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
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too, check the links in the description to have your name added to this list. All the best, and see you next time.
spoiler: No, we have not. & One, but completely unremarkable. And a couple objects in the Solar System.