Another Interstellar Object Detected in the Solar System
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circle e = 0
earth e = 0.0167
ellipse e < 1
parabola e = 1
hyperbola e > 1
The orbital plane of the solar system is not aligned in any special orientation relative to nearby stars or the Milky Way, so we would expect interstellar objects to arrive from all directions with equal probability.
[1]: https://twitter.com/AscendingNode/status/1171845027099795456
But also thinking that the larger the angle to the ecliptic, the less likely it was something that just happened to be in a very large orbit around our solar system.
From the discussion above though it sounds like the eccentricity tells us that anyway.
It seems that "the Sun moves through the Milky Way at about 20 km/s faster than the local average", or "local standard of rest (LSR)".[0] With the components being ...
11.1 km/s toward the galactic center
12.24 km/s extra in the direction of galactic rotation
7.25 km/s toward the north galactic pole
These objects probably came from stars with relatively low velocities relative to LSR. There might be some moving a lot faster, but the detection window would be much smaller.
Even with a smiley face this is still a tiresome and rude response.
The line I quoted is the very last line in the book, and is equal parts fascinating and chilling, a very apt end for a great book.
I highly recommend you read it. If you are in the USA and have a library card, may I suggest the Libby app for Android and iPhone? Or of course buying it second hand from online bookstores is also an option: looks like a new paperback is about $4.55 at smile.amazon.com, used is about 1 to 3 dollars, Kindle version is $7.59. I don't recommend the other books in the series, they don't live up to the original, in my opinion.
A similar book is Eon by Greg Bear, although less pure sci-fi exploration and more sci-fi adventure.
Ironically, Arthur C. Clarke never intended for Rendezvous With Rama to be the start of a trilogy when he wrote that, even though it's an obvious trilogy hook in hindsight. It never occurred to him until readers kept asking when the other two books were coming out.
The fact its eccentricity is 3 means its going through the solar system extremely fast (relative to the orbits of other things at comparable distance), and is going to exit again after slingshotting around the sun, that means its origin is extremely likely to be extra-solar because we know of no real mechanism for a body to generate such extreme speed while originating from within the solar system.
https://upload.wikimedia.org/wikipedia/commons/b/b7/Kepler_o...
In this image, red has an eccentricity of 0.7, green 1.0 and blue 1.7, the sun would be the focus. The the green and blue "orbits" never return, just like a parabola/hyperbola never curve into an ellipse, think of a graph like y=x^2.
With the uncertainties that come from fitting early observations, these numbers can change as more observations come in. At 1.07, it would still be possible that the final orbit turns out to not be hyperbolic. At 3.0, that's much less likely.
What makes this discovery exciting is that it would be the second object of interstellar origin that we've discovered in our own solar system (and both discoveries are fairly recent). That's a new class of object to be studied and presents an opportunity to learn something new. The fact that these two discoveries are temporally close suggests that we'll discover many more as our technology and technique improve.
/s
The closer the eccentricity is to 1 without being equal or less, the more "curved" the trajectory is and the nearer its closes approach to the sun will be.
Is this true? I thought it depends on the object’s speed. You can have an object with e=3 have a closer approach to the sun than an object with e=2 if the first object is traveling sufficiently faster.
In other words, at a given perihelion, you can change an object’s e by accelerating or decelerating. Not a orbital mechanics major, just played too much KSP.
Talking about the "speed" is potentially unclear as an object's speed can vary greatly within its orbit.
If it was flying by slowly, it would get caught by the sun’s gravity and end up in a circular orbit around the sun. If the orbit was perfectly circular, it would have an eccentricity of 0.
If it was flying by a little bit faster, it might barely get caught by the sun and end up with an orbit like Halley’s comet where it comes close to the sun once every hundred years and then flies off to the far reaches of the solar system before coming back again. It would have an eccentricity of 0.9-ish.
If it was flying a little bit faster, the sun’s gravity would try to catch it, but it would fail! The object would “swoop” around the sun then go flying back the direction it came, never to return again. It would have an eccentricity of about 1 or a little more (Less than 1 means it’s in orbit, 1 or more means it’s not coming back).
If it was flying REALLY REALLY fast, the sun’s gravity would try to pull it in, but this time the object has other plans. It barely even changes course and rockets through the solar system in an almost perfectly straight line. Its eccentricity would be something like 89 (there’s no upper limit, although at a certain point the object would have to travel at close to lightspeed to acheive certain really high eccentricities if flying close to the inner solar system).
This object (the real-life one we’re talking about) is going faster than the “swoop” object but slower than the “other plans” object. Its path is being bent somewhat by the sun’s gravity, but it is going to leave an never come back. So its eccentricity is 3.
One last thing: eccentricity is PURELY a math thing that describes circles, ellipses and curves. It’s just that when you’re talking about orbital mechanics, it gets interwoven with other aspects of an object’s orbit, like its velocity and its altitude at the closest point in the orbit.
An interstellar object cannot be flying by slowly enough to enter a circular orbit. If it were, it would already have been in a circular orbit. Trajectories can be extrapolated both into the future and into the past. It has enough momentum to escape the Solar System if and only if it came from outside the Solar System.
This assumes the only interaction is the gravitational pull between the Sun and the object. A close approach to Jupiter, for example, might slow an incoming object into an elliptical orbit, or speed a Solar System object into a hyperbolic escape trajectory.
Orbits are time-symmetric, so an interstellar object being captured into a stable elliptical orbit would be equivalent to an object in a stable elliptical orbit escaping the Solar System (again, ignoring other influences).
Stars tend to get torn apart, go into the accretion disk, and then eventually fall in. But we don't have a big black hole in the solar system.
Do we have any sense of how large this object is? Or is that a silly question that only non-astronomers like me ask?
[0]https://twitter.com/AscendingNode/status/1171913641647493120 [1]https://en.wikipedia.org/wiki/Coma_(cometary)
"Not aliens. And surely they're common. But we just haven't been able to detect these things until recently. It's new to us, not new to the universe."
[1] https://twitter.com/twit_spires/status/1171939194282762240
There's a lot we don't know about the space between solar systems or the space outside of our own heliosphere. This is evidenced by our lack of understanding of when (or if) Voyager actually left our solar system. We just don't know enough to say. Having the opportunity to see something that came from outside our solar system is a good thing for science.
https://www.nytimes.com/2013/09/13/science/in-a-breathtaking...
The first such object, ʻOumuamua, was both interesting (because it was the first one we saw) and surprising (because of its apparent odd shape as indicated by its observed light curve).
Overall I think we’ll discover that they are more common than we think which makes me wonder if we could use them to piggy back probes on them to the outer solar system and beyond since they move quite darn fast.
Some of these objects are also not very dense so some ablative enclosure might also work.
In either case, you are going from 0 to 60 more or less instantly and the results on your fleshy meat body will be the same.
You could try to run real fast in front of the car, away from it, but you are limited by your meat body's technology to ~10mph. You still hit the car at a difference of 50mph. Meat paste once again.
To avoid a painful collision, you'd need to get up to speeds of about 57mph, which is pretty hard for your body to do. And if you could get up to 57mph, why do you need tha car? There's no friction in space, so you'd just keep going until something bumped you.
On impact, only the nearly massless front bit of the net needs to accelerate instantly. The acceleration gradually spreads back to the probe, which is then accelerated gradually to match the object.
After it matches, there is still a great deal of energy in the stretched-out net, which in principle could accelerate your probe to be as much faster than the object as it started out slower than.
Another way to think of this is with a non-stretchy tether perpendicular to the object's path. The object hits one end, and the probe swings around behind it, gaining 2x before it gets to the other side. It could let go at various other points to head off in some other direction at less than 2x.
This is not too different from what we do when we fly probes past planets to give them a speed boost. In that case, the tether is gravity.
It would take about 47 seconds, and the spring would elongate by a maximum of 530 km. To withstand this tension (100 kN), the steel wire (ultimate tensile strength ~400 MPa) would need to have a cross-sectional area of 250 mm², or diameter of 16 mm.
Given this wire diameter, and a Young's modulus for steel of 200 GPa, the spring itself would require a diameter of ~42 cm and ~200,000 turns, if we allow it to stretch completely during acceleration. Fully relaxed, the spring would be 3.2 km in length.
This works out to at least 130 m³ of steel, or 1000 metric tons, which is somewhere around USD$500k. Eminently affordable.
Of course, that's a drop in the bucket compared to the cost of launching a 3.2 km long, 1000 metric ton slinky into outer space.
I am actually more worried about the propagation of tension in the tether being restricted to the speed of sound in the material. It seems like the end would just snap off, for any realizable material.
For comparison, the New Horizon probe to Pluto and beyond left at 23 km/s.
With a thousand km of graphene-fiber tether standing perpendicular to the object's path, it would take 45s to accelerate the probe at a peak of 484 km/s/s. For a 10kg probe, that would put 4.8e9 N of tension on the tether.
Graphene has a tensile strength of 130000 MPa, or 1.3e11 N/m^2, so the cable would need to be some 20cm thick.
Boosting to a higher speed would reduce the cable thickness needed proportionally. At 19 km/s, quite doable, it's 10 cm. However, boosting 1000 km of 10cm cable to 19 km/s would take quite a fair bit more fuel than just boosting the probe itself to the target speed of 41 km/s.
(If my maths are right, and the rail of the US Navy's 2km/s railgun is 10m, the projectile has an initial accelleration of about 20,000 gs. Though its internal complexity is fairly low.)
Keep in mind that if you manage to harpoon your extrasolar whale, you haven't landed, you've only attached yourself to it. If you thought ahead and packed a bungee cord, rather than a completely inelastic cable, you could take up the initial acceleration, but would then find yourself dealing with the elastic rebound. You'd eventually contact at twice the original negative delta, assuming elastic limits on the cord weren't exceeded.
(Keep in mind that you were initially travelling faster, slower, or with some relative motion to the interstellar whale, and hence are implicitly counting on your harpoon cord to take up the difference. Unlike Ahab, you don't have the medium of water to supply friction or shock absorption.)
You could carry airbags to cushion the impacts. This was actually done for the Mars Pathfinder mission. The critical differences between Pathfinder and Extrasolar Ahab is that Pathfinder had an aeroshell and parachutes, all of which reduced the terminal impact eleasticity accelleration to well below Mars escape velocity, as well as a substantial surface gravity to deal with, while Extrasolar Ahab has the cold hard vacuum of space and a microgravity measured in single-digit metres/s^2. Rather than bounce and come to a rest, you'll bank off. Instead of Ahab, you're now "Fast Eddie" Felton, and your balls are no longer on the felt.
The problem in both these cases is elasticity, so what you're looking for is something that's deformable rather than elastic, probably at both the 'poon cord and crash buffer side. The longer you can stretch out (so to speak) the accelleration and impact, the softer your ultimate kiss.
https://invidio.us/watch?v=E65F86kMu48
At which you've probably got one more question:
https://invidio.us/watch?v=uJixQ16L5zc
To which I can only reply: as you wish.
The question specifically addressed lithobraking. Which means a terminal state on the surface with matched velocity.
But how much delta-v one can extract from a bungee jump is just as interesting a problem as how do you break from a huge delta-v and no atmosphere. Maybe one can even direct the jump into a useful direction: interstellar body based propulsion.
In short: to have any sort of survivable encounter with the object the relative velocities need to be so small you have essentially "matched their speed". Those last 0.5 km/s you might gain aren't important compared with the 29.5 km/s you need to put in.
you don't match deltav, you'd match trajectory. you may be able to do that at the cost of more or less deltav, depending on how clever and patient you are. once you've matched trajectory, you'll (basically) stay matched, as you're in space and there's nothing to disturb you.
That remark makes more sense in the context of missile defence than when talking about space travel.
From what I know from reading on Helios-A and Helios-B, we already have a probe which can go over twice the speed of what I thought I saw the comet is traveling at. So couldn’t the probe match its velocity (dunno why I said Delta V before) to the comet, if even just for long enough to land without total destruction?
And if you don't match it well enough that you end up roughly the same place you're going to have a fast, and therefore violent, encounter.
Elsewhere I saw what I thought was the speed of the comet, which was around 69k mph. Didn’t Helios 1 and 2 do something like ~150k mph[0]?
Assuming those numbers are correct (please say so if not), then what would stop an intercept from being technically possible (even if very very very hard)?
To actually hitch a ride with another object you have to match their velocity _and_ their location at the same time.
If the object you are trying to catch started further from the sun than you, and was already moving faster than you, then you can't match its speed and location by falling toward the sun: when you arrive at the same location, it will have fallen further than you and hence picked up more kinetic energy per unit mass than you did, and it started off moving faster than you to start with, so it's still moving faster.
Dunno why I said DeltaV, but clearly it was inappropriate.
Yeah, but we could go to other stars already, in like a zillion years. Voyager is on an interstellar path, although it isn't pointed at a nearby star. If the object has made the journey it might take the same delta-V for us as an interstellar trip, but it would happen a whole lot faster.
Does anyone have more helpful links on this topic?
I'm not sure if they've figured out how big it is, or what other analysis they can do of it.
Eye-balling the animation someone else link to, it looks like it will be in our solar system area for about half a year.
I have no idea if we have telescopes good enough for this. Does anyone else know?
Hope a rewarding target comes up.