Daniel and Kelly’s Extraordinary Universe - What was the pioneer anomaly?

Episode Date: March 23, 2021

Daniel and Jorge dig into the mystery of why the Pioneer spacecraft's path surprised scientists. Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

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there the good stuff podcast season two takes a deep look into one tribe foundation a non-profit fighting suicide in the veteran community september is national suicide prevention month so join host jacob and ashley shick as they bring you to the front lines of one tribe's mission one tribe save my life twice welcome to season two of the good stuff Listen to the Good Stuff podcast on the iHeartRadio app, Apple Podcasts, or wherever you get your podcast. Well, my first hope is always aliens, but my first thought is that it's probably a boring mistake. So as a scientist, your mind goes through. Straight to the most dramatic explanation?

Yeah, we're all hoping that somebody out there hits the science jackpot. Everybody wants to find a thing that rocks the world. Yeah, you know, people might not realize that 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 prize? Humanity gets wiped out? Yeah, maybe, but think about what we might learn along the way.

In our dying moments. Hi, I'm Horam, a cartoonist and the creator of PhD comics. 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 smashing 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 iHeard radio. 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 done. 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, that 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 a 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? It's a little suspicious they 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 there's an exciting, fascinating explanation. Something new might be going on.

Or sometimes it's something routine. It could be either one. Absolutely. And people might remember a few years ago, we thought we had discovered neutrinos going faster than the speed of light. I won't say we there because I wasn't among the group of people who thought that was real. When humanity does something good, it's the royal we, including Jews. So when they mess it up, it's them.

It's the Italians. them Italians I won't 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 I should tell you how old I am A little bit Wow that really does teach you

But usually as in the case of the fast and then light neutrinos It's just a mistake In that case they forgot to plug a cable incorrectly and so their calibration was wrong and they mismeasure 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 120 years ago that was the first clue that the universe was quantum mechanical. Yes, it was very 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,

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 was 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. Yeah.

It involves spacecrafts and planets and basically just need to word 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 scratched the surface, Daniel, and see if we can win the lottery here. So today on the program, we'll be talking about what is the pioneer anomaly? Now, it's anomaly, right? not anemone.

That's right. I always get the two 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 70s 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 of course, it's still out there, right? Pioneer 10 and Pioneer 11. 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 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 to Questions at Danielanhorpe.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 of pertaining 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 70s. and I think are now a very long way away. I... no idea. I don't know. 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 happen.

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 may be marked like a turning point for scientists 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. Whoa. You heard about it in high school? like in physics class or how did you hear about it from your physics parents I was a nerd big shocker so I was 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 tell me more 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 get confused when people say spacecraft

because I imagine, you know, Battlestar Galactica or, you know, people in a cockpit or something. But really, we just mean like, you know, any device we launch into space is called a 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, the first scientific object, 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 10 was launched in March of 72 and Pioneer 11 in April of 73. 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've sent to visit close up. But in the 70s, 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 prime time 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 prime time Emmy. That's the good one, right? Well, it depends on, you know, what you're going for. So they launched this spacecraft in 72, and they launched like a brother, like a sibling sister spacecraft in the next year. Yeah.

Pioneer 10 went to visit Jupiter, and then Pioneer 11 did Jupiter and Saturn. And this is the end of a series. Like these are 10 and 11. There was Pioneer 6, Pioneer 7, Pioneer 8, Pioneer 9. Those are in sort of solar orbit. They're like experimental spacecraft to develop the technology.

But these are, of all lasted for decades. Like, we heard from Pioneer 10 last in 2003, which is like 30 years after we launched it. Wow. Now, it's kind of weird because if you're like Pioneer number 13, are you still a pioneer? It's like being the 13th first one to do something.

That's true. But Pioneer 10, 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 10. More recently, we sent Voyager 1, which was launched in 77, 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 do these spacecraft look like? They basically look like a big satellite dish, which is how they communicate back to us. And then there is 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-grade telescope on it, something to analyze plasma, something to analyze radiation. And then they 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 radioisotope thermoelectric generator. What? 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 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 as 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. Now, 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 it 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, a 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 threw it out 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 has 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 triangulate. Like if we talked to it one day and then we talked it the next month and we can sort of as the earth move, is that how we can tell where it is? Yeah. Also because we can tell where the signal is coming from, right? We can locate it 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 like our model of where we think it should be, right? You want to keep up to date and like, is this thing going to the right direction? And is it going to crash into Jupiter or just fly

by? Right. All right. So then we threw this a spacecraft 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.

That's not a little. Like if I miss an address by 100 kilometers of 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 anomalous force, is 10 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. Wow. 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. The other clue was that the same thing happened for Pioneer 11. Wasn't just like some weird thing like, oh, maybe we shot Pioneer 10 off in the wrong direction or made this measurement early on. Like the same thing happened to another spacecraft. I see. Did it happen for Pioneer 1 through 9? 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 missions, 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 spacecraft? 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. Have you ever wished for a change but weren't sure how to make it? Maybe you felt stuck in a job, a place, or even a relationship.

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These are a spacecraft we launched in the 70s out towards Jupiter and Saturn, and they sort of got off course for some mysterious reason. Daniel, these are spacecrafts that are. 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. But you know, the half-life of their plutonium batteries is like 87 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 threw trash out into space. And he'll be there forever. But we labeled our trash, right? We put our names on it. We said exactly who we are and what we're like. It found come conquer us and or eat us. This is where we are.

Experiment on us. Yeah. It's conveniently 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 gravity. It's not just the sun that's pulling on these things. It's all the planets and all the moons and all the rocks in 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 hold 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 is that it's very, very precise data. And so it allows for a 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 sort of afraid a little bit like, oh my God, what if I made a mistake?

Like, what if I am totally doing this or 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 the wrong units. Like there was a European group and American group and somebody put something in in pounds and somebody else interpreted it in 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 LHC and cause new weird stuff to happen as a way to communicate. Actually, that would be a pretty you cool science fiction story, right, discovering aliens through particle collisions. Alien pranksters. Alien physics pranksters. Exactly. Exactly. Aliens, if you're listening, I welcome that. Please mess with our data to Large Hedron Collider. Send us a message. The first physics promcom.

All right. So what were some of the things that they thought could be happening here with the pioneer anomaly? 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 uncertainty there, but it can't explain an effect of this size. All right. So it wasn't our measurement of the planets. Could it 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 11, 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 effect. 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. Then that's when people started to get creative, I imagine. Yeah, they started to get creative. 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 infrared photon. I knew you'd work in aliens somehow. I always do. Wait,

does that mean like if I put a flashlight out into space and turn it on, it would have started 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 depend on the shape? Like a hot sphere would give off photons in all directions, but maybe like, I don't know, like something it 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 is not giving off heat in the same direction everywhere.

But there was another important clue, which is 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 87 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. 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 sort of 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, 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. 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, it doesn't really fit. It wasn't just that day. 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. 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 studying 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 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. You can't see it or detected because we think it only has a gravitational interaction. And remember, gravity is super duper weak.

So usually we're only sensitive 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 10 and 11 are like a local probe where 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. There's 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 is 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,

layman 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, 30, almost 40 years. Yeah, people really worked on it for a long time. And it was in the 90s that people did as 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 Uranus 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 was sort of a question like are we going to find some boring

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 win 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. Have you ever wished for a change but weren't sure how you. to make it. Maybe you felt stuck in a job, a place, or even a relationship. I'm Emily Tish Sussman, and on she pivots, I dive into the inspiring pivots of women who have taken big leaps in their lives

and careers. I'm Gretchen Whitmer, Jody Sweeten, Monica Patton, Elaine Welteroff. I'm Jessica Voss. And that's when I was like, I got to go. I don't know how, but that kicked off the pivot of how to make the transition. Learn how to get comfortable pivoting because your life is going to be full of them. Every episode gets real about the why behind these changes and gives you the inspiration and maybe the push to make your next pivot. Listen to these women and more on She Pivots, now on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. The U.S. Open is here, and on my podcast, Good Game with Sarah Spain,

I'm breaking down the players from rising stars to legends chasing history. The predictions will we see a first-time winner and the pressure. Billy Jean King says pressure is a privilege, you know. Plus, the stories and events off the court and, of course, the honey deuses, the signature cocktail of the U.S. Open. The U.S. Open has gotten to be a very fancy, wonderfully experiential sporting event. I mean, listen, the whole aim is to be accessible and inclusive for all tennis fans, whether you play tennis or not. Tennis is full of compelling stories of late. Have you heard about Icon Venus Williams' recent wildcard bids or the young Canadian

Victoria Mboko making a name for herself. How about Naomi Osaka getting back to form? To hear this and more, listen to Good Game with Sarah Spain, an Iheart women's sports production in partnership with deep blue sports and entertainment on the Iheart radio app, Apple Podcasts, or wherever you get your podcasts. Presented by Capital One, founding partner of IHart Women's Sports. Imagine that you're on an airplane, and all of a sudden you hear this. Attention passengers.

The pilot is having an emergency, and we need. think you could do it it turns out that nearly 50% of men think that they could land the plane with the help of air traffic control and they're saying like okay pull this until this pull that turn this it's just like doing my eyes closed I'm I'm Manny I'm Noah this is Devon and on our new show no such thing we get to the bottom of questions like these join us as we talk to the leading expert on overconfidence those who lack expertise lack the expertise lack the expertise They need to recognize that they lack expertise.

And then, as we try the whole thing out for real. Wait, what? Oh, that's the run right. I'm looking at this thing. Listen to no such thing on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. was a big mystery for decades back in the 70s, 80s, and 90s. Spacecraft we threw out there 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-2000s and did a really detailed study. and they think they've cracked it. Oh, wow. In the mid-2000s.

So all this time since the 70s, these spacecrafts were out there off course and people just sort of shrugged it off for a while or 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 ever seen before and make a more detailed study than anybody's error 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 peas? You know, it's like if somebody told you, hey, I noticed your car mysteriously moves an inch

every night. And you're like, well, I don't know. How can 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 are always chewing away on these puzzles and these questions. All right. So then in the 2000s, 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 70s.

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 analyses 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 work with like an old school programmer to create software that could read these tapes and clean it up. So they get sort of a longer time series on the data than anybody 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, 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 try 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, than 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 like 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, 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 like to assume everything's a sphere at 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, 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 duracil

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 electricity. 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. 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 40 years ago. You know, we have, like, blue clearance 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 this involved, like, 15,000 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 this spacecraft and then put it out into space with the heat source and see if it would deviate the way that we 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 their calculations, which include more time information and a much more detailed model of the spacecraft, actually match really well what we see. Oh, 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. Exactly. 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 you had two flashlights out in space and one of them was a teeny 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, the way this spacecraft 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 alien. 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 11 apparently had the same hot back end, and that's why the same thing happened to Pioneer 11. 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 is 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 going to 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 so then this is sort of in the community this is the most accepted explanation of what happened like everyone feels like all right these researchers totally nailed it they 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 10 and pioneer level So that sort of anomaly has been solved.

But there are still plenty of anomalies in how spacecraft move, not just Pioneer 10 and Pioneer 11, 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 flyby 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 as 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 going to 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. Yeah. All right, well, that's the pioneer anomaly. And I guess we can reclassify it now, Daniel, as the pioneer anomaly 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 then, these distances are huge and there's a lot that can happen out there when you go out into deep space. Yeah, Pioneer 10 is more than 12 billion kilometers from Earth. It's tens of light hours from Earth. And moving away really, really fast, it's destined to reach another star system in about 2 million years. That's about 67 light years from here. So maybe in 2 million and 67 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 if we turn it around, Daniel. Let's see if we can turn this around. 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. is a production of iHeartRadio. For more podcasts from IHeartRadio, visit the IHeartRadio app, Apple Podcasts, or wherever you listen

to your favorite shows. Why are TSA rules so confusing? I'm Manny. I'm Noah. This is Devin. friends and journalists with a new podcast called No Such Thing, where we get to the bottom of questions like that.

Why are you screaming? I can't expect what to do. Now, if the rule was the same, go off on me. I deserve it. You know, lock him up. Listen to No Such Thing on the IHeart Radio app. Apple Podcasts or wherever you get your podcast. No such thing.

I'm Dr. Joy Hardin-Bradford, host of the Therapy for Black Girls podcast. I know how overwhelming it can feel if flying makes you anxious. In session 418 of the Therapy for Black Girls podcast, Dr. Angela Nielbornet and I discuss flight anxiety. What is not a norm is to allow it to prevent you from doing the things that you want to do, the things that you were meant to do. Listen to Therapy for Black Girls on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. It's important that

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