Daniel and Jorge Explain the UniverseDaniel and Jorge dig into the mystery of why the Pioneer spacecraft's path surprised scientists.
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Hey, Daniel, what's the first thing you think about when you see something in space you don't understand?
Well, my first hope is always aliens. But my first thought is that it's probably a boring miss stand.
So as a scientist, your mind goes straight to the most dramatic explanation.
Yeah, we're all hoping that somebody out there hits the science jackpot.
Mm.
Everybody wants to find the thing that frocks the world.
Yeah, you know, people might not realize its Science is a little bit like playing the lottery. It's mostly wrong numbers, but occasionally you get.
Lucky and you win the alien jackpot. What's the price you might need to get wiped out?
Yeah? Maybe, but think about what we might learn along the.
Way in our dying moments. I am more hamdmade cartoonist, the creator of PhD Commics.
Hi, I'm Daniel. I'm a particle physicist, and I'm constantly on the hunt for something weird in science.
Not in your department in science in general, there's plenty of weird things in your department.
Weird stuff growing where it shouldn't be. But no, I'm looking for weird stuff in the data.
Hoping to win that jackpot. Is your data like it's a scratch of kind or like you make up the numbers.
No, we are just looking at particles smashed together and hoping that something that comes out of it is unexplained. It's weird. It's something that our current theories of physics do not predict.
Well.
Congratulations to all of you because you've won the jackpot. You are listening to our podcast, Daniel and Jorge Explain the Universe, a production of iHeartRadio.
And your prize is that you get to hear all about the incredible, amazing mysteries of our universe, all the weird stuff that's going on out there, all the little hints we have about weird stuff that might be going on that could be clues that reveal deep secrets about the nature of reality.
Yeah, and just like a real lottery, this episode might be a winner or a dud. We'll find out. We'll have to scratch off the surface.
The price is the same either way.
That's right.
The price is right, meaning nothing, you get what you pay for.
But yeah, science is full of interesting mysteries out there, and it does happen a lot, doesn't it, Daniel? Did the scientists look out into the world or try an experiment or do something and things don't happen the way you expect them to happen.
Yep. Everybody out there in graduate school knows that no experiment goes right the first time. But usually the reason you got a weird result is that you messed it up a little bit. You didn't calibrate things, or you plug something in backwards, or you misread your instrument or something. Usually there's a conventional explanation. But what we're all looking for are those moments when you've done everything correctly but the answer is not what you expected.
Yeah, don't they say that the real moments in science are not the Eureka moments, but the hmm, that's interesting moments exactly wait a minute moments.
There are sometimes those moments. There's a fantastic audio tape that's floating out there of recording of two astronomers listening to one of the first pulsars ever seen. They happen to be recording themselves for reasons I don't know, while they were observing, and you can hear them going, wait a second, look at this. Oh my gosh, is that what we think it is? WHOA, that's interesting.
Really, it's for real. Wasn't acted out, So those suspecials that were being recorded.
It's for real. It's for real. I encourage you to go out there and check it out. In fact, maybe we'll dig it out for our episode that's coming up on how pulsars were discovered. But yeah, most moments of scientific discovery are like, dang it, my experiment didn't work. Hmm, well, maybe there's a better explanation, you know, after you check off all the boring explanations. Sometimes it is an exciting, fascinating explanation. Something new might be going on.
Or sometimes it'd something routine. It could be either.
One absolutely and people might remember a few years ago we thought we had discovered new trinos going faster than the speed of light. I won't say we there because I wasn't among the group of people who I thought that was real.
And humanity does something good. It's the royal we including ys. So when they mess it up, it's them. It's the Italians, them Italians.
I won't to touch that. But as soon as that paper came out and I saw that it had been written in Microsoft Word, I was like, no, there's something wrong with this paper.
What do you mean. I wrote all my papers in Microsoft Word.
Yeah, point made.
Actually I wrote them in Adobe FrameMaker, which should tell you how old I am.
A little bit. Wow, that really does dat you. But usually, as in the case of the faster than light new Trinos, is just a mistake. In that case, they forgot to plug a cable in correctly, and so their calibration was wrong and they mismeasured the speed. But sometimes these are famous experiments in the history of physics. We see something we don't understand and it's actually a clue. It's the first hint of a dramatic realization of uncovering something we had no idea about. And a great example is the photoelectric effect, which was an experiment around one hundred and twenty years ago. That was the first clue that the universe was quantum mechanical.
Yes, it was illuminating and electrifying at the same time.
For humanity and very effective.
Yeah, So today we'll be talking about one such mystery in science, and in particular in space science, that happened a few years ago. Daniel, Right, how long ago was this or is it still ongoing?
It was resolved a few years ago, but it went on for several decades. This is an outstanding mystery that puzzled people, that caused them to dig deep into their attic of ideas for possible boring and exciting explanations for what could be happening to this spacecraft.
Yes, it involves spacecraft and plants and basically you just need to ward space and mystery and it's an interesting journey right here.
Amazingly, there's almost no talk of aliens in this whole topic.
Not yet. It's strashed the surface Daniel, And see if we can win the lobbry here. So today on the program, we'll be talking about what is the Pioneer anomaly. Now, it's anomaly, right, not anemone. Just get the too confused.
It's not an underwater sea creature. It's not something you want deep fried and served before your dinner. It's an anomaly. It's something that's not understood, that's anomalous, and.
It's something that happened in space around what time.
Well, it has to do with the Pioneer spacecraft, which was launched in the seventies and has one of these incredible careers. You know, they expected to go on for several years and then operated for decades and decades and decades, And of course it's still out there, right, Pioneer ten and Pioneer eleven are still out there flying out into the depths of space being pioneers.
Of course, now I have to admit I did not know what the Pioneer spacecraft is or the anomaly. I was a little puzzled by this, but as usual, we were wondering how many of you out there and know or knew what this Pioneer anomaly is.
So thank you to everybody who volunteered to answer these questions. If you'd like to participate for a future episode, please don't be shy. Write to me two questions at Danielanjorge dot com.
So think about it for a second. If someone asked you what the Pioneer anomaly is or was, what would you say. Here's what people had to say.
I don't know, but I imagine it's an abnormality pretending to spacecraft or something.
I'm not totally sure what the Pioneer anomaly is. I can only guess that it has something to do with the Pioneer spacecraft that were launched in the early seventies and I think are now a very long while away.
I no idea.
I have no idea what the Pioneer anomaly was, but I assume it has something to do with the Pioneer spacecraft and obviously something that you would not normally expect to have happened.
I think that the Pioneer anomaly was maybe like this first irregularity found about our universe, and since it's the Pioneer anomaly, I think that this maybe marked like a turning point for sciences and made them more curious about what other anomalies can be found in our universe.
All right, not a lot of name recognition here, No, I was a little surprised.
I thought this was a little more famous. I remember hearing about this in high school and thinking, ooh, that's cool. I bet that's something real.
Well you heard about it in high school, like, oh yeah, like in physics class, or how did you hear about it from your physics parents.
I was a nerd, big shocker, just kind of interested in this stuff, and you know, anything out there in space that was unexplained, anything that might be a clue as to how something is working in the universe, I gobble that stuff up. So when I heard that we didn't understand where this spacecraft was and what it was doing and why I was doing these weird things, I thought.
Oh, I think the real anomaly is that you used the past tense when you said you were a nerd.
It's not up to me to evaluate that.
All right, Well, there is something called the Pioneer anomaly, and let's break it down for people. Daniel, what is the Pioneer anomaly?
So, as expected, it's an anomaly that has to do with the Pioneer spacecraft, and specifically, it's that we didn't understand where it was going and why it seemed to be going off course for reasons we did not understand.
Okay, so it was a spacecraft, meaning like a satellite. I always keep confused with people say spacecraft because I imagine you know, Battlestar Galactica or you know, people in in a cockpit or something, but really would just mean, like, you know, any device we launched into space is called the spacecraft.
Yeah, it's not a satellite because it's not in orbit around Earth or any other sort of body. It's just sort of sent out there to explore. And it's called Pioneer because it really was a pioneering mission. It was the first thing from Earth, first scientific object sent out to explore the outer Solar System. It was the first man made object to go through the asteroid belt, for example. It was the first close flyby of Jupiter. Like the first close up pictures of Jupiter came from Pioneer.
So when was it launched. It was a while ago, right, maybe older than us.
It's been a nerd since longer than I have. Pioneer ten was launched in March of seventy two, and Pioneer eleven in April of seventy three. And you know, these were iconic missions. Before this, we didn't really know what things looked like out there. We had telescopes from Earth that were pretty good, I guess, nothing compared to what we have now. But if you call up in your mind an image of Jupiter, you probably have a pretty detailed image thanks to Hubble and thanks to all the spacecraft we sent to visit close up. But in the seventies. If you tried to do that, all you could have was like a blurry smear. We just didn't know in detail what these planets looked like until we went to visit them. So this was the first spacecraft to go and do that. Wow.
Even our telescopes couldn't get us a good picture.
I mean they were all right, but nothing compared to what Pioneer could do. And it was an exciting moment even for the public. When these pictures started to come back. They had like a primetime television show to release these to the public, and people were glued to their screens. That TV show actually won an Emmy.
Really, they had a whole show where they just revealed the photographs.
Yeah, exactly. It was exciting. People wanted to know, so it was really popular. It was you know, back in the day, every sort of launch was a special moment, and these kind of pictures they were priceless. They still are now.
Was it a daytime Emmy or a primetime Emmy? Those are two very different things.
I think it was a primetime Emmy. That's the good one.
Right, Well, it depends on you know what you're going for. So they launched a spacecraft in seventy two and they launched like a brother, like a sibling sister spacecraft.
And in the next year, yeah, Pioneer ten went to visit Jupiter, and then Pioneer eleven did Jupiter and Saturn. And this is the end of a series like these are ten or eleven. There was Pioneer six, Pioneer seven, Pioneer eight, Pioneer nine. Those are in sort of solar orbit. They're like experimental spacecraft to develop the technology. But these have all lasted for decades, Like we heard from Pioneer ten last in two thousand and three, which is like thirty years after we launched it.
Wow. Now it's kind of weird because if you're like Pioneer number thirteen, are you still a Pioneers, like being the the thirteenth, first one to do something that's true.
But Pioneer ten, you know, it was the furthest object from humanity for a long time, and it was like the farthest humans have had an impact on the universe was Pioneer ten. More recently, we sent Voyager one, which was launched in seventy seven, and it was going faster, so it's now the furthest object from humanity, even though it left later.
Now paint a picture for us, what what do these spacecraft look like.
They basically look like a big satellite dish, which is how they communicate back to us. And then there's like, you know, a cube of electronics strapped to the back, and that's where you have like instruments and you know, things that make measurements. This one has like a cosmic ray telescope on it, something to analyze plasma, something to analyze radiation. And then they've got a few things sticking off of them, like these big arms that stick off, and that's where the power sources are. For example, these things are powered by radiation. There's a radio isotope thermoelectric generator. Well, that's plutonium in it, and it's basically just plutonium is decaying and that the energy from the decay turns into heat, which then they turn into electricity and that powers this thing. It's like a plutonium battery.
Whoa, it's a nuclear powered spacecraft basically.
Right, Yeah, how else could you power this thing? Solar panels wouldn't be effective after decades when you're so far from the Sun that it it just looks like another star. And we couldn't charge up our batteries and send them out there. So really nuclear power is the only way to power these very very long lived spacecraft, all.
Right, So we sent it out, and we sent it out to Jupiter and Saturn, and something happened along the way.
Something weird happened. Yeah, the weird thing is that it wasn't flying the way that we thought it should. Aw. Pioneer turns out to be sort of unexpectedly a really really sensitive instrument to measure gravitational pull of everything in the Solar System, and that's because it almost never fires its thrusters. It's just sort of like a ball we threw out into space. A lot of the other satellites that we send out there, like Voyager, it's got a bunch of thrusters and it's constantly firing them to change this direction. So it's hard to predict exactly where it should be. But Pioneer, it's just spin stabilized and we just launched it out there, so we can use sort of Newton's theory of gravity and then Einstein's modification to predict exactly where it should be at any given moment. And when they measure to see where it actually was. It turns out it was kind of off course.
Wait a minute. First of all, we just threw it out there. It doesn't have like, you know, thrusters to steer it or to change its direction.
It does have some small thrusters and a little bit of fuel, but these are just in case it needs a course correction. But yeah, unlike later spacecraft, it's primarily just like a rock that we throw out into space. Now we keep it spinning right. That helps stabilize it to go in the right direction. But essentially we just toss it out there and then we just measure to see where it went, and that tells us something about like the gravity that it experiences along the way.
WHOA, that's wow. And how do we know where it is? If we just throw it out on into space.
It sends us messages and it answers messages, and we can tell how far away it is by how long those messages take to come back. And we can also tell how fast it's going by the Doppler shift of its messages. The faster it's going, the more the wavelength is changed of the messages that return. So we have those two pieces of information how far away it is and how fast it's going.
And I guess we triangle it, like if we talked it one day and then we talked it the next month, and we can sort of as the Earth move, we can Is that how we can tell where it is?
Yeah? Also because we can tell where the signal is coming from right and located in the sky, and so we can tell where it is, how far away it is, and how fast it's moving. And then we compare that to our model of where we think it should be. Are you want to keep up to day and like is this thing going in the right direction? And is it going to crash into Jupiter or just fly by?
Right?
All?
Right? So then we threw this space grab into space and it didn't go where we thought it would, Right, that's the anomaly.
That's the anomaly. It was hundreds of kilometers off course. Something was pulling on this thing. It was slowing it down in a way that we did not understand. There's some small acceleration of this thing towards the Sun that didn't have an explanation from any known physics. Weird hundreds of kilometers off course.
That's not a little It's not a little like if I if I miss an address by one hundred kilometers being another state.
Yeah, it's actually a really really tiny effect, but it adds up over the thousands and thousands kilometers of its journey. The effect of this force, this unexplained anomalist force, is ten billion times smaller than the acceleration we feel here on Earth from the gravitational pull of the Earth. So that small effect really adds up over the lifetime the decades of this craft's flight to get it hundreds of kilometers off course.
WHOA all right? And so we knew one thing about it, which is that this mystery acceleration was directed towards the Sun. That's one clue.
That's one clue. The other clue was that the same thing happened for Pioneer eleven. Wasn't just like some weird thing like, oh, maybe we shot Pioneer ten off in the wrong direction or make a mismeasurement early on, like the same thing happened to another spacecraft.
I see, did it happen for Pioneer one through nine?
Those guys didn't go out into the outer Solar System, so they didn't get a chance to probe that.
Oh I see, they weren't true pioneers.
Yeah, and the Voyager, which went out sort of in the same area. They had lots of complicated thrusters and were always doing these adjustments, and so they weren't nearly as precise probes of gravity. They weren't just like pure flying.
Rocks, all right. So that's the Pioneer anomaly. The big mystery what was happening to the peace craft that was steering them off course. So let's get into what could be possible explanations for this effect and also how it was possibly fixed. But first, let's take a quick break.
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All right, we're talking about the Pioneer anomaly. These are spacecraft we've launched in the seventies out towards Jupiter and Saturn, and they sort of got off course for some mysterious reason, Daniel, these are spacecrafts that are still out there, right. They're going to be out there for a long time.
They're going to be out there forever. They just keep going, right, There's nothing we can do to stop them or pull them back. They're just sort of headed out into the galaxy.
They won't run out of batteries.
They will run out of batteries eventually. You know, the half life of their plutonium batteries is like eighty seven years, so it's going to go for a while. But yeah, eventually it will run out of battery. But that's not going to stop it. Right, it doesn't need battery to go. It just has its velocity and it just keeps flying.
Oh wow. Like basically, we torew trash out into space. It'll be there forever.
But we labeled our trash, right, we put our names on it, and we said exactly who we are and what we're like found.
Come conquer us and or eat us.
This is where we farment on us.
Yeah, it's comedily pointing towards us. Right, yeah, exactly, and we put a plaque on it. We said exactly how to get to Earth. We put like a pulsar map, so if you knew where the pulsars were in the galaxy, you could exactly triangulate where our solar system was. We put a picture of humans on it. We even recorded some sounds from Earth and put it on there, as if like they would know how to play a record and know how to interpret that.
So we threw these spacecraft out into the outer Solar System and they started veering off course for some mysterious reason. Now did people freak out or were they just sort of puzzled about this?
At first, they were just puzzled and they figured, well, we must have made a mistake somewhere, or there's some tiny little effect that we hadn't accounted for. Because you know, it's not just as simple as you toss a rock out into space and then you do gravitational calculations. There are lots of really small effects. You know. One set of small effects is like, well, there's a lot of different sources of graph It's not just the Sun that's pulling on these things, and it's all the planets and all the moons and all the rocks and the asteroid belt and all the tiny little things in the Kuiper Belt, and you know, even other stars provide tugs. So at first people thought, oh, we just haven't been as careful as we needed to to sort of tie up all the loose ends.
I see, like there could have been like it may be passed by a big asteroid that maybe pulled it off course or something.
Yeah, or even simple things like maybe we're analyzing the data wrong, you know, we mismeasured it or misinterpreted this result or something like that. First, when you see something weird in your data, that's your assumption is that, oops, we messed up, or we just weren't thorough enough. And the cool thing about Pioneers, that's very very precise data, and so it allows for really detailed test and so you can go, like, go through your whole list of ideas for what could be affecting the flight of this thing, add them all up, and then compare them to the number. It's a really valuable way to check your understanding.
Right because I imagine, you know, like you said, your first wish is that it's aliens. But I imagine you're Also, I sort of afraid a little bit, like, oh my god, what if I made a mistake, Like what if I am totally doing this where I have a typo in my formula or something. Right, does that emotion also pass through you?
I'm sure it does, you know, for those guys, you remember there was one Martian probe that crashed because somebody typed the number in in the wrong units, Like there was a European group, an American group, and somebody put something in in pounds and somebody else interpreted it and kilograms and oops, and then the whole thing crashed and burned. So yeah, mistakes do happen, absolutely, yeah, just.
Don't work with those Americans and their non international system.
In my personal research, there's very little opportunity for aliens to affect our data. I mean, that would be pretty awesome if aliens like change the collisions at the LAC and cause new weird stuff to happen as a way to communicate. Actually, that would be a pretty cool science fiction story, right, discovering aliens through particle collisions.
Alien pranksters, alien physics pranksters.
Exactly, Aliens, If you're listening, I welcome that. Please mess with our data. It's the large Hadrang glider send.
Us the message, the first physics prom com All right, so what were some of the things that they thought could be happening here with the pioneer anomenally.
Well, the first thing that comes to mind is just the location of everything in the Solar System. So they went back, they did a really detailed check and they thought, for example, like, how well do we actually know the location of all the planets, you know, Earth and Jupiter and Saturn. If those are off by a little bit, could that explain you know, a little gravitational tug. And you know, we know these things really well because we've been watching these planets for a long time and they mostly just obey gravity. So we have really really detailed models. We know the location of these planets down to the meter, and these effects are just too small. So, like we think we know the gravity from all the planets and all the little things in the Solar System, there is uncertainly there, but it can't explain an effect of this size, all.
Right, So it wasn't our measurement of the planets could be the measurement of you know, asteroids, because there is a lot of dark asteroids out there.
There were some asteroids out there, but those are all really small. You know. Remember, gravity is really weak, and so to have any sort of effect, you either have to be large or you have to be close. So because the same thing happened to Pioneer eleven, we didn't think it was like a one off event that just like some object happened to get near one of these things. So it seemed like it had to be some sort of more systemic thing. Another thing people thought about is like, well, what about the solar wind? Right, the Sun is pushing on things. It's not just tugging on them with gravity. It's actually pushing on everything. You know, it's sending out streams of particles. You could use that as a solar sail to navigate the Solar system. So if you're like hunting down for tiny little effects, you might want to consider the effects of the photons and the protons and the electrons that the Sun is streaming out.
Right, but the solar wind is pushing things out. But here something was kind of pulling the spacecraft towards the Sun.
Right exactly, So it's the wrong direction. If anything, you would expect the solar wind to accelerate it to push it further out into the Solar system, make it go faster. So we needed some other effects, something that was tugging it back into the Solar system. And so this long list of basic checks were done, and none of them could explain what was going on.
None of them are sort of strong enough to account for the deviations of hundreds of kilometers. So it wasn't the basic stuff. And then that's when people started to get creative.
I imagine, yeah, they started to get created. They thought, well, what if there's something else on the spacecraft that's basically giving it a little push. You know, what if there's like effectively a thruster, Because think about the batteries on these spacecraft. These things generate heat, and things that are hot radiate photons, and when you radiate a photon, you're basically getting pushed. You know. If you shoot off a photon to the left, then by conservation momentum, you're going to the right, and everybody, everything that is hot is giving off photons. Like me and you, we glow in the infrared. Right, you put on night vision goggles like the Predator, you can see a human body because it's giving off in for a red photon.
I knew you would work in aliens somehow, you do. Wait, does that mean, like if I put a flashlight out into space and turn it on, it would start to go like it would basically act like a rocket.
Yes, a flashlight is a rocket. Absolutely. It throws particles out the back, and so it has to go the other direction. Now, if you put two flashlights shining in the opposite directions, it won't go anywhere. They'll balance each other. So the pioneer people thought, well, it's got these things on it, but they glow in every direction, right, and so if heat is the same everywhere in the spacecraft, that's not going to effectively give it a push.
Wouldn't It depends on the shape, Like a hot sphere would give off photons in all directions. But maybe, like I don't know, like it's something that looks like a dish, might not.
No, you're right, And that's a really interesting clue. And people thought for a while about this, like maybe the complicated shape of the spacecraft, it's not giving off heat in the same direction everywhere. But there was another important clue, which was that this effect wasn't dropping as a function of time, like it wasn't fading, and we know the heat from these batteries should be fading, like this is a radioactive thing, it decays over the half life of eighty seven years. These things eventually cool and then just become dead. And so if it's due to the heat of the batteries, you would expect this thing to fade with time. But the data we had showed that it was constant. So people thought, well, can't be the batteries.
I see, it wasn't cool enough.
It wasn't getting cool all.
Right, So then what else did they think it could be.
So that's when it got exciting. They thought, well, we can't explain this using any sort of known physics, any solar wind, or any gravity or any heating of the spacecraft, so let's get creative. And people thought, well, maybe we've accidentally created something which measures like the expansion of the universe, because they thought maybe space is expanding inside the Solar System and it creates this weird gravitational potential. And we know that gravity and time are connected because, for example, if you go near a black hole, time slows down for you, so over vast stretches of space, potentially time is getting slowed down as you move through these like expanded space, whereas our clocks, the ones that we're using to sort of predict where this thing goes, these really precise atomic clocks basically assume that space is flat. So if we're measuring time differently than something that's flying out into the Solar System, then maybe that could explain it.
Mmmmm, meaning like maybe the clock on the spacecraft is wrong or do you mean like it's actually in a different time.
It's actually in a different time. Yeah, this falls under this whole set of ideas, like the non uniformity of time, right, And we've talked a lot in the podcast about how my clock and your clock can disagree but both be correct because there is no universal sense of time. So this is an idea sort of along that direction, like maybe we're measuring the expansion of space and those gravitational effects are distorting the clock on the spacecraft. Not that it's wrong, but you know it's different, it's just differently timed.
I see. So maybe the idea is that maybe it is it was supposed to be, but our measurement of where it is is wrong because the timing in the clock on board is different than we think it should be.
And that was the general concept, like maybe something in this direction will help us, because we know gravity and time are connected. But they couldn't actually make it work. They try to like get the math to all work out and say, is this consistent with general relativity and what we know about the expansion of the universe? Would that explain that? And it could never be made consistent, and so it would have to be like some weird deviation have to be some special case of how time is affected by gravity for some reason only in our solar system. And so, you know, when you start to develop like a new idea for how to explain some weird science, you want as simple a new idea as possible. You don't want to have to like add all sorts of weird bells and whistles and exceptions and stuff. And so this started off sort of promising and then ended up being like, hmm, doesn't really fit.
It wasn't just that it was in the wrong time zone or daylight savings that couldn't explain it either.
No, I mean I make that mistake all the time, and they usually blame it on aliens, which is why I miss a meeting, But no, they couldn't explain this using any sort of general relativistic effects on the clock or even simple modifications to general relativity to allow for effects on the clock of the expanding space in the Solar System. So that didn't work out.
You can't blame the engineers, and you can't blame Einstein or general relativity. What else could it have been.
Well, people got excited for a while when they thought maybe it was dark matter. Right, we've accounted for the gravitational sources that we know about the planets and the rocks and the Sun, but we also know that most of the gravity in the universe isn't from the stuff that we can see. It's actually from this weird invisible matter. We still don't understand that's everywhere, and we think that it fills the galaxy. In fact, extends beyond the galaxy and is five times as much of it as there is normal matter. So if you're still ding details of gravitational effects, you might expect to have to take into account the dark matter.
Interesting, Yeah, like our Solar System could be or is probably bathed in dark matter. Right, that could potentially affect the gravity of of things We send out into space.
Absolutely, dark matter definitely is here. It's everywhere. It's all around us. There's dark matter with us in this room. The dark matter all around the Earth. We can't see it or detective because we think it only has a gravitational interaction. And remember gravity is super duper weak, so usually we're only sensitives to dark matter if there are huge amounts of it, you know, like galaxy sized amounts to affect how the galaxy spins. It's really hard to detect like local blobs of dark matter. So people got excited when they thought maybe Pioneer ten and eleven are like a local probe, or they're telling us how much dark matter there is here.
Interesting, But wouldn't if there was some anomaly in dark matter, wouldn't it affect all the other planets.
Too, Yeah, exactly, it would. And we also don't think that there is that much dark matter. We know that there's five times as much dark matter in general in the universe, but we don't think in our Solar system there's that much because that doesn't clump up we think the way normal matter does. Like if you took the normal matter in the galaxy and just spread it out throughout the whole volume of the galaxy, it would be pretty thin. That's the way dark matter is. This five times as much of it, but it's much more spread out than normal matter is, so sort of in the volume of the Solar System, it's like one millionth of the mass of the Sun of dark matter, I see.
So it couldn't be that either. So then they couldn't blame it on a technical issue or sort of a theoretical issue, And so it was a big mystery, I mean for decades, right, Like they've seen this anomaly for you know, thirty almost forty years.
Yeah, people really worked on it for a long time, and it was in the nineties that people that has really detailed investigation went through all these possible explanations and couldn't explain it. And then people had a lot of fun coming up with theories of new physics to try to explain it potentially, And it's sort of like a standing question in science for quite a while. People even try to explain it using like weird modified gravity, like maybe gravity doesn't work the way Einstein and Newton thought we did, and somehow gravity changes when you get out into the outer Solar System. But you know, that doesn't really make sense because we understand how Pluto and Neptune and Urinus operate. So there are a lot of questions about what could explain this, and a lot of crazy ideas thought up to explain it, none of which were ever really very compelling or which worked. So it's sort of a question like, are we going to find some boring explanation for what this is? Or is somebody going to come up with a new idea that actually, you know, makes it all click together and tells us something new and deep about the universe? Right?
Are you going to get a try again when you scratch off the surface or are you going to a million aliens in the process. All right, well, let's get into how this mystery was finally resolved, if it was resolved at all. But first let's take a quick break.
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All right, so the Pioneer anomaly was a big mystery for decades back in the seventies, eighties, and nineties, space craft we throughout their into space. We're veering off course, Daniel, How was it all resolved in the end?
If it was so, we actually do think we have a pretty good understanding of what happened by now, and it's due to some sort of like data archaeology by some researchers really dedicated, really interested in understanding how this worked. They went and found some old data in the mid two thousands and did a really detailed study and they think they've cracked it.
Oh wow, in the mid two thousands. So all this time since the seventies, did these spacecrafts were out there off course and people just sort of shrugged it off for a while, or that they just gave up.
Or what.
Well, you know, when there are these puzzles in science, it's not always easy to know how to crack them, and so sometimes they'll be out there for a long time decades. Even people like well that's not understood, but nobody really knows what to do about it. So finally somebody said, well, I'm going to try to go back and find some more data, dig out some old data nobody'd ever seen before, and make a more detailed study than anybody's ever done before, and maybe we'll figure it out.
Wow, that's wild to me, Like, how do you sleep at night? Like, let's say you're the scientist or the engineer who worked on this, Like, how do you ever be at peace? You know, It's like if somebody told you, hey, I notice your car mysteriously moves an inch every night, and you're like, well, I don't know, how could you go to sleep?
I think that's why smart scientists have great ideas in the middle of the night, because their brains are always working on these things, always chewing away on these puzzles and these questions.
All right. So then in the two thousands, a group of people said, hey, we want to figure this out. So they sort of dug through all the old data. But that was kind of hard, right, because this is data from the seventies.
Yeah, they literally dug through old data and they were specifically focused on this question of the heat from the batteries and whether or not it really was decaying over time. And what they discovered is that we didn't actually have all the data. Some of the earliest data from the spacecraft was like stored on magnetic tapes and not really included in most later analyzes because it was kind of a pain to go and find it and recover it and process it and stuff. So they did a bit of like archaeology, and they found more than a dozen boxes of magnetic tapes stored under a staircase at JPL in Pasadena, and they worked with like an old school programmer to create software that could read these tapes and clean it up. So they got sort of a longer time series on the data than anybodybody else had.
Like data on what the position of it, or like the signals we were getting from it, or what.
On the position of it it specifically the earlier positions. Remember we talked about how we didn't think it was just heat coming off the spacecraft unevenly because it would have faded with time, and it didn't look like it was fading with time. So to trying to answer that question in more detail, they said, well, let's look at earlier data. Data when it had just left the Earth to see if we can spot this effect earlier on.
I see you're looking for a weird effect on where you think it should be different from when them were where it is, right.
Yeah, exactly. So you're basically comparing curves. Right, you have the curve of what you expect and the curve of where it actually was, and now you're trying to come up with a new expectation. You're like, can we tweak how we understand this thing flies so that what we expect matches what we observe.
And you also have to sort of look back in time in the Solar system, right, like in this back then, what where were all the planets and asteroids and all that? In order to think about where it should have been exactly.
It's a complicated calculation, and to do this right, you need to know not just where it was, but you also need to know, as you were saying, where it's giving off heat. Like the shape of this thing really affects how it glows, because, as we were talking about before, it's not just a sphere, right. Physicists always likes to assume everything's a sphere first order, but the details matter when you're making really really precise measurements. And this thing has two big hot batteries on one side and then like a cool dish on the other side. But it also has a bunch of instruments that use that electricity, and so as they draw current, they get hot, and as they heat up, they glow and these kind of effects. It's just the glowing heat from these things is big enough to explain the effect that we're seeing.
Yeah, and I think, you know, you say batteries, and that makes me think of you know, like a duris a battery or a car battery, But really these are like nuclear reactors, right, they're generators.
Yeah, exactly, They're not fission or fusion. They're just sort of like slow rolling radioactive decay that generates the electric But yeah, they are nuclear reactors. But also everything on the spacecraft that uses that electricity eventually leaks some of that energy. Nothing is perfect, right, and it leaks that energy into heat, just the same way everything that you use that has electronics in it will eventually heat up. Your computer heats up as you use it, right, there's no like fire burning inside your computer. It's just inefficiency from the use of electricity. So if you have an object on a spacecraft that's drawing electricity, not even just the batteries, but the equipment on the spacecraft gets hot as it uses the electricity. To understand the effect of all this stuff, you need to know like exactly where everything was on the spacecraft and how hot it got. These days, we can do that pretty well. We have like really fancy software to model this kind of stuff, but you know, we don't have the records that match that software from a really really old instrument, Like this thing was built forty years ago. You know, we have like blueplearants drawn by hand by the original designers. So these researchers had to go in and build a model of the sort of heat flow of Pioneer spacecraft by hand like later. And it's involved like fifteen thousand individual pieces like exactly where this cable goes and exactly how thick that piece of aluminum it was, and like this is a huge effort. Wow.
So yeah, they had to basically create a virtual model of the spacecraft and then put it out into space with the heat source and see if it would deviate the way that they were seeing in the data.
It's really incredible precision. You know, think about like when you drive your car, do you expect your car to slow down when you turn the headlights on? Right? You don't expect it to, but actually it does. Right. Turning on the headlights slows down your car because you're basically shooting photons away from your car. So this is the kind of effect that we're looking for. It's amazing that it actually happens and they were able to figure it out. So now there are calculations which include more time information and a much more detailed model of the spacecraft actually match really well what we see.
So they think they solved the mystery.
They think they've solved the mystery.
Turns out it was the plutonium in the power source next to Saturn.
Except it's just uneven heating right eventually over many years. The fact that one side of this thing is hotter than the other means that it gave off more photons, which gave it a little bit of a push. It's like if you had two flashlights out in space and one of them was a teensy bit brighter than the other one, you would get pushed away from that flashlight a tiny little.
Bit, and that explains why it was being pulled towards the Sun, because you know that the way this base craft is designed, you know, you always want to point the dish back towards Earth kind of right, and so that means that the hot stuff is sort of in front of you, which was slowing it down.
Yeah, we're pointing the hot bits of this thing out towards the Aliens and the cold side back towards Earth. So yeah, that effectively slows it down a tiny little bit.
I guess the lesson is, you know, it's always better to have a hot back end.
I'm not going to touch that at all, but Pioneer eleven apparently had the same hot back end, and that's why the same thing happened to Pioneer eleven. The story all sort of fits together and makes sense. And I love these sort of science stories when it all just clicks together and the explanation matches the data and it all just sort of works. It's like, man, math is correct, physics works, the universe actually makes sense. It's incredible.
I guess you're simultaneously impressed by yourselves but also disappointed that you're so good at figuring out the universe.
Kind of yeah, it's not as exciting an explanation as like we discovered a new way that time flows or gravity is broken or something like that, or we have a clump of hidden dark matter in the Solar System. That would be more exciting. But you never know, Like science is about exploration, which means you never know what you're gonna find. Usually it's boring dust and rubble, but sometimes sometimes it's a real diamond, it's a gem, something that gives you a clue about the nature of reality, and you never know, which is why you just got to keep scratching.
All right. And then this is sort of in the community, this is the most accepted explanation of what happened. Like everyone feels like, oh right, these researchers totally nailed it. They it totally explains it, or is there still some sort of uncertainty about it both.
I think people accept this as an explanation for what happened to Pioneer ten and Pioneer eleven, so that sort of anomaly has been solved, But there are still plenty of anomalies in how spacecraft moved, not just Pioneer ten Pioneer eleven, but every spacecraft that does one of these sort of gravitational slingshots ends up going off in a direction that we don't quite understand. This is called the fly by anomaly. Basically, every time one of these things happens, it doesn't quite work out the way we expect, and nobody really understands it. So there's a long list of things we don't understand about how things move into Solar system, even you know, as basic it's just like gravitational mechanics about things moving in the Solar system, still have questions that need to be answered, right, which.
Is all the more impressive that they can. I'm going to say we because this is a good thing. So I'm gonna claim the royal we here. We can like land spacecraft in Mars right and like know exactly where it's going to land on the planet. That's so amazing.
It's really incredible what we the scientists and engineers have accomplished. It's too bad what they messed up on.
All right, Well, that's the Pioneer anomaly, and I guess we can reclassify it now, Daniel, as the Pioneer nomaly or the Pioneer story, or.
The high precision test of science. That is the Pioneer spacecraft.
That's not as catchy, but maybe more accurate. Again, another reminder of how you know vast space is. I mean, this thing is still within our backyard, just the Solar System. And even even then, these distances are huge and there's a lot that can happen out there when you go out into deep space.
Yeah, Pioneer ten is more than twelve billion kilometers from Earth. It's tens of light hours from Earth and moving away really really fast, instin to reach another star system in about two million years. Now, that's about sixty seven light years from here. So maybe in two million and sixty seven years we'll get a message back from the Aliens saying thanks for.
Your garbage, Thanks for your garbage. With the hot front.
End back end, it's a hot back end, only.
We turn it around. Dan, Let's see if we can turn this run.
And we'll back into this cultural misunderstanding with the aliens.
All right, Well, we hope you enjoyed that. Thanks for joining us, See you next time.
Thanks for listening, and remember that. Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeart Radio, visit the iHeartRadio, app, Apple podcasts, or wherever you listen to your favorite shows. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact. But the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. House US dairy tackling greenhouse gases. Many farms use anaerobic digesters to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you as dairy dot COM's Last Sustainability to learn more.
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