We created Astronomy Cast to be timeless, a listening experience that’s as educational in the future as it was when we started recording. But obviously, things have changed in almost 7 years and 300 episodes. Today we’ll give you an update on some of the big topics in space and astronomy. What did we know back then, and what additional stuff do we know now?
Astronomy Cast episode 300 for Monday, April 1, 2013 – What We’ve Learned in Almost 7 Years
Fraser: Welcome to Astronomy Cast, our weekly facts based journey through the cosmos. Where we help you understand not only what we know, but how we know what we know.
Fraser: My name is Fraser Cain, I’m the publisher of Universe Today. With me is Dr. Pamela Gay, a professor at Southern Illinois University Edwardsville, and the director of Cosmoquest.
Fraser: Hi Pamela, how are you doing?
Pamela: I’m doing well, how are you doing?
Fraser: Good. 300 episodes.
Pamela: We’ve got a lot of audio out there that is about 150 hours of audio recorded and edited by poor innocent Preston, for the most part.
Fraser: Well that’s 300 episodes of just Astronomy Cast. We had the question shows and we did the Weekly Space Hangout; we did a lot. The total amount of audio that we’ve recorded is way more than that.
Pamela: Almost all of it is available between our podcast and our YouTube channel so if you want to learn more, check us out on YouTube.
Fraser: Do you remember when we first did the podcast and we had like ten or twenty and people would catch up in a couple of days and then just nag us? Nagging e-mails like “Why haven’t you recorded more?”. We don’t get those any more.
Pamela: For a while we used to actually get “I logged in at ‘such and such’ and hour and it wasn’t up yet!” and that was insane. Now people are more forgiving because we do travel a lot and go on summer hiatus. Three hundred episodes!
Fraser: Yeah 300 episodes, that’s good. We’re getting them up there.
Fraser: We created Astronomy Cast to be timeless, a listening experience that’s as educational in the future as it was when we started recording. But obviously, things have changed in almost 7 years and 300 episodes. Today we’ll give you an update on some of the big topics in space and astronomy. What did we know back then, and what additional stuff do we know now? The concept of this show was kicking around in our heads for years and every time we’ve wanted to get at it, we’ve both had a really hard time thinking of some of the big stories that have really changed.
Pamela: I don’t know about you but the thing that I found the most surprising that has changed is actually something that is kind of mundane. For me the biggest change was that we went from thinking that Jupiter gets hit by a giant rock from space every 500 years to every few months. That isn’t exactly the ground-breaking, lets-rewrite-the-textbook-change that people might expect in 300 episodes?
Fraser: That’s it!? That’s the big update that you’re aware of now is that Jupiter gets hit more often than…
Pamela: It’s the most surprising thing that seemed least likely to get changed that much.
Fraser: I guess we got that bit of insight into that with Comet Shoemaker-Levy 9 but since then have spotted lots of other rocks hitting Jupiter.
Pamela: Yeah, there are lots of things that we expect to be, no pun intended, earth-shattering scientific discoveries. The fact that you have a pretty good chance of catching Jupiter consuming rocks is just one of those things that I think is really kind of awesome in a subtle science kind of way.
Fraser: Okay so lets peel this like an onion: We’re going to start close to home and talk about the earth and some of the stuff that is in the earth moon system and then go outward with the concepts that are new… or new-ish. With the earth I think, this year, we got hit by meteor at Chelyabinsk and that was, I think, a surprise. It wasn’t Jupiter getting hit but we’ve been talking for years and years about the risk and the general public had their eyes opened to this possibility that rocks come from space and crash into the planet and could cause a serious loss of life.
Pamela: This is one of those things that you and I disagree on the importance of. For me it’s it’s like “Meh… we knew that was going to happen, big deal. Phil Platt wrote the book a long time ago, it’s all good.” But it was a huge news event because of the dashboard cam. I’m not sure which is more revolutionary, the dash cam or the fact that their are a lot of windows exploded in Russia. Sure, rocks fall from space and we get hit periodically.
Fraser: I think you’re exactly right, this is no surprise to us. We’ve know how big it is and how often it happens, it’s really kinda right on schedule. I think for me, I wanted to add this one to the list and you under protest, was just that it became the awareness of the whole world. Everyone started to get on that same frequency as us. Maybe we haven’t discovered something new but now it’s more of a shared human experience that we should be a little afraid of rocks coming from the sky and we should take action to prevent this as a problem.
Pamela: That’s true.
Fraser: Yeah, that’s kinda where I stand. Lets start with something new that we can both agree on and that is how much water there is…
Pamela: Yeah, world after world we have, over the past several years, slowly but surely found progressively more evidence of water from initial radar returns of the moon indicating that the south pole basins might have water. We then had Phoenix landing on Mars and digging up ice. We now have Mars Curiosity continuing to find evidence of moisture. We have Messenger and Radar returns from Mercury indicating that Mercury may have water so it’s kind of a matter of if you find something that is permanently shadowed or Mars, and thus cold, you’re going to end up finding water there. That’s just kind of awesome. It opens up whole new possibilities for how easy it’s going to be to visit places and produce fuel and hydrogen processes and eventually go and live on Mars. The moon’s water is a little hard to extract, I don’t see that becoming “Mars is a harsh mistress type, Ag stations on the moon” but it’s still an interesting future to look forward to.
Fraser: There are craters that are in permanent shadow of the moon that you could theoretically build your space colony or lunar colony on the surface of the moon and extract the water from these permanently shadowed craters. There were these missions that impacted the surface of the moon in 2009 and sprayed up water particles into space and a lot more than what they were expecting.
Pamela: Now that was kind of over-stepping it. It sprayed up a lot of dust and they did find there was a few percentage, by volume, water in that dust. It was minerals that had water as a part of the mineral composition. One thing that a lot of people start to envision is that there are frozen craters that have impact residue of comets just waiting. You scrape off the dust, scoop up a handful of ice and have drinking water. This is not the case. These are literally minerals that have water imbedded into them and it would take a lot of energy to extract them. Luckily, throwing part of a rocket into the moon is a fairly high energy event and it did allow us to detect that water.
Fraser: The amount of water on Mars is a lot more significant than anyone was expecting and both the current amount of water that is there right now but also the amount that was there in the past.
Pamela: This is one of those things that when we first started this show there were hints that maybe some of these channels that we see on Mars happen to be old river beds but people kept trying to figure out how to explain them using wind process, aeolian processes instead of liquid processes, fluvial processes. Back when we were first starting to get money to go to the lunar and planetary science conference in 2007 we were unsure. People were open to the idea that maybe it was water but today people just take for granted that these channels that we see appearing to flow out of craters are actually created by water flowing out of craters. When we see these weird craters that look like they splattered stuff all over the place, we’re like “Yeah!”. Something his frozen land, melted it, and splattered watery muddy stuff all over the place. It’s now just accepted that Mars is a world with liquids.
Fraser: The first evidence from Spirit and Opportunity was very tantalizing that we saw these minerals that would only be created in the presence of water.
Fraser: Yeah but now with Curiosity the evidence is overwhelming. You have long periods of time when there was abundant amounts of water available on the surface of Mars in a liquid form for a long period of time. The evidence is mounting that there a lot more water under the surface of the planet now. This is not like big vast rivers and oceans under the surface but like water mixed in with the regalif, down a few feet or a few meters.
Pamela: There is some sort of water table of briny water
Fraser: Yeah but that there was vast amounts of water on the planet in a liquid form for a long period of time and this is really exciting and one of the really big steps that we need to be able to find life, hopefully, with future missions.
Pamela: Mars Curiosity is happily finding those tumbled river stones and those tear drop shaped soil deposits from that flowing water. It’s straight out geology.
Fraser: I think on an interesting side note is that spacecraft last longer than anyone was expecting. We always talk about how Spirit and Opportunity were supposed to be 90 day missions.
Pamela: They were supposed to be dead before we started this show.
Fraser: They were supposed to be dead before we started this show! Spirits now dead… but Opportunity is still going. It’s dragging parts along the surface.
Pamela: It’s gimped with one wheel lifted.
Fraser: Hubble has been repaired and repaired again.
Pamela: The Cassini is another one of those missions that keeps going and going and going.
Fraser: I think that’s something that now when the engineers say “Well this is only going to work for 90 days”. Unless there is something that is going to run out in 90 days the expectation is that those missions are going to last a lot longer.
Pamela: Herschel ran out of coolant so Herschel is no more. Many other spacecrafts however just keep going and going.
Fraser: So I think one of the other big surprises is that we learned a ton about Vesta and that was big thanks to Dawn.
Pamela: This was one of those “Wow that came out of nowhere” surprises as well. This is the asteroid that we knew was somewhat interesting. It’s huge as far as asteroids go; it’s one of the top by mass and size. As we studied it from earth we were able to realize that it had some really interesting topography and rotational characteristics. It was worth visiting. Once we got there what we realized that the interesting looking crater that we saw on it’s south pole was the mother of all craters. This is a crater that when Vesta got hit, the entire asteroid crumpled. There are wrinkle ridges and it’s rotation was probably altered in the process. We also learned that there are processes that we can’t even apriori anticipate that happened. With an object as small as Vesta you wouldn’t expect to find boulders but Vesta is covered in boulders. Where are these objects coming from; why are they not getting flung out into space to become very tiny asteroids on their own. We’re having to rethink the processes of what crumble, what effect, what wrinkle, what are all the different things that you can do to an asteroid that end up producing what we see when we look at the maps that we get from Dawn.
Fraser: I think it’s great. Again seven years ago we had the best images that we had of Vesta were just these hazy radar scans of it.
Fraser Yeah, Hubble but it was nothing more than a potato, as you call it, you know, far away. But now we’ve got these images of Vesta done at like sub-meter scales. It’s amazing the amount of resolution that we are seeing Vesta with. It’s a whole other world now. Of course we’re on this line because we’ve got Vesta but we don’t have series yet as of when we’re doing episode 300.
Pamela: Come 2015 we’ll have not just series but we’ll also be getting Pluto on the Horizons mission.
Fraser: Pluto! So we know that in seven years from now we will have at least two things that we can talk about.
Pamela: I think by episode 500 we’ll be able to cover those.
Fraser: Okay cool. You mentioned Jupiter and then jumped to the head of the episode with your thoughts about Jupiter but that is really significant the fact that Jupiter is smashed a lot more often than we were ever expecting. It kind of has implications for the other planets in the solar system like Saturn or… us.
Pamela: We’re still trying to figure out if Jupiter is just the safety blanket that protects us from asteroids or if it’s presence stirs things up more than it protects us. We’re still working out all of the details. Luckily, the evidence that we’re getting hit more often than we thought for earth isn’t there. The 1 in 500 year asteroids luckily appear to be staying 1 in 500 unlike Jupiter where they are one every few months.
Fraser: I think we’ve covered the solar system a bit. Lets move out a bit to the larger Milky Way, our local environment. I’d say that one of the biggest stories for the whole of space exploration and astronomy now is the prevalence of extra-solar planets. It’s not a surprise if you had told me seven years ago…
Pamela: For you it’s not a surprise, but for many it is a surprise.
Fraser: When we started recording this show we already knew of a couple of hundred extra-solar planets and did a couple shows on them. Now the number of extra-solar planets is in the thousands and the variety is filling out our expectations but also giving us a bunch of surprises.
Pamela: Here we’d always imagine that as stars similar to the sun: starts that are high in metal content and are middle of the mass range for stars. They’re not too massive which means that they give off vast amounts of light. We thought it blew the region empty. We figured that stars that were as big as ours and not too tiny and thus wouldn’t have the mass to form planets. We figured sun-like stars probably, occasionally, most likely, had planets. What we’re finding is that really massive stars, the ones that we thought blasted their entire region empty, have planets too. Those little tiny stars we assumed there was no way they could have planets but they do as well.
Fraser: Big planets and little planets and planets that are close in and planets that are far out…
Pamela: The one thing that we seem to have gotten right is that you do have to be high metalicity. So far we haven’t found any planets in the globular clusters and we haven’t found any orbiting random very low metalicity star. You need to have the high metalicity but that means that our region of the Milky Way seems to be rife with rock or orbiting stars.
Fraser: So have we learned anything about our Supermassive black hole? I think we were still on the fence as to what percentage of galaxies have Supermassive black holes.
Pamela: I wasn’t
Fraser: You weren’t? But now it’s fairly certain that they all do?
Fraser: Alright well lets move on to something else then which is kind of even bigger, dark matter. One of our earliest ten shows were about dark matter and since that time astronomers have been working hard to figure out what dark matter is.
Pamela: We haven’t gotten that far in terms of figuring out what it actually is. We have more and more evidence that it’s not some new factor in gravity that we forgot to take into account. We already knew that from results with the bullet cluster from prior to the beginning of the show back in 2002. Since then, using a variety of different surveys, we’ve been able to start mapping the 3D distribution of dark matter. Now we understand that more or less it does trace out where the visible matter is located but there are places where it’s at a higher density than the visible matter might cause you to anticipate. There is places where it’s at a lower density than the visible might cause you to anticipate but more or less the two follow one another. It’s really neat to see these three dimensional structures of how the dark matter is clustered throughout our universe. These maps have been put together using a technique called microlensing where you look at how light from objects in a variety of different distances is twisted like going through a carnival mirror by the gravity of that dark matter. By deconvolving all the mutations that happened to the light, we are able to trace out how much dark matter is in certain areas. We still don’t know what it is but we know where it is.
Fraser: There are some really interesting experiments that are gearing up now to answer questions about what dark matter might be. I know there was a number of experiments that are being done that are trying to get to the bottom of what dark matter is. They’ve had some interesting and tentative results. I think we’re still five years too early to say we’ve got a 6 sigma detection of dark matter on what it is. I think we’re close..er.
Pamela: It’s one of the frustrating things of the detectors is that they aren’t quite there yet. This is where we were when we were with the Higgs Boson. When we started this show there were tantalizing results from the Tevatron up in the Chicago area that maybe from a lab had detected the Higgs Boson. It wasn’t enough of a detection for anyone to stand by and say “Yes we have”. We had hints and I think we’re at that same stage with dark matter. We know what’s required to detect it both in terms of detecting it in an accelerator like CERN or detecting it in a heavy water detector like Sudbury or Kamiokande or any of these other detectors that are generally used to detect neutrinos We don’t have the sensitivity yet to say for certain that we know that were looking at. It’s like looking through binoculars that are out of focus and guessing that you can see a bird on a fence post. You’re probably right but there is a chance that it’s a squirrel or just dust on your lens.
Fraser: I think there is enough resources now. Your analogy is perfect for the Higgs Boson which we’ll talk about in a second. You get these tantalizing hints which helps you narrow down what kind of equipment and experiment that you’re going to need to better accurately say yes or no to the right level of scientific certainty. You get these tantalizing hints that you’re going on the right path and then we follow up with much better and finer versions of the experiments. I think it’s right around the corner and I will bet that when we have this conversation again in five or seven years, dark matter will be feeling like it’s… we’re pretty sure we know what it is now, or at least what its characteristics are. I sort of put dark energy on the list… we don’t know anything else about it.
Pamela: No… no (laughing)… no… that’s all we know.
Fraser: Yeah it’s still there.
Pamela: It’s still there.
Fraser: Have we defined whether or not it’s increasing? Are we going to get the big rip or not?
Pamela: So as near as we can tell, and these numbers are constantly getting refined, the amount of dark energy per volume of space has been constant since the formation of the universe. It’s one of those things that should bother anyone who has ever learned about the conservation of energy. Why is it that as the volume of the universes increases the volume of dark energy per unit volume stays constant? That’s just troubling. If the universe is getting bigger then the density of dark energy per unit volume should be getting lower but it’s not so where is it coming from? Maybe it’s a Scalar field, maybe it’s this, maybe it’s that quiescence has gotten thrown in… we don’t know anything other than it’s there.
Fraser: If you want to know everything we know about dark energy feel free to go back six and a half years and listen to the episode then. It’s about the same. Lets talk about a different kind of particle which is neutrinos We’ve discovered that they can change their type.
Pamela: Yes and this is actually really good information. When I start learning astronomy everyone talked about the solar neutrino problem and how we weren’t detecting the neutrinos that we should be detecting from the sun. When I was in graduate school there was a huge debate as to whether or not neutrinos have mass. We figured out before this show started that they do have mass and the fact that they have mass opened up the possibility that the problem with solar neutrinos is that they chance identity part way to the earth from the sun. They bounce between electron neutrinos and tau neutrinos and neutron neutrinos and it turns out that it’s true. There’s been a series of three different experiments over the course of us recording these 300 different episodes. Each of those different experiments have shown neutrinos of a different flavor than what was created or a different type than what was created indicating that as they travel they are taking some of their mass and converting it to energy or taking some of their energy and converting it to mass and it changes type.
Fraser: So take our episode on neutrinos and throw it out because it’s garbage now.
Pamela: It’s not totally garbage.
Fraser: (Laughs) Right.
Pamela: We talked about the possibility of this happening but there weren’t three different experiments confirming it yet. We just had the hints of what we though reality was.
Fraser: There for a while neutrinos moved faster than light… then they didn’t. It was a mistake in the experiment
Pamela: Someone didn’t screw something in the right way.
Fraser: Lets move onto the other particle which is the big one: the Higgs Boson. We recorded an episode leading up to it. We have one called “The Large Hadron Collider and the Search for the Higgs Boson”.
Pamela: What’s kind of awesome and I think has been disconcerting to many of a journalist, is that the Higgs Boson is just pretty much what we expected. It’s a happy little boring particle that isn’t doing anything exciting, it doesn’t indicate that there is anything wrong with the standard model of physics, it doesn’t indicate that there are any supersymmetries out there and those of us that are content with the standard model, because really supersymmetry is complicated and it just seems like people are making up particles with funky names, there wasn’t any necessity for all of the particles in supersymmetry and the Higgs Boson says that there isn’t any necessity for any of that. If there is an underlying physics that is waiting to be discovered, we haven’t found it yet.
Fraser: I think one of the earliest shows that we went into, I think it was like episode four or five, was talking about the big bang and talking about what we know about the age of the universe and how it expanded and so on. We were going over and over 13.7 billion years, 13.7 billion years… turns out we were wrong!
Pamela: I was always careful to say 13.7 plus or minus .2. With those error bars I was still fine so this is why you need to use error bars.
Fraser: But 2013 at the Plank observatory he gave us the most accurate size of the universe.
Pamela: It came out with 13.82 billion. What’s kind of funny is to go back and look at all of the results from further and further years that the Wilkinson microwave anisotropy probe and then the first results coming out of Plank and the longer we looked at the universe, the older it got. It sounds obvious at the few-years level but it kept getting bigger and bigger where from 2004 it was 13.7 then 2010 it was 13.77 and then with Plank in 2013 it was 13.82. Along the way we’ve also gained barionic matter so the amount of normal stuff of atoms and photons and electrons and all of the normal stuff that we’re used to dealing with has gone from an estimated 4% to an estimated 4.9% of the universe.
Fraser: So we’re still a solid number three?
Fraser: After 27% dark matter and 68% dark energy
Pamela: And the amount of dark energy has gone down from 72% to 68.3%
Fraser: Not that the amount of dark energy has dropped since we’ve started recording this show just that the accurate measurement of what it is and what it’s always been is…
Pamela: We better understand it.
Fraser: Yeah, well I’ve got one last little sort of speculative thing. What would be some big discoveries of some big announcements; some big announcements that allow us to overturn some other shows. For example: Lets say, although Curiosity isn’t equipped to, it finds evidence of life on Mars.
Pamela: Curiosity can find fossils but I can’t imagine that life has had enough time to create something that would create fossils.
Fraser: Yeah I’m saying that if the search for extraterrestrial intelligence turned up as a signal then we could add to the things that we now know. There is life on Mars; things we now know, there are aliens in space; things we now know, we now understand what dark matter is or what dark energy is. What is some other stuff that one good experiment or one good result would give us some big answers?
Pamela: It’s hard to imagine what amazing result would overthrow things because those are the things that usually come out of left field. The discovery of dark energy is something that no one could have anticipated. It was one of those factors that we all learned about and then disregarded and set to zero. Now dark energy is there. Lamda has a value. Have to redo all of the equations and all of the textbooks. I think if we found life it would be a “Yes, we anticipated that sort of thing now-a-days”. I find it hard to imagine given how closely we’ve considered the probabilities of different things happen, what would be that real rewrite-all-of-the-text-books-throughout-everything-you-know kind of discovery.
Fraser: What is something that maybe you’re waiting for more confirmation. It feels in your heart that it’s probably true but we’re just waiting for a little more confirmation.
Pamela: I think the one thing that we don’t know yet is what is the prevalence of life forming where there is liquids. We have the opportunity should we ever get ourselves to Europa, Titan we can look there, Mars we can look there. So many moons around Jupiter and Saturn have liquid water. We believe that under their surface or trapped in cavities there is water. If we can start finding life on multiple worlds it would tell us that it’s easy for life to be created but if we don’t find it anywhere it means that it’s probably hard. This starts to answer questions about the final issues we don’t know anything about with the Drake equation. It still doesn’t tell us how long the civilizations usually live. It still doesn’t answer the Firmy paradox but at least it gets us to know if life is common or if life is rare and that’s something that we know nothing about.
Fraser: Well happy 300 Pamela.
Pamela: Happy 300 to you too.
Fraser: Here’s to 300 more.
Fraser: Thank you
Pamela: Thank you
This transcript is not an exact match to the audio file. It has been edited for clarity.