#8 Malena Rice - Planet Nine, Oumuamua, Misaligned Exoplanets

welcome one and all to the cool worlds podcast with me your host David Kipping this week it is my great pleasure to be joined by Molina rice Molina completed her PhD at Yale under the mentorship of the legendary Greg Laughlin one of the most Innovative scientists I know in the field of astronomy and it obviously rubbed off on her because Molina 2 has been incredibly Innovative both during her PhD and since that time afterwards so after finishing she went on to move to MIT as a prestigious 51 pegasi fellow and I think she was there for just one year before moving back to Y as a junior faculty member so obviously Yale saw something very special in her were desperate to get her back and she's now a professor there so she's just started at Yen's building a new group I wanted to catch up with her while she was visiting New York and hear about what kind of research will she be planning on working on and what are the problems that she is most excited about so in this convers ation we touch on three big topics that all are interlined with her research program we talk about going from the solar system and thinking about planet 9 how could we look for this strange object within the solar system using existing telescopes even before future Generations come along how can we do it right now then we talk about Interstellar asteroids meteors even comets we get into om mua mua and whether we could detector of those in the near future and finally we step forward into the exoplant regime and I think those three aspects which seem unrelated they really speak to the unifying nature of M's work so please do enjoy this conversation with Professor Molina [Music] rice so Molina you are involved in a search for Planet 9 which is this enigmatic object that we heard about possibly being in the out of the solar system 5 10 years ago now and you are trying to search for this object but maybe before you tell us about this search which I think everybody's going to be fascinated by maybe you can give us a little bit of the backstory about how it is that planet 9 came to be a possibility in the solar system right so the solar system extends a lot farther than our classical picture of just the eight planets that we know of and Pluto and the dwarf planets there is a lot more out there that is bound to the solar system all the way out to the or Cloud that's at thousands of astronomical units so Earth Sun distances and in between the Kyper belt and the or Cloud there remains a large space of just just areas that you could hide things that haven't yet been discovered in the solar system so uh specifically the idea of Planet N9 arose because of the extreme trans neptunian objects in the outer solar system so these are some of the most distant asteroid Comet like objects that are kind of between the Kyper belt and the orc Cloud uh that we're only able to see because some of them are on these really elongated orbits where they get close to the Sun at some point within their orbit and the trans neptunian objects that have been found to date appear to be preferentially clustered on one side of the sky so their orbits are very elongated they're not circular so they sort of have a direction to them and they seem to be preferentially clustered on one side and not the other so if you run this in a simulation and you say how can we possibly get that to work uh it turns out if you add another planet to your simulation that's just on the opposite side of the sky it can help to force all of those other orbits to stay in place not not exactly in place but they oscillate back and forth in a very confined Direction instead of kind of spreading out across the sky over time which we would expect otherwise so it's it's hypothesized to explain this apparent coincidence that these objects which are all beyond the orbit of Pluto they F than Pluto yeah um is sedna one of these cuz that was one of the objects that demoted or kind of led to the demotion of Pluto right yeah so sedna is one of the brightest of these object so it's probably one of the most famous ones there are about maybe 10 to 15 of them that are known now they're continuing to be slowly discovered so the number is trickling upwards okay so you you were probably uh you're pretty young you probably an undergrad at this time or something right when this was being announced right so this must have been quite impactful to was a scientist when this announcement was made uh do you mean when Planet 9 wased yeah when when the first was it 2005 I'm trying to remember that the oh when Pluto was demoted no no um yeah Planet Knight I guess it must have been later than that yeah cuz it was 2006 I think that Pluto was demoted and then Planet 9 the the battig again and uh brown paper that was that was actually in 2016 so that was quite a uh but Shephard and tro found sedna uh at least a year or two before that I forget exactly which year so it was sort of in between the sequential like Pluto was demoted they continued to find more and more of these dwarf planets and then this idea of Planet 9 arose as we continued to discover more in the distant solar system right I guess that makes sense cuz s is one of these objects so you have to had s in the bag already so this object what what would be the properties of this object this planet n object yeah so I think this is what makes Planet 9 so exciting because if it existed it would be a sub Neptune type planet and these planets are incredibly common in exoplanet systems but we don't have one in the Solar system something that's between the size of Earth and Neptune uh so if Planet 9 was there it might actually suggest the solar system at least in way as a bit more similar to the exoplanet systems than if it didn't exist uh and it would be very cold so it would be very very far from the Sun uh probably a very Frozen world not particularly hospitable to life or anything but still just a different type of planet that we haven't seen in our solar system yet and can you give us some numbers like what what kind of mass would it be compared to the earth like how many times of the earth separation that's One AU how many Aus out would it be yeah so the mass um it would be about 5 to 10 Earth masses so it would be pretty firmly not a super Earth probably would be more of a gas giant type of Planet but smaller than Neptune um so ice giant uh and it would be about uh 300 to 800 astronomical units from the Sun so so that's about 10 times further than Pluto uh is the closest type of Planet 9 that you would get and then it could extend all the way out to 800 times further from the Sun than the Earth is so it's getting very very little flux from the sun it's very poorly lit and uh very low temperature as a result uh but we don't really what the simulations tell us is what its orbit could be and what its mass would be so other than that we have no idea what kind of atmosphere it would have for example except for what could exist at that temperature range but simply the fact it is so far away explains why it is that astronomers thus far have not because that that might be an immediate question it's like what if there's a huge Planet out there I think a natural reaction would be how come we don't know about it but it's just it's just the sheer distance to this thing yeah which is also kind of incredible because you know we can study galaxies that are much much farther away we can study the cosmic microwave background and the only reason that there Still Remains so much undiscovered in the solar system is that these objects aren't really giving off a lot of light and so we're looking at sunlight that has to go from the Sun to Planet 9 all the way back to Earth and you have a lot of attrition during that process so there actually is a lot of parameter space so this kind of range of masses and distances where you could be hiding planets and there have been ideas of maybe there are other planets that are not this initially proposed Planet 9 it could look very different and could still be hiding in that space where we haven't seen anything so I think that's what makes this type of search so exciting is there are a lot of kinds of planets you could hide out there certainly if you could hide something sub Neptune sized you could have mars-sized things you could have lots of you could have earth-sized objects that uh aren't so strongly I guess searched for simply because Planet 9 is the one that there there has been more evidence for uh but that doesn't mean that you couldn't hide other planets that we just don't see gravitational perturbations from as strongly it's kind of a theorist dream right because it's a it's you can just put whatever you want into this space to explain and I know there's been these wild papers of like it could be a primordial black hole and uh I think a lot of that made the news cuz people were like wow that's it's amazing that there's stuff out there in our own solar system that we still wouldn't know basic questions like that um I have to ask what do you think the community gauges on this do you think uh it's been a I guess it's been uh you know s years or so since then now since it's been released but has the community kind of got behind this and been like okay Planet 9 must be there do you think there's overwhelming skepticism or do you think it's somewhere in the middle like what what do you think the the planetry scientists feel about planet N9 I would say it's quite divided uh there are certainly people who think Planet 99 does not need to be there the is probably a detection bias uh there are others who think there's very strong evidence for Planet 9 uh there have been papers that have suggested this orbital clustering as better explained by a different iteration of Planet 9 also so there's been a lot of kind of back and forth between different groups saying what could this look like do we need a planet you could certainly hide a planet but do we need it to explain what we've seen and yeah I would say there's no clear consensus which is sort of the fun space to be in in science where you know no one really knows for sure what the answer is and I think that is what makes it so compelling to explore yeah so it's like a version 9.2 9.3 we've had of this planet right so you've been obviously uh I said at the beginning you've been looking trying to look for this planet 9 signature um in visible wavelengths so this would be mostly reflected light um I guess it could be producing it could be warm you know maybe have some internal heat as well as well um but maybe youd need an infrared camera to be able to detect that uh you've been trying to use Tess to detect this the transiting exoplanet survey satellite to always check as I get that and um it seems like that would be a very difficult premise because Tess is a 10 cm probably similar size to some of these things that the back even smaller you know 10 cm size telescope which collects hardly any light how could it work that such a small aperture telescope could possibly detect something that our largest telescopes have thus far not been able to find tell us about that yeah so the benefit of tests is that even though it's a very small telescope it's in space and it can continuously observe a particular part of the sky for months at a time so anytime that you're observing something from the ground you have at least invisible wavelengths you have to stop during the day because the Sun comes out and you need to have these data gaps that can make it much more difficult to find find something that's really faint if you don't know where it is so test is really convenient in that it doesn't have these data gaps it stares at each part of the sky for almost a month at a time so you have a lot of data that you can combine together to find uh something faint like Planet 9 uh and it has tremendous Sky coverage so because it's in space we're able to observe the entire sky at some point during the test mission whereas on the ground depending on where your telescope is you might not actually have access to the entire Sky mhm so yeah Tess is not going to be able to see planet 9 in individual images it's just too small it's not sensitive enough for that but if you add together images from about a month then you actually would be able to start digging out much fainter objects using all of that data together kind of stacking the the photos on top of each other in this case yeah so what's nice about something like Planet 9 is you can distinguish it from stars and things within the solar system because of its motion so it is moving fast enough that you can tell it's not a star a star would just stay in exactly the same spot for the entire month uh but it's moving much too slowly to be a foreground asteroid so asteroids that are closer to us we're going to see pass by really quickly things that are very far away look effectively static and Planet 9 would just move 5 to 10 pixels over the course of a month which is something that we shouldn't see for any else because we don't know of anything that far out in the solar system there's nothing else that we have discovered at 300 to 800 astronomical units because we wouldn't see it unless it's Planet sized yeah so so when you do this stack I mean it sounds like that' be difficult if I um imagine like a racing car going past on the and it was a dark dark night and this racing car had no lights on it whatsoever maybe just a tiny LED or something just a tiny amount of light coming off it and I took a very short exposure I wouldn't see it and so if I just if I you know some of them have like the sport mode on the cameras it tastes like this whole sequence just kind of what Tess is doing but if you took those images and you stacked them uh the car's as you said is moving this the the planet n is moving so if I just naively put all those photos on top of each other uh I'm not it's still going to be it's still going to be a tiny signal cuz it's moving it's smeared out across and I probably would struggle to recover it so how how do you correct for that with the stacking technique yeah so we we use something called shift stacking which is you shift your images along the path that you expect the object to potentially be on and then stack them together uh and this is tricky because we don't know where Planet 9 is it could be anywhere we just know about how far it would move and about how bright it would be so we actually need to check all of the possible paths for Planet 9 and shift and stack the images and see if anything interesting comes out of it so what we do is we we mask out all of our stars we mask out asteroids we try to subtract out everything else in space that we know of and see what can we dig out of the noise what Still Remains once you've removed everything else so in addition to looking for Planet 9 we're also checking to see are there other really distant solar system objects that might come out of this because anything that's very slowly moving um where Planet 9 would be moving even more slowly than other extreme trans neptunian objects for example but any of those can come out uh pretty nicely if you know where they are and then if you don't know where they are then you can check a lot of paths and then um try to figure out which of the signals that come out of there are realistic ones which generally requires additional follow-up observations with a different telescope but it's a nice way to pull out candidates from across the sky we already have this giant data set that we can use for this incredible data mining um kind of opportunity that exists just to learn more about our solar system and then afterwards then you can take the groundbased telescopes and say okay well we have a sense for where we think these objects are we can point our telescopes and check with another telescope and verify that it's reproducible and that we're seeing it again I love the fact that test was not designed to do this you're really pushing it to do something this little 10 cm telescope does not want to do this and you're pushing it into this discomfort zone of trying to make it do this awesome science it's it's really wonderful um and so yeah you so it must be challenging computationally as you said because you're you propose a path but there are so many possible paths so is that the idea you kind of suggest something that looks like um one of you take all the possible candidate solutions for Planet 9 that maybe uh bakan and brown suggested when they wrote their first paper or have iterated since you take those possible paths and you you run your algorithm okay nothing there try a different path keep going keep going keep going until basically you hopefully would get one of those or several of those reveal possible candidates is that kind of help I mean how do you do that path Choice yeah so it is effectively that but it's actually relatively simple because Planet 9 is so far away so what we're looking at is actually just the Earth is orbiting the Sun and the test satellite is orbiting the Earth and so uh because of that as the Earth and tests are moving past the sun you get some motion when you're just staring at one point in the sky uh where you you see that objects in the outer solar system will move a little bit not because they're moving themselves but because Earth is moving past them and Planet 9 would be so far away that it would just effectively look static to us so what we're seeing is just this motion that's in the plane of Earth's orbit and we're just looking for a shift of a few pixels in that One Direction so that makes it a lot simpler you don't have to check like is it moving up and down is it moving and these kind of weird horizontal/vertical ways it's it's just one direction that you're checking and uh that makes it a lot easier it's actually counterintuitively a lot easier to look for something like Planet 9 in this Mission than it is to look for near Earth objects unless they're really bright then then you can see them right away but if they're faint they're pretty tricky because they have these curved paths and that makes it a lot harder to actually recover them if you just have to look along small straight lines it's a lot easier than all the possible curved paths that an asteroid could take so you've got some candidate stuff in the in the some candidate TN certainly that we mean trans neptunian objects stuff Beyond Neptune uh from this work you're not sure yet about planet 9 that's work ongoing but do you think um do you think Tess is the best bet I mean I guess to some degree you must feel confident about it being a good way to do this experiment is it the most likely Mission if any mission is going to do this of finding PL n in your opinion I think of the space missions certainly so if we're talking about missions then yes uh I think the ver rubit Observatory is going to be able to search much deeper than we're able to with tests and so uh there's going to be a tremendous amount of data that comes out of that Observatory year so that's coming up yeah so if it's not found with tests then the ver ruin Observatory hopefully would find it or at least would tell us more of where it couldn't be which is tricky because it's hard to say that it's definitely not there just because you didn't find it uh but that is going to be able to search very thoroughly in a way that we haven't really been able to do before so test is kind of an intermediary leading up to there to see are we able to pull it out beforehand but if we're not then hopefully the that search will either pull out Planet 9 pretty quickly uh with its all sky survey or we'll figure out maybe our picture of the solar system is fairly complete and we don't actually have another planet which I think would also be a really useful result yeah and then you've got a mystery to explain with this clustering still that would still be a persistent problem I bet I bet you're hoping though that obviously it'd be great if a Reuben you know will survey this part of the sky and reveal the answer probably fairly definitively but I assume you're hoping you get there first before with test that'd be probably more exciting to kind of jump the gun a little bit and get ahead yeah I think it would be like we have the data set and we might as well use it so I think it would be really fun to find it it would be really fun to find other outer solar system objects and yeah I mean I guess it would be nice to find it but are you skeptical do you think it's probably not there what's your personal hunch I try to stay very agnostic on this because I have seen so much back and forth of you know we really think it's there really don't think it's there and in my opinion whether or not the current evidence is considered robust enough I think it's still useful to check so I think we should we should look for these things until we are quite confident that they're not there because it is such a giant value add to the solar system if we just had another planet and we would be able to learn so so much every single planet in the solar system is so valuable because we can't study exoplanets anywhere close to this kind of resolution uh and we have learned so much about the diversity of planets from both angles from both the solar system and exoplanet systems uh but we can't we can't really study S Sub Neptunes in particular up close in this kind of way through any other Avenue just yet and maybe someday we'll send a probe to Alpha centor or something and maybe there will be on the way yeah well you might use you might use P9 as your your in your your refueling station or something right gravitational lift from planet I mean it would be hisor and I think what's interesting from the historical perspective is you yeah you mentioned this and I think Constantine batan has said to me before that he's 99% sure that it's there and then I know there's others who are like 99% sure that it's not there and so it's just interesting because we're all essentially faced with the same data uh how are scientists coming to such extreme different views obviously this doesn't happen for most things in science like about climate change it's pretty much 99% in One Direction right and it's it normally arrive at consensus and so I think it's interesting that there is no consensus and so uh it'll be once we know the answer for sure I think it's going to be fascinating to piece back that story and see what what led each each side the wrong way you what was and and are the lessons there for future observations and Beyond the solar system as well yeah um but on on this and on the topic of History I do have to it's just a natural segue to go into this on on because that was a historic observation and we mentioned uh Vera Ruben which is this tasket coming next year and a lot of people are excited about the prospect of that discovering more Mo mu so maybe again I'm using term MO mu and some people are like what the hell is Mo mu maybe you can explain what is an Interstellar asteroid is that the the technical term or I just call them om but maybe there's a I love that word it's just so nice so I I think the technical term is Interstellar object because we don't know if they're asteroids they could be uh like the second one that was found looked more like a comet so it's small object so it's something that's from out this is how do we know it's from outside the solar system because it's we only see it when it's in the solar system yeah so you can track the object you can see how it's moving inwards and outwards and actually fit an orbit to it and if you try to fit an orbit to an Interstellar object only two of which have been found to date it is on a hyperbolic orbit so it's not bound to the solar system uh we would see it hopefully if we catch it coming in we'd see it coming in and then it just leaves and then we never see it again so there was one of these that was discovered UA in 2017 that was this historic amazing Discovery where uh we had never seen one of these before it was tens of meters in size which is pretty large for an Interstellar object it was predicted that there should be lots of little rocky bodies floating around but not enough large ones that we would actually expect to see them within a short amount of time with just one of our groundbased telescopes already existing yeah so am MOA MOA was really odd because it had this uh kind of like it looked like the McDonald sign kind of a light curve so makes you hungry looking at yeah right so it it was not round we think because it it had this kind of wildly varying light curve that made it look like it was probably either this elongated object or like a pancake like object uh so it was tumbling and it had this kind of strange light curve that we ended up pulling out of it uh and there have also been these observations that showed that it was perhaps accelerating out of the solar system uh which is also kind of there have been ideas for oh maybe it was outgassing but then people searched for what could have been causing the outgassing and didn't really see any of the molecules they might have expected so it is unfortunate that we can't follow it up again really because it's already on the way out of the solar system it's I guess it's probably still in the solar system but too far for us to see it it's probably Beyond neptun now or where is it it's a good question uh it probably depends on what you mean by Beyond Neptune because it came from up and down but it's I doubt it's more I doubt it's beyond the or Cloud so it's probably in the solar system too far for us to clearly image it anymore it's got too faint as it's moved away yeah and of course there borisov and borisov is a much more familiar looking object than it it there's been a huge amount of stories of course about om mua and people speculating about what it might be but um borisov has had far less attention right like the media just does not care about bis but tell us what is borisov then why is it so uninteresting from the from the media perspective but interesting I think still to us yeah so borisov was the second Interstellar object that was found in 2019 uh it was named after an amateur astronomer who found it with the telescope that he made himself which is incredible yeah and so that one looked a lot like a comet from the solar system so it was much easier to explain I think the fact that it was discovered again was kind of strange because it's another large body from outside the solar system and it wasn't previously thought that we should have that many free floating rocks that are that big outside that we would see um objects at this kind of occurrence rate where we saw two within the span of two years although we haven't seen any since and it's not clear to me whether that's just oh the pandemic kind of stalled a lot of things and maybe some telescopes weren't online or if that is really telling us a lot about the occurrence rate of these objects um so borisov seems like a comet so it looked like something that was probably ejected from an extra solar system that was in the outer Realms and then ended up just passing through our solar system and I think it's still a really interesting object but it's it had less puzzling features it didn't have this weird shape to it it didn't show a clear acceleration I I don't think although it's a comet so even if it did that wouldn't be too surprising in that case yeah so borisov um obviously didn't uh totally surprise us but it is what's interesting between those two is that it's as a comet you'd expect it to be brighter at least naively I'm I'm not someone who works on comets but I would naively expect an icy object with a cometry tale would be far brighter than a dark asteroid and I think the the reflectivity the arbo of om was indeed quite dark had like this darkish red kind of color um and so that would suggest that it would be far easier to find the comets and so all things being equal you'd have to have far more of the dark things of than the cometry things to to end up with a one: one ratio of them right does that has anyone sort of looked into the statistics of that what does this imply about the population of these two types of objects in the greater beyond the solar system right yeah I would need to check how much closer one of them came to us than the other as well um but I think the problem is we're not really sure what kind of population AAA would have come from and there are these ideas that maybe this was a Shard of molecular hydrogen ice I think or like a nitrogen Iceberg or something that formed in a molecular cloud during the star formation phase or U maybe it was just some kind of weird asteroid that we're not used to in the solar system or who knows what it could have been really but that makes it really hard to say what the underlying population was and it's not clear whether a MOA and two I borisov came from a similar background population or if they're just completely different kinds of objects so I think there's just so much uncertainty when you're trying to use I would say these are sort of two separate n equals 1 populations and it's difficult to know like you would have to make some assumptions to extrapolate from that how how many of these things are out there and are they the same are they not the same how much of this was like because it's not repeatable right we can't go back and revisit these objects and check again for our theories we we sort of just have to wait for more of them so yeah ver Rubin Observatory should hopefully find quite a few of them or that's what projections are suggesting and there's this really cool idea uh through the European Space Agency I think to actually have an Interstellar Comet Interceptor mission where I think they had already been planning to do some kind of comet Interceptor and then they the discovery ofd it those two Interstellar objects came by and they said oh well if there's a good opportunity and we find the right objects then was your a former adviser involved in that Greg was was that one of his ideas yeah I don't think it was his idea but I think he he might have been involved I think his graduate student Daryl Selman is definitely involved in it but I'm not sure how involved Greg is in that one yeah but that was a wonderful idea to I mean if we could do a sample return or just even do Mass spectroscopy or something on the surface of a of an install object I mean that'd be a mind-blowing discovery for science um the the rates I mean you have been thinking a little about these these rates of these objects um and I guess what's nice is that there's kind of a simple uh physics element to this that if you want to get something to leave another solar system because presumably this stuff must have formed in a solar system somewhere it's hard to imagine this stuff could just form spontaneously in a in a gas cloud um it's just you always have enough overdensity to eventually lead to a star or planet or something in that situation so if you had that situation how could you ever Propel something with enough energy to leave an entire solar system what kind of interactions or history might we speculate for Moa and uh is that consistent with our understanding of what plantry systems even look like yeah so a lot of exoplanet systems have been found with the planets very tightly bound to the star so they're very very close into the star and that's just because of our detection biases it's easiest to find those and they're the ones that Transit uh but if you look at systems that have wider orbiting planets they're much better uh projecting or ejecting uh Interstellar objects outwards uh so they start off as just normal asteroids or comets within the system and uh even within the solar systems formation we think that Jupiter probably ejected a lot of material during that process uh because the these wider orbiting planets can give this gravitational lift to objects that they can get out of the solar systems this is similar to we had mentioned maybe Planet 9 could do this for getting to Alpha centor uh if you want to send something out of the solar system you can use the planets uh particularly Jupiter is very good at ejecting material because it's very massive and on a wide orbit uh but also all the gas giants in the solar system are capable two did that right they they slung around so I'm actually not sure that was I think they did The Grand Tour and they missed I think Voyer 2 prettyy much hit every planet except for maybe Neptune it like missed one of them or Uranus yeah but I think yeah they did a grand tour and I think Voyer one hit Saturn and then went up out of the plane I think that was the difference but anyway we can someone's probably going to fat check that but yeah I guess the point is that we have used this effect ourselves in the solar system in an artificial environment but this should also happen naturally as asteroids get too close to these objects yeah yeah so uh particularly early on in the solar system we think that the giant planet sort of migrated around and they disrupted the asteroids that were within the solar system at that time and a lot of material was ejected so if something similar happens in exoplanet systems which if you just extrapolate they're probably in many ways similar to the solar system if we don't think that we're special and unique in this way that uh might be a little bit uh more unnatural so it it seems like wider orbiting planet should probably exist in other systems we've certainly seen some although they're trickier to find uh and protoplanetary dis images have suggested a prevalence of many of these kind of Neptune to Jupiter Siz planets that might be carving out gaps in these dis images that have come back so while it's hard to actually see those planets directly mostly because they have very long orbits you need to track them for many years to actually confirm that they're there uh they there's some evidence that is like from various directions is suggesting that they might exist in other systems and they'd also be very good at producing a background of interstellar objects so you're saying that if we if we took a a Jupiter Mass planet and it was orbiting at the same distance to the Earth or maybe SK Clos like Mercury or something around the Sun even though it's the same mass as our own Jupiter it's so close into the star so deep within the gravitational well of the solar system that even it cannot deflect collect these objects out and so the progenitor of oma must have likely been a it must have interacted at some point with a with a massive planet on the edges of a solar system yeah okay yeah so yeah and that is an area that we know less about the population from I guess the only real probe we have is maybe microlensing is maybe our best probe and direct Imaging to some degree yeah um microlensing is very sensitive to massive well even very small planets far from their star so does it look consistent if you sort of take the I'm sure there's going to be some degree of extrapolation but if you take the the hints of how many objects are out there is there enough to how how many om mes would you expect to detect with that population with some population of asteroids in those solar systems how many would we end up with seeing with um say Reuben in the next few years yeah so this is related to a project that I did a few years ago that was kind of extrapolating from protoplanetary dis images that maybe these neptune-sized planets on relatively wide orbits are fairly common so if you assume that the gaps carved out in protoplanetary discs are caused by planets you can figure out what Mass those planets would need to be as well as what orbits they would be on uh and then suggest well if those planets exist then they're actually quite good at ejecting Interstellar objects and if if all of that is true and if Interstellar objects are following a kind of power law like size frequency distribution that we see in the solar system then we'd probably get one or two amua mua sized objects each year uh and up to tens to maybe even a hundred smaller objects that uh that is a little shakier because you assume a lot by extrapolating to different sizes but we have a lot of potential to see not just even one or two but potentially like tens of these objects with the ver Ru Observatory and it really just depends on how many of them are actually there because we should be sensitive to them if they are there but you mean each year or in total of the like a decade of observations or something each year yeah so we should certainly see at least a few with Farah ruin Observatory and then it's just a matter of depending on how common they are uh maybe we'll see a lot of them if you actually have a lot more smaller objects so you can you can imagine if we have a few of these larger objects that we've already seen that means we probably have a lot more small objects in the solar system we have far more small asteroids than larger ones because the larger ones break up into smaller ones yeah and then I guess the idea would be that we find these objects and then the Interceptor is sort of parked ready to go it's like we set out so like it's over there just shoots off and tries to get there it would be I mean I think the the the the uniqueness of om MOA the the one offness of this object is what um is really driving me as a scientist to want to know the answers to what these other objects look like um of course there has been we have to bring it up that there has been speculation about this object being a light sale and that has obviously kind of dominated the uh the coverage the media coverage especially of om mua and um that's come with pros and cons right it's got a lot of attention to this important work of looking intercell objects but um it's also been frustrating maybe to some planetary scientists who think these objects uh you know are perfectly consistent with natural and that and there's something there that's um that's interesting enough without it being aliens right there's something like this is already pretty fascinating these objects alone I have to ask what is your sort of uh take on um the the the idea that this object is so anomalous that it that it's implausible to explain naturally or do you see this as something that can be explained with within the bounds of physical reality yeah so if we think about what we saw with New Horizons and its extended Mission uh this object aroth ended up looking kind of like a snowman uh so it it was like two sort of flattened circular bodies kind of fused together so probably initially was a binary yeah so sort of two fused pancakes uh so because of that I think it would actually be really useful to study the outer solar system a bit further and just see if these pancake like objects are very prominent but if they are I think that would be a pretty strong case for maybe maybe the shape at least wasn't so unusual and then perhaps we can with more of these objects learn more about is the acceleration something that could be explained naturally but I think for me I try to tend towards the least spectacular explanation possible until I really cannot hold on to that anymore yeah so aam Razer yeah aam Razer so yeah so that's kind of where I stand where I I will continually try to probe the most natural explanation until it just there's no way that it works and then then we'll move on to considering other possibilities and I would love if it was aliens that'd be cool like if we had aliens sailing through the solar system a lot that would be really fun yeah um yeah but I I would need to be seeing maybe more of those spacecraft coming through or like other lines of evidence as well in order to fully get on board with something like that and and I guess your work does kind of pour a little bit of cold water on it because with these raid estimates you're saying it could be as many as you know 10 per year potentially with ver Ruben so maybe then I think one of the arguments that was initially made was this it'd be very surprising you know the rate calculation doesn't make sense like panars which was what originally discovered om Mo mua uh should not in any feasible calculation have discovered an old mu Mo it's it was just it implies that there are so many of these things that nature cannot possibly produce them and someone is directing these things towards us but it sounds like um maybe we should be a little bit more careful with that argument and the there are plausible bounds within the rate calculations of ejecting stuff that could potentially reproduce panars getting one of these in its entire lifetime is that right yeah yeah and I think we'll see if we see absolutely nothing with the verin observatory that would be shocking to me because that would make it seem like wow maybe this was some kind of crazy coincidence but then you know do coincidences exist in science um but I think we are going to see more because we saw borisov and borisov was like a comet and so if if ver Ruben Observatory didn't see any of those it would be kind of incredible that we already saw two of them with just existing instruments now your work is so diverse because you you go all the way from planet 9 which is in the solar system to Interstellar objects which are leaving the solar system and then of course to my BR and berter exoplanets which are obviously outside of the solar system and um you've you've approached many of these problems with a fusion of both you know unique observational techniques for finding these things certainly in the case of Planet n and um a deep understanding of the dynamical uh history and origins of these objects what what makes them tick how do they get into the into these unusual orbits and nor has a very unusual orbit clearly as you said it kind of comes also out of the planes look like very torted over compared to the solar system but maybe that's not surprising cuz Al solar systems are kind of arbitrarily tilted yeah um but there's another kind of tilt that you've been measuring that I I did want to talk to you about and that's the the Tilt between the planet and a star around other stars in exoplanet systems and that's that I think when you first hear that if you've never heard of this technique before it's amazing that's even possible to measure this because we cannot see these planets we don't have really I mean in very rare cases we have some photos of them but even you had a photo of a planet it wouldn't tell told you much about that that angle um how is it that we are able to measure the misalignment angle between a star and a planet and maybe you could also be more precise with that what do I mean by a misalignment angle what angle am I actually talking about there yeah yeah because there are a lot of angles in these systems and the one that I've been specifically looking at is the angle between the planet's orbit and the Stellar spin so there's also the planet itself can be tilted in different directions so the Earth is tilted by 232° uh but that that's a lot harder to probe so that has been studied in a couple of exceptional cases but is very hard to study for more systems so this is the angle just to clarify this is the angle that if I imagine the star spinning and I draw like a a rotation axis through it like North Pole to South Pole that that Rod that went through the star and then I equally I take the plane the disc of the orbit and I stick a rod that sticks up vertically from the center it's that it's the angle between those two rods almost in space that you're trying to measure yeah yeah so that's that's much more measurable than some of these other uh angles that exist in the system uh where it's just telling you whether your planet's orbit is going the same way the star spins or if it's going backwards relative to the way the star spins which is strange but not necessarily non-existent it looks like there's some hints for that in other systems uh or if it is orbiting sideways and there are also hints of that in other systems like who ordered that yeah yeah so it's like in the solar system the planets aren't perfectly aligned with the way the sun spins so our orbits are tilted by about 6° and there have been a lot of studies of could Planet 9 have done that could something else have done that uh but it's pretty close to aligned but there are a lot of especially hot Jupiter systems so the systems with really massive planets really close to the star often are more tilted and they're kind of the planets are orbiting sideways or backwards or in these weird directions and this is something that we can actually study using radial velocity observations so we're looking at the Doppler shift of the star due to the tug of the planet uh and it turns out that if your planet is actually transiting your star it'll cover up different parts of the Stellar limb so your star is spinning uh there's lots of different spins within the system but as your planet is moving around the star it will cover up different parts of the Stellar disc so you get the part that is moving towards you that is at some points covered up by the planet the part that's moving away that's at other points covered up by the planet and you end up with a tiny extra Doppler shift so you get this little warp in your overall Doppler shift curve uh because of this planet being in front of different parts of the star so this is called the Roser mlin effect and it's something that we can use to actually measure mostly for pretty large planets so largely hot Jupiters but also starting to push towards smaller planets as well uh this angle between which way they're orbiting relative to the way the the star spins so if it if you imagine a vanilla system where everything's aligned perfectly aligned um the let's say the star is spinning in kind of a arbitrarily clockwise sense relative to some Observer and if the if the planet is going around the same sense then that means uh the as viewed from Earth in this in this situation it's a lot of angles to get your head around that you be seeing the uh star spinning uh let's say towards you on on the Leading Edge and so uh you'd be blocking out the blue shifted part of the Star first yeah and so you'd get a net red shift yeah the overall the star would appear redder than it usually would yeah and so that's what you like a red shift then go back to normal and then a blue shift and then back to normal forever for a long time or not forever but until it comes around again M and so that would be your align system but you're saying that there are systems which you which don't look like this at all that they're doing something completely different and that's telling you there's a there's a huge misalignment angle yeah there's nothing else that could cause that right it's it's pretty unique yeah yeah it's pretty unique and uh you would get that classic sort of symmetric curve where you expect the the upwards uh like again net red shift and then blue shift if it's aligned but if it is going backwards and you'd get the blue shift and then the red shift so it' be just flipped the other way uh or you might just see exclusively a red shift or exclusively a blue shift if it's just moving upwards and that that would be a sideways orbit so that's saying your planet is never covering the red shifted part it only covers the blue shifted or vice versa it has to be massively tilted over for that to be true yeah yeah okay so we see these these range of alignments um what is and we're measuring this this cool rust mlon effect uh what how do we what are the possible explanations for for how planets given that I think this was unexpected right because as you said the solar system is pretty you know everything's pretty quiescent pretty calm look at these exop plant systems we see tons of not just plants but hot Jupiter plants plants massive plants very close to their start and yet somehow those these big boys have been somehow twisted over um what are the possible explanations as to how this is happening yeah so you could possibly during the protoplanetary dis stage so before the planet is actually formed you could tilt your disc and then your planets just form within a disk that's been tilted and then that would lead to a tilted Planet ultimately so you'd probably need another star in the system or something else that allows you to tilt that disc but that's one way you could do this or you could have dynamical scattering between planets in the system that might lift up one planet from its initial orbital plane and potentially eject the other planet as usually kind of the traditional hot Jupiter formation mechanism where you launch a planet onto a very extreme orbit and eject the other planet which is like Om type case right that must have been yeah it's it's not a planet but that must have been its history to have been scattered essentially off another object yeah right and there have been rogue planets found so there probably are planets that have been ejected from different systems the solar system might have actually had a planet ejected or multiple planets ejected early on and so that's a whole other like kind of like a muaa but much larger uh kind of field which is also very interesting and so so basically the two ideas are it's it's either planets messing with each other within presumably they formed within a dis and so they're originally all flat but then subsequently it's like these toddlers in the playground start messing around with each other and they all fly off in different directions or it's the entire playground itself the the disc from which they form the nursery is in in itself that is somehow tilted over that seems almost The Stranger one how I can kind of imagine and we've talked about examples of how it could happen plants messing with each other but how could the entire disc be twisted compared to a star yeah so if you have another Stellar companion then it can cause the disc to sort of move around relative to the Stellar spin axis uh so depending on where the companion is relative to your disc if it's outside of the disc plane then it can cause your disc to sort of shift around uh relative to the plane of the binary companion so it's like a lurking star that's kind of yeah so a wide orbit and it's just slowly tugging yeah uh and you can have shorter orbits but you usually don't get hot Jupiters forming from those because you truncate your planetary disc if your star is too close to it so uh yeah if you have another star in the system it can produce a lot of interesting other effects that could like flip your system this this could also be after the disc has dispersed you can also flip planets once they formed if you have another star there to do it I can't help think of Uranus because Uranus of course is tilted over and it's tilted over compared to the in a different angle now we're talking about really it's its spin axis is tilted over I think it's almost 90° or maybe a bit more than that compared to the rest of the solar system and it kind of also dragged it I think it dragged its satellit along with it and so they're also in that plane but you could imagine if it captured a moon it might capture the moon preferentially in the same plane that all the other planets go around because that's where most stuff tends to be and so then you'd have a huge spin orbit alignment and of course the explanation for that would be an impact at least that's that's what people tend to argue for Uranus is that maybe something smashed onto it and on it lopsided it and it got knocked over maybe it's a bit extreme but could something impact a star and tilt it over like that from its disc or we I guess that would be so disruptive maybe the entire disc would not survive such an event yeah I think it would be challenging to tilt the entire star uh you might imagine ways that the outer layer of your star might be able to kind of move around in a line and that's assuming that your star isn't all rotating together which is probably true that it's not all rotating in exactly the same kind of synchronized motion it's a ball of gas and so you could have certain layers of the gas rotating at slightly different speeds um but yeah I think this is very much a stellar interior's question like just how well can you decouple one layer of the star from another because they would be inter interacting with each other you'd get some Shear between those layers and so uh over time you would probably equilibrate to not have layers that are completely decoupled from each other yeah and so and another way to maybe get some insight on the two ideas whether it's the dis tilting or the the planets interacting with each other um I guess the problem with hot Jupiters as a sample is that they are inherently weird systems only 1% or even less than 1% of stars have hot Jupiters so they're not like the normal way which planets are made um and they're also presumably the product of some kind of extreme event in the solar system like some kind of extreme scattering event or very rapid dis migration that you think would be pretty disruptive to other planets indeed that's tends to be what we see it's very rare they have other companions in those systems they tend to be lonely the hot Jupiters so um it would be I know you've been working on systems which don't look like hot Jupiters as maybe a way of getting some insight especially these resonant systems so maybe you could tell us about why is it that a resonant system is particularly a useful laboratory for understanding the possible differences between these two models yeah so the resonance systems are a unique case in that uh by resonance we mean that these are in mean motion resonances specifically so there are different kinds of resonances but this is one where one of the planets is orbiting say twice for every one time an outer planet is orbiting uh they have this very synchronized motion that actually causes them to interact with each other more closely because they come to conjunction where they're very close together much more often than if they had yeah more random like the moons of Jupiter do this right yeah yeah so the moons of Jupiter in a famous llas resonance the 1 to two to four uh which has been seen in I think at least one or two other exoplanet systems but the resonances are actually kind of rare in exoplanet systems and there have been all these ideas for why that is because if you try to simulate how planets migrate within a dis they naturally end up drifting into resonances so they end up being trapped within these configurations that are very stable um and then they stay there and when the disc disperses the question is what happens to them and it seems like maybe a lot of them become unstable so as your dis is dispersing you have extra forces that are kind of influencing the orbits of your planets and they might become unstable as you're changing the environment slowly uh so that could disrupt a lot of the residences but we do see that some of them remain so we still see similar to Jupiter's moons uh that kind of configuration in a small percentage of planetary systems and we think that those are probably some of the most quote unquote pristine planetary systems and that they retained that primordial configuration that is you don't really naturally produce resonances after your disc has dispersed so you would you wouldn't expect that there have been a history of extreme scattering in such a system right that that doesn't make sense with the story of how it gets into a resonance like this yeah if you had scattering you would destroy resonance right away it's a pretty delicate configuration so if you look at the tilts of systems that have resonances then you know that those tilts are probably pretty pretty good at tracking where the disc was because you don't expect a lot of dynamical evolution after the dis has evolved otherwise it would have probably destroyed your resonance at some point and so looking at those we end up seeing that also some of those systems are a little bit tilted so not very tilted but up to about about 20° tilted and if we recall the solar system is tilted by about 6° so that kind of tells us at least in terms of how tilted over we are maybe the solar system is pretty normal uh we have quite a few planets that interact with each other kind of in a more stable way at least in the immediate term we're not losing a planet anytime soon and and we're also a little bit tilted just like a lot of these exoplanet systems yeah I I mean I almost uh well I can I certainly agree with what you just said I can almost think see it the other way though that the it implies maybe that the solar system is not like a complete outlayer but perhaps un a new one of the quietest dynamical systems in a way right because you have um you have this six degree tilt which amongst the spread of all resonance systems would be in the lowest uh what tertile is that the word like the lowest third more or less of your your distribution so yeah amongst the quietist and then on top of that this is just the resonance systems that you're looking at which is not representative of all planetary systems of course and we we know there's lots of planetary systems which do have scattering events in their history and clearly the solar system uh seems to not be in a resident state but a fairly pristine state to some degree and so um I guess that that makes me wonder what are your feelings about the uniqueness of the solar system or the the Rarity of the solar system maybe it's a better way of saying it how how how common do you think this situation is so in terms of the tilts we have seen a lot of very tilted hot Jupiter systems but those are actually quite rare systems they're only around about 1% of sun-like stars so those are quite intrinsically rare systems and I would say we would need to make more measurements of non-hot Jupiters to confirm are there a lot of other kinds of systems that are commonly tilted or not even if they have smaller planets within them and those that aren't hot Jupiters uh I think it's it's a difficult question how common is the solar system because there's so many ways that you can decide like if you make the Box very small and you say if it's like the solar system it must have an earthlike Planet it must have a Jupiter it must have eight planets then suddenly you're diminishing ruling out all of these different kinds of systems there's nothing left it's just the solar system so I think with our current detection techniques we don't have a fully complete answer certainly to whether the solar system is common along a lot of these axes in terms of the tilts I wouldn't say it's too unusual it's looking like Jupiter sized planets are maybe not incredibly common although not incredibly uncommon maybe 10% of sunlike stars or so uh and then it it really just depends on how you define something that's like the solar system and I think that's a loaded question yeah it's it's a it's a mystery that we're obviously still trying to work on and I think it's a fascinating one and um I do like your answer because I think the it bothers me with the rare earth hypothesis sometimes that we say well you have to have a large Moon you have to have you know exactly this amount of water and this size Planet but that's just our story and we we're kind of back engineering our story in a assuming this is the only way to get to to Rome but maybe there are other paths to Rome as well right there are other ways of getting to this situation so um it's both it is an import important question to understand the architecture and frequency of our solar system and you're doing wonderful work trying to break into that but uh I'm I'm pleased that we're keeping an open mind about the not being too overly anthropocentric about it it's all about what we look like right um so I mean this has been great uh I'm going to let you go but maybe you could just tell us uh if people want to learn more about your research where can they where can they find you yeah I have a personal website that has a pretty comprehensive list of I try to include bite-sized overviews of all the papers that I've LED at least and have so far been able to maintain that pretty consistently and uh yeah I think this this podcast is is one great place I also have been on the Astros sound bites podcast and was a co-host for that for the first 55 episodes so yeah I I pop up here and there I'm fairly googleable I'll put those links in the in the description as well so people have them well thank you so much this has been excellent thank you yeah thanks so much for having me so that was my conversation with Professor Molina rice I hope you enjoyed it as much as I did I think for me speaking with Molina it reminded me of just how interconnected so many different aspects of science truly are and yet at the same time unfortunately how we have often lampooned them into different categories for an example in many universities there is not a single Department that studies planets in fact you'll often find two separate ones a planetry science department they'll often focus on the solar system and then maybe in the astronomy Department you might have folks such as myself and I guess Molina is in astronomy Department as as well where they focus on exoplanets but that boundary is artificial because of course in reality we're both studying the same types of objects and if we truly want to understand their nature we're going to have to ultimately combine forces and interconnect and have that Synergy of those two fields that unfortunately often been missing and so I'm really I really enjoyed hearing about Molina's work of how it was bridg ing that Gap going all the way from the solar system looking for Planet 9 which itself not only has implications for the solar system but implications for the occurrence rate of Neptunes Across the Universe and where is our mini Neptune that we were supposed to have in our solar system how do these things form it connects to all of that and yet we of to make these fake dividing lines that they have to be treated separately so I really applaud what m is doing and I think it's important that we keep those lines of communication open that we do not shut the door to one another and I think that is actually slowly happening uh not just between the solar system and exoplanets but we're seeing that line sort of break down in many different fields asrology is a really great example and similarly the search for exal intelligence seti or techno signatures is another fantastic opportunity to bridge so many different fields together of course nobody can be an expert on everything and I'm certainly not anything M claim to be an expert on everything none of us can learn the entire volume of science we do have to specialize but keeping that door open to be aware of what is happening in these other fields and potentially see the connections is incredibly valuable so I hope you enjoyed that conversation I certainly got a lot out of it if you are enjoying these conversations in General on the cool wordss podcast then one way you can support is to head to cool worlds.com ssupport that's coolworld la.com ssupport where there we kind of have like a patron but it's not exactly Patron it comes directly to a research fund that is it so the way this works is that you know if I am able to have my research pot of money funded by you guys or partially supported by you guys it means I have to spend less time writing proposals I have to spend less time claing for money through Federal resources which ultimately gives me more time to do my Outreach work to make these podcasts make the videos and of course do amazing science which connects to all of the work that we do on the Outreach side as well so that's my pitch to you if you're interested in supporting what we do that is the best way is to directly support research in the cool boards lab directly through that fund so please do check that out coolo lab.com SLS support So until the next episode see you around the Galaxy

Channel: Cool Worlds Podcast

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Id: Yfqp11D8MKY

Length: 65min 23sec (3923 seconds)

Published: Fri Nov 24 2023