Oumuamua is not the only interstellar interloper.
If you follow space news, then you will have definitely heard of Oumuamua, a visitor from
another planetary system.
This object, discovered in 2017, was the first ever object to get an “interstellar” designation
from the IAU, but interestingly, we actually know about a few more of them.
So, what are these objects?
How do we know they came from beyond our solar system?
And what are they doing now?
I’m Alex McColgan, and you’re watching Astrum, and together we will examine what
we know about Oumuamua and the other interstellar interlopers.
There are a lot of predictions in the science community as to how many extrasolar objects
pass through our solar system.
Some think we regularly see visitors, with up to 10,000 per day passing within the orbit
of Neptune.
That seems like a lot, so let’s figure out why scientists think this figure is so high.
The first thing to understand, is that our solar system extends way beyond the orbit
of Neptune.
Beyond Neptune is the Kuiper Belt, and beyond that is the Oort Cloud.
The Oort Cloud contains potentially trillions of comets that are gravitationally bound to
our Sun.
Some of the comets that we see that pass by the Sun likely came from and will return to
this Oort Cloud with their extremely elliptical orbits, taking 10s to 100s of thousands of
years to do so.
Some of the comets we see from the Oort Cloud would never have come to the inner solar system
were it not for massive third bodies which perturb these comet’s orbits with their
gravity so that they fall towards the inner solar system.
These third bodies are often other stars.
You see, the solar system is not stationary like we sometimes may perceive, but we are
constantly moving, orbiting the galaxy.
As we move in our orbit, we cross paths with the gravitational influence of other orbiting
stars.
Even distances of a couple of light years can be enough to perturb a comet so it comes
crashing down towards the Sun.
On the other hand, it can also be enough for the comet to be pulled away from the solar
system altogether, joining the ranks of the hundreds of trillions of interstellar interlopers
found in the galaxy.
As an Oort Cloud like body is likely not unique to our solar system, it must mean that comets
are constantly being lost and others are being captured by stars throughout the galaxy every
day, although generally speaking, what we’ve seen of Oort Cloud objects so far imply that
the majority of comets in our Oort Cloud did originate with our Sun, because they are mainly
quite similar in composition.
As the solar system travels through the galaxy, we also cross the path of interstellar interlopers
that have been pulled away from their original home systems.
They often approach from Vega because that’s the direction our solar system is heading
through the galaxy.
While the Sun does capture some of these objects, most are travelling so fast relative to us
that they pass right through the solar system, only having their direction of travel changed
as they pass by the gravity of the Sun.
Oumuamua is one such object.
It was originally thought to be a comet when it was first discovered, and got given the
classification C/2017 U1, but upon further investigation, it was reclassified as asteroid
A/2017 U1 when no coma around the comet could be seen, becoming the first object to ever
get a reclassification like that.
Once the orbit of Oumuamua had been established, it also became clear that it was travelling
too fast for it to be in orbit around the Sun.
We say that the object like this one has a hyperbolic trajectory.
Because its velocity will see it leave the solar system altogether, it likely didn’t
come from the solar system to begin with.
The International Astronomical Union had the unusual task of having to create new a classification
of object just for Oumuamua.
They decided upon I for interstellar, so Oumuamua’s designation now is 1I/2017 U1.
Oumuamua is unusual for a number of other reasons.
As it is like an asteroid, it must have originated from the inner part of its home system, so
how did it get ejected and make its way to us?
Is it from a collision of huge proportions?
Alternatively, maybe it really is a comet, but as it travelled through interstellar space
over millions or billions of years before it got to us, it has been coated in dust,
meaning that the volatile materials typically found on comets weren’t exposed to the Sun.
The other weird thing is its shape.
I have always seen Oumuamua referred to as cigar shaped, but because it is less than
a kilometre long and only around 35m across, even the most powerful telescopes couldn’t
resolve more than a pinprick of light.
It’s been given this shape because its brightness pulsates over its 7-hour rotation period.
This is because we receive more light from its reflection when it appears longer from
our perspective.
However, this could apply just as easily to a saucer shaped object.
It also appears to be tumbling rather than rotating along a set axis.
Its shape and rotation could lend weight to the theory that it originated from a collision.
Another weird attribute is that it accelerated away from the Sun, only by a tiny amount,
but more than it should have if it really was a non-volatile asteroid.
So now some scientists think it might be comet like after all, and that it was ejecting only
gas rather than gas and dust like we normally see from comets.
However mysteriously, no coma or tail was ever detected.
To be sure, the Spitzer Infrared Space Telescope spent 30 hours trying to get any kind of reading
on it, but couldn’t, meaning this object emitted nothing in the infrared.
Typical comets have comas and tails that Spitzer can spot, like in this image.
If there was an acceleration, but it’s not a comet, then what caused it?
This point in particular got people thinking that this wasn’t a simple rock, and that
maybe there’s more of an alien origin to this object.
This theory received more credibility when it emerged that this object was also 10 times
shinier than a typical comet, meaning it reflected light like a metal.
However, before you get your hopes up too high, SETI listened for any radio signals
emanating from the object, and nothing was detected at all.
Even the faintest half watt signal would have been detected had it been there.
So, at the end of the day, we don’t have enough information to prove something either
way, and it is now too far away for us to send a spacecraft after it, so I’ll let
you decide for yourself.
It’s intriguing though, nonetheless!
But as I mentioned, we’ve also had other visitors from outside the solar system, but
this next one is a little more conventional.
Being the second “I” object, it’s been given the designation 2I/Borisov.
Zooming in on Borisov reveals that this object had a big comet like coma and tail, almost
the size of 14 Earths across.
We couldn’t see it with the naked eye though, as the closest it got to the Sun was beyond
the orbit of Mars in 2019.
Borisov was roughly the same size as Oumuamua, about half a kilometre across.
After its closest encounter with the Sun, it began falling apart.
This is reasonably normal for a comet of this size passing by at this distance.
Also, it’s composition, while uncommon, isn’t particularly unusual either.
Because it passed through the solar system at a greater distance than Oumuamua, its hyperbolic
trajectory wasn’t hugely affected by the Sun’s gravity.
So overall, apart from its I classification, its a somewhat unremarkable object.
Now moving on to some other interesting interstellar objects that do not have the I classification.
C/1980 E1 was originally a solar system object with an orbital period of 7.1 million years.
The furthest its orbit used to take it was an incredible 1.17 light years from the Sun.
However, it passed a little too closely to Jupiter during its last approach in 1980.
Jupiter’s gravity accelerated it just enough for it to get a hyperbolic trajectory, and
so this object will eventually become an interstellar interloper itself when it leaves our solar
system in a few million years.
On the other hand, we have had the opposite happen, where interstellar objects have had
their velocities slowed down enough by the gravity of Jupiter that they became captured
and locked into our solar system.
Again, I mention Jupiter specifically because it has been determined that other planets
aren’t massive enough to do this, and it has to be a third body beyond the Sun and
the comet that does the slowing down or speeding up.
Machholz 1 and Hyakutake C/1996 B2 are potentially such captured interstellar comets from another
planetary system.
The giveaway for objects like these are their highly elliptical orbits, and their very unusual
compositions compared to the majority of other comets.
This makes them interesting and viable targets for future missions, as the solar system might
have done all the hard work for us in capturing interstellar objects and putting them within
arm’s reach.
There’s one more giveaway that an object might have extrasolar origins.
And that is if it is orbiting retrograde to pretty much everything else in the solar system.
An example of an object like this is 514107 Kaʻepaokaʻawela.
What makes this object especially interesting is that it is also an asteroid, unlike most
other interstellar objects we would expect to see.
It could be that the volatile materials have already burned off if it was once a comet,
meaning it would have been captured very early in the solar system’s past.
Its orbit is also unusual in that it is locked in a 1:1 orbital resonance with Jupiter.
Now, if there really are plenty of interstellar objects passing through the solar system,
its clear that we need better equipment for detecting them.
One of the new Vera C Rubin Observatory’s mission goals is just that.
When it begins operations in 2021, it will use its wide angled field of view to scan
the sky for all sorts of asteroids, comets and interstellar objects.
Want to know more about this impressive project and what it hopes to achieve?
Check out my video I made about it here.
So, there we have it.
Although Oumuamua is beyond our reach, there are plans in place to have a spacecraft ready
to go to visit the next one at a moment’s notice.
What secrets will we find on objects like this?
Only time will tell.
But for now, subscribe for more space videos, and so you won’t miss out on future updates
on interstellar visitors.
Thanks for watching!
And thanks to my patrons and members who support the channel, if you find value in these videos
and want to support the video production process too, check the links in the description to
have your name added to this list.
All the best, and see you next time.