'Omuamua is the first object ever discovered to be of interstellar origin
that passed through our solar system. But now some astronomers are suggesting
that it may in fact be of an alien origin, but not everyone's convinced, and
for good reasons. Welcome back to Launch Pad, I'm Christian Ready your
friendly neighborhood astronomer. In October 2017, astronomers discovered a
new kind of object that was unlike anything that we had seen passing
through our solar system before, namely because it was...well, literally passing
through our solar system. The object was the very first of its kind, an
interstellar asteroid that was discovered after it had passed closest
to the Sun and was on its way out of the solar system. Even though the object was
too far and too faint to be resolved as anything other than a point of light,
astronomers were able to measure its light as it varied over time. They
concluded that it must be a rotating cigar-shaped asteroid. And that's a
really strange shape because we don't seem to know of any cigar-shaped
asteroids in our own solar system. But its velocity and trajectory are also
very strange. It seems to have slingshot around our Sun from interstellar space
and is heading out into interstellar space once again. The object was given
the name 'Omuamua; Hawaiian for 'messenger from a distant place arriving first'. On
October 14th 2017, 'Omuamua passed within 0.16 astronomical units from Earth.
That's relatively close. Even then we didn't even discover it until after it
had slingshot around the Sun and began heading out of the solar system. By
November of 2017, it crossed Mars' orbit and by May of
2018 it had already passed Jupiter's orbit. In other words, 'Omuamua is
moving fast - about 25 kilometers per second fast. However, even at that speed it
won't leave our solar system for approximately another 20,000 years.
Still, 'Omuamua is getting farther away from us and growing fainter with each passing
day. But that hasn't stopped astronomers from making yet more interesting
discoveries about the strange object. Over the summer, a team using the Very
Large Telescope in Chile noticed that 'Omuamua
was actually accelerating as it was leaving the Sun. Now this behavior is
very strange for an asteroid but it's not really too strange for comet because
that's what comets do; they release gas and dust as their surfaces are warmed by
the Sun. The outgassing can act as a thruster which can help
accelerate the comet forward a little bit as it leaves. But 'Omuamua never
showed any evidence of significant outgassing. There was no characteristic
coma around the comet, there was no tail, nothing that would suggest that 'Omuamua
was cometary in nature. So astronomers began to consider other possibilities
that might help explain 'Omuamua's acceleration. In a new paper from Harvard
University, astronomers Shmuel Bialy and Avi Loeb
investigate the idea that maybe it's solar radiation pressure that could be
accelerating 'Omuamua. Light exerts pressure. It's a very weak pressure to be
sure, but in the vacuum of space that pressure can build up over time and
accelerate an object. However, in order for sunlight pressure to accelerate 'Omuamua,
it couldn't be shaped like an asteroid or even a cigar so much as it
would need to be shaped like a well like a very very thin pancake less than a
millimeter thick and about 50 meters across. Such a geometry would make
'Omuamua a light sail instead of an asteroid. Light sails have been proposed as a
pretty inexpensive method of sending spacecraft to other planets and even out
to other stars. All you need is a very large and highly reflective sheet of
material that is facing the Sun or maybe even like a laser propulsion system on
the ground. Now in their paper, the researchers demonstrate that a
millimeter-thin sail could in fact survive interstellar travel around the
galaxy. It could survive minor impacts from particles of the interstellar
medium, it could handle torques induced by sudden rotations from stellar winds,
it could even deal with galactic cosmic rays penetrating over tens or even
hundreds of thousands of years. However, we've
never actually seen a solar sail in nature so the authors of the paper go on
to consider artificial origins. And since 'Omuamua passed very close to Earth, it
may have very well been an intentionally sent probe. Okay, now that
I've told you the back story, let me say that I find these claims of alien
origin to be very unconvincing. 'Omuamua did pass close to Earth, but that does
not mean it was intentionally sent. It could just be that it had to pass
close enough to Earth in order for it to set itself up on a trajectory that would
allow us to discover it in the first place. In fact, it's estimated that there
could be something like a thousand of these 'Omuamua-type objects passing in
and out of our solar system every year. The Large Synoptic Survey Telescope will
be able to make very wide field, yet very deep images of the entire sky every
several days. It will be able to capture all kinds of new asteroids comets and
even interstellar interlopers passing across the sky, So I think we're going to
be seeing a lot more examples that will help us to understand the nature of 'Omuamua
far better. Another problem is that 'Omuamua is moving
way too slowly to be suitable for interstellar travel. An interplanetary
light sail, let alone an interstellar light sail, would need to be kilometers
wide in order to accelerate to thousands or even tens of thousands of kilometers
per second 'Omuamua is just too small and too slow for that job. Now the whole idea
of radiation pressure as the source of acceleration was invoked because 'Omuamua
doesn't seem to be a comet. But just because it doesn't seem to be a comet
doesn't mean that it isn't a comet. Whenever we see comets with their
beautiful comas and tails, we're seeing dust bursting out from inside the comet.
But if 'Omuamua had been tumbling through interstellar space for all of these
years, it's entirely possible that galactic cosmic rays or magnetic torques
or even encounters with other stars could have fundamentally changed its
surface chemistry. Maybe the only thing that is
outgassing from 'Omuamua is just gas itself, and that's gonna be really hard to detect.
In other words, 'Omuamua may in fact be outgassing like a comet and
that's what's accelerating it out of the solar system. Invoking aliens is a great
way to make headlines but it always turns out to be a losing bet. A recent
example was Tabby's star. One hypothesis to explain its erratic drop-off in light
was that maybe there was a civilization around the star that was building a
Dyson Swarm. That is, a an array of collectors to harness the star's energy.
It was a wild hypothesis, but that's what everybody seized on. And people started
to get really disappointed when they found out that sure enough, it was dust
that was causing the drop-off in light from the star. You know, in science we get
things wrong all the time and that's okay because by getting things wrong we
eventually get to the right answer. But when astronomers from Harvard University
make claims of alien probes, the public assumes that they must be right.
They're from Harvard after all! So when we find that there really is a natural
explanation for 'Omuamua's acceleration, well you can see how this is gonna
play in the public. Now don't get me wrong, I would love it if we had
conclusive evidence that we were not alone in the universe, but we've got to be
careful and thoughtful as we explore an incredible universe in which we live. So
if you'd like to join me on this journey through this amazing universe of ours, I
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out on any new video. Until next time keep watching the skies.