On October 25, 2017, astronomers from NASA's Minor Planet Center sent out an announcement
that they needed help confirming the trajectory of an interesting object.
Known as C/2017 U1 PANSTARRS, the object was moving quickly through the Solar System, on
a path that would take it out into deep space.
Astronomers were happy to oblige, providing dozens of observations within a few days,
confirming that yes indeed, we were looking at the first asteroid that had come from interstellar
space.
It turns out that C/2017 U1 PANSTARRS, later given the Hawaiian name Oumuamua, or "a
messenger from afar arriving first", had already made its closest pass to the Sun on
September 9th, 2017, traveling at a top speed of 87.4 kilometers per second.
It whipped around the Sun, and then continued on its hyperbolic orbit out into deep space
again.
It passed near the Earth on October 14, then crossed the orbit of Mars on November 1st,
by May 2018 it'll be farther than Jupiter, and get past Saturn in early 2019.
Astronomers around the world have been making continuous observations of the asteroid, using
some of the largest telescopes on Earth and in space.
But they've got to work quickly, by mid-December, it'll be too dim to observe with any of
our instruments.
I know you've known about this asteroid for several weeks now, so I'm going to make
this video worth your while with some cool new info.
Astronomers have been studying Oumuamua as much as they can for an object speeding out
of the Solar System so quickly.
For starters, they've absolutely confirmed that it didn't come from within the Solar
System, the orbit is definitely hyperbolic, taking it out into deep space again.
According to the observations, the asteroid approached the Solar System from the direction
of the constellation Lyra, and must have been traveling for hundreds of thousands of years
from that general direction.
Astronomers have also confirmed that the object is very similar in composition to the other
asteroids and comets in the Solar System, which means that the formation process that
happened here is similar to how planetary systems evolved around other stars.
I mean, that's not a huge surprise, but it's nice to have another line of evidence.
What are surprises, however, are the shape and color of Oumuamua.
It's extremely dark, with a reddish hue, absorbing about 96% of the light falling on
its surface, about the same as freshly poured asphalt.
It's also tumbling as it moves through space, rotating once every 7.3 hours.
It also has a strange shape, measuring about 400 meters long and possible a tenth as wide.
We actually don't know of anything else in the Solar System with this ratio of length
to width.
In fact, nothing beyond a ratio of 3:1 has ever been seen.
I'm not going to call it cigar shaped, I refuse.
It's more Rendezvous with Rama shaped.
I'm sure you're wondering "how" astronomers know it has this funny shape, and the key
is the fact that it's tumbling.
Astronomers measured its brightness over time, and watched how it got brighter and dimmer,
essentially reflecting more or less sunlight.
By measuring the maximum and minimum brightness, they were able to determine the scale of its
size.
In other words, it's about 10 times bigger in one dimension than the other.
Because the asteroid is tumbling so fast, and hasn't fallen apart, it needs to be
dense, likely made of rock and maybe even metal - no ices.
And so, by estimating what it's made out of, and by comparing its brightness, they
can calculate its overall size.
I'm sure you're wondering, where did this interstellar interloper come from and how
did it get here?
A group of researchers dug into this question.
They compared the dynamics of the Solar System with the movements of nearby planetary systems
in the Milky Way.
They calculated that the number of interstellar asteroids should actually be larger than the
number of interstellar comets.
In fact, they estimate that there could be 30,000 interstellar asteroids passing through
the Solar System at any time.
The Milky Way is probably rich with asteroids like Oumuamua, formed in the debris disks
newly forming planetary systems.
The planetary formation process kicks these objects out into deep space, free to wander
from star to star.
We'll probably discover more of them in time, as asteroid surveys get more comprehensive.
Of course, these will have to remain rough estimates.
Oumuamua is leaving the Solar System and it's never coming back for a closer look.
In 11,000 years, it's going to be a light-year away from the Sun.
But what if we could get a better look.
What if we could send a mission to catch up with Oumuamua and study it close up?
I'll talk about that in a second, but first I'd like to thank:
Jordan Barnes Martin Øien Søfting
Barry van Biljon
And the rest of our 810 patrons for their generous support.
If you love what we're doing and want to get in on the action, head over to patreon.com/universetoday.
Oumuamua is one of the most fascinating objects to visit the Solar System, and planetary scientists
would love any way of studying it closer, like they did with the Rosetta mission or
the upcoming encounter of OSIRIS-REx with asteroid Bennu.
Close observations would give us an insight into planetary formation in other parts of
the Milky Way.
But Oumuamua is well on its way out into the depths of space again, beyond our reach.
But if the researchers are right, there could be a few interstellar asteroids in the Solar
System at any time, we just need to find them, and then act quickly to intercept them.
It turns out that this object came within about 60 times the distance from the Earth
to the Moon, but astronomers hadn't discovered it until 5 days after the flyby.
Future asteroid surveys like the Large Synoptic Survey Telescope which scans the skies regularly
has a much better chance of turning up an interstellar asteroid with a similar hyperbolic
orbit.
Once we're detecting them regularly, then there could be an opportunity to intercept
them.
But the reality is that it takes many years to go from mission idea to its actual launch.
You're not going to see a fully fueled SLS rocket waiting on the launchpad to hunt down
an interstellar asteroid with 3 days notice.
The more realistic idea is to chase it down.
Right now, Oumuamua is moving 26 km/s away from the Solar System.
That's faster than the fastest spacecraft ever sent on an escape velocity from the Solar
System.
Shortly after its discovery, a group of rocket scientists came together to propose Project
Lyra, a mission that could chase down, and even go into orbit around Oumuamua.
If a mission was launched in 2018, with a velocity of 26.75 km/s, it would take about
20 years to arrive at its destination.
Of course, that's not realistic, and a mission would more likely take 5 to 10 years.
At this point, the spacecraft would need to be going 33 to 76 km/s and the mission would
take 30 to 75 years to catch up.
If you could launch a mission in 2027, you'd probably catch up with it at a distance of
100 to 200 AU from the Sun, about the current distance of the Voyager spacecraft, which
means you'd need a radioisotope thermoelectric generator to supply power.
And the only kind of propulsion system that could get that kind of velocity would be some
kind of ion engine.
These put out miniscule thrust, but can keep pushing the spacecraft faster and faster for
days, months, even years.
The reality is that it's not a great idea to try and catch up with Oumuamua.
It could be possible, but not worth the investment.
Instead, it makes sense to develop a spacecraft, and have it ready to go for when the next
interstellar asteroid shows up.
What an amazing discovery.
We always suspected these kinds of interstellar asteroids were out there, but it's incredible
to actually find one.
And to think that there could be tens of thousands of them buzzing through the Solar System at
any time.
It shows us just how connected we are to the rest of the Milky Way we live in.
And maybe, just maybe, a mission will be developed that gets to study one up close.
Just imagine what we could learn about the formation of other Solar Systems.
What do you think?
Should we set aside the resources to catch a future interstellar asteroid?
Just think what it would tell us about the formation of the galaxy.
Let me know your thoughts in the comments.
In our next episode, we talk about how Mars lost its atmosphere millions of years ago
and what we could do to get it back.
Let's get on with the playlist.
First up, Scott Manley's excellent coverage about the discovery, and then a video from
John Michael Godier, who's been doing a great job staying on top of the news.
A video from the Hubble Space Telescope about the Pan Starrs survey.
A talk from the SETI Institute about the search for objects beyond Neptune.
Finally a video from the Large Synoptic Survey Telescope about how they're going to find
asteroids.
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