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Voyager 2
The gravity of the Earth is a tough thing to escape, but breaking free from the gravity of the Sun is on a whole other level. But humans have achieved this amazing accomplishment, and right now there are several spacecraft leaving the Solar System and never coming back.
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This episode is sponsored by: Casper, Swinburne Astronomy Online, 8th Light
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Female Speaker 1: This episode of Astronomy Cast is brought to you by Swinburne Astronomy Online, the world’s longest running online astronomy degree program. Visit astronomy.swin.edu.au for more information.
Fraser Cain: Astronomy Cast episode 384, Escaping Probes. Welcome to Astronomy Cast, your weekly fact-based journey through the cosmos. We’ll help you understand not only what we know but how we know what we know. My name is Fraser Cain. I’m the publisher of Universe Today and with me is Dr. Pamela Gay, a professor at Southern Illinois University, Edwardsville, and the director of Cosmoquest. Hey, Pamela, how are you doing?
Pamela Gay: I’m doing well. How are you doing, Fraser?
Fraser Cain: Good. I hope you had a great summer and now begins a brand new season of Astronomy Cast. I’m not gonna say what season it is because I actually haven’t done the math.
Pamela Gay: Nine!
Fraser Cain: Eight? Nine?
Pamela Gay: It’s season nine.
Fraser Cain: We are beginning season nine of Astronomy Cast with today’s episode, all about probes escaping the solar system. I hope you had a great summer.
Pamela Gay: I did, and I’m happy to say we have Clean Coaters back as one of our show’s sponsors, who you’re gonna hear their advertisement as well as one for Swinburne Astronomy Online.
Fraser Cain: And others.
Pamela Gay: Yeah. So, life is good. The show is good. Still waiting to hear on grants but that is the way of life. You and I are back from Dragging Pond and Penny Arcade and we’re ready to put out week after week of this show and keep you all happy.
Fraser Cain: To science the hell out of this.
Pamela Gay: Exactly. Do you have Martian fever?
Fraser Cain: I do. I totally have Martian fever, I gotta say. I am so excited to see The Martian. And I’ve actually heard that some initial reviews have already come out and apparently it’s terrific. I am really looking forward to this movie.
But few things happened over the summer. We won a Parsec Award for The Guide to Space, which is, of course, the video series that I do over on my Universe Today channel. So, if you haven’t already, check that out. Do a search for Guide to Space.
Pamela Gay: And we won a Communicator’s Award for 365 Days of Astronomy. So, if you haven’t checked that out, check that one out over on astrosphere vids, but really 365daysofastronomy.org because it’s mostly audio.
Fraser Cain: And I wanna just remind everybody that we do these episodes of Astronomy Cast as a live video, so, if you wanna hang out with us all you have to do is go to the Astronomy Cast page on Google+ and you can see the upcoming events. We do the show for about 30 minutes and then we actually stick around for another half hour and answer your questions about space and astronomy. So, if you want to have some questions answered, join us for the live portion of the show and put your questions in. We don’t have time, necessarily, to answer the stuff by email, but usually we have lots of time during the actual show to answer whatever questions pop up. All right. Let’s get on with the show.
Female Speaker 1: 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.the digit 8 T-H L-I-G-H-T.com. Drop them a note. 8th Light: Software is their craft.
Fraser Cain: So, the gravity of the Earth is a tough thing to escape, but breaking free from the gravity of the Sun is on a whole other level. Humans have achieved this amazing accomplishment, and right now there are several spacecraft leaving the Solar System and never coming back. All right, Pamela. I’m trying to think here. Let’s talk about escape velocity for a little bit first.
Pamela Gay: Okay.
Fraser Cain: What is involved to escape the gravity of a thing?
Pamela Gay: First of all, it’s basically an energy thing. We don’t think of it that way but that’s where the equations come out. You have a certain amount of potential energy from an object’s gravitational pull and that energy wants to be used to suck you into the center of mass of whatever thing is pulling on you.
The other thing you have is the kinetic energy that is associated with your motion. In order for you to escape something, you need to have your kinetic energy that’s carrying your forward balance out that potential energy that’s trying to suck you down.
Now, exactly how much energy is required depends on the distance between two objects. As you get further and further and further away from an object, you can go slower and still escape. This is why it’s easier to escape the Earth if you start out at the International Space Station and why, if you compressed the Sun down to 3 centimeters across and made it a black hole, you could never get away, but you can fly away from the Sun the way it is right now.
Fraser Cain: Right. And so, when we consider all of the spacecraft that are leaving the Earth, they launch off the surface of the planet. They get up into Earth orbit, so they’re still trapped by the Earth, and then if they wanna escape the Earth’s orbit, they have to kick in extra velocity to overcome that gravitational potential. Right?
Pamela Gay: Right.
Fraser Cain: How much harder is it to go from just getting up into orbit to then being able to actually escape the gravity of the Earth?
Pamela Gay: If you wanted to go from the surface of the planet to far, far away, not escaping the Sun but escaping the Earth, you need to be going a little over 11 kilometers per second. But, if you start from the International Space Station or someplace like that, you already have a lot of velocity because you’re going around and around the planet and not on a ballistic trajectory. You need to add about three kilometers per second to your orbital velocity if you’re in low Earth orbit, and that extra three kilometers per second will allow you to fly away. So, once you get to orbit you don’t have to accelerate nearly as much in order to escape our planet.
Fraser Cain: For those of you playing the Kerbal Space Program, that’s the point when you stop having that nice orbit around Kerbin and then you can actually see that your orbit has changed to now you’re orbiting the Sun, just like the rest of the planets. That sort of gives us a basis point, then, to talk about sort of how hard it is to actually send these spacecraft right out of the Solar System itself. How much harder is it to then send something so it’s never coming back to the Solar System?
Pamela Gay: If you wanted to send it from Earth straight away from the Sun –
Fraser Cain: Which is where I keep all my spacecraft.
Pamela Gay: Exactly. And just have the instantaneous velocity of I’ve got all the kinetic energy I need to get away, you’re looking at about 42 kilometers per second, which is kinda faster than anything we’ve built so far. So, what we currently do is we aim towards a planet. Pick a planet and gravitational assistance helps us get there, adds a little bit of velocity. We fire thrusters along the way. Through this combination of steady acceleration and gravitational boosts whenever we can get them, we creep our way up so that we can eventually escape because once you start getting out to Saturn, at Saturn the velocity you need to escape the Sun is just about 14 kilometers per second. So, it drops rather quickly.
Fraser Cain: Right. I see. So, as you kind of leapfrog your way from planet to planet and you get yourself out further away from the Sun, the amount of velocity that you need to be able to escape the Solar System comes down as you’ve gotten further and further out.
Pamela Gay: Exactly. This slow accumulation of speed is also just a lot easier than that sudden burst. If you think about it, going from 0 to 60 in point whatever seconds the fastest sports cars are now doing, that’s rather hard. That’s kinda hard on the car. It uses a lot of fuel. There’s a lot of shock to your system as you get mushed into your car seat. But if, like I do in my ancient Jeep Wrangler, you gradually accelerate from 0 to 60 over a distance that annoys everyone around you, this is a more steady process. It doesn’t require quite as much gas even in my ancient Jeep Wrangler. And a similar approach is used with spacecraft. It’s slow and steady, gets faster with fewer things broken.
Fraser Cain: Okay. Great. Then what spacecraft have we managed, and by we, of course, I mean scientists, NASA, managed to be able to send on a trajectory that’s gonna have them leave the Solar System entirely?
Pamela Gay: We have five spacecraft that are in the process of doing this. Pioneer 1, Pioneer 2, Voyager 1 – actually Pioneer 10, Pioneer 11, Voyager 1, Voyager 2, and of course, the New Horizons space probe.
Fraser Cain: The most recent spacecraft kicked out of the Solar System. Where are these spacecraft sort of located? Are they all following a very similar trajectory or have they been sort of sent off in different directions?
Pamela Gay: What’s really cool is they are heading off in four very different directions. This has to do with how they encountered different worlds at different points in those worlds’ orbits. With Pioneer 10, you have a spacecraft that was on its way to Jupiter, slung passed Jupiter, headed out of the Solar System in one orbit. Pioneer 11, originally slated to go to Jupiter if Pioneer 10 didn’t make it. Pioneer 10 made it, so redirected towards Saturn. Headed out of the Solar System in yet a new direction.
With Voyagers 1 and 2, we think of them today as these spacecraft that saw all the things, visited all the worlds. But that wasn’t how they were originally budgeted. They were originally budgeted more as visiting Jupiter and Saturn, and depending on how the first one encountered Saturn’s moon Titan, redirect or not to Pluto. The decision was made let’s really investigate Titan, so, no explorations to Pluto took place, but we did redirect to Uranus and Neptune on extended missions.
Fraser Cain: They had to know that the potential was there, that you could go – in this case, that the planets were all lining up in this, literally, once in hundreds of year lineup, where you would be able to go past Jupiter, Saturn, Uranus, Neptune and out. I guess they got that speed boost from each and every one of these planets that they went by. I guess the Voyagers, Voyager 2, got the most speedup from all them because it got two gravitational assists from every single one of these planets.
Pamela Gay: This comes down to what is the difference between what a spacecraft is capable of and what it is funded to do. This is a problem that we’re facing right now with the New Horizons space probe. New Horizons is, in theory, on its way to 2014 mu69, one of the least exciting objects, by name, in our Solar System. But while its name is kind of yuck, this is an icy body that potentially will be the first one not in the Pluto system to be visited by a spacecraft. The thing is, even though they’ve done the firing needed to redirect the spacecraft, we don’t know if New Horizons is going to get its mission extended. And if it doesn’t get its mission extended, no science for you. It seems like a no brainer –
Fraser Cain: It’s gonna get its mission extended. Come on. Voyager still gets extensions to its mission. So, New Horizons is totally gonna get its mission extended.
Pamela Gay: It’s a difference in cost, though. With Voyager 1 and 2, these are two spacecraft that are still returning data, still getting followed, sent commands on a regular basis with the Big Ear, but they’re a fraction of a human being working on them. New Horizons is a whole lot more than a fraction of a human being and if it does another flyby, there’s a lot of cost involved in all the scientists and all the post-docs. And heck, just the press releases alone cost more money than a lot of people currently have to fund everything they do. So, if it’s the choice of a new spacecraft to go visit Titan or Europa or one of those, or getting a few images back from an icy blob, that’s gonna be a very hard decision for somebody to make. And I’m glad those aren’t decisions that I make.
Fraser Cain: As always, I speak for all of Canada when I say we’re glad to take over any of your spacecraft and keep them running and gather lots of science.
Pamela Gay: You know, we do periodically give away our spacecraft. WISE was one, but I don’t see that happening any time in the near future with New Horizons.
Fraser Cain: Let’s talk about – I mean, we’ve talked about all of the inner planets, all of the inner Solar System, all of that planetary stuff. Let’s talk about the kind of science that pretty much has been done or will get done outside of – I guess, with the Voyager missions and with the Pioneer – after each spacecraft really has finished its primary mission. I’d love to talk about some of the discoveries that have already been made and maybe some of the discoveries that are yet to – remain some of the big milestones that we’re looking forward to, until that final Veegur encounter in the next few hundred years.
Pamela Gay: Right. That was such a bad movie. I hope that future never comes.
Fraser Cain: Let’s talk about the Pioneer first, since those were the earliest, Pioneer 10 and 11.
Pamela Gay: The Pioneer missions, first of all, they were the ones that brought us our first digital images of – and digital is really a stretch here because they were really taking scanned analog-ish images and sending them back. It was basically early television. You’re right on that boundary where we’re trying to be fully digital but we don’t quite know how.
Their big accomplishment that they get remembered for is the early images of Saturn, rings, moon bits, Jupiter, moon, Ganymede image. But their big discovery was they flew through the asteroid belt and discovered that the asteroid belts aren’t rich in little tiny particles just waiting to destroy spacecraft. We didn’t know if that was gonna be a problem or not. We knew that the big stuff was spread apart. They left lots and lots of room to not get hit by a big thing that had previously been discovered. But we didn’t know if there was a ton of little stuff. Turns out there wasn’t.
They also went on to make major measurements of, within our solar system, gas and dust and cosmic rays coming from beyond our solar system. They were the ones that helped us understand the density of everything out there.
Fraser Cain: And so once they wrapped up their flyby of Jupiter and Saturn?
Pamela Gay: Uh-huh.
Fraser Cain: But they still were doing science. And I think one of the big ones, of course, is this idea of the Pioneer anomaly. Right?
Pamela Gay: The Pioneer anomaly is one of those things that they weren’t really designed to measure, you might say.
Fraser Cain: While you’re out there, discover a new mystery, uncover a new mystery and then help us solve it.
Pamela Gay: The Pioneer anomaly, I think we did an entire show on that.
Fraser Cain: Yeah. We did a whole show on the Pioneer anomaly. But just the quick version.
Pamela Gay: The quick version is their rate of travel didn’t quite meet with what we expected. We can tell this based on how long it takes signals to go back and forth. This, essentially, anomaly to their trajectory took a long time to figure out and had a whole lot of possible explanations. The annoying thing was it wasn’t just Pioneer 10 and 11 that had this anomaly. It was also the Voyager missions but in slightly different ways. Go listen to the show we did on it.
Fraser Cain: Yeah. Yeah. What else did Pioneer discover while they were out there?
Pamela Gay: The interplanetary medium was one of their big things; exploring the environment of Jupiter; discovering its nasty magnetic field, that’s the kind of thing you can’t really see from Earth. Mapping the magnetic field of Saturn was also on the list. Studying the solar wind, and just realizing that atmospheres are so complicated. We were able to see from Earth the banding of Jupiter; the variations across the surface of Saturn. But the better the data we got, the harder it became to explain all of this. Which is one of those study problems with astronomy: get the scientists more data and they become temporarily more confused. They figure out what they have; they get more data; they become confused again. This is the study of process of science and filling in the details. Those initial pictures that we got just kind of blew everyone’s minds.
Fraser Cain: Let’s move on then to the Voyagers. I guess this is the perfect example, right, of filling in all the pieces because the Pioneers helped us – gave a pile of questions, and the Voyagers came through, answered some, and then, with the higher resolution, asked more questions. Right?
Pamela Gay: From the Pioneer missions, we were able to start to realize Saturn’s atmosphere is kind of awesome, and there’s this moon, Titan, that also appears to have an atmosphere. With Voyager 1, there was a whole lot of emphasis put on the Titan flyby. In fact, the Titan flyby that Voyager 1 did was the reason that Pluto wasn’t initially explored on this first tour through the Solar System. They arranged the spacecraft to get the best, closest images they could without endangering the spacecraft. It seems like a strange thing, just one little moon. But when that one little moon has a rich methane atmosphere, you do the mission redirection.
Fraser Cain: And of course, with Cassini after, they put a lot of emphasis on Titan, keep coming back to it again and again and again, and seeing all these amazing further details: the lakes of liquid methane and rain and weather systems and all that kind of stuff. So, it’s that same conversation. They have an inkling of what’s going on and then they bring another spacecraft around to take another look. What else happened with Voyagers?
Pamela Gay: The Voyager missions took the idea that the Pioneer missions had of being the envoy of humanity one step further. With the Pioneer 10 and 11 missions, we had these gold plates that showed a man and a woman, basic details on how to find us, which I personally find slightly disturbing. Highlighting how to find the Earth isn’t necessarily something we should be doing, but we did, nonetheless. But with the Voyager 1 and 2, it went to a new plaque as well as a record with numerous sounds, voice clips, heartbeat, all recorded by different elements of humanity. With the Voyager missions, we acknowledged these were the spacecraft that are going to be the first things, potentially, to encounter other worlds. We wanna put our best gold plate forward as we continue to explore.
Voyager 1 and 2 also brought us the ever-evolving “We’ve left the solar System!” “No, we haven’t.” “We’ve left the Solar System.” “No, we haven’t.” Which we’ve talked about many times.
Fraser Cain: But have we left the Solar System?
Pamela Gay: I think Voyager 1 finally actually left the Solar System.
Fraser Cain: Depending on your definition.
Pamela Gay: Yes.
Fraser Cain: But has left the heliosphere. Right?
Pamela Gay: Yes.
Fraser Cain: And of course the heliosphere may move past Voyager again in the future, but until that happens, Voyager has left the helio – has left the Solar System. Although, has it made it through the Oort Cloud? Has it made it – so, it really has a lot more Solar System to go through by other definitions.
Pamela Gay: Exactly. It has left the region under the greatest domination by the Sun. But just like a lot of people’s waistlines, the size of that area is a constantly changing number.
Fraser Cain: What other science – I mean, that’s one of the sciences and one of the questions that it really helped answer after going past Neptune is just what’s out there? Right? What is the interstellar/interplanetary medium like both within the heliosphere and also outside of it? What other kinds of things has it uncovered while it’s been out there?
Pamela Gay: Voyager 1 and Voyager 2 – for Voyager 1, it’s definitely the exploration of the heliosheath, the heliopause, the termination shock, all of those different interplay between the interstellar medium and our Sun’s magnetic field and the area swept out by the solar wind. Those are really the key things it did after exploring Jupiter and Saturn.
With Voyager 2, we, of course, had a couple more worlds that got explored. It went on to first fly past Uranus and then to Neptune, where we got our first glimpse of what we think is a captured Kuiper Belt object. Of course, we hadn’t confirmed back then that the Kuiper Belt existed, but it was believed that Neptune’s moon, Triton, was probably very similar to Pluto. Now, we’re starting to understand that yes, it is but no, it isn’t because Pluto is very, very confusing. I expect once they’ve downloaded more than one and a half gigabytes of data, you and I will do another show on Pluto. But for now, we’re waiting for someone to say something other than, “Oh my god, it’s awesome and we don’t understand it!” Which is kind of what everyone is doing right now.
Fraser Cain: We could do a show on Pluto right now, and then do another one because there’s great pictures on both Pluto and Charon and the moons, now. There’s so much amazing results. There are mountains made of ice!
Pamela Gay: Yes! These are mountains that are as big as the Rockies here on Earth on an object way smaller than the Earth’s moon.
Fraser Cain: But made of ice! Just imagine that. It’s crazy. Let’s just move on then to New Horizons. I guess the whole point with New Horizons, obviously, it saw Jupiter. It saw Pluto and that was amazing, but it still has more left in the tank, as well. It’s got some future science to do.
Pamela Gay: They’re hoping to be able to get not as good as they got with Pluto and Charon, more like what they got with Nyx and Hydra. They’re hoping to get more images of at least one more Kuiper Belt object. Again, this is all pending senior review and determining whether or not they get that extended mission and that extended budget. But for now, they have – well, first of all, they completed the round of everything in our solar system that’s ever been called a planet. We had the Dawn spacecraft make it to Ceres early in the summer; New Horizons make it to Pluto at the end of the summer. We have now gone to everything ever called a planet.
But more than that, we didn’t have any really good images of Kuiper Belt objects. We didn’t have any really good data on which to base our understanding of these icy bodies in the outer solar system. Michael Brown and others have been turning these things up every couple of years, but knowing where they are, knowing where they orbit, knowing the mass of a lot of them, that’s all awesome. But that doesn’t tell us about the geology. That doesn’t tell us about whether they’re active. It doesn’t tell us a lot of things that you require images for. New Horizons got us those images.
Fraser Cain: And it’s got the one, obviously, the most famous Kuiper Belt object, but hopefully it will grab – it’s gonna fly past another object, maybe another, in the next couple of years. 2019, I think, is when the next flyby is hoped?
Pamela Gay: That’s the current hope. Again, it’s 2014 nu69 is the unelegant name of that object. We’re hoping. It’s now down to the politics, and sadly, there’s not enough money to fund everything. And if you think about it, we have Lunar Reconnaissance Orbiter still returning awesome data at better than half a meter per pixel of the Moon. Do you wanna kill that spacecraft? We have Mars –
Fraser Cain: Nobody wants to kill any spacecraft. No.
Pamela Gay: We have Mars Opportunity on a continuing mission as it roves around. We have all of the orbiters around Mars. We have an entire series of spacecraft to cover, most of them heading off into extended missions. Something has to die. We know it’s gonna be Hubble as part of it, but what else is gonna die? That’s the question.
Fraser Cain: Let’s talk about the far future. Is there any more science that’s gonna be done from these spacecraft? How long have they got, doc, is what I’m saying.
Pamela Gay: We’ve already lost a few of them. Pioneer 10 was lost in 2003, which, if you think about it, this is a spacecraft launched before either of us were born and it kept going until 2003. That’s pretty exciting. Pioneer 11, last contact in 1995. Voyager 1 and Voyager 2 are still returning data, and they’re letting us continue to probe. We don’t know how much longer they’ll last, but it’s thought that at least a couple tens of years, maybe, we’ll be able to continue getting data back from these guys. Again, this is less than one person worth of time. Mostly it’s money to do the Big Ear measurements, but that’s pretty awesome.
And again, New Horizons, we have no idea how long that spacecraft will last. It, again, has this radio isotope for a generator, so, it can last a long, long time. It becomes a question of how much money does it get to keep returning science that people can process.
Fraser Cain: Right. Will there be a time when it sort of runs of things to look at? Things to measure?
Pamela Gay: Just like the Voyager probes and the Pioneers before them, as it continues further and further out in the Solar System, it has this ability to study the Sun’s magnetosphere, to study the interstellar material. It has spectrometers onboard that allow it to sample the random isotopes that it encounters allows the way. As it’s already proven, as it looks back at our Solar System, it can also do certain unique science. For instance, as the Sun’s light passed through Pluto’s atmosphere, we were able to better understand that atmosphere. Now, it’s a little far away to be measuring things like that, but there are other look-back science that it can do as it continues to move out.
Fraser Cain: And when will any of these probes reach another star?
Pamela Gay: Well, there we’re looking at, I believe, it’s the thousands of year line. They’re not exactly headed straight towards anything useful at the moment.
Fraser Cain: Right. So, we’re gonna need some kind of futuristic, alien civilization to find our spacecraft, merge with them, and return.
Pamela Gay: I hope that doesn’t happen.
Fraser Cain: That would be awesome! Let’s wrap this up. I know you put a bunch of spacecraft-related episodes into the list, so, get ready for a lot of planetary robotic exploration.
Pamela Gay: And if you wanna learn more about New Horizons and how citizen scientists played a role, go over to cosmoquest.org. We did a whole bunch of stuff this summer as part of NASA’s discovery program. We also collected some of the best memes that came out of Pluto because people got very bored waiting to find out if New Horizons had lived or died, and all that boredom got channeled into memification of all the things.
Fraser Cain: That is awesome. Awesome. Okay. Well, thanks, Pamela.
Pamela Gay: Thanks, Fraser.
Male Speaker 2: Thanks for listening to Astronomy Cast, a non-profit resource provided by Astrosphere New Media Association, Fraser Cain, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at astronomycast.com. You can email us at info@astronomycast.com, tweet us @Astronomy Cast, like us on Facebook, or circle us on Google+. We record our show live on Google+ every Monday at 12 p.m. Pacific, 3 p.m. Eastern, or 2000 Greenwich Mean Time. If you miss the live event, you can always catch up over at cosmoquest.org.
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Duration: 33 minutes
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