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article imageOp-Ed: Interstellar objects – More incoming, but what, when and where?

By Paul Wallis     Oct 1, 2019 in Science
Sydney - The recent discovery of two interstellar objects, comet 2I/Borisov and asteroid Oumuamua in the solar system has raised the bar for expectations and predictions. Expecting more is one thing. The more pressing question is exactly what might be coming.
So far, we’ve had only 2I/Borisov and Oumuamua confirmed as interstellar. The mere prediction of more arrivals doesn’t address many issues that are very relevant. In our system, these things are pretty much part of the system, with predictable orbits and behaviours. The point here is how these (as far as we know) usually orbital bodies happen to show up in another solar system.
So much to learn
There are many possible scenarios here and a lot to learn. Contrary to the usual imagery, the galaxy is very much three dimensional. Not everything just orbits around on a dinner plate. Stars and cosmic phenomena are at different levels, inclinations from 0 degrees, etc.
We’ve gone from a situation where there were no known interstellar objects were in the system, to a sort of slow parade of bits and pieces zipping past. This has almost 100% certainly happened in the past, but now we have a chance to map these arrivals, and backtrack to see where they may have originated.
We can learn:
• Were they kicked out of orbit?
• Did some force pull them away from their stars?
• If so, what, when and where? Are they coming from the same direction, or different directions?
• What, exactly, has sent them here, and how?
Gravity is perfectly capable of sling shotting just about anything to anywhere. That’s one possible primary cause, but there are other possibilities, too.
• Movement of large bodies creating a random slingshot effect as they pass, knocking things out of orbit.
• System disruptions throwing fragments out in to interstellar space.
• Cascade effects of disruptive forces spraying smaller fragments ahead of them.
Interstellar space isn’t “empty”. Not everything we see is necessarily part of a system. There’s a lot of material floating about in space, which will also respond like dust as a car goes by. So it’d be nice to analyse these objects, plot their arrival, and see what’s causing the movements.
A possible scenario goes like this: A few million years ago, something big disrupted a large mass of interstellar materials and/or objects in a solar system, firing a spray of asteroids, comets, etc. as it passed. The cascade of objects acts like a scattergun, spreading debris around. It was big enough to move objects like the new comet and asteroid. What else did it move? Are there any threats on the way? If so, how do we manage them?
Local issues
There are also a few glaring anomalies in the interstellar objects scenario. Our own system has a large amount of material called the Oort Cloud around it. This part of the system includes a virtual shopping list of bits of everything, well out beyond the orbit of Pluto.
A lot of this material is left over from system formation, and some of it may have been “acquired” in the last few billion years. There’s a lot of dust, comets, ice, planetesimals, etc. The overall solar system when you include all these objects looks chaotic, but is actually pretty stable. So this situation is atypical fron what we know by definition, and therefore needs to be studied closely.
Have we just adopted a stray new comet and a new asteroid, or are we looking at the start of a whole new wave of objects caused by the scenario above? Can these incoming objects disrupt the Oort Cloud, sending bits of it into the inner system? The arrivals may seem slow and random to us, but if there really are more coming, what is coming, and how much of it?
My guess would be that we’re looking at a new, specialised branch of astronomy, mapping the interstellar incursions and plotting possible future entries. Not all massive chunks of rock travelling at 60K per hour are harmless. We could acquire a new moon, or a small collection of random objects intersecting Earth orbit. Some could disrupt space missions, or crash into other planets, with whatever effect.
Time to start looking, guys.
This opinion article was written by an independent writer. The opinions and views expressed herein are those of the author and are not necessarily intended to reflect those of
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