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March 04 2019

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The dawn of a new era in human spaceflight
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Ep. 521: The Deep Space Network

We always focus on the missions, but there’s an important glue that holds the whole system together. The Deep Space Network. Today we’re going to talk about how this system works and how it communicates with all the spacecraft out there in the Solar System.

In this episode we mentioned donations and tours. Click to learn more!

Download MP3| Download Raw Show with Q&A| Show Notes | Jump to Transcript or Download

This episode is sponsored by: Barkbox

Show Notes

Deep Space Network – 3 facilities
Goldstone Deep Space Communications Complex
(Official site for Goldstone)
Madrid Deep Space Communications Complex
(Official Site for Madrid DSC)
Canberra Deep Space Communication Complex (CDSCC)
(Official site for CDSCC)

Operations Control Center at JPL

NASA Eyes website – see DSN’s current communication targets live


Announcer: This episode is brought to you by BarkBox. For a free extra month of BarkBox, visit BarkBox.com/astronomy when you subscribe to a six or 12-month plan.

Fraser: Astronomy Cast, Episode 521: The Deep Space Network. Welcome to Astronomy Cast, a weekly facts-based journey though the cosmos where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain, publisher of Universe Today. With me, as always, is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hey, Pamela, how you doing?

Pamela: I’m doing well. How are you doing, Fraser?

Fraser: Great. Sorry, everyone. We are recording this episode live at a different time, and that’s because I wasn’t here on Friday, and that’s because I was in Costa Rica with my good friend Dr. Paul Sutter on our next Astro Tour. I’m not even gonna remember which number this is now. I think it’s No. 4, but this was amazing. We were in Costa Rica, we got a chance to see the Arenal Volcano, got to do river cruises, lake cruises – well, one of each so not “s”. We saw many different kinds of monkeys.

Probably my highlight was the hummingbird forest or hummingbird preserve where they set up, I don’t know, 40 hummingbird feeders, and there was probably 100 hummingbirds, like 10 different kinds of hummingbirds up in the cloud forest. It was absolutely amazing. We had a great time. Thanks everyone who joined us.

And we recorded an episode all about dust, which I think is a topic we haven’t covered too much. So, dust and how that led to the BICEP2 results being overturned, so it’s sort of a fascinating story. And Paul was on the Planck team that helped overturn the results, so he had an inside scoop on the whole story. So, we’re gonna put this in as a bonus episode at some point this week or early next week. All right, Pamela, I don’t know if you had anything to say? Should we just go right into the show?

Pamela: Well, I mean, if you wanna join us on future Astro Tours, check out astrotours.co, and you can join me in the future. I’m gonna be going along with Fraser, and we are going to be doing in June a Joshua Tree National Park trip. This is the All-Stars trip with us, Paul Matt Sutter, John Godier, Skylias. It’s kinda gonna be amazing. So, if you looked before at the price and went, “Oh, no, can’t,” well, look again because the prices went down, and we’re really hoping that you can join us out under the dark skies.

Fraser: So, the price has been reduced, so go back to astrotours.co, and then just go to the All-Stars Party, and you can see the new price. The reservation date has been pushed back a couple of weeks. You’ve still got a couple more weeks to make a decision on that, so definitely go and check that out. All right, let’s get into the show. So, we always focus on the missions, but there is an important glue that holds the whole system together, the deep space network. Today, we’re gonna talk about how the system works and how it communicates with all the spacecraft out there in the solar system.

All right, Pamela, it is a big oversight. I know some people will spend some time talking about the Deep Space Network, but I don’t think people really think about how we are getting all of this data from all of these missions back on earth at different distances, some of them are in different locations. What is the mechanism? And that’s the Deep Space Network. So, what is it?

Pamela: It is three different sites on the planet Earth that are distributed from east to west here in the United States: out in Goldstone in California, or near Goldstone – Goldstone is actually a ghost town that now I really wanna go to after prepping for this show – outside Canberra in Australia, and outside of Madrid in Spain.

These three different locations, the way they’re spread out from east to west mean that once you’re located high enough above the planet Earth, you are always within sight of one of these three facilities, each of which is built kind of within a natural bowl in a valley between various mountains. This protects the telescopes from all the radio noise that you can get here on the surface of the planet, allowing them to focus on everything out there somewhere.

Fraser: All right, so you’ve got three facilities at essentially three different portions on the globe so that at least two or one is always being able to see the entire sky so that all spacecraft can always be communicated with. What are the actual facilities like? What are they?

Pamela: Well, they are each a set of different telescopes. This is one of the things that I think gets missed in the story a lot. It’s not like there is the Goldstone telescope. Well, there is the Goldstone, but Deep Space Network at Goldstone is actually a suite of a bunch of different telescopes. Madrid is a suite of a bunch of different telescopes. And each of these different facilities has one 34-meter telescope, has two or more – let me start that over. Each of these facilities has one 34-meter high-efficiency antenna, so this is the “hey, I got you, we’re listening close right now”. There’s also two or more 34-meter beam waveguide antennas, there’s some 26-meter dishes, and one 70-meter antenna per facility.

And it’s these 70-meters that we’re used to seeing in the pictures. They’re big, they’re dramatic. Goldstone, in addition to being used to receive sound, is also used to – well, it’s also a radar dish, and so there is the occasional death to things like bees when they’re igniting the radar on it to not just catch the radar signals but measure precisely where all of this stuff is in space.

Fraser: So, at each facility, there is the collection of telescopes, and the big one is the 70-meter telescope, and then there are these other ones as well. And people always make this joke to me when we talk about how we’re able to still communicate with the Voyagers and New Horizons, and they’re so far away. “Oh, we can communicate with a satellite that’s billions of kilometers away, but I can’t receive a cell phone signal.” If you were willing to care a 70-meter telescope in your pocket, you would always be able to get a cell phone signal. That would be no problem.

Pamela: Unless you were, of course, one of these 70-meter telescopes because they’re in radio quiet zones. So, there’s a certain irony. They way they’re set up, they are good for everything that is 30,000 kilometers and higher above the surface of the earth, but you start getting lower down, and the shape of the planet, the mountains that surround them, all of these different things serve to isolate them from signals. So, this is where the deep space and the Deep Space Network comes from is, well, you have to be high enough above the surface of the planet to make sure you’re always within sight of one of these different dishes.

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Fraser: All right, and so then how does operationally, how does this actually work?

Pamela: It’s all controlled out of the Jet Propulsion Lab out in Pasadena, California. This is a NASA facility that is owned and operated by Caltech. It actually had its roots as an Air Force facility back before 1958, got transferred over to NASA with the beginning of, well, Mercury and all of those humans going into space, and it was set up as a way to get signals back from the Mariner missions to get signals back from all of these early missions in the 1950s. Now, with Explorer, it wasn’t all that formalized.

It was more a matter of we’re gonna send these facilities out, we’re gonna have mobile radio receivers out in places like middle-of-nowhere Nigeria. Nigeria isn’t in the middle of nowhere, but where they went sure was. And this combination of distributing human beings around the world with radio dishes meant that we could distribute spacecraft around the solar system and get the signals back to Earth. Unfortunately, planetary rotation does mean you have to distribute things around, and as we launched more and more facilities, it became clear that we needed to have a permanent facility here on the planet Earth dedicated to listening to what was going on out there.

Now, in the 1960s when this was really starting to pick up steam, we had the 1966 version of this which included Goldstone, which has always been included in the network. Then we also had Woomera, Australia, Canberra, Australia where we still have locations. At that point, we included Johannesburg, South Africa as well as Madrid, Spain, and then of course we had launch support out of Cape Canaveral and the Ascension Islands.

Over the years, the facilities have become fewer in number but more and more important in what they’re able to do, and they’ve added more and more dishes that increase their capacity. And at this point, we are in the numbers in the 60s where they have numbered each successive dish as they have continued to upgrade the systems at the various locations. And so, out in Goldstone, we have Nos. 11-14 in ‘74, but today, if you go to Deep Space Network now, you’re gonna find, well, those numbers aren’t entirely the same as dishes have been replaced and upgraded.

Fraser: If you actually go – I mean, this is one of the best things that you can do – go to…it’s eyes.nasa.gov/dsn, and then go to the Deep Space Network Now. And so, just as an example, at the time that we’re recording right now, out at Madrid, the big dish is talking to the Mars Reconnaissance Orbiter, and the next dish is also talking to MRO, and then one is talking to ACE – I’m not sure which that is – the Advanced Composition Explorer, and then the other one is talking to OSIRIS-Rex. Our of Goldstone, one is talking to STEREO A, another is talking to the Geotail, one is talking to Juno, and one is talking to Hayabusa-2.

In Canberra, the big telescope is offline right now, but one of them is talking to Voyager 2, one is talking to Juno, and the other is talking to Voyager 2. So, you can just see. Go to Deep Space Network Now, and you can see exactly which dishes are talking to which spacecraft, how long it takes for the information to get, and this is what I love. For example, Voyager 2, it takes 1.39 days for the light to get to and from Voyager 2 because of its distance into the solar system. Just an amazing technical accomplishment. And you can see why the amount of data it can get is so low because they’re so far.

Pamela: And as we’re starting to get more and more of these small space probes out at great and greater distances, some of which count as no longer in our solar system, we’re also having to expand how the network works. And one of the things that they’re working on doing now is increasing the way the dishes work so that they can array them together and get multiple individual dishes working as an array to all listen in on the same signal. And this ability to combine dishes has been used before. There were issues with the Galileo probe when it was out at Jupiter where it just didn’t have a high-gain antenna that worked the way it was supposed to.

And so, they had to use, well, more resources than were originally planned to get what data they could back down to earth. And at various points throughout history, when there have been issues with spacecraft, they have combined multiple telescopes, they’ve brought in additional telescopes, sometimes using the Parkes telescope in Australia, so that they can catch these weaker signals to rescue spacecraft that just might need an extra hand up.

Fraser: Now, I mean, radio waves are one of those few wavelengths where you can actually quite easily in real-time or even after the fact combine the data signals together, so are they using interferometry –

Pamela: They are.

Fraser: – to combine the signals? And then I’m sure many of these dishes were brought in for the Event Horizon Telescope where they turn the entire planet into one big telescope to be able to observe the supermassive black hole at the heart of the Milky Way. So, I didn’t know that they used that method to be able to get some of those weaker signals as necessary. That’s really interesting.

Pamela: And what’s interesting is there are a lot of assumptions that get made about how these different telescopes get used and where they do and don’t get used. I’ve heard quite often, and I suspect we’ve even screwed up and said it before here on this show that Arecibo gets used as part of the Deep Space Network, and it does not. The Deep Space Network is specifically these Goldstone, Madrid, and Canberra facilities, and where the confusion comes in is Goldstone has other dishes that are used for other things. It uses its large dish also for radar work, and Goldstone and Arecibo work together as radar facilities to help us measure asteroids and other objects as needed.

And there’s a few other radar dishes out there: Haystack Observatory in Massachusetts, there’s facilities out in the U.K., so we have other radar dishes around the world. But it’s this combination of Arecibo and Goldstone are two of our main radar dishes, and Goldstone is also part of the Deep Space Network that leads to some of these confusions. In general, this is a facility that is quite happy to sit there going, “We shall listen to spacecraft and leave science to all those other dishes out there.”

Fraser: And so, I can sort of imagine that in some cases, all the spacecraft are out there, and they’re gathering up all of their science, and then they’re waiting for their turn to transmit the signals home. And so, we would probably get more science from these spacecraft if we had more facilities. Is it like the more mission you have, the more capacity you need in the network? Are one of these behind one of the other?

Pamela: With the Space Flight Operations Facility that they’ve built out at JPL, they do a lot of cue systems where they’re like, “Okay, so this spacecraft is here in this orbit. It will be visible to the earth at this point, so we schedule it now.” And so, there’s a lot of careful choreography that goes into getting signals back to Earth. We also are starting to find that radio systems are cheap enough to build and are efficient enough to build that some places like the advanced physics laboratory out on the East Coast at Johns Hopkins University, they’re in some cases building their own receivers.

We also see that some of the European Space Agency facilities have their own radio receivers. And with the ability of smaller institutions to get all of their data down for themselves, it’s this balancing of, yes, the Deep Space Network does need to build more telescopes that it can use to receive the signals from these distant space probes, but at the same time, some of these space probes can also just send their messages straight back to their principle investigator’s institution.

And the Deep Space Network isn’t for all the lower Earth orbit stuff. It’s only for the more distant objects, and that frees up the network as well when it doesn’t have to listen to things like Discover as it – well, Discovers are on planet Earth.

Fraser: So, I mean, do you think that we’re at a point where bigger telescopes are gonna be necessary? More telescopes? Or do you feel like we’re at a point where – I mean, it’s interesting to see how the Europeans have their own version of this. I’m sure the Russians have their ability to communicate with all of their spacecraft, and yet when needed, I know you get these – sometimes you’ll see this in press releases where some really interesting thing is happening at a time when, say, the European network isn’t gonna be able to see it, and so NASA will pitch in.

As I mentioned, right now, the Deep Space Network is observing the Hayabusa mission, so you can see that they’re getting involved. So, I mean, do we see this collaboration between the different nations coming together to be able to help each other out as scientists?

Pamela: There is definitely a great deal of collaboration that goes on. This is part of the treaties in many cases between the different nations where there are trades for getting instruments to fly in spacecrafts, getting time on the Deep Space Network, getting data. All of these different things can be traded with no-cost agreements where the U.S. will provide something that they pay for on their side and get something that isn’t money in exchange that has real value for us. So, when we look to missions like Hayabusa, yes, they totally use the Deep Space Network. SpaceIL is going to be using the Deep Space Network with their little Beresheet lander when it gets to the moon.

And all of these different agreements work together to get more science done. Now, one of the interesting things to me in terms of how do we choose to expand the Deep Space Network to meet the coming needs of the future. We have two things happening simultaneously. One is the miniaturization of the transmitters that are going on spacecraft where we’re capable to more effectively send back signals than we could in the past, and we can send back tighter signals than we could in the earliest spacecraft. And on the earth, that same miniaturization is making our systems more and more sensitive.

So, as we’re able to essentially shout into the void more effectively with all of our spacecraft, we are also able to more effectively listen in from the surface of the planet. As this trade-off continues, yes, we’re going to continue to need these large dishes, but how do we choose to expand? And it looks like the answer is going to be building arrays of dishes instead of building the large single dishes that we built in the past.

Fraser: And that was sort of my next question was do we need a bigger dish? But it sounds like that’s not the plan. The plan is more but smaller.

Pamela: And the other thing that we haven’t figured out that’s definitely going to affect long-term planning is what is the role of CubeSats going to be because a CubeSat by its nature is not going to be able to have a massive power source and a massive high-gain antenna to send data back to the earth. And if we move to building more and more CubeSats like the ones that we sent to Mars alongside the InSight lander, that may necessitate changing how we think about the Deep Space Network.

Fraser: It’s interesting as well, I mean, even just the name, right? Deep Space Network, you imagine that it is this network out in the solar system of all of these spacecraft that are sending all these communications back and forth, but it’s all just here on Earth. The point is that it’s communicating with space, with stuff that’s out deep in space, and as you mentioned, not orbiting close to the earth, but out, the missions that are out exploring the solar system. But if we did wanna take it to that next level and actually expand the infrastructure off Earth, what would you wanna do?

Pamela: So, the irony of expanding the Deep Space Network off Earth –

Fraser: Into space.

Pamela: – is then you have to have all of the receivers on Earth to receive the signal from the Deep Space Network that you’ve now put into space. So, there’s a certain level of irony involved in that, which tells me, “Let’s not do that.” I think what we need in order to expand the capacity of the Deep Space Network is I’d like to see more redundancy in sites, more redundancy in the receivers that we’re using.

One of the issues that we have today is if you need to do maintenance on one of the receivers, if you wanna upgrade one of your receivers, you have to take it offline, which means that there can be gaps in coverage for some of those space probes that are out there that require specific of the receivers here on Earth. So, greater redundancy and greater coverage. You never know when the weather is going to strike, the world is going to rumble, something’s going to happen that knocks one of these facilities offline. So, for me, it’s all about the redundancy and keeping it on Earth to in this one case reduce the irony.

Fraser: Now, we talked briefly about some of the science that gets done using these facilities, but I wanted to sort of talk a bit about what kinds of projects can you use this, when you’re not just communicating to spacecraft and you’re actually using these dishes for astronomical science. What are some projects that they’ve gotten involved in?

Pamela: Well, as I mentioned, the Goldstone also has the capacity to be a radar. This means that when asteroids get close enough to the planet Earth, we are capable of using radar to determine their shapes. Essentially, you blast them with light, and where there’s a hollow on the asteroid, it takes longer for that light to bounce back to earth. Where there’s a hill, it gets back a little bit faster. And this is one of the cooler uses.

Now, in addition to this, they can also of course be used to listen to the radio waves that are coming from objects near and far, whether it be listening to Jupiter and the interactions of its magnetic field, and the lightening, and all the fabulous other things that generate radio signals from Jupiter. That’s one possibility. You can also listen to active galactic nuclei in many cases. These accretion discs around supermassive black holes are giving off radio light. Their jets are giving off radio light. Young stars, T Tauri stars, have radio emissions.

All of these different sources that give off light in these longer wavelengths that are identical to the ones that your radio picks up, and much longer – much, much longer – as well, all of these longer wavelengths are things that these facilities have the capacity to study. And of course, there’s always that capacity that we don’t use all that often to go searching for extraterrestrial intelligence.

Fraser: Was that you setting up for us to search for extraterrestrial intelligence?

Pamela: No, that’s just me setting up to prevent all of the emails of “but you didn’t say…”

Fraser: They would be wonderful tools for searching for extraterrestrial intelligence, but they’re busy, and very rarely are they ever called on to do that, and that’s why you’ve got the private antenna like the Allen Array and things like that and the SETI Institute. People don’t, I think, realize. I mean, using these big radio telescopes for searching for aliens is a no-no. The SETI Institute uses private funding and their own private radio telescope network –

Pamela: The Allen Telescope Array.

Fraser: – the Allen Telescope Array to be able to do their own searches. And I think occasionally, like a couple of times, they’ve transmitted signals out into space to let the aliens know that we’re here.

Pamela: And that’s the Deep Space Communications Network, just to be confusing when you google. So, Deep Space Network, DSN, is how we listen to spacecraft and sometimes radar image asteroids. The Deep Space Communications Network is completely separate, and that is how we send signals potentially to other life in the solar system and beyond.

Fraser: And we won’t get into the argument on whether that’s a good idea or not.

Pamela: It’s true.

Fraser: Cool. Well, that’s awesome. I’m excited. I’m really glad we covered this topic because it is literally like if this system wasn’t functioning, none of the other science would be getting back to Earth. It is the bedrock that all of the stuff requires.

And you just watch the Deep Space Network Now and just watch who’s communicating, and your brain starts to understand a little bit more about just where the spacecraft are in the solar – this orientation, which I think we lose sight of that the earth is spinning, and the spacecraft are out there in the solar system, and they’re moving around, and there are times when you can communicate with things and times when you can’t, and I love to be able to do that. So, thanks for going into this topic.

Pamela: Well, and thank you for being here and thank you, audience, for being here. And before we end, I just wanna take a brief –

Fraser: You remembered.

Pamela: I did remember.

Fraser: That’s awesome.

Pamela: I just wanna take a moment to thank some of our Patreons. We thank patrons right here on air, and if you want to hear your name read out and know how grateful I am for everything that you do that lets me pay Susie –

Fraser: Before you read the names, can I just give one quick explanation why this is important?

Pamela: Yeah.

Fraser: When you look at what’s happening on the internet today, various people are trying to figure out business models to be able to operate what they do. You’re seeing either really awful advertising or people gathering up your information on your cellular phone and then selling it, selling your personal privacy information. You’re seeing paywalls going up which are block people’s access to be able to get information. And so, what are the options for us as content creators? We want our information to be an educational resource that can get out there and be available to as many people as humanly possible.

We don’t wanna block the information, but at the same time, as you mentioned, Pamela, we wanna be able to pay Susie, our editor, we wanna be able to cover our hosting cost, we wanna be able to pay for service. Still, to this day, I think you and I are still doing this on a volunteer basis, and that is because we’ve chosen getting the content out there over us being able to put it behind some kind of paywall and do it. So, Patreon is the solution that allows a small group of people to be able to fund what gets done so that the largest possible group of people can receive the podcast without having to put it behind a paywall and without having to put a mountain of advertising on it over top of it.

And as we can move towards it being more of a Patreon-covered model, then you move into, I think, this beautiful future world where a small group of fans help allow a piece of content to exist, to be available to a larger group of fans, and it is a beautiful system, and we’re in this uncomfortable in-between times where we have to have advertising or people have to start putting things behind paywalls. So, I think it’s just important. Even not just in generally specifically for this podcast but for any content that you enjoy where you’ve got a much smaller, more intimate relationship with the creators who make this kind of thing.

You can support their work directly, and it doesn’t take a lot of people to be able to make the content that you love available forever across all of the platforms and not have to put it behind paywalls and stuff. So, again, just wherever you are, if there’s things that you enjoy, consider supporting them directly, and, of course, consider supporting what I do on Universe Today, and what we do here with Astronomy Cast, and what Pamela does as well. So, that done, thanks to…

Pamela: Thanks to John Jorst, Jordan Young, Burry Gowen, Ramji Anatmatu, Andrew Polestra, David Trogue, Brian Kegel, The Giant Nothing, Laura Kettleson, Robert Polazma, and Emily Patterson. And there will be more names next week. Thank you all so much for being here.

Fraser: All right. And thanks, Pamela, for bringing the brain. We’ll see you next week.

Pamela: Bye-bye, everyone.

Announcer: Thank you for listening to Astronomy Cast, a nonprofit resource provided by the Planetary Science Institute, Fraser Cain, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at Astronomy Cast. You can email us at info@astronomycast.com, tweet us @AstronomyCast, like us on Facebook, and watch us on YouTube. We record our show live on YouTube every Friday at 3:00 p.m. Eastern, 12:00 p.m. Pacific, or 19:00 UTC. Our intro music was provided by David Joseph Wesley, the outro music is by Travis Searle, and the show was edited by Susie Murph.

[End of Audio]

Duration: 34 minutes

Download MP3| Download Raw Show with Q&A| Show Notes | Jump to Transcript or Download

March 02 2019

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March 01 2019

SpaceX CCtCap Demo Mission 1

Liftoff currently scheduled for 2019-03-02 07:49 UTC

SpaceX is targeting Saturday, March 2 for launch of Crew Dragon’s first demonstration mission from Launch Complex 39A (LC-39A) at NASA’s Kennedy Space Center in Florida. This test flight without crew on board the spacecraft is intended to demonstrate SpaceX’s capabilities to safely and reliably fly astronauts to and from the International Space Station as part of NASA’s Commercial Crew Program. [press kit]
Good Luck, everyone!
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Ep. 520: Transients: What They Are and Why They Matter, Part 2

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This is our second episode in a two part series where we look at Transients in astronomy. In last week’s episode, we talked about things that change here in our own Solar System. Now we’ll talk about everything else in the Milky Way and beyond.In this episode we mentioned donations and tours. Click to learn more!

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This episode is sponsored by: 8th Light

Show Notes

Transient astronomical object
dwarf nova outbursts
gamma-ray bursts
tidal disruption events
gravitational microlensing
variable stars


Pamela: This episode of Astronomy cast is brought to you by 8th Light, Inc. 8th Light is an agile software development company. They craft beautiful applications that are durable and reliable. 8th Light provides disciplined software leadership on demand and shares its expertise to make your project better. For more information, visit them online at www.8thlight.com. Just remember, that’s www.8thlight.com. Drop them a note. 8th Light: software is their craft.

Fraser: Astronomy Cast, Episode 520: Transients, Part 2. Welcome to Astronomy Cast, your weekly facts-based journey through the cosmos where we help you understand not only what we know but how we know what we know. I’m Fraser Cain, publisher of Universe Today. With me, as always, is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hey, Pamela, how you doing?

Pamela: I’m doing well. How are you doing, Fraser?

Fraser: Great. For the people who are listening to this show, it’s been a week. For us, it’s been about five minutes. That’s because –

Pamela: Not even that long.

Fraser: Not even since we wrapped up recording our last show to when we’re doing this show because I’m gonna be gone next week, and so, in fact, probably when you’re listening to this, I will be in Costa Rica with Dr. Paul Sutter will be as part of our Astro Tour as we explore the jungles, and beaches, and mountains, and volcanoes, and the dark skies of Costa Rica. And if you wanna be a part of any of these kinds of trips, go to astrotours.co. Pamela’s gonna be taking you to the American Southwest. It’s possible that I’m gonna be going back to Iceland at some point, so there’s a lot of really interesting trips coming up, so check it out.

Pamela: And I hope to see you in Tucson and Vegas.

Fraser: Excellent. All right, this is our second episode in a two-part series where we look at transients in astronomy. Last week’s episode, we talked about the things that change here in our solar system. Now, we’ll talk about everything else in the Milky Way and beyond. All right, Pamela, when last we saw our heroes, we were talking about asteroids, and comets, and things crashing into the moon, and things crashing into Jupiter, and potential extrasolar comets blasting through the solar system. But this idea of transients, the fact that the universe changes, extends out way beyond the solar system – all the way out.

Pamela: It is true, it is true, and the techniques that we use to observe transient phenomena don’t really change, but how they move through our images, how they vary in our images does change from inside our solar system to outside our solar system. Let’s face it, things inside our solar system, it’s a lot easier to see them moving, and so the fact that an asteroid is flying by the earth, that makes it a transient phenomenon. Now, as we look out at the sky, the fact that Barnard’s Star is creeping across the sky at a measurable rate does not make it a transient object. That just makes it an object that has a large motion. Now –

Fraser: Well, and that’s astrometry. I mean, that’s a whole other super fascinating science, and thanks to Gaia, we now know where a billion of these stars are moving, but yeah, it’s things that move, or flash, or change more rapidly than that ponderous movement of Barnard’s Star.

Pamela: And it’s the kind of thing that a lot of people don’t realize is going on. One of my favorite moments of “Oh. Oh, dear, that doesn’t work the way you think it does” was reading a Keats poem where he referenced wanting a love as constant as the stars. And stars are anything but constant, and –

Fraser: Oh, Keats.

Pamela: – they sometimes explode, and I don’t want that kind of love, thank you very much. Please keep mine as constant as a rock.

Fraser: Sometimes they change in brightness, and sometimes they explode just like real relationships. And they’re all moving.

Pamela: Yeah, yeah, but it doesn’t mean you want that.

Fraser: And eventually, they end up in a black hole.

Pamela: So, Keats was so wrong in what he thought he was gonna get, and in considering that, let’s consider all the things that go flash, flare, and flicker in the night, and one of the things that came up in our last episode was how our own sun likes to do things like fling coronal mass ejections out at us. And it turns out that while our sun from our perspective does throw some pretty amazing temper tantrums that lead to some pretty spectacular aurora borealis, it turns out that it has nothing on some of the other stars scattered out among our galaxy. There are young protostars that put out flare events that are 10,000 times more energetic.

Fraser: Hundred thousand times. Some of the flare stars can go 100,000 times brighter than the most powerful flares that our sun throws out. Tiny, little red dwarf stars. It’s crazy.

Pamela: And there are some stars that are known to do this more often than others. They get classified as flare stars. But this is definitely one of those cases of having to get lucky when doing your research because there is a chance, a non-zero chance that every single time you go to the telescope and look at a star, it’s just gonna be going, “Hi, I’m a star.” And what you really are interested in is that moment it goes, “Hi, I’m going to destroy my entire solar system with a flare right now.”

Fraser: Again.

Pamela: And those are the scientifically interesting moments. And so, the trick is how do you catch all those moments?

Fraser: Well, you just asked yourself my next question. How do you catch all of those moments?

Pamela: Well, in the future, it’s gonna be with the Large Synoptic Survey Telescope, at least for the part of the sky that it can see. For now, we have a variety of different surveys scattered all over the world looking at different parts of the sky that are night after night working to observe as much of the visible sky as they can and comparing the measurements of brightness from one night to the next to identify those things that have outbursted in their own unique way. So, we have flare stars. That’s one way. Those are often young stars, hot stars, energetic stars. B-type stars like to flare in some cases.

And all of these hyperenergetic young stars, angry stars, they aren’t at least blowing themselves apart. We also have cases where we don’t know which star it’s going to be, we don’t know when it’s going to be, but let’s face it, supernovae are another kind of transient event. They are that star that explodes once rather than flaring over and over and over.

Fraser: I did an episode on habitability around red dwarf stars, and we looked into these flares that happen. And, yeah, the 100,000 times the amount of radiation would cook any life, and these planets are much closer to their star than we have here, so you can’t comprehend the amount of energy that is being dished out to one of these planets and that some of these stars flare every day. It’s crazy how different these places are than the sun, but as you said, there are other ones that will flare. Now, you went straight to things exploding, but there’s an in-between stage, so –

Pamela: Well, there’s lots on in-between stages.

Fraser: Lots of in-between stages. So, why don’t we talk about novae first, and then we’ll go full supernovae next.

Pamela: So, we have basically the life and death of stars is one of change. Baby stars like to go flare a lot, middle-aged stars pulsate. That’s not so much as a transient event. It is a change in brightness.

Fraser: I guess we should talk about mere variables.

Pamela: So, we have all the pulsating variables, the Cepheids, the RR Lyraes, the Mira variables. We have the random –

Fraser: Actually, you know what, I’m gonna stop you because what’s actually happening with some of those different kinds of variable stars is mind blowing. If you could actually see them up close, what’s actually happening to these stars is just tremendous. So, instead of just naming them like it’s some kind of library catalog, could you just take a second and talk about – I mean, we did a whole episode on those variable stars, but just to give people the sense of some of the most dramatic versions of this.

Pamela: So, stars are very carefully balanced between gravity trying to collapse them in and light trying to push out and expand them. And a star like our own sun is for the most part nice and completely stable in radius. It has various harmonics built up on its surface, various soundwaves are moving through us out our atmosphere, and so it has these little small-scale pulsations from place to place. No big deal. It’s a star. It’s doing a star-like thing.

Well, at certain points in stars’ evolution, as they very gradually change in density, temperature, and radius, they can hit a point where as the light goes out, the temperature is such that instead of pushing outwards on the star that light starts getting absorbed into the gas in the outer layers of the star, and so the star’s like, “Ooh, not getting supported as much as I’d like. Gonna collapse now.” And as it collapses, it gets brighter, it gets brighter, it gets brighter, and that energy that is stored in the atmosphere also gets given off, and all of this gives the star an extra push expanding it outward.

And so, a star will hit a resonance point where it is collapsing down and pulsating out, driven by energy getting stored in the gas and its outer atmosphere. This sets up long-term pulsations that can last millions of years and elder stars, the RR Lyraes I mentioned, are small ones that pulsate over a period of hours. Cepheids are larger ones that pulsate over periods of days or tens of days. And when I say pulsate, I mean they’re actually changing radically in radius, in color, in brightness such that we can see stars in other galaxies undergoing these kinds of pulsations.

Fraser: Just amazing. Can you imagine what it would be like to be on a planet around one of these stars and seeing the outer envelope of this star expand over the course of hours to a dramatically larger size and then again over the course of hours shrinking back down into a much smaller size and changing in brightness? It’s one of those things – people always ask me, “What’s a thing that you wish you could see up close?” and I wouldn’t wanna be too close, but I would love to see one of these variable stars doing its thing from a safe distance.

Pamela: I know. I haven’t done it before, and I should’ve. I now really wanna work out the change in energy received by a planet that is on average at the center of a habitable zone for one of these stars and see does it go in and out of the habitable zone at the extremes. This is math I can do, and I now want to do.

Fraser: Great.

Pamela: Oh, man, you’re giving me ideas.

Fraser: Nice. There you go. And then it’ll turn into a science fiction story. Now, I was about to get you talking about novae, and then I side-turned into variable stars. Let’s go back to novae now, which are the next level of flashes of brightness.

Pamela: So, there are a whole variety of different novae that recur at varying levels. There are some novae that we see that repeat like clockwork. These are ones where you have a situation with a white dwarf star, a star roughly the mass of the sun that is compressed down to roughly the size of the moon and is no longer generating its own light through nuclear processes. It’s just radiating away the heat that it has stored from when it was a star. And if one of these is in a binary system, and it decays to get close enough to its neighbor, it can become a cannibal and begin stripping material off of that neighbor.

And as that material spirals in towards the white dwarf forming an accretion disc, that disc of material can periodically get large enough in mass that it just blows itself apart. So, in this case, you have recurrent novae that are driven by, well, cannibalism of one star off of another. We also have cases where it’s unclear do these things recur consistently or not and various levels of do they recur consistently or not where you have, again, a white dwarf cannibalizing its neighbor where it pulls down the material, and the material on its surface goes kaboom, clearing off the surface, clearing out the accretion disc.

It’s a little bit more violent, and each of these kinds of situations has distinct spectra, has distinct patterns. You can actually look at some of these stars from night to night and see the variations in brightness as that hot disc of material moves around and is viewed at different viewing angles. These are fascinating systems that change in brightness because they are binary stars, because there is this hot disc giving off its own light, because this disc may explode occasionally, and because stuff that lands on the surface of the star may explode occasionally. There is a lot of explodiness going on in this system that finds all sorts of different ways to have transient light in the sky.

Fraser: And actually, we just did an article on Universe Today again about a nova that’s been going off every year like clockwork for millions of years. So, it’s this process where it’s pulling this material off of a companion star, accreting it onto the surface, it builds up to a certain size, it detonates like a bomb off the surface of the white dwarf, and then the whole process starts again. It clears out the material, and then it starts again. And it’s been building this gigantic gas – this sort of shell of dust and gas around the star from millions of these nova explosions. But for each one of these white dwarves, there will be the final explosion.

Pamela: So, that material funneling down onto the surface of the star doesn’t always get politely cleared off through explosions. Sometimes it just gradually builds up, and builds up, and builds up until the total mass of the white dwarf exceeds essentially the supporting power of the electron degenerate pressure that is holding the star together. So, in these systems, it’s not like pushing out and gravity pushing in that is supporting the star so that it doesn’t collapse down into a black hole. Instead, it’s all of the electrons in the atoms of the white dwarf that are going, “Don’t come near me,” and –

Fraser: “It’s my space.”

Pamela: Yeah. It’s the electron degeneracy pressure of all of these electrons trying to abide by the Pauli exclusion principle and all maintaining their own energy levels, spin up, spin down, not gonna break any rules. Well, at a certain point, they just don’t have the capacity to push one another apart, and through this electron degeneracy pressure support the star any longer. And when that pressure, when that electron degeneracy pressure gets overwhelmed, everything goes kaboom, and this is when you get a Type Ia supernova.

Fraser: And this is just one example of a supernova. There’s the ones where you have a big, young hot star – and of course, we’ve done whole episodes of this – and they detonate, or they are left with a black hole, or they’re left with a neutron star, and each one tells a story that astronomers can use to understand what came before. And as we mentioned as well, they’re used as standard candles to help understand the distance of things in the universe.

Pamela: And these two different objects, supernova and asteroid discussed in the last episode, are really the two main justifications for all these global surveys that are going on of the sky. We’re trying really hard to understand what is the future of our universe. Will we die by fire, or ice, or great rip, and I don’t even know how to consider that. And that future evolution of space-time is going to be defined by understanding the rate at which our universe has been expanding since the earliest days, which we see through supernovae.

Now, the other thing is how is the earth going to live and die, and hopefully death by rock is not our definitive future. And the way we prevent ourselves by going the way of the dinosaurs is by finding any rock that is potentially going to hit us. So, when we go surveying for transient objects, when we build all of these different telescopes designed to find transient after transient after transient, our justifications are measuring the future of the universe and preventing death of the planet Earth. But all this other science is like free extras, so I have science for you, I have science for you, I have science for me in the form of all these Cepheid variables.

And fundamentally, even the Kepler telescope with its planet hunting capacity was a transient searching telescope where it was looking for the changes in brightness due to planets passing in front of the stars.

Fraser: And that’s where I was gonna go next, right? In the previous episode, we talked about this idea that we can observe stars and watch occultations as an asteroid passes in front. The universe is a really big place, and things pass in front of other things all the time in ways that are really amazing and teaches a bunch of really interesting stuff about the universe. So, can you talk just a bit about the transit method of transients?

Pamela: So, in this case, we have a distant system that has its own planets, its own asteroid belt, its own disc of material. We’ve seen examples of all of these kinds of phenomena, and that distant solar system stuff passes in front of the star that it calls its home star and blocks out some of that star’s light.

And we can learn about what is doing the blocking by how that transit occurs, and we can, by measuring the star’s motion in and out of the plane of the galaxy, by measuring how it gets Doppler shifted is the scientific way of saying it, we can measure how much mass is in that material, and we can start to get really cool and detailed measurements of distant solar systems that start to give us more detailed pictures of how normal or abnormal is our own solar system, and it’s looking like we’re pretty weird.

Fraser: Right. We thought we were normal. We’re not normal.

Pamela: No.

Fraser: But you mentioned when we were talking about, for example, when you watch an asteroid pass in front of a star and dim the star depending on where you are on earth, you can learn different characteristics about the asteroid. You can learn whether it has a moon, whether it has a ring, whether it has an atmosphere. There are all these really interesting things, so what can you learn about the object that is passing in front of the star and what happens when a star – actually, we’ll get to that in a second, but when stars pass in front of other stars.

Pamela: So, with planets’ discs passing in front of their home stars, the two basic pieces of information that you can get at if you have a nice, discreet planet is what is the planet’s radius, what is its distance from its home star, and what is its mass. Now, for these three things to all happen, you need to have a planet that eclipses its star, passes right in front of it, allowing us to measure how long it takes to get in front of the star, how long it takes to get out from in front of the star. That gets us its radius. We need to be able to see this multiple times. That gets us its period of motion.

And if we can measure the Doppler shifting that’s going on, how that planet is in turn using its gravity to move the star that it’s going around, that will give us its mass. So, we can get pretty detailed understandings. Now, one of the other weird things that happens is there are examples out there of discs of material going around stars that get involved in this whole eclipsing act, leading some really weird long-term eclipses. Now, these kinds of events don’t allow us to measure the mass in that disc, but they do allow us to say, “Huh, yeah, other stars have dust discs,” and even that is pretty cool science.

Fraser: And then sort of to take that to the next level, right, you can have this situation where the two stars are perfectly lined up so that one acts like a lens to the star that’s behind it, and that star that is lensing, you can then learn a tremendous amount about that star or the one that’s behind it.

Pamela: And this is gravitational microlensing. And so, what we’re looking at – and this was done a lot by the survey projects, MACHO and OGLE, that looked at the large and small Magellanic Clouds and towards the inner spheroid of our own galaxy and looked to see do any of those background stars suddenly appear to get brighter because a foreground object has passed in front of it, and that foreground object’s gravity bends light that would otherwise never get to our telescope into our telescope – well, into the telescope of everyone in our general direction.

So, that gravitational bending that gets extra light to us, the observer, that’s the gravitational lens part of it. And it tells us where that otherwise hidden material is and has actually allowed us to see stars that have planets that potentially have moons in places that we don’t otherwise have the capacity to be looking for planets. It allows us to go looking for, well, are there rogue Jupiters wandering another solar system, wandering our galaxy. The answer appears to be no. What is the number of rogue black holes out there? Can you use black holes to explain dark matter? The answer appears to be no.

So, these searches for gravitationally lensed nearby stars that are lensing background things in either the galactic sphere, spheroid in the center, or in the Magellanic Clouds, these events help us find the invisible material that is in our galaxy and help us realize just what is the diversity of stuff that we don’t otherwise get to see. It’s gravity making the invisible visible.

Fraser: And the one thing as we start to wind down this episode is we’re very familiar with the sorts of things that we can see, and all the things that we’ve talked about today are all about using phenomena, that essentially visible light, the kinds of things that you would see in your normal telescope, but there’s a whole bunch of other transient phenomena that exist in other wavelengths. Things in the radio waves, things in the x-rays. So, could we just talk briefly about that, that once you expand what you’re looking at, another whole level of interesting changing objects show up?

Pamela: So, this is where you start to get magnetars, neutron stars with extremely strong magnetic fields that periodically rearrange their magnetic fields and give off massive amounts of gamma ray radiation. This is where you start to be able to look at distant, actively-feeding galaxies like the BL Lac object and see flickering and flaring in the core of a distant galaxy. This is where you start to get, well, gravitational waves are a transient event, just not one you’re gonna see using the photometry technique that we’ve largely talked about today.

Gamma ray bursts in all their forms are a transient phenomenon, in some cases linked to massive supernova that have magnetic fields called hypernova, in some cases linked to the crashing together of a pair of neutron stars where we also get gravitational waves. All these different things are showing that our universe is not a constant place. It is not that unchanging place that it was thought of to be by the ancients, and unless you’re a crazy person, you certainly don’t want a love as constant as the stars.

Fraser: I love this idea that for the longest time, astronomers would pick a thing, and they would look at it, and then they would study it, and then they would do some research. And then we moved to this idea of surveys, things like the Sloan Digital Sky Survey where you would try to just take a picture of everything so that everybody could have a picture of everything that was in the entire sky.

But that’s not enough. We are now moving to this time where we have to be able to see everything that’s in the sky all the time. So, it’s the difference between a photograph and a video that we are now moving to an age of astronomy that is the video version of where old astronomy was the photograph, but it’s even weirder than that.

Pamela: Well, this is what we always wanted. You have to –

Fraser: I know it’s what we always wanted. Now we’re finally getting it, right?

Pamela: Right, we have the technology.

Fraser: And the final step is to in addition look across all of the spectra at the same time, so you’re not just recording a video of the entire universe in purely visible, but you’re gonna wanna do that in gamma rays, and in x-rays, and in radio waves, across all the different spectrums to see every single thing that the universe was doing when we weren’t looking.

Pamela: And one of the biggest frustrations is while we have the capability with optical telescopes to take images of a large chunk of the sky at once, while we have that capacity with infrared telescopes and some ultraviolet, we do not have the capacity to take wide-angle, high-resolution images in all these other colors of the rainbow. And the electromagnetic spectrum makes it hard for us to do large-scale detailed surveys of a lot of the sky, but we’re gonna get there. We’re gonna get there.

Fraser: Well, that’s it.

Pamela: Maybe.

Fraser: And so, we are entering the golden age of transient astronomy, and as you can see, there’s a lot left for us to be able to do, so lots of work to be done into the future. Well, that was great. Thank you so much, Pamela.

Pamela: Thank you, Fraser.

Fraser: Oh, wait. You should say some names.

Pamela: Wait, we have to read names. Yes, thank you. We’re gonna remember.

Fraser: I remembered.

Pamela: So, we love our Patreons dearly, and we’re just learning a new way to end this episode. And I’d like to end this episode by thanking a few more of our fabulous Patreon donations. This week, I would like to thank Nate Dutweiller, Joe Wilkinson, Raymond Buzinski, James Platt, Jonathan Tronson, Philip Walker, Elod Avron, Paul D. Disney, anti-user, and Scott Bieber. If you too would like to hear your name read by me in an overly enthusiastic and grateful tone of voice, just support us on Patreon. Thank you so much for making this show possible. We wouldn’t be here without you.

Fraser: Thank you, everyone. We’ll see you next week.

Pamela: Bye-bye.

Announcer: Thank you for listening to Astronomy Cast, a nonprofit resource provided by the Planetary Science Institute, Fraser Cain, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at Astronomy Cast. You can email us at info@astronomycast.com, tweet us @AstronomyCast, like us on Facebook, and watch us on YouTube. We record our show live on YouTube every Friday at 3:00 p.m. Eastern, 12:00 p.m. Pacific, or 19:00 UTC. Our intro music was provided by David Joseph Wesley, the outro music is by Travis Seale, and the show was edited by Susie Murph.

[End of Audio]

Duration: 32 minutes

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