“The privilege of being a scientist is that we can maintain our childhood curiosity”
Professor Avi Loeb discusses the controversy of ruling out every possible scenario in uncovering the origin of an extraterrestrial object that was spotted in our Solar System in 2017 - even the chance it could be a message in a bottle from an alien civilisation
For our readers, please could you provide a bit of background on ‘Oumuamua?
It was discovered just a year ago, 19 October 2017, when it passed close to the Earth. It’s a relatively small object, tens to hundreds of metres. We don’t exactly know the dimensions because we don’t have any images of it. It is the first interstellar object to have been discovered in the Solar System in the sense that it is unbound to the Sun, and it is similar to having a guest to dinner that comes from another country. By ‘speaking’ or examining this guest you can learn about the culture of their country without having to visit and pay an aeroplane ticket.
This object, surprisingly, was very weird. It’s nothing that we have seen before in the sense that its shape is very extreme. What we see is the reflected sunlight, and the brightness of the object varies by a factor of ten, which implies that it is at least five- to ten-times longer than it is wide, but we don’t know exactly how it looks. Everyone’s seen these images of the cigar shape, but we don’t know [if this is true]; this is just an artist’s impression. It could also be a pancake. Observations of this object with NASA’s Spitzer Space Telescope indicate that it is a very good reflector. It’s relatively cold and does not absorb much sunlight.
People thought of it as an asteroid, and it doesn’t fit the pattern of our Solar System’s asteroids. In the Solar System the asteroids are at most three-times longer than they are wide, but then even if you say, “Okay, well, its shape is unusual by chance. It’s an outlier.” Even then most of the asteroids that you can imagine being ejected would come from the outer parts, where their ejection speeds would be relatively small.
Is finding an object like this quite common?
Another thing that is very unusual, we wouldn’t expect this object to be found in the first place because I actually wrote a paper about a decade ago predicting how many rocks from outside the Solar System we should see. The expected abundance is about 100 to 100 million-times smaller than needed to explain ‘Oumuamua, and so it tells you that is very abundant.
So then you need to assume that other stars are producing something weird much more often than we expect the Sun to do. You need something like a thousand trillion objects being ejected per star during its lifetime.
So, in addition to that, the most intriguing part of it is that it moves on a trajectory that deviates from one that is shaped just by the Sun’s gravity. Now that is usually attributed to outgassing – in other words, ice evaporating on a comet’s surface to give a rocket effect that pushes it in the other direction – and the problem with that is we don’t see any evidence for gas or dust coming off this object, so there is no cometary tail. On top of that, if there was it would have also created a change in the spin of the object, and we don’t see that.
What about ‘Oumuamua’s orbit is very unusual?
It’s moving mostly due to the Sun’s gravity… mostly. But there is a correction to the orbit. We can measure the orbit extremely precisely and we know the mass of the Sun, so Newton’s law of gravity tells us exactly how the object should move. But there seems to be a deviation with the orbit.
The force that needs to act [on ‘Oumuamua] is a small fraction of the force exerted by the Sun, but in fact it is very big because in order to generate this deviation via a cometary tail, you need to evaporate a major fraction of the mass. So it is not easy to get these levels of deviation, and the propelling mechanism isn’t being seen. This looked very weird to me.
What was the reaction to your scientific paper suggesting that this could be an artificial object made by an extraterrestrial civilisation?
So I wrote this paper, which was refereed in the standard procedure. It was accepted for publication within three days, which I found extremely unusual, but it’s a prestigious journal called the Astrophysical Journal Letters. But I don’t understand why some people have an issue with it. In fact, the reporting in the news appeared after the paper had already been accepted, and some people didn’t know it was and said, “Oh, the people weren’t
“It’s nothing that we have seen before in the sense that its shape is very extreme”
refereed… it’s just speculation.” But it went through the standard procedure!
Here is the standard procedure in science: there is data. You look at the data. If there is an anomaly, you are trying to explain this anomaly. In this case there is an anomaly; this deviation. So people try and explain it in terms of cometary outgassing, but there is no cometary outgassing as far as we can tell. So what do you do?
You have two options. Either to say the data is wrong, or to say let’s look for another explanation, which is what our paper does. Our paper says maybe it’s the force from the radiation of the Sun that is pushing on it, and that’s it. So we wrote the paper; we put it out.
This is prejudice if you dismiss a possibility.
I was shocked at first to see so much reaction from the press. That’s another thing. I just followed the logic of Sherlock Holmes, basically saying when you’ve excluded the impossible, whatever remains, however improbable, must be the truth. I don’t have a prejudice. I just want to find the explanation for this extra push, and that’s what we put in the paper.
What’s behind your creative thinking in this regard?
The privilege of being a scientist is that we can maintain our childhood curiosity. We don’t need to pretend that we know something we don’t. Children learn about the world by asking questions and by being innocent, but not pretending. When they become adults they start pretending they know more, they start trying to look respectable, they start to pay attention to titles and I hate that. Even though I have a lot of titles. But I just hate to give up on this privilege of being a scientist and being straightforward and honest about what you know and what you don’t know.
It’s quite possible, and quite likely to some people, that this will be ruled out when we look at the next object. Let’s leave it on the table and then rule it out. Now if this is ruled out, something else must be ruled in, and the fact that this object is weird implies that, in respective, we will learn something new. We will learn that the galaxy produces weird objects in some environments that we don’t know in a number that is much larger than we expected.
It’s sort of like going to the beach and looking at seashells and suddenly seeing a plastic bottle and you say, “What’s that? Where did it come from? Could it be artificially made?”
Do you think we are alone in the universe?
I don’t have a prejudice that we are alone, because a quarter of all the stars in the universe have a planet in the habitable zone where liquid water can exist on the surface and the chemistry of life, as we know it, may be happening elsewhere. So why should we be so arrogant as to say that we are the only civilisation out there?
I think out of modesty, just modesty, we should all think we are not alone and then search. I’m not saying that we have any conclusive evidence at the moment, but we should just search for it and not have a prejudice against it like some people’s reactions, even though they have no evidence.
That’s very bad; it’s similar to what the Church did when Galileo was arguing that the Earth moved around the Sun.
So what about ‘Oumuamua makes you think it could be an artificial light sail?
We tried to explain the extra push that it feels by saying that the light from the Sun is pushing on it. In order for that to be effective it needs to be very thin, less than a millimetre. It appears to have a large area-to-mass ratio. Therefore, based on the amount of sunlight that we see reflected from it, it has to be at least 20 metres (65 feet) in size, and that sounded like a light sail. This is technology our civilisation is currently developing for space exploration and I actually chair the Advisory Committee for the Breakthrough Starshot Initiative.
I would admit that my imagination is limited to what I know and that’s usually the case for everyone. The fact that I’m involved in [the development of] this technology inspired me to think in this direction, but it is quite possible that other civilisations have mastered this technology. This could be a message-in-a-bottle situation, which means instead of detecting a signal, which people
“So why should we be so arrogant as to say that we are the only civilisation out there?”
have thought about in the past with detecting a electromagnetic signal, we would detect an object.
Playing devil’s advocate to your own statement, what arguments are there against the idea of it being an artificial object?
That’s the point. Other than cometary outgassing nobody has a suggestion for what could produce this extra force. What I’ve heard is people saying maybe the observational paper is wrong, but the observational paper has a lot of data points and it takes the statistical significance of 30 standard deviations. Usually for a signal to be significant you need three or five; it makes researchers very happy if they have five standard deviation signals. This one had 30, so it’s clear beyond a reasonable doubt that – in the eyes of the observers that did the observing – there is this anomaly that it gets an extra push. The pressure is on what produces it.
If you do the numbers you work out that a significant fraction of the mass of this object will need to evaporate to push it enough. Yet it needs to be pure material that does not appear in dust, because cometary tails are usually apparent because of the dust. More over, people have looked for gases of various types and didn’t see that. So to me, when you don’t see something it doesn’t exist. If it’s not a comet, then what is it?
If this were an alien space probe, where do you think its home system would be?
We can’t track it back to a star because that would imply that it’s ejected from a particular star at very high speeds, which would be unlikely. Most of these objects in a stellar system are in the Oort Cloud and they move at a fraction of a kilometre per second and you need – for the typical speed of a object at rest – you need to be kicked by something in the order of 20 kilometres per second (45,000 miles per hour). This would imply that it’s ejected from the inner part of the stellar system, roughly where Jupiter is [compared to the Solar System]. But then there are fewer objects there.
The number game appears a bit implausible given what we know about the Solar System. But we don’t know which star it came from. Maybe it [‘Oumuamua] took 100 thousand years to come to the nearest star. Then suppose it’s not the nearest star, it’s another one a million years away. Then you need to know the motions of all the stars and where they were a million years ago and figure that out. We cant reliably go back a million years and figure out exactly where it came from.
Are extra efforts being made to look for more objects that originate from beyond the confines of our Solar System?
Yes, that’s the key. So you can imagine two ways of getting more data. One is to chase this guy, but the problem is current chemical rockets can’t do it, and the second is look for another one, and that will be possible in the future. With this existing survey [the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) in Hawaii] we discovered it, so maybe we just need to wait a few years for the next one. However, in a few years there will be a survey that is much more sensitive called the Large Synoptic Survey Telescope and that will be an excellent survey for finding additional ones.
If we find more of the same then we will have all our telescopes ready and everyone will be alert. That’s an important point in my paper that it alerts the community to the importance of finding more data on such things. When the next one comes along everyone will be motivated to rule out this or that, and so we will get much more information. There is nothing better to a scientist than more information, unlike a politician. In politics, sometimes less information is better because you can justify your views, but in science the more information you have the better. The problem is we don’t have enough.
Would it be possible to send a spacecraft to such an object?
Yes. You could even meet it halfway if it moves at the same rate as ‘Oumuamua. What you don’t want to do is wait until it runs away from you, because then it's too late.