'Oumuamua: Our first interstellar visitor - Chris Lintott

one of the things I really want to get across in these Gresham lectures is the many different ways that science happens sometimes just occasionally it happens in the way you read about in books where somebody comes up with an idea designs an experiment and goes and tests it but a lot of the time things are more chaotic than that uh I see a few nods in the audience so clearly people a agree um sometimes science happens to us uh things occur that change our view of in this case the universe and that's the story of tonight's lecture this uh small object umu mua that shot through the solar system in 2017 and left us uh with new ideas and an awful lot of new questions uh as well the gram College lecture that you're listening to right now is is giving you knowledge and insight from one of the world's leading academic experts making it takes a lot of time but because we want to encourage a love of learning we think it's well worth it we never make you pay for lectures although donations are needed all we ask in return is this send a link to this lecture to someone you think would benefit and if you haven't already click the follow or subscribe button from wherever you're listening right now now let's get back to the lecture um I did think I'd start though uh with some of the traditional form of science the very methodical careful uh work carried out for example by people uh dressed like this uh this is the clean room at the jet propulsion laboratory when this is a bunch of scientists trying to work out well if you've ever had a problem getting a Jam Jar open this is the scientific equivalent this uh spacecraft that's what it is sitting in front of them is the Osiris Rex spacecraft which journeyed to an asteroid called benu which is a near Earth asteroid it crosses the Earth's orbit and in fact has uh the highest chance of any large asteroid that we know about of hitting Us in the foreseeable future uh the foreseeable future being sometime in the 22nd century um I don't think you have to worry at all until possibly the year 2080 something so um looking at most of you we're fine for now even even I will be be long gone I suspect effect um but as iros Rex went to benu here it is here's a closeup of the asteroid and on the right is the sampling tool that was deployed to take samples from the asteroid and bring them back to Earth and it was designed to work on a solid surface but as you can see in a second as it hit the surface of this asteroid it found basically rather than a solid object this body which is a few kilometers across turned out to be a rubble pile essentially about as structurally sound as a sand castle that you might have built on the beach uh and this caused problems it did indeed manage to sample lots of the material and return it to Earth here's the capsule sitting at the end of last year uh on the Utah desert looking brilliantly like something out of Science Fiction um but instead of getting a few large lumps what they got was a pile of rubble and so there were good things about that one of them was that even by scraping the outside of the collector this is the outside of that Jam Jar you can see that there's dust and material on the right there they actually got 70 G of material from the outside of the collector which is more than they were trying to get of the asteroid in total um some of that material is now here in London at the Natural History Museum it's been distributed to scientists around the world who will study it um but until yesterday they hadn't managed to get into the collector itself there was so much material it had jammed uh and you know know they couldn't hit it against the side or you know we've all done that and and had things go wrong so they had to build special tools but I wanted to celebrate them because yesterday this happened this is the inside uh and we now have this pristine asteroid sample uh here uh on Earth and about a third of this will be distributed to um labs around the world for analysis we want to understand Ben's composition we might after all want to divert it away from us one day um but we're also interested because it's a pristine relic of a time about 4 and a half billion years ago when the planets in our solar system were forming they may well have formed out of building blocks like this asteroid and so as well as defending ourselves um we can learn uh from objects like this one let me take those two ideas in turn I think having mentioned that benu might hit us I should reassure you that we're actually doing okay in terms of planetary defense in particular um there have been many ideas about how if we saw an asteroid coming towards us what we might do some of them for example uh in Hollywood films where they suggest for some reason you send um Bruce Willis and a team of oil Executives to blow it up that spoiler alert doesn't work very well uh or another film where they just send Bruce Willis uh I don't know why it's always him he's clearly a clearly a specialist um my favorite idea for years was that if you saw an asteroid coming towards you as you can see this material is quite dark uh it's it's blackish and that's quite common uh for neero asteroids and so my favorite suggestion is you still send Bruce Willis uh we want to make sure he's still got a job um but instead of blowing it up or attaching a rocket motor all you do is paint the asteroid white that then changes the uh properties of the interaction of the asteroid and the sun uh it gets a change in momentum and if you do that early enough the asteroid will deflect and not hit the earth uh unfortunately recent calculations say that You' need to do it thousands of years ahead of any impact and we don't have the ability to predict that far ahead so uh Bruce really is out of a job what we can do instead is brute force and this was demonstrated a couple of years ago by a mission called Dart which um brutally attacked a small asteroid called dimorphus dimorphus is the thing on the right here this is a a double asteroid and they'll be important later it's a binary they go around each other the large one's called dimus uh and the small one is dimorphus it's a few hundred meters across um and what DART did was take a spacecraft about the size of a mini um and head directly for uh the smaller of the moons and so these are images from the D probe which was launched uh to impact this small asteroid this is really a test of Technology it's can we can the the spacecraft steer itself accurately enough to hit this small Moon as you can see they look rather like benu it's this rubbly surface uh not really solid but Dart scored an absolute Bullseye these are the last images that it sent back um as you can see and then that's the last image that came back we only got the top bit and we had the strange experience of watching a mission control full of scientists who built this spacecraft celebrating wildly as their craft destroyed itself um the reason that this was done it it seems slightly odd I mean okay we want to show that we can hit the thing but the idea was also to show how much an impact like this can deflect the asteroid that seems a bit odd after all you know I set questions for students that say okay we've got two snooker balls if I hit one snooker ball with another if you know the mass of the snooker balls you can and the speed you can calculate what's going to happen to the other s snable I'm very very good at snooker in theory uh the practice I I leave to others um however because the asteroid is a rubble pile when you hit it it's not like a solid ball hitting another solid ball you get material thrown up into space and that can help you um it can have a sort of Rocket effect or it could hinder you um and actually the impact of Dart into dorph was much more spectacular than anyone thought it was going to be um the team were rather reluctant for people to go out and look with backu and telescopes but many of those who did saw the asteroid Brighton uh and with the Hubble Space Telescope we got this spectacular view of a long tail of material this is dust that's thrown up from the asteroid streaming through the solar system over many thousands of kilometers for many months afterwards and by studying the orbit of dimorphus around dimus the larger Moon we're able to measure the deflection and it turns out that we're pretty good at this so if we'd seen an asteroid of this size a few hundred meters coming towards us we had 10 years notice we'd be able to launch a copy of Dart uh and deflect it and stop it hitting us so the question is whether we'd have 10 years notice and I'll come back to that at the end of the talk uh you can live in Peril and possible Doom until then I figure that will make sure everyone listens uh to the rest of the talk but I did say that these asteroids were useful not just uh for not or interesting not just because of their threat to us but because they tell us about our Origins as well they they're the building blocks from which we build planets we've actually got quite good as well of seeing that process unfold um one place we could look to do that is actually really prominent in the night sky at the minute this is a beautiful picture by my friend will Gator uh of the Orion constellation which perhaps some of you recognize you've got the three stars in the belt got Beetle Juice or bers at the top and then hanging down from the belt um there is the sword of Orion um and in that sword if you go out tonight I'm sure it's clear we're giving a lecture inside so it's must be clear outside if you go out and look up even from the middle of London if you look at the stars in The Sword you'll see that one of them is fuzzy it's not an actual star and this has been long n it's this one it's about halfway down this is actually the great Orion Nebula it's our nearest star forming Nursery this is a spectacular Hubble Space Telescope that shows nitrogen hydrogen oxygen gas glowing in this uh Stellar Nursery that's about 1,500 light years away relatively nearby in terms of the structure of the Galaxy this nebula is lit up not because the gas itself is intrinsically hot but because it's heated by a small cluster of stars that's visible at the center of the nebula um they're called the trapezium they're visible ible in a small telescope uh and even through uh the 6in reflector I have in my garden I spend ages looking at this teles this object because you can see this three-dimensional structure this gas wrapped around these stars that have just formed in the heart of this nebula William herel the great English Observer who discovered with his sister the planet Uranus um was the first one of the first to write about this as a star forming region and he described the nebula as being compos Ed of the chaotic material of a thousand future Suns and I think that captures something of the drama of these objects you've got new stars forming their light the winds from those Stars sculpt the ghast around them that can trigger further star formation and allow PE allow stars to form out of the gas um and we learn a lot by studying these things but we can also look very closely at the stars that are forming this is something that the Hubble Space Telescope in particular specialized in and these four dots this is I'm afraid going to be a talk about blobs so you've had the nice images now just relax in we're going to talk about blobs uh at the heart of each of these dots is a newly formed star these are stars which have just switched on so nuclear reactions at their Center have just got going um and what you can see in each of these cases is that silhouetted against the bright background of the gas in the nebula there is a shadow a silhouette uh which is a disc of material around that star now these are Big discs um on average these four are about 60 billion miles across which is about 7 and a half times our solar system if you think of Neptune as the the edge of the Sol system an idea we'll come back to um so that they may be big compared to our Sol system but we think these are in fact solar systems in the making as well as gas in the nebula we have dust silicon carbon tiny grains maybe a tenth the size of sand grains um and as they get caught up in the formation of the star they form because of their angular momentum into these diss um and the discs we now know have structure so if we look not with a Hubble Space Telescope but with a telescope that's tuned to the microwave region of the spectrum to very shortwave radio really but what astronomers called the submillimeter or microwave then we can see some of these discs in Exquisite detail we use that frequency because it gets us to the cool parts of the solar system so here are three Planet forming discs Stars at the center um ignore the well there's a zoom in on the right there that in the middle that shows detail but what I want you to see is that these discs have structure they have gaps in them they have rings and that structure is caused by planets that are forming within the dis so once you form a planet it can sweep up the dust in its orbit and so we now think these all these stars are a few million years old and so we're looking at places where planets have formed within the last few million years probably Big Planets Jupiter sized or more but we're seeing their effects on the dis I'm a particular fan of the middle one which is a star called tww hydri um because that first Gap that you can see is one astronomical unit from the star in other words it's the same distance from the Star as the Earth is from the Sun so you can imagine looking at our inner solar system 4 and a half billion years ago and seeing exactly this we can also see that this is an evolutionary process that this forming of planets and sweeping up of dust takes time these are a recent view just from Lasher of 20 such discs all from this telescope called Elma up in the high Chile and Andes uh it's an amazing place and an amazing telescope but they are ranged from youngest in the top left to oldest in the bottom right and you can see what starts off as quite a amorphous duse diffuse structure becomes a regular disc and then those gaps appear by the time you get down to the bottom right and so planets form after the dis so you have the star collapse you have the disc and you have planets the fact that we can watch this happen is one of I think The Unsung triumphs of astronomy in the last 20 years and I don't think anyone even though building Elma uh 20 years ago realized we were going to get this sort of grandstand view on planet formation now to explain what we're seeing we have a couple of options um one option which is beloved by by many of my colleagues is of course to build a a high resolution computer simulation to take the physics that we understand of these quite complicated systems which involve fluid dynamics and the heating of the Star Plus uh friction between grains in the disc plus the gravitational interaction of the newly forming planets but we can throw all that in a very large computer and we could build a convincing model with music apparently um that I don't know if we have copyright clearance for the music so we'll stick to the image um and what you could see in this beautiful this is a simulation it's not an animation but what you can see is that these gaps grow naturally and then you start to gain some planets and it's rather beautiful and it's all very very convincing the trouble is that the simulation's cheap um there is a fundamental mystery at the heart of our understanding of Planet formation and that's going to be a key part of this evening's lecture so let's ignore the simulation just talk about first principles what we're building these planets out of are things like this this is a actual Interstellar dust grain it was captured by a spacecraft called Stardust there was sort of a precursor to Osirus Rex actually it visited not an asteroid but a comet it flew through the coma the atmosphere of comet vilt 2 and returned to Earth with lots of nice cometry particles but by accident without planning some particles got stuck on the back of the detector now a few of those were Comet bits that had bounced off the spacecraft and ended up there but it was also the back was exposed to Interstellar space and so six particles I think that were passing through the solar system happened to be captured by the detector and they were found by a bunch of Citizen scientists online in a project called Stardust at home that spent their life looking at dust grains and looking for ones that looked unusual uh the unusual ones were extracted tested in the lab and said this is a piece of another solar system um as you can see it's pretty small there's a scale bar at the top and it's this irregular structure and the reason it looks like this is that it started Life as a bunch of little spherical grains gain think sand grains and when they Collide in a dis like those we see around these young Stars they stick together and they stick together because of chemical reactions but also because they often in the outer bits of the solar system have ice water ice or carbon monoxide ice surrounding them and you get two nice icy grains you stick them together my friend Helen Fraser does this uh on in Zero Gravity on a plane that does this so she gets a few minutes each time to try and stick dust grains together um I think I've probably underestimated the or not explain the complexity of her experiment but that's fundamentally what she's doing um and this works and so over time what's happening in those discs is you're slowly sticking together bigger and bigger things until you go from dust grains to Aggregates like this one to maybe as much as a pebble and if you start sticking Pebbles together they're moving together that can happen between the friction then you end up with things maybe the size of a boulder so I have a I have my own simulation uh of this process for you which I think is as Hightech as the previous one so this is a bowl of water uh it's being stirred to simulate the disc so this is the rotating disc and then we're going to introduce some grains in this case of pepper uh into the bowl and this will be utterly unspectacular cuz initially you won't see the pepper but as it rotates friction brings them together the pepper grain start sticking together and they become visible in the video because they've grown so this is exactly the same process um I'm not saying planets are made of pepper but you you get the idea so this works fine until you get to Boulders and the TR is once you go from here to a boulder when I Collide two Boulders together I don't get a bigger Boulder I get Rubble I go backwards I get smaller things and so this is a problem I've broken the chain of getting larger and larger and growing towards the planet now once I get to things roughly the size of I don't know one of the buildings around us here in the city when I climb two skyscraper size things together I get Rubble but I get a lot of it and gravity can pull that back together so once you get to big things and they Collide gravity is important and so we can grow from skyscrapers to planets we understand how that happens and we can go from dust grains to Boulders but we don't know how to quickly jump that Gap in the middle as long as you let me click my fingers and cross that Gap I know how to form planets but there's this fundamental problem in the middle and that's the problem that I think a solution may have appeared in our solar system we weren't looking for it this wasn't the result of a targeted search for a solution to this problem nor was it particularly a targeted search for objects like the one I'm going to talk about um the discovery was made by telescopes in these two small domes which are in an observatory on top of the Hawaiian island of Maui um it's an experiment called panars which is funded by a Consortium of academic institutions and the US Air Force to look for threatening near Earth asteroids so the fact that we know that there's nothing more threatening than benu that's large and heading our way is primarily due to pan stars and and surveys like it what they do is they scan the whole sky and they look for moving objects and in October 2017 they found such an object this is these are images from the 19th of October on the left the red lines by the way are areas where there's no data available the US Air Force having funded this Mission realized that it if you're looking for moving objects in the sky you Al also find things the US Air Force doesn't want you to find and so they remove bits of the sky from our data uh to hide what they're doing then they have to remove bits of the sky that don't hide what they're doing because otherwise so so the red lines are just that but I don't know if you can see in the red circle which I added uh it would be really nice if the Air Force would Circle the things we're looking for but we have haven't got there yet um there's a very faint smudge it's a little line um and that's a moving object it seemed unusual it was followed up by a larger telescope on the neighboring big island of Hawaii on monia by cfht the Canada France Hawaii telescope and that image is much clearer on the right now this time they're moving the telescope to follow whatever this new object is so the dot is the new object the lines here are stars that move relative to the thing so we know it's moving relative to the stars um in the bottom there's also a close-up image um and all it really tells you is that this is a pointlike source it's not a big thing it's not a comet at this stage with a tail it's just a dot in the sky and at this point most people are thinking this is in fact an interopa from the outer solar system so our familiar model of the solar system with the planets with Mercury Venus Earth Mars Jupiter Saturn unus Neptune um that's just the the inner bit of our solar system most objects in the solar system uh live out in What's called the art cloud which is about a third of the way to the nearest star and this is the vast reservoir of icy bodies left over from when the solar system was forming um that feeds into our store of comets that we see icy bodies that come into the inter inner solar system so people are thinking this is a comet and they began to plot its trajectory and it was immediately unusual so there's the solar system um the dotted line shows the path on which this object traveled it came down from up in the north came rapidly into the solar system slingshotted around the Sun and by the time it was discovered was already heading off into the distant Galaxy back into deep space and we found it after it had been through the inner solar system there's an animated version here it's got a few other objects in uh but it's this red line coming in here uh and there's the slingshot and then it heads off out into deep space and this trajectory was unusual enough that we realized it was realized that this was the first Interstellar object the first large object bigger than a dust grain that we'd seen coming from another solar system or at least from Beyond ours and so the CR at the beginning about the name well it was originally classified as an asteroid then it was named then it was decided it was a it and eventually they gave it the designation the international astronomical Union gave it the designation one I the first Interstellar object and the name umu mua now it's a Hawaiian name because it was discovered in a Hawaiian Observatory uh in Hawaiian um emphasis comes from repetition so mua means far away so muu is really far away and umu is O is a scout um so it's the Scout from really really far away which is rather nice and I'm now going to show you and I want you to be impressed please this is lecture three so I know at least some of you are up for this um this is the best image that we have of this object that I'm basing an entire lecture on ready try to contain yourselves it's the thing in the blue circle and I added the circle and we never saw it as more than a DOT sadly um this is an image from the very large telescope one of of the most powerful instruments we have hence the name um again tracking the object so that the Stars blur in the background but we never re saw it as more than a DOT and so it became a bit of a challenge what can astronomers learn about an object if all we see is a DOT well the first thing we can do is we can say this is the kind of astronomy I like we ask simple questions we know it came from Beyond the solar system because we've seen how it is moving um we can say what color is it it turns out it's slightly reddish uh and that's typical of stuff in the outer solar system so you could compare this with I know Charon one of the moons of Pluto or uh perhaps some of the objects in the koip about the rubble that shares an orbit with Pluto it wouldn't look out of place and so that means it's probably icy and it's probably spent a lot of time in deep space or at least formed whichever solar system it came from on the outer edges of its solar system you can swap it there so that that makes sense the other thing that we can do if we've measured color and we've seen it's a DOT we can keep looking at it and it was followed for a few months and it actually showed remarkable variation in brightness so this is each dot here is a measure of brightness when it's high up it's bright when it's low down it's Fain and this is from a whole cluster of the world's most powerful telescopes but you can see there's this pattern where it goes up and down in brightness and then it goes up quickly and then down but it's not a regular pattern it's not um a simple periodic relationship and so the changes in brightness are quite big um it's about a factor of 10 uh between its brightest and it Fain is it caused Havoc we're trying to plan to observe it so we've got this unknown object that's changing brightness wildly so the astronomers who did this uh had to be really on it and very quickly there were two hypotheses about what's causing this change in brightness and they're Illustrated and normally for these lectures I I've been trying to make my own slides because I want to give you the most original and interesting content I had to borrow this next one this is an illustration by my friend Luke dones about the two reasons why umura might have been changing in brightness and he's using a local object to stand in for UAA so the two options are on the right you have uh STR on the surface we could have colored patches we could have dark patches and light patches and so if you imagine the cat rotating the brightness of the cat would change over time um I'm told by Luke he tried to make the cat do this but apparently difficult to coordinate um so that's possible you can imagine inventing a pattern that would match what we've seen But if you look in our solar system with one honorable exception Saturn's moon I apus which is half dark and half white we don't see on small bodies and we know that umu is small because it's a DOT um on small bodies we don't see variations in in color really they tend to be pretty monochrome so this is possible but unlikely uh in the other example we have a stretched object and if you have a stretched object and this was the press release image that you will have seen perhaps as the most common um visualization of umur if you have a long object object then its brightness depends very much on whether you're looking uh Edge on or side on so this will look very different from this if that makes any sense and if it's if it's rotating then you get a change over time and in fact it's not just rotating it's tumbling so it's not just it's going end over end but twisting as it does so and if you model that you can reproduce the light curve pretty well now the original estimates were that this thing must be 400 m long 10 times or maybe even as 20 times as long as it is wide so it's this really extreme sort of cigar shaped thing later estats I think most people now would be a bit more restrained they would now say it's more pancake than um cigar maybe six times as long as it is wide but you've still got this elongated structure tumbling through the solar system why is it tumbling not sure maybe a violent start wherever it came from something flick it into uh into Galactic space we're not sure uh but that explains the change of brightness and before you stare too long at this artist's impression I want to remind you that this is the best image that we've got right uh not this or this this we're talking about the real stuff but we think it might have looked like this so you know we we can imagine but we must always remain grounded in reality there were two other odd things about this object so the color unusual but not that unusual the shape pretty unusual compared to the asteroids that we've studied in the solar system there were two other unusual things one is that that trajectory where it came in originally seemed to be close to something called the local standard of rest what that means is it seemed before it encountered the solar system to be moving along with the nearest stars to us so is that unusual don't know we've only seen one of these things but if you were going to throw these things randomly around the Galaxy you wouldn't expect it uh to be following the nearby Stars so maybe it comes from one of those nearby stars and then the real Myster is that as we watched it recede from the solar system we're expecting it to slow down because of the gravity of the sun leaving the solar system takes energy you have to climb out of the Sun's gravity well and Escape UMO did slow down a bit but much less than we thought there was some accelerating Force pushing it out of the solar system this would make sense if it was a comet we've seen comets this is the close-up nucleus of Cher OFA which is visited by I mostly put it in so I could say Cher ofera because once you've learned to do that you use that skill as often as possible it's like trying to pronounce the Icelandic volcano that caused uh the dust storm more than a decade ago Esther FL if you were uh asking anyway chero sea the other chero sea story is that it was uh nicknamed chewy gooey by the scientist who built the probe that went there until they worked out that both chero fanga were still around and would prefer not to have their Discovery shortened so we can call it 67p uh this is the comet we know best Rosetta spent uh more than a year in orbit around it and as you can see this is it in active phase and there's this jet of material shooting out so comets which are made of ice don't melt evenly when they come into the inner solar system you get these dramatic Jets and so that will have a rocket effect pushing this thing in this image up and so if a mu mu was only a comet then this acceleration would make no sense but it's only a point of Light how do we explain this acceleration so we have a a first visitor to the solar system we don't know where it came from but we know it came from somewhere else it appeared unannounced it moved through the solar system silently we know we checked we pointed radio telescopes at it just in case there were signals being sent uh there weren't or at least none that we could hear but now it's speeding up as it leaves almost as if it's fired its engines and all of these thoughts combined with the fact that Arthur C Clark wrote a book called rendevu with Rama uh back uh 50 years or so ago which describes the visit to the solar system of a mysterious long cylindrical object which passes silently through the solar system and despite in the book um people going to visit it and exploring it inside it's obviously artificial uh it remains mysterious and disappears off into the uh rest of the Galaxy firing its engines as it go so you know this idea that maybe this is exactly the behavior that one would expect uh from an alien spacecraft was something that occurred to to lots of us at the time it also occurred to a Harvard astronomer called ABY lob uh who believes uh very seriously that this is clearly an alien spacecraft and has written a 250 page book explaining why the rest of us are too stupid to agree with him um but it's a serious scientific point we have an unusual set of properties should we consider uh an alien spacecraft as a possibility it's so tempted to say yes and leave but actually I think there are good explanations for the unusual things that we know about umura so I'm going to tell you about them and then I'm going to try and convince you that it's interesting anyway the trouble with mentioning aliens is that people always want it to be aliens I tried to write a book um called it's never aliens which was going to be a story about all the things that turn out not to be and I got a a oneline review from a potential publisher that just said but we wish it was which is fair but this is still an exciting object but let's deal with the unusual things firstly the shape this this elongated shape and its color well if you talk to people who study the small bodies of the solar system even like my friend Michelle banister they'll tell you that the most unusual thing about this object is that we've studied it in this this detail at all if you ask the people who control the very large telescope to look at a random asteroid that's only 200 M across of which there are millions and perhaps billions in the solar system they're going to tell you they've got better things to do looking at Jupiter and distant galaxies and planets around other stars and all the other things that we're doing as astrophysicists so if you took it and put it amongst its peers in the solar system it may not appear that unusual in shape or color the fact that it's close to the local standard of rest that it's moving with the Stars it turns out it's not that close and that you could have got uh that alignment by by luck um and then there's this acceleration this fact that it fired its engines or or sped up as it left the solar system well we think we've got a couple of explanations for that as well one is that um things are changed by time in space next time you get a chance to look at the full moon you'll see the familiar Seas the dark areas which are are lava and then the brighter areas on the moon which are the highlands on the whole those are older areas but where a crater is punched into the surface for example the large crater at the bottom of this image here you can see I hope that there are bright rays of material that shoot out across the surface and they're bright because they're fresh they're material that's been dug up from underneath the surface and distributed across a large percentage of the the lunar surface they're now exposed to particles called cosmic rays which come from the Sun but also come from the galactic environment these high energy particles hit the surface of the Moon all the time we're protected down here on Earth for the most part by our magnetic field but on the moon uh the surface is exposed as cosmic rays and over time over millions of years they will darken nowu mua must have been exposed to cosmic rays as it traveled through the Galaxy perhaps for billions of years before it reached us they would have had the effect of getting of exciting and getting rid of water or um other volatiles carbon monoxide carbon dioxide from the outer layer and so you end up with an object which is an icy core with a crispy crust around it it kind of celest your Magnum uh if you like without the stick obviously um the there's a marketing opportunity in there somewhere they will tell the agression that we need our own ice creams uh anyway you get so so this is the idea so it's a hidden Comet and so when it comes into the solar system and warms up you may get less activity than expected but you may still get these Jets and so we wouldn't have seen the activity because it wasn't dramatic enough for even our largest telescopes but you can get this accelerating effect or if you don't like that idea we have others um the there's a group of uh astronomers led by Daryl seelman who think that published papers like this one that claim that perhaps it was made of hydrogen so perhaps it was a hydrogen iceberg that formed somewhere like the Orion Nebula in one of these dark star forming nurseries um and has traveled through the Galaxy and the point here is that you can heat hydrogen up and you would have got these Jets of material without um us being able to detect it so you can you could sort of sneak way and this way personally I think dehydrated Comet icy shell crispy shell and IC Center is the way to go um but there are other arguments and that's all we know about umura there very satisfying this lecture because we will never know anything else about this object we can't go and Chase it it's gone too quickly and too far um it's lost to our telescopes and very soon we won't even have the accurate accuracy to go and trace it even if we we wanted to in the future if we invent I don't know the lint talk drive that can go close to the speed of light we won't know where it is interesting though and I think probably luckily for all of our sanity when we're arguing about whether this first indell visitor really is an alien spacecraft or not we have been visited by a second interloper this is a humble Space Telescope image of an object called Comet boraso which has discovered in August 2019 um by a remarkable astronomer borisoff is a technician uh at a large Observatory um uh in um Kazakhstan I believe um but in his spare time he's an astrophotographer and so not during his day job but in his night job I guess as an imager of the Skies he discovered this Comet which turned out to be on a similar trajectory to umu it's come from outside the solar system it traveled through the solar system um and it this this image is taken when it's about 300 million kilom away and I should say the thing on the left here that's a Galaxy it just happens to be in the background um but the blue thing is a comet as you can see it's got a tail it's behaving much more like a normal Comet so we know that we can get normal inst Stellar objects as well borisov is exactly what was predicted it had an interesting encounter with the solar system system over time these are images of the nucleus the center of the Comet and you can see on March the 28th it seemed to split up into two pieces a few hundred kilometers apart this is typical of comets that get too close to the Sun and break up and so we have an icy visitor from another solar system and if you think about the geometry of the solar system that I showed you earlier which has that or Cloud that reservoir of comets in the outter solar system it makes sense that Interstellar objects would be comy because it's easier to escape the sun's pull if you're already a third of the way to the nearest star than it is if you're all the way down here in the inner solar system at the bottom of the gravity well so Rocky asteroids which tend to be found near the sun won't have escaped perhaps lots of these comets on the outskirts do so we now have two of these things I was convinced that this morning was going to see the announcement of a third one but no so far uh we're still waiting 5 years on from our second Interstellar object but actually there are clues in our solar system that suggest that these things are very common indeed and the first set of Clues the most important ones come from that outer edge of the solar system where uh Pluto lives um Pluto of course definitely not a planet as I've mentioned in all of my lectures so so far much to the distress of at least three people online but it's not a it's not not a planet because it's not interesting like we didn't decide it was boring in fact this image from the New Horizons probe which flew past it in 2014 showed that it was much more interesting uh than we thought it's a world with some differentiation it has this heart-shaped plane of water ice now known as Sputnik PL plita it actually has mountains of water ice frozen solid it has these dark uh patches actually rather similar to the color of umura it has a complex interaction with uh its large Moon Chon but it is only one of many millions of objects that live in the koer bout our Solar System's outer asteroid Bel this region where Planet formation this process of adding uh grains together to form Boulders and boulders together to form somehow skyscrapers and skyscrapers together to form planetesimals and then onto planets didn't proceed as far as it did out in the coer belt what we have is the rubble of a failed construction project there wasn't enough time to build a planet before the sun got going uh and heated up the disc and expelled most of it and the denisons of the coper belt are interesting in many ways New Horizons when it went past Pluto headed off through the CER belt and the team looked for another object that they can visit they actually used the hble Space Telescope to look in the direction that their probe was going and tried to discover an object to order something close enough that they could divert to and they found it in a small world called araco which is only a few again a few hundred meters across um this is the closest image color image we had of it from that flyby um it flew by on New Year's Day 2019 from a distance it looked beautifully like a champagne bottle which is great as we got closer it's much more snowman likee but the key thing here is that this is not really one object it's two that have collided you can see there's a bright ring between the two spheres between the snowman's head and body and that's where these two objects have gently drifted into each other and stuck together they're icy it's slushy when you when you combine the two things and so this is a double object and in fact lots of the worlds that we know of in the coper Bell are binary rather than solitary Pluto even has its Moon chent which is much closer in mass and size to Pluto than any of the major planets the next one down is the Earth Moon but uh Pluto and Shon are much closer big things like Aris uh another of the large cop objects are double um many of the small worlds seem to be and of course the Comets like 67p Cher G that live out there um this could well be a double object as well it looks a lot like araco and so somehow we formed these binary or double worlds and the best explanation for that is that the coer belt was once a thousand times denser than it is today instead of having a few percent of the total mass of the Earth spread out amongst these bodies we might have had six or seven Earth maths worth of stuff out in the solar system so where did it go well we have a theory for that as well we have to abandon the idea that our solar system is a nice stable place this is a simulation of the first billion years of our solar systems history and we're looking here at the outer solar system so the Rings are the orbit of the four giant planets Jupiter Saturn Uranus and Neptune and the green things are the coell objects that are left over so if I run this uh the time is in the top in millions of years the first billion years few few hundred million years nothing happens everything's nice and stable you can see the planets are moving about very slightly that's because of their Mutual gravitational attraction Jupiter's pulling on Saturn s Saturn Uranus and Neptune have a collective effect on Jupiter Uranus and Neptune interact but nothing really happens for 600 700 million years but in this simulation when we reach about 800 million years and we'll slow it down a resonance is achieved Saturn and Jupiter start lining up and all hell breaks loose so what happens is Jupiter and Saturn get themselves into a pattern where they're they line up in the same part of their orbit every few orbits and that gives a regular kick to the rest of the solar system so it's like if you're pushing somebody on a swing if you already always push at the same point you get a much better uh response from the swing that causes havoc in the outer Solar System Jupiter tends to move inward Saturn tends to move outwards Uranus and Neptune swapped places I don't know if anyone noticed that in the animation and the coer bell is scattered out into the Galaxy and so what we see in our CER belt Pluto and friends are the survivors of this most dramatic event we think that our solar system donated 10 to the 16 so what's that that's something like let's say a 100 million billion objects to the Galaxy and if every other Sol system does that objects like umu mua are the most common macroscopic objects the most common things in the Galaxy there are billions and billions and billions of them out there they're passing through our solar system all the time calculations show with a large aabar that there's almost always something the size of UA within the orbit of Neptune we're just extraordinarily bad at spotting them because they're small they're dark and they move fast and so we shouldn't really be surprised that we saw AA mua we should be surprised that we've only found two of these things and this is the answer to the mystery that I left open at the start of the talk how do we jump from things that are Boulder sized to skyscraper sized well a mu mua few hundred meters across is a flying skyscraper that dis of material around the young star will be peppered with these Interstellar objects flying through from other solar systems and Suzanne felner and Michelle Bannister have proposed the idea that the seeds of Planet formation come from these Interstellar objects uh get started quick way of building a solar system the equivalent of a ready meal I guess if you start with the dis capturing these objects then you can quickly grow a planet all right you have to form planets somewhere the slow way somebody has to do do it the hard way somewhere in the dim distant past of the Milky Way there was a star with a Long Live disc that could have formed planets which would then have scattered 10 to the 16 Interstellar objects those would have kickstarted more planet formation and suddenly you have this runaway process that spreads very quickly through the Galaxy and allows us to form planets rapidly and makes it so that we live in a universe where planets are common and there are worlds to explore so though omura isn't I promise it's not an alien spacecraft there's too many of the things and the fact we found two and we'll find more tells us that it still I think has a message for us which is that what's happened here that in explaining our Solar System we've got no choice but to consider ourselves as part of a galaxy connected by these Scouts these Messengers that wander between the Stars thank you very much and now by my book chis thank you very much and that's we just take a moment is on there you see it's on the cover so it is relevant in the in the blue fantastic well wow well we've had it all we've had a world that's not a planet but uh it's sort of like one of those things like if it looks like a planet and it smells like a planet why is it not a planet small okay it's too small we're going to keep coming back to Pluto I I promise to get it into every talk now excellent and then we've also had um a flying Magnum that was that was a highlight so loads to loads and loads to talk about lots of questions um and I think actually right okay let's just hit the alien issue right now cuz I'm I'm not going to lie to you Chris that is a feature in quite a lot hello the internet of these of these questions so just to pick up on that last point you made and I think sort of collect some of these questions together so obviously there's a degree to which some in humor some not so in humor there's a disappointment this isn't an alien this isn't um Arthur Clark's Vision this isn't a spaceship but actually um I thought it was really interesting how you said well if we can get past some of our expectations not just about what we should be looking for what we should be seeing or what we would like to see but actually it's really exciting to like the the implications of something like this could actually be really enormous for how we consider the universe is that about that's right and I think one of the things umur taught me and I've changed what I'm working on to to pay attention to to things like this is that we should be ready to be surprised by the universe this is our solar system right we've lived in it for a while we've sent probes into it we've mapped it yes all right we find new asteroids daily there's a catalog of a few million of them um this is our backyard and yet umu tells us that we can be caught unawares that the unexpected can still happen that actually in the solar system there may be types of object we haven't thought of yet there may be a population of hidden comets in the distant Sol system there may be things in unusual orbits there may be an alien spacecraft lurking between Mars and Jupiter that we have at family we don't know and so particular I'm working on this thing this is the ver Rubin Observatory this is going to do a new survey of the sky which we'll find in its first year we think 6 million asteroids and one response to that is to say great we've got lots more asteroids the other is to say okay which 10 of those are most unusual and what are their properties and what do they tell us now my guess is that they'll tell us about details of how the solar system formed and uh how it perhaps has evolved in the 4 billion years but we should consider the possibility of looking for what we called techno signatures so spacecraft in there as well but we can do that by looking for weird astronomical things and only when we've ruled out an astronomical origin then I'll turn around and say okay maybe maybe but for aurura there there's no evidence it's anything other than a really fascinating astronomical object great so you're not quite you're not taking aliens away from off they're not off the table completely no they're just slightly to the side and if they shouldn't be your first I mean I think where I I disagree so a ay L who who is the advocate of these things would say that they should be the first thing we think of that when we see something unusual we should say is this aliens before we do anything else and that's fine but it doesn't really get me very far because the answer is always maybe uh what I have to do is see if there's another alternative explanation first and then get driven to the um more extreme or or or more unusual kind at the end okay so if we maybe challenge some of our expectations or maybe aspirations then we might be able to ask different kinds of questions which always really interesting for science so let's take a question from the floor a couple of observations the the uh those two objects one eye and two eye um remain unique um of course when the ver Rubin telescope starts starts operating then we may find a lot if we don't and in particular in the case of the the more mysterious one which is which is one IU then given that it is and I'm told this by people who understand these things it is in principle possible to send a mission to it um should we do so yeah so so a few questions there so yeah so with the Rubin telescope we think we're going to find about a hundred of these interstar objects but that number could be 10 or it could be a thousand it depends slightly on how optimistic we're feeling um because we're trying to extrapolate from two I should say we've work I've got PhD student Matthew Hopkins who's been working on this and um we can predict what these things will be like based on what we know about the Galaxy and we think that even if we find 50 of them may still look odd because it is on the extreme It's Not Unusual it's unusual but it's not a complete outlier so we shouldn't be surprised if the first 10 that we find all look like borof they look like comets we will find a population of we think we'll find a population ofu like things but we don't know so we'll have to find out there's also a NASA Mission um that is again looking for near Earth asteroids that will launch in 2028 which will find lots of these things so in 10 years time we should have a few hundred and then we can can say something sensible can should we should we launch a mission to aumu if we could I definitely would be fascinating there are all sorts of questions about it as you've seen um for a sensible budget um and a sensible time scale I don't think we can get there in time because the problem is we only watched it for a few months and so the error on its trajectory is large and so I think we're close to the point now that even if you had all the money in the world and you could launch with our best rocket a satellite right now you wouldn't necessarily find it even if you could hit the speed so I think it's gone sadly I think that's true but I would suggest you look at something called project L yeah yeah I know about yeah I love their optimism I'm going to take one more question should say by the way we're going to do another episode of the gesan podcast any questions so we can answer more questions so do send them in and I promise I'll get to them yeah um what are the chances of New Horizon finding further objects and would we find out important things if it did yeah it's a good question so um the New Horizon's team um spent a lot of time using Hubble looking for a third object that they can go to they don't have much fuel left on board so they can't really divert so they need to find something um in the D direct line and they've more or less given up on that what they're doing instead is they it does have a telescope on board so it's doing observations of uh relatively nearby Co objects after all it's much closer to them than we are and so we're actually building up a library of images taken from quite a long distance but much less than we have of these objects so it's sort of become an astronomy satellite um it's also monitoring the the effect of the sun on the outer solar system so it's still doing science but I don't think we'll get another flyby like we did with arov unless we get really lucky okay great well thank you so much there's lots and lots of questions unfortunately we're out of time but as Chris has just kindly volunteered to do another any further questions podcast look out for that and I'm sure if your questions on here you'll get to it even if it is about aliens it's still not aliens I'm sorry Chris lot [Applause] everyone

Channel: Gresham College

Views: 142,147

Keywords: Gresham, Gresham College, Education, Lecture, Public, London, Debate, Academia, Knowledge, Astronomy, Science, Physics, Oumuamua

Id: bB4-unZyubw

Length: 59min 4sec (3544 seconds)

Published: Mon Feb 05 2024