It isn't often that I get to announce that a visitor from another star system might be
passing through our solar system right now.
This newly discovered object, known as A/2017 U1, appears, if its trajectory is indeed hyperbolic,
that it is not gravitationally bound to the sun, meaning that it may have originated in
entirely different star system.
The idea that comets and asteroids from other solar systems could enter ours is not a new
one, and indeed was expected to eventually happen.
We know from models of our own Oort cloud that comets tend to get ejected out of the
solar system far more often than the get deflected into the inner solar system.
In fact, the difference is pretty dramatic, estimates are that as many as 90-99% of all
comets leaving the Oort cloud are being ejected into deep space.
As a result, it seems reasonable to assume that this is the case for other star systems
with similar Oort clouds and that lots of comets, and also asteroids and planets, are
wandering interstellar space and could pass through other star systems including our own.
This particular object is thought to be about 160 meters in diameter, and somewhat reddish
in color.
On October 14, it passed a mere .16 AU from earth, and while that's 15 million miles,
it's still quite close on solar system scales.
Incidentally, the object was not discovered until October 18, after it had passed by earth.
If the object is from another star system, it could be a dead comet or an asteroid.
If it were an active comet it would exhibit a coma as the ice it would contain evaporates,
it does not have this.
So it must either be a comet that was exhausted in another solar system before being ejected,
or originated from it's original inner solar system as an asteroid.
While tantalizing, and one wishes we could capture this object, that would be exceedingly
difficult since it's passing through at about 16 miles per second.
However, it is possible for Jupiter to capture interstellar comets with its immense gravity,
though its thought to be the only planet that can do this.
And, in fact, there are two candidates for this.
Both Comet Machholz 1 and Hyakutake C/1996 B2 have unusual compositions when compared
to the solar system's other comets.
Capture, however, won't happen with this object, unless of course its orbit is shown to be
elliptical, in which case it's from here.
If it isn't from here, where might this interstellar object have originated?
It would probably be impossible to tell, though it is coming from the direction of Vega, a
star made famous by the movie Contact, and for being a very bright night sky star.
We also know that Vega has lots of dust and material around it.
But we probably will never know for sure.
As an aside, it might surprise you however that this is actually not the closest interstellar
material to earth.
We have it down here on the surface.
Material from space, some of it interstellar, rains down on earth constantly in the form
of dust.
And, suspected interstellar grains were collected by the Stardust spacecraft and returned to
earth.
Plus, they are also found in primitive meteorites.
Unfortunately, this visitor object won't around long and is already on its way out, and was
far too dim to be seen outside of large telescopes anyway, but the study of captured exocomets
or asteroids passing through will offer us an opportunity to learn about the chemical
compositions of other solar systems and how they compare to our own.
Thanks for listening!
I am futurist and science fiction author John Michael Godier currently eyeing A/2017 U1
suspiciously, where is it from and what does it want and be sure to check out my books
at your favorite online book retailer and subscribe to my channel for regular, in-depth
explorations into the interesting, weird and unknown aspects of this amazing universe in
which we live.
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