The Supermassive Podcast - 45: BONUS - Have you heard of "Ploonets"?

Episode Date: October 13, 2023

What is the furthest distance away we’ve ever observed? Why hasn't Venus lost its atmosphere from solar winds? Is Mercury a Ploonet? And how stable is the moon's orbit? It's another bonus episode with Izzie Clarke, Dr Becky Smethurst and Dr Robert Massey. See Micheal Brill's brilliant photos from Antarctica here. Read listener Andrew Street's article of Cassini's final moments:  Tracing Cassini's fiery death was like seeing a heart monitor flatline Send in your questions to The Supermassive Mailbox by emailing [e-mail], tweet @RoyalAstroSoc or find us on Instagram @SupermassivePod. 

Hello and welcome to another bonus episode from the Supermassive podcast from the Royal Astronomical Society with me, science journalist Izzy Clark, astrophysicist Dr Becky Smethurst and the society's deputy director Dr Robert Massey. So before we dive into everyone's questions, I think we've had some really lovely messages from listeners this month becky can you read up this this next one oh sure okay so this one's from andrew street who writes dear supermassive folks which i enjoyed that very late to the party i know but i only recently discovered the podcast and i've been busily devouring the catalog like becky i am borderline obsessed with zan and wanted to share this link with you. Because I am insanely fortunate, I was one of the handful of people

invited to the Deep Space Network site at Tidbinbilla. I'm gonna guess. Tidbinbilla near Canberra. I would say that. Invited to the Deep Space Network site at Tidbinbilla near Canberra back in September 2017

for the final transmission from Cassini. And as was discussed on your episode, it was indeed a deeply emotional experience, so much so that I wrote a piece about it for The Guardian, and that's the link that Andrew has sent. It's still one of the most glorious and moving experiences of my life, and yes, I still have that packet of unopened Cassini tissues. Keep up the great work, which I originally wrote as stellar work, but then realized that was both too inadvertently punny and also occasionally accurate. Cheers, Andrew.

Oh, thank you so much for that, Andrew. That was so lovely to read. And we'll be sure to link that Guardian article in the episode description for anyone who wants to read that. Oh, such a lovely message. I really smiled when I got that one. And I'd like to award Michael Brill

from the Australia Antarctic Division as our most remote listener who has emailed from Antarctica with some amazing photos of the night sky. I'm going to put these on our Instagram. And the first photo was taken at Wilkins, the ice runaway service in Casey Station in Antarctica. And it was taken during the setup stage of the runway mid-September and the second photo was his last night at Mawson station before heading home which was taken a couple of years

ago and the skies I mean that's just incredible that you said I mean we I mean I already know the southern hemisphere skies put the northern hemisphere skies to shame but I think being in Antarctica you really get the full you know just like perspective on that like you know we usually see the center of the milky way fairly low down here but in this picture he sent it's just like i'm here arching out overhead and it's just you know you can see the color of all the individual stars you know when we talk about blue stars and red stars that blue stars being hotter red stars being colder it just pops up in such amazing clarity in this image where you know there's probably so little light pollution so little air pollution oh no humidity or anything it's just incredible you know if if

the greenwich astronomy photographer of the year yeah um but then the second image he sent is is also just as spectacular because it's the aurora australis that he's captured, the southern lights, this incredible green glow, which usually, I mean, I've seen it before in Iceland where you just see this like, you know, maybe one or two ribbons. But I mean, what he captured was just incredible. It's like the entire sky is green. So if you get a chance to go on our Instagram or Twitter

and see these images do because they really are absolutely spectacular yeah thank you so much for sending those in michael also i love who gave you like the the you know the authority to start awarding awards um like you were like i am going to award it's because that's something i could do and robert could do sorry no i'm gonna play the producer card as well and therefore it is me hello okay so let's go into some questions robert amelia has this question about telescopes what is the furthest distance away we've ever observed for the telescope and how can we improve telescopes in the future i love the podcast and really want to be an astrophysicist when i'm older yeah you go amelia yeah you can do it

exactly great great to hear from you million yes and good luck with that we really want you to be an astrophysicist as well the answer is we we sort of can see as far as we can now and the reason is that when you look at very very distant things you're looking back in time and you get to a point where you reach the age of the universe so the fundamental limit is you can't see anything before the big bang when the light can't have traveled more than 13.8 billion years. However, there were complications around that. So firstly, I was thinking about this and I thought,

well, actually, the most distant stuff we detect is what's called the cosmic microwave background, the kind of residual heat of the Big Bang. And that is sort of from originating more than, well, 13.6 billion years ago and it's about 40 billion light years to that now and then if you think about things instead you're probably thinking of things like galaxies and stars and so on the most distant one we found so far is with the james webb space telescope probably predictably because that's what it was designed to do to look at these

very very distant objects and that we're seeing them as they are very early in the universe and the galaxy referred to which like many of them isn't going to have a particularly exciting name this one is called jade's gs z 13 uh dash zero and it's so far away that it's lights taken us 13.6 billion years so 13 600 million years to reach us so we're seeing it very early after the big bang how long after depends on exactly which model you have in the universe, but then arguments about how fast it's expanding. But because of the expansion of the universe, because the universe has got much bigger since then,

that same galaxy would now be 34 billion light years away. So that's a really very long way away. Now, your other part of your question about how can we improve telescopes in the future, the general advice of telescopes is that, predictably, astronomers just want them to be bigger. And the reason we want them to be bigger is because they gather more light. The fundamental thing about a telescope is to get lots of light and concentrate it into a detector. So the more light, the better.

The bigger the telescope gathering, the better. And also build more sensitive detectors. But we're kind of there with detectors and how much light we can get you can't really get much more into them so it's about building bigger telescopes and the one to look out for in 2028 five years time it was the european extremely large telescope i don't know what they'll have after that you know i think we've talked about this but with the overwhelmingly large telescope the stupendously large telescope but anyway anyway, this is being built in Chile. It'll have a mirror 39 meters across.

Just think about that. Absolutely enormous. If you look at the building, they're halfway through construction and the building looks like a stadium to house this thing. It's crazy. This thing is steerable. And it'll be big enough to see Earth-like planets around the nearest stars. So that's one of the reasons we're quite excited about it. And there are also plans to put more telescopes in space as well to be successors to James Webb and to Hubble.

The LUVOIR one might launch in around 2039 or so. So I was thinking about this. I'll be quite old by then, but still around to enjoy the elt the stat i've heard is that it will give us better resolution than hubble but from the ground which is kind of crazy yeah that's incredible yeah and becky joe has emailed to ask mars lost its atmosphere from solar winds because it has no magnetic field but venus also doesn't have a magnetic field but why hasn't Venus lost its atmosphere from solar winds? Well that's a great question Jo and you've stumbled on a very large debate there well done so first of all Venus is losing its atmosphere at about the same rate that Mars is Earth is also doing the the same. And it's also a balance between sort of like molecules having enough energy to escape, like molecules in the atmosphere having enough

energy, so they're traveling fast enough to escape the gravitational pull of that planet, right? And so the one thing you have to remember is that Venus is almost eight times heavier than Mars. So even though, though yes it is too blasted by the solar wind and all the radiation from the sun uh it can hold on to its molecules in its atmosphere that much better um which you know hang on where am i going here this is so small these notes um yeah so it can't so even though that venus is also being blasted by the solar wind and obviously at much stronger concentrations because it's that much closer to the sun, it can hold on to its atmosphere that much better. And its atmosphere is 92 times thicker than Earth's.

So it's a very dense atmosphere as well. But there is a lot of debate about whether the solar wind and the lack of its magnetic field is the reason that Mars lost its atmosphere. you know, the solar wind and the lack of its magnetic field is the reason that Mars lost its atmosphere. Because, like I said, Earth is losing atmosphere at the same rate as Venus and Mars, roughly speaking, you know, like, it's not exactly the same value, but between astronomers, it's roughly the same amount. And that has a magnetic field. So there was a paper by Gunnel and collaborators from 2018, who found that sort of atmospheric loss rates are independent of whether a planet has a magnetic field or not and actually sometimes magnetic fields can speed up that loss rate because you can escape through poles um because there's you

know sort of uh not as much protection there and so instead you have to take everything into account for a planet so it's mass it's So it's mass, it's size, it's atmospheric composition, it's magnetic field, it's gravitational pull, everything. And that, you know, has really important knock-on effects as we start to search for candidate habitable exoplanets as well. Because, you know, we think of habitability as, you know, if it has a magnetic field, it's going to be more habitable. But is that not necessarily the case then? Do you not have to have a magnetic field to hold on to you know a denser atmosphere for example so it is a big debate that's currently sort of ongoing it is the leading idea for why mars lost its atmosphere and also because it is a lot smaller

you know it is like half the size of earth so it can't hold on to it as easily so that the solar wind could have a bigger effect but there's probably a lot of things at play there um it's still an open area of investigation ah well good question joe and robert teresa arispe has this question on plunets that's p-l-o-o-n-e-t-s okay so recent research has suggested the idea of plunets former large moons of giant planets that become planets in their own right when something happens to gravitationally tear them away from their host planet, so they are instead directly orbiting a star. Given our own Mercury's strange properties,

such as its large core in proportion to its mantle and its unusually elliptical orbit, is it possible that Mercury could be a plunet, perhaps one that once had a thick ice shell such as the galilean satellites could it be a lost moon of jupiter or saturn as a result of early planetary migration or maybe even a moon of the hypothetical planet five required in migration models someone's been doing yeah someone's done some reading a lot of good questions there i hadn't come across the term plunits before and i thought oh this is fun and it was actually that it was described as them but there's a journalist amanda koozer one of you please written about this

said oh it was charmingly goofy and i tend to agree and it was invented by a team led by a Colombian astronomer, Mario Acquire, in 2019. And we actually published it in our journal. This is the Royal Astronomical Society, so you should have already known about this. But they're hypothetical exomoons, so moons from planets that are in orbit around other stars that have escaped their host planets. And that might happen. The idea is that if you have, say, one of these Jupiter-like planets in other solar systems that we see that have ended up close to their star

as a hot Jupiter, the idea is they migrated inwards. And as they migrated inwards, they'd lost some of these worlds. And probably what happened, because they interact with the gravity of the other planets in the system as they move in, probably what happens is that a lot of these plunits end up crashing into the planet or the star or the star in the center but some of them might survive a lot longer and they might be able to grab some of the material in the forming solar system and end up as planets now we don't have our solar system is either either it's unusual or it's just that we haven't seen many like it yet and that's because the kind

of telescopes we've got was the observational bias we don't have a kind of hot Jupiter or even a hot Uranus in our solar system so so we haven't got quite that setup so I don't think it would be that would explain Mercury and as for planet five and planet five is this planet that might have existed between Mars and Jupiter before being ripped apart from the asteroid belt. If that existed and migrated or was torn apart or went into something, possibly is the answer I think. The only thing I can think about this is that Mercury, although it's a small planet, it's still a reasonably decent size. So to have something that big it's fairly unusual. There's only a few examples in our solar

system of moons that are that big so whether it would have been enough to form in that situation i just don't know but this is the kind of thing where we probably ought to i don't know do an episode or something on the origin of the solar system and talk to people who know about the dynamics of these things but yeah a great set of questions stories i'm sorry i can't answer it completely i mean sorry i was literally just making a note to make episode on origin of solar system. Let me get it, job done. Okay, Becky, Dan Kelly on Instagram has a question about the moon.

He says, hello. So we're constantly on the lookout for space objects on a collision course with Earth, but nothing is ever said about objects hitting the moon. Have there been any objects colliding with the moon in our observable past? And how stable is the moon's orbit around the Earth? Would it ever be possible for something to strike the moon and change its orbit and send it flying away from Earth or into Earth itself? Let's end on a bit of existential classes. Yeah. So first of all, let's start with the, have there been any objects

colliding with the moon in our observable past yes many every single crater that you see on the moon is from an impact with say an asteroid or comet so if you break out your binoculars or a telescope when it's not a full moon at least when you've got a shadow running down the moon you can see loads and loads of craters and you can see see that the mare, mare, Robert? Mare? Take that. Seas of, you know, French seas of tranquility, things like that, that are thought to be from these collisions with asteroids, you know, create lava that would then solidify into these seas as well. So all those features you can see on the moon are essentially, we think, from

impacts with the moon. So the sort of Earth-moon system and the inner solar system as a whole really went through this period known as the late heavy bombardment, around about 4 billion years or so ago, where there was a higher number of collisions than usual that occurred. And we can really see that record on the moon. It really is a fossil of all of those now as for things hitting the moon and knocking it out of its orbit technically with something big enough and traveling fast enough you could impart enough energy to change the you know any object's orbit you know the moon included no matter how stable its orbit was before that you know and that's what the dark mission has done when it collided with that asteroid do you remember it

collided with a dimorphous in orbit around didymus and we managed to see that we've changed its orbit and that was sort of this idea of could we redirect an asteroid if it was necessary um but in the case of the moon like if you were you were going to do this as an evil super villain like you would need um a dwarf planet essentially to do this right you would need something like 500 kilometers and above let's say like in terms of like size of something that you would need to not to give to impart enough energy to the moon to counteract earth's gravitational pull and to change it and there's not really any of those dwarf planets knocking around these parts of the solar system so it's not something you can really easily get your hands on to change the orbit of the moon and the other thing is even if

there was a large asteroid on a collision course you know sort of with the moon at first i mean the earth's gravitational pull is that much stronger than the moon so it would likely pull it off course and it likely not hit the moon it would likely hit earth instead so you know unless it was the late heavy bombardment there's just so many of them coming in you know that was they were bound to hit the moon as well so thankfully i don't think dan that this is very likely at all that this would happen. But as I said, theoretically, yes, this is possible. I want to add one thing to this, actually.

Well, two little things. One is that we've definitely also seen things hitting the moon. Oh, yes. Frequently, we see flashes on the moon's surface. And there was one back about 10 years ago when something the size of a car hit the moon and there was a bright flash. And the and the other thing i was thinking 10 years ago so it wasn't it wasn't the tesla then it wasn't the tesla no that's somewhere else maybe that's next on the list yeah the other i was thinking actually as you're talking about knocking the moon off orbit i thought you know for those people who remember space 1999 and the premise from that you know then um isn't gonna happen that was the idea you

know that that that that's uh definitely 70s vintage science fiction uh series you know explosion on the moon surface knocking off goals and as you as you absolutely right you say becky it's just not that easy also there was that recent film as well was it moon fall where the moon fell to earth i don't know if that was because of a collision or what but like yeah that was also a science fiction gibberish i didn't recommend that one in my no i did not he definitely that has not made space content club absolutely not okay well thanks everyone and keep the questions coming you can email podcast at ras.ac.uk tweet at royal astro sock and we're on instagram at supermassive pod and you should definitely send in those questions because then next time we're back with an episode which is a dedicated q and a episode so start thinking now get them sent in as soon as you can because we

want to try and answer as many of your questions because they really are absolutely excellent. As we heard in this bonus question, you definitely test us, you do your reading, you come up with some fun ones. I also really enjoy seeing Robert and Becky squirm when something crazy comes up. Every time. It's really entertaining. So until me and Robert squirm again next time,

happy stargazing, everyone.