In Rendezvous with Rama (by Arthur C. Clarke), a mysterious object is discovered passing through the Solar System. The object has a strange shape — it’s a giant cylinder. It was discovered by the Spaceguard survey, designed to find objects that might impact Earth (so-called near-Earth objects). Spoiler alert: the cylinder is a spaceship sent by super-intelligent aliens to prospect for other space life.
Guess what? Rendezvous with Rama just happened in real life!
A month ago (Oct 19, 2017), the Pan-STARRS survey discovered the first object passing through our Solar System. (Like Spaceguard, Pan-STARRS was designed to find near-Earth Objects.)
The object is on a hyperbolic trajectory: it is simply passing through the Solar System. It feels the Sun’s gravity of course, but it is moving too fast to be bound to the Sun. It is just zooming through for a quick visit before it heads back to interstellar space. Here is a sweet animation of its path:
The object has been officially named 1I/’Oumuamua.
The name comes from Hawaiian ʻou.mua.mua, meaning “scout”, (from ʻou, meaning “reach out for”, and mua, reduplicated for emphasis, meaning “first, in advance of”) and reflects the way this object is like a scout or messenger sent from the distant past to reach out to us. (Source: Wikipedia)
A couple of things about ‘Oumuamua are pretty strange.
First, it passed very close to the Sun (within about 0.25 Astronomical Units) but it showed no signs of activity. When comets approach the Sun, small jets release water vapor (and other volatiles), creating a giant coma and tails. The Rosetta mission got up close to comet 67P/Churyumov–Gerasimenko and saw its jets in action:
Why doesn’t ‘Oumuamua have jets (or a coma or tails)? Maybe it’s rocky with very little ice. But it’s possible that ‘Oumuamua contains ice but only under the surface. There is a class of objects called Damocloids, that have comet-like orbits but no activity. The Damocloids are thought to be extinct comets, which passed close to the Sun so many times that they completely lost their water and volatiles. Maybe ‘Oumuamua is similar.
Second, ‘Oumuamua has a weird shape. It is super-stretched along one axis, which is about 10 times longer compared with the other two axes. It’s been called a cigar, but it might look like a cucumber. Or a baseball bat. Or a carrot. It rotates every 8 hours or so, tumbling along the shortest axis. (Like a cigar/cucumber/baseball bat/carrot thrown up in the air).
There is some disagreement between different groups on just how stretched-out ‘Oumuamua is; it could be at little as 3:1, more like an interstellar potato than a cigar. But, the cigar people have the better images!
The sad thing is that we will probably never know what ‘Oumuamua really looks like. It’s just too far away to get a resolved picture. To do that we would need an image from way up close. We’ve sent spacecraft to intercept comets and asteroids to see what’s really going on there. But ‘Oumuamua showed up too suddenly and is moving too fast. We’ll never catch up (at least not for decades). Big frowny face.
‘Oumuamua’s origins story probably goes something like this. It formed as a “planetesimal” (a planetary building block) in a disk orbiting a young star. Somehow it did not end up being incorporated into a planet. Instead, the gravity of the growing planets kicked it onto a stretched-out (eccentric) orbit, then kept kicking it until it was ejected into interstellar space. The most efficient ejection happens when a system with more than one giant planet becomes unstable. Here is an animation of an instability from my own research:
As you can see, when the giant planets go unstable, the whole outer disk of comet-like objects is completely ejected from the star, left to roam interstellar space. (Of course, some planets might share their fate, and some might even harbor life…). Comet-like objects are thought to be much more abundant than rocky ones, and also to be much easier to eject (rather than to be thrown onto the star). That is why we think it likely that ‘Oumuamua is closer to an extinct comet than to a rocky asteroid (see here for details).
There are a couple of final things that we can learn from ‘Oumuamua. Of course, let’s keep in mind that this is just one object. (How much do you learn about a movie from the first frame? How much do you learn about clouds from the first raindrop?)
First, ‘Oumuamua is small! It’s only about the size of a large stadium. That’s much smaller than we usually think the building blocks of the planets were. Is ‘Oumuamua a fragment created in a collision between building blocks? That might explain its weird shape, but at this point it’s just a guess.
Second, humanity is lagging behind! If this object was really sent by super-intelligent aliens, then we are just watching it pass by. Sure, we’re learning some interesting stuff but we don’t have the capabilities to catch up to ‘Oumuamua and make sure it’s not a real spaceship like in Rendezvous with Rama. I guess that means that we’re not even smart enough to end up in a Galactic zoo…. Sheesh,
The astronomy community is super-jazzed about ‘Oumuamua and I’m sure the story will keep unfolding over the coming months.
UPDATE: Upon writing this article, I was not aware of Project Lyra, a study of how to intercept and analyze ‘Oumuamua. This exciting concept is nicely-summarized in this article.
Questions? Comments? Words of wisdom?
- ‘Oumuamua on Wikipedia
- Nature paper by Meech et al
- Jason Wright’s blog post asking whether ‘Oumuamua could be an alien spacecraft (spoiler: doubtful)
- My own paper with some thoughts on ‘Oumuamua