'Oumuamua hit the headline back in 2017 when it was first detected by the Pan-STARRS telescope. Many theories abound about this mysterious object, but here we've compiled some of the oddest things about 'Oumuamua.
Potential conspiracy theories aside, we do know, or think we do, some things about this distant visitor from another world.
1. We have absolutely no idea where it came from
'Oumuamua still holds many secrets, and we may never be able to answer. One such question is where it actually comes from.
We do know that it entered our solar system from the rough direction of the constellation Lyra, but that's it.
Whenever 'Oumuamua wandered off from its parent solar system, stars were in a different position to today so it's, at best, an educated guess as to where it came from.
Owing to its incredible speed relative to our Sun, we do know it's highly unlikely to have originated from our own Solar System. Also, it will not likely be captured into a solar orbit and will only be a passing visitor.
It might well be possible that 'Oumuamua has actually been galavanting around the galaxy for millions, if not billions, of years prior to visiting our home solar system but we may never really know for sure.
We also know that it approached us from, more or less, directly above the rough plane where most planets and interstellar objects orbit the Sun. This means it did not have any close encounters with any of the main planets in our solar system on approach.
But a team of scientists who conducted recent work thinks they might have a clue. They believe we can actually narrow its origin down to one of four, star candidates.
After accounting for some gravitational interaction with our solar system, the scientists consulted data from the European Space Agency's Gaia mission to help them reconstruct its path prior to paying us a visit.
In their estimation, it could have come from either red dwarf HIP 3757, sunlike star HD 292249, and two other stars without such manageable nicknames as of yet.
2. We don't really know what it looks like
Although there are many artistic impressions of 'Oumuamua circulating around the net, we actually have no idea what it looks like. To date, scientists have only been able to see it as a small speck of light through their telescopes.
We do know that it is tumbling through space and appears to be, more or less, cigar-shaped. In that sense, it is about 10 times longer than its width. Interestingly, most interstellar objects tend to have a length to width ratio of, at most, about 1 to 3.
Scientists know this because the interstellar object's brightness (or amount of reflected sunlight) varied by a factor of 10 every eight hours or so. This strongly implies that 'Oumuamua has an extremely elongated shape.
Not only that, but using the same observation data scientists have been able to conclude that it must be tumbling throughout space. It, in effect, acted like flashing light as it made its inexorable journey towards us.
We've now lost sight of it as it was only in the Solar System for a few days. Despite this, it does have a very low albedo, like a hard metal surface, reddened by cosmic rays. Other than that it is anyone's guess exactly what this mysterious alien visitor looks like in reality.
3. 'Oumuamua got a little speed boost as it approached us
At some point during its approach towards us, 'Oumuamua appears to have received a small speed boost. Observations from the Hubble Space Telescope and ground-based observatories noticed that its acceleration increased which slightly changed its course from what was initially predicted.
“Our high-precision measurements of ′Oumuamua’s position revealed that there was something affecting its motion other than the gravitational forces of the Sun and planets," said Marco Micheli at the European Space Agency.
Whilst we may never actually know for sure, there is some hypothesis why this happened. Davide Farnocchia, of the Center for Near Earth Object Studies (CNEOS) at NASA’s Jet Propulsion Laboratory, said:
"This additional subtle force on ‘Oumuamua likely is caused by jets of gaseous material expelled from its surface. This same kind of outgassing affects the motion of many comets in our solar system."
But this is just a hypothesis. Unlike other space object visitors, like comets, 'Oumuamua's outgassing was not observed. It's likely the outgassing jettisoned small amounts dust particles from the surface which was enough to give it a little kick in speed.
4. It's the first interstellar object we've managed to observe
'Oumuamua is the first confirmed interstellar object we've ever been able to observe in our solar system. Despite this, scientists were expecting one at some point.
This kind of event has, in fact, been expected for many decades. Interstellar space likely has billions upon billions of roving objects like asteroids and comets.
It was an inevitability that some of these small bodies would eventually come for a visit.
But, they also warn that we should not be tempted to draw too many general conclusions from 'Oumuamua. Especially as it doesn't seem to fit our general understanding of more common visitors like comets and asteroids.
Our current observations appear to indicate that star systems regularly eject small comet-like objects all the time. This means there would be many more of them drifting through the chilling void of space.
Future ground- and space-based surveys could detect more of these interstellar vagabonds, providing a larger sample for scientists to analyze. Many scientists can hardly contain their excitement at the anticipation of observing the next one.
Unless, of course, we find it's on a direct collision course with Mother Earth!
5. We don't really know what it's made of
Things like comets, once they enter our solar system, tend to kick off lots of dust and gas as they approach the Sun. But all observations made of 'Oumuamua show this was not the case with this mysterious visitor.
For this reason, some scientists have considered classifying the object as an asteroid. But, as described above, it may have kicked off some dust particles and/or gases, giving rise to a small speed boost at some point during its approach.
We do know that it is highly reflective. Especially given its relatively small size.
When compared to other solar system-type asteroids 'Oumuamua is at least ten times more reflective. Beyond that, we can't be absolutely sure what it is made of.
Other researchers at the Queen's University in Belfast, note that it does appear to have a strange reddish surface color. They believe this could mean it has a carbon-like protective crust rather than being made of metal.
They also noted that it might have, at one time, looked more like a regular comet. Its prolonged exposure to cosmic radiation has transformed its composition beyond recognition since.
Furthermore, there might still be ice at the core. If the carbon-like crust had a thickness of at least 20 inches or more, then it would have been sufficiently-insulated from the Sun’s heat and prevented any visible trails from occurring.
But all of this is mere speculation at present. We may never know for sure.
6. It's not going to stay around
'Oumuamua is only going to with us for a very short time indeed, relatively speaking of course. Having already crossed the ecliptic of our solar system it's well on its way back into the void of space.
It is currently exiting our solar system at around 26 km per second by some estimates and will take over 20,000 years to finally leave us. That's a blink of an eye on galactic timescales.
To add to our frustration, it's relatively difficult to observe it with existing telescopes now. Scientists hope to actually be able to send a probe to the object at some point in the future.
With current technology, this is not possible at present. Even the fastest object ever launched by man into space, Voyager 1, is currently topping 16.6 km per second.
It's quite likely we'll never be able to catch it anytime soon even with ambitions to use laser propulsion probes and solar sails. We may just need to wait for the next one to arrive.
7. It shows we are not really prepared for future Earth impacts
Whilst we have systems in place to potentially detect life-ending impacts from space, 'Oumuamua shows us they might not be up to scratch. But this deep space visitor practically took the scientific community by surprise.
Its apparent near-Earth trajectory was also something of a worry. Whilst we've 'gotten away with this one', if it had hit Earth, it would have easily erased an entire city.
Estimates of its destructive power indicate that it could have equaled over 2,050 Hiroshima bombs detonating at the same time. It could have vaporized everything within 50 km of its impact zone.
This would have killed hundreds of thousands to millions of people. If it hit a large population center, of course.
Whilst it was detected by the Pan-STARRS telescope, which was designed to detect this kind of thing, its sudden appearance shows us that more work needs to be done. There are currently more sophisticated systems, like the Large Synoptic Survey Telescope, under construction, we may need to redesign our early warning systems.