fuel to start with is
| important.
| Sharlin wrote:
| You still need propellant mass. Energy in itself doesn't
| get you anywhere. But in practice you'd probably be
| better off electrolyzing water ice which is ubiquitous in
| the outer Solar System.
| scotty79 wrote:
| Unless you just want to colonize this hydrogen iceberg,
| and live on it for next thousand years, recycling all
| other elements indefinitely as you cruise through the
| galaxy.
| rfreytag wrote:
| Insulating the fusion reactor from the solid hydrogen in
| Oumuamua could prove difficult.
| masklinn wrote:
| Put Oumuamua at the front? It's not like drag is a
| concern.
| btilly wrote:
| Matching speeds with it for this operation would take much
| better rockets than we have available.
| koheripbal wrote:
| I think the theories of it being an artificial alien probe were
| definitely more sci-fi fodder.
|
| I'd always imagined that an alien intelligence might have
| seeded every solar system in the galaxy with a probe to monitor
| for evolving intelligence - but after Oumuamua, I realized it
| would be far more efficient and reliable to have swarms of them
| coasting through systems periodically to check on them. ...or
| maybe both.
| crimsonalucard1 wrote:
| Is there an element or compound in the universe that will remain
| a gas at 0K? Does everything become solid at that temp?
| radioactivist wrote:
| Helium does not solidify down to the lowest temperatures that
| have been achieved (at standard pressure). Though it does
| become a superfluid, which is a distinct phase of matter from a
| gas/liquid.
| nickhalfasleep wrote:
| 0K implies no Brownian motion at all (no thermal energy), so
| there would be no force to keep the molecules apart.
| caymanjim wrote:
| To be pedantic, it's impossible to get to 0K due to quantum
| fluctuations. Even empty deep space is over 2K. In laboratory
| settings, we've gotten way below 1K. I don't think anything
| qualifies as a gas at that temperature. It'd be a solid or a
| BEC.
| radioactivist wrote:
| This is true, but doesn't have anything to do with quantum
| mechanics -- the third law of thermodynamics is basically a
| statement that you can't cool things to absolute zero.
| crimsonalucard1 wrote:
| Your input caused me to google a video about this:
|
| https://www.youtube.com/watch?v=kswiDQ2aAKA
|
| Very intereting!
| aj7 wrote:
| https://m.timesofindia.com/home/science/Lowest-
| temperature-e...
| eganist wrote:
| Intuitively I would think so since 0K is a motionless state. By
| definition everything would be solid because nothing would be
| capable of e.g. filling a given volume, or for that matter,
| doing any action at all.
|
| But this isn't my field of expertise.
| dmitrygr wrote:
| Complete lack of motion would violate Heisenberg uncertainty
| principle ("no motion" == "I know both momentum and location
| with zero uncertainty" and that's not allowed)
| whatshisface wrote:
| No, you can have zero momentum. However it comes along with
| having a position wavefunction that fills the whole
| universe.
| jandrese wrote:
| The universe kindly requests that you do not divide by
| zero.
| dmitrygr wrote:
| Precisely. But that doesn't work for OP's question since
| the whole universe isn't at 0K.
| interestica wrote:
| > However it comes along with having a position
| wavefunction that fills the whole universe.
|
| I love that this sentence exists. Because it's absurd and
| enlightening at the same time.
| rrmm wrote:
| Hey let's probe the boundary conditions of the universe.
| outworlder wrote:
| Careful now, you don't want to crash the simulation.
|
| It already slows down when you are moving too fast.
| NikolaeVarius wrote:
| The boundary condition is that at some arbitrary point
| god smacks you and tells you to knock it off
| rrmm wrote:
| Sorry God!
| pppaul wrote:
| BE condensate
| https://en.wikipedia.org/wiki/Bose%E2%80%93Einstein_condensa...
___________________________________________________________________
(page generated 2020-06-03 23:00 UTC)