Planetary Radio: Space Exploration, Astronomy and Science - Solving Cosmic Mysteries Deep Under the Earth

Episode Date: June 12, 2006

Art McDonald is Director of the Sudbury Neutrino Observatory, two kilometers deep in a nickel mine in northern Canada.Learn more about your ad choices. Visit megaphone.fm/adchoicesSee omnystudio.com/listener for privacy information.See omnystudio.com/listener for privacy information.

Cosmic Mysteries revealed from under the Earth, this week on Planetary Radio. Hi everyone, welcome to Public Radio's travel show that takes you to the final frontier. I'm Matt Kaplan, and I hope you're not claustrophobic. Frontier. I'm Matt Kaplan, and I hope you're not claustrophobic. Our show, so at home among the stars, this time descends two kilometers under the surface of our planet. That's where a remarkable and gigantic instrument of exploration has been unearthing secrets about the inner workings of our sun, the biggest explosions in the universe, and why we're not all made of antimatter. Our guest is Professor Art McDonald of Queen's University, Ontario. Art directs the Sudbury Neutrino Observatory, or SNO. Note that it's called an observatory, not just a detector.

We'll learn why in a few minutes. Bruce Batts will pay us his usual visit, bringing visions of the night sky and another chance to win a Planetary Radio t-shirt. That's later on What's Up. News, news, news, news, news, beginning with the publication in Nature of more Cassini radar findings about cloud-shrouded Titan. The spacecraft actually collected this data

as it passed over Saturn's moon back in February of 2005. But this is the first write-up in a peer-reviewed journal. What's that you say, Bucky? You let your subscription lapse? Well, there's Emily Lakdawalla's write-up in her weblog. You'll find it at planetary.org slash blog. While you're there, you might scroll down a bit to see a Mars rover-powered turntable. Yes, that's right. It's a $125,000 record player that claims to rely on the same motor that turns the wheels of a rover.

Some people have way too much. The crew of the International Space Station thought it had fixed their oxygen generator. The darn thing quit again after just seven hours. Now they're going to replace a power supply. Don't worry, there's still plenty of O2 left. Our longtime listeners know we've been following the still-unfolding tale of the Pioneer anomaly. Slava Turashev and his JPL team have announced they have successfully recovered almost all of 30 years of data from the two spacecraft.

There's a detailed update at planetary.org. And finally, get out your pencils. We've got a new space word for your vocabulary list. It's planemo, which is short for planetary mass object. Think bigger than Jupiter, smaller than a star, and traveling the galaxy more or less independent of any star. Canadian researchers have found four new planemos, and all are surrounded by disks of dust and gas, perhaps enough to generate planetary systems. But life

on any of these planimo planets is unlikely. Planimos may be warm, but they're definitely not stars, so it's just too cold in the space around them. Everyone wants to look for life on Mars, but if we find it, how will we know we didn't bring it there ourselves? That's a question for Emily, and here's her answer. I'll be right back with Art McDonald of the Sudbury Neutrino Observatory. Hi, I'm Emily Lakdawalla with questions and answers. A listener asked, the Mars rovers were basically built by human hands. How do we know they didn't contaminate Mars with Earth life when they landed? This question goes straight to the heart of a whole field of technical research titled Planetary Protection.

At first, people were mostly worried about bringing the Andromeda strain from space to Earth with sample return missions. However, now that we are searching for life on other worlds like Mars and Europa, preventing the forward contamination of these potential habitats with Earth microbes is a serious concern. So serious, in fact, that there is an international treaty, to which the U.S. is a signatory, stipulating that exploration must be conducted in a manner that avoids harmful contamination of celestial bodies. What did the rovers have to go through to keep their cargo holds clear of microbial stowaways? Stay tuned to Planetary Radio to find out. It took eight years to build and fine-tune.

Working at the bottom of a two-kilometer mine shaft didn't make things any easier. But once scientists turned on the Sudbury Neutrino Observatory, it started doing exactly what it was designed to do. Trillions upon trillions of neutrinos pass through it every day. Out of this torrent of particles, maybe nine or ten react with the heavy water in the giant acrylic sphere, each generating a brief flash of light as it obliterates itself.

Those flashes are carefully monitored and analyzed by Art MacDonald and his Canadian, British, and American staff. Professor MacDonald occupies the University Research Chair in Physics at Queen's University in Kingston, Ontario. He also directs the Sudbury Neutrino Observatory. SNO, as it's called, solved a major mystery about the sun with its first published data.

It has gone on to help answer questions about the formation of our universe, and even helps give astronomers early warning of new supernovas. Art McDonald, thanks very much for joining us on Planetary Radio, first of all. Let me start with a bit of a stretch. Is it wildly inaccurate to say that within our solar system, the planets and, in fact, our star, the sun, are, in a sense, just impurities in a sea of photons and neutrinos? Oh, impurities is hardly a way to describe us, I would suggest. Nonetheless, there were a tremendous number of photons produced in the original Big Bang,

as well as neutrinos. There are neutrinos being produced continually in the nuclear reactions that power the stars. There are bursts of neutrinos that occur when a supernova or collapsing star occurs. And if, as we are able to do, you can go to a very deep site where you're shielded by rock above you, and if you take great care with respect to the surroundings in terms of purity and elimination of radioactive materials, then you are able to observe these neutrinos and other remnants of the original Big Bang in situations that enable you to make very sensitive measurements of their properties, and that's the game we're in.

In fact, in your facility at the bottom of that nickel mine, I have read that there's the lowest incidence of radioactivity of any spot on Earth, at least any spot humans can reach. Well, in terms of operating laboratories, we are 20 to 30 times lower in terms of the numbers of cosmic rays that reach experiments in our laboratory than others. And we also have gone out of our way to make the entire laboratory a clean room, similar to the sort of thing you would find for semiconductor fabrication, such that the local radioactivity is controlled to a high degree.

So, yes, we think we've created the lowest radioactivity location that has been created so far. I hope that people will visit your website. We'll put the link up to the Snow Lab or Snow website on our site because people really need to take a look at the description of the site and maybe even more impressively, the images that were taken while snow was under construction. It is absolutely an amazing device. I mean, really, if it weren't surrounded by water, you could probably have rented your

lab out as a science fiction film site. Actually, in an interesting side topic, our lab has been the subject of a Hugo-winning science fiction novel called Hominids by Robert Sawyer. The laboratory is two kilometers underground in one of Inco's international nickel company's most productive mines. And so they're taking thousands of tons of nickel out of the same shaft that we use to travel back and forth to reach our facility. Needless to say, it's a standard underground mining environment until you get to our laboratory, and then it's about 10,000 times cleaner in terms of air quality inside. So you don't see any dust motes in the air when you look towards the lights in our facility. The detector itself is about the size of a 10-story building.

It has as its core 1,000 tons of heavy water on loan from Canada's reserves, a value of about $300 million. It has 10,000 light sensors that cover the majority of the sphere surrounding this central volume, and it is all immersed in about 7,000 tons of ultra-pure light water to shield against the radioactivity that is produced simply from natural radioactivity in the surrounding rock. By the time you get down that deep, the natural wall temperature is about 40 degrees Celsius. We cool it all down to 10 degrees in order to make the light sensors behave in a very quiet way. And we've been taking data since 1998 with this configuration.

This container of heavy water is a clear acrylic sphere surrounded, as you said, by their photomultiplier tubes, which are on a structure which in itself is quite impressive, a geodesic sphere. Yes, Buckminster would love this. He sure would have. Bucky would have loved it. Exactly.

The sphere made from acrylic is certainly the largest construction of its nature that had been done at the time. The amount of dust that is on all of the roughly one million parts of this detector is about the amount you could pile on your thumbnail. So something like eight years to build, went into operation, as you said, in 1998, and in 2001, almost exactly five years ago, you published your first results, and they were of monumental importance to the physics community. Well, we were able to show something that was outside the so-called standard model of elementary particles. That is, we could show clearly that neutrinos change from one of the three types, the type produced in the core of the sun, to other types before reaching our detector. And the heavy water was central to this.

We could make measurements that others had not been able to make. And in the process, we were able to solve what had come to be known as the solar neutrino problem, in which too few neutrinos were observed in comparison to the numbers calculated from what appeared to be very reputable solar models that fit all the other properties of the sun. In fact, the pioneers in this field, Raymond Davis, who received the Nobel Prize, and Koshiba from Japan. Actually, Ray Davis passed away just this past week. We have very fond memories of him as a pioneer of this field.

You have a tribute to him, I know, on your website. Indeed. Their pioneering work had led to this puzzle that, fortunately, we were able to solve with the use of heavy water. And this problem you talk about, this was a 30-year mystery, which said that either something was strange with these neutrinos, or the sun was not working the way theorists had come to believe it must work. That's right. Because the strange thing about neutrinos would have been outside of the standard model

for elementary particles, there was great reluctance to assume that that was the case. In the standard model, neutrinos are thought to not change from one type to the other, and in fact, to not have a finite mass. What we were able to do with heavy water is to measure two things simultaneously. First of all, the total number of electron neutrinos, which is the type that is produced in the core of the sun by the nuclear reactions that power the sun,

and the total number of all neutrino types, all so-called active neutrino types, electron, mu, and tau neutrinos. That second thing is something that had not previously been measured. And so we were able to make a comparison and to discover that, in fact, there were only one-third of the total that remained as electron neutrinos when reaching our detector, whereas the total number of neutrinos was in very good agreement with the calculations of solar models. And so it was quite clear that electron neutrinos were changing from one type to another in passing through the sun and reaching our detector underground. We'll hear more from Art McDonald of the Sudbury Neutrino Observatory when Planetary Radio returns in a minute.

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The Planetary Society, exploring new worlds. Welcome back to Planetary Radio. I'm Matt Kaplan. We're talking about particles this week, not just any particles, but particles spewed out by our sun and other stars at a rate of trillions of quadrillions every second. And yet it takes a huge instrument like the Sudbury Neutrino Observatory in Canada to detect just 10 or so a day. Before the break, Snow's director, Art McDonald, told us how the observatory solved the mystery of the sun's missing neutrinos. But did this just open up a whole new can of fermions? Now, did this cause physicists to breathe a sigh of relief, or did you cause them additional headaches?

I don't think physicists ever feel that a clear indication of something new about the world around us is something that is a negative thing. In general, what they regard it as is a clarification of our understanding of the world, and it does send the theorists back to the drawing boards in terms of attempting to understand in detail how neutrinos fit into this standard model of elementary particles. That in itself is leading to some very interesting theories. The leading theory that explains how neutrinos have a finite mass

is also a theory that could, in the early universe, help us to explain why it is this universe is now essentially entirely matter and very little antimatter. When you find something new, you usually are able to go on and attempt to solve some other things with this new information, and that seems to be happening in this case as well. We should talk about the future, not just of snow, but of Snow Lab. And you surprised me by telling me shortly before we started recording that the snow instrument itself is slated to stop collecting data at the end of this year, but it's far from the end for SNOLAB. That's right.

First of all, in terms of SNOW, the SNOW collaboration, 130 scientists from Canada, U.S., and U.K. looked at the measurements we're making and decided that by the end of this year, with this latest phase of the project, that by the end of this year with this latest phase of the project, we would be limited more by our ability to calibrate the detector in terms of our objective now, which is to try to pin down in detail the parameters of these new theories that include neutrinos in the standard model. We'd be limited more by the systematic uncertainties in our ability to calibrate than we would

by simply higher statistical accuracy on the measurements. And so we said, fine, we'll decide that we've done everything we can do and we will remove the heavy water. There is the possibility, and another collaboration has formed, which is seeking support to replace the heavy water with so-called liquid scintillator that would give us even more light output than the heavy water does by about a factor of 100 and enable us to look at lower energy neutrinos from the sun. Now, in terms of Snow Lab, we also have a grant from Canada Foundation for Innovation

to expand the laboratory and create space for four or five other experiments that can benefit from this ultra-low radioactivity environment, experiments that would look for the particles that make up the 25% of the universe that we now think is so-called dark matter, that which you don't see when you look out on a starry night, and also very rare radioactivities that occur perhaps a few times a year, even in a large mass of material called double beta decay, that may give us, again, further information about the question of where neutrinos fit into the standard model,

and also answers perhaps to this question of how come we're all made of matter and don't have a lot of antimatter hanging around. Art, is there some chance as our ability to detect neutrinos improves to perhaps begin to use these detectors or observatories in the way that optical telescopes are to tell us more about the sources of these emissions? Well, we're already instrumented in our detector and several others around the world to detect collapsing stars or supernovae. We have a network among these detectors that would enable us to tell the astronomers with a couple of hours lead time where such a supernova might be taking place in our galaxy.

So it is an astronomical observatory from that point of view. Also, there are some fantastic detectors being developed, one of them one kilometer cubed under the polar ice cap, the South Pole, in which light sensors look for the most energetic neutrinos from the farthest reaches of the universe, unimpeded, of course, by other matter or by magnetic fields. And that, in addition to one that's being developed in the Mediterranean, will be able to map the whole sky, looking for neutrinos produced in some of the most energetic processes that can take place in astrophysics, such as acceleration in the vicinity of black holes.

So observatories of various sorts and of a more general nature are certainly the order of the day for what is now being called particle astrophysics as a field in general. Fascinating. The first time I've heard that term. Well, it's becoming much more commonly used as these particles enable us to do things that you can't do with the normal light that's used by typical astronomical observatories.

Particle astronomy. It is particle astronomy. Art, it is always fascinating to hear how our visible world that we deal with, particularly on this show, with things that are generally larger than a molecule and smaller than a star, can be so influenced by particles that are streaming through us every moment of our lives, but we would never detect without tools like the Sudbury Neutrino Observatory. And I'm so glad that you called it an observatory instead of a detector. Well, other people go to the tops of mountains in Hawaii to get away from the sky shine from the cities.

We go underground in northern Canada to get away from the northern lights. It's not a different thing than the astronomical observatories that use light instead of particles like neutrinos. We are out of time. Thank you so much for joining us on Planetary Radio. My pleasure. Professor R. MacDonald of Queen's University in Kingston, Ontario is also director of the Sudbury Neutrino Observatory Deep

Underground in Northern Canada. We will be back with Bruce Betts in this week's edition of What's Up right after this above-ground visit or return visit by Emily. I'm Emily Lakdawalla, back with Q&A. How do we know that the rovers didn't contaminate Mars with Earth microbes? The answer is that the rovers were very, very, very clean.

Assembly was conducted in a clean room by workers wearing coveralls, gloves, hats, and face masks. They cleaned every surface frequently with an alcohol solution. A planetary protection team sampled exposed surfaces and performed tests to demonstrate that each met a strict standard limiting the number of bacterial spores. Anything that could be was baked to kill microbes. The core components are isolated behind filters fine enough to keep any internal microbes from escaping. Planetary protection didn't only apply to the rovers themselves. When the Delta launch vehicle's third stage separated from the spacecraft,

the two objects were traveling on nearly identical trajectories. To prevent the much dirtier rocket from hitting Mars, that shared course was deliberately set so that the spacecraft would miss Mars if not for its first trajectory correction maneuver. All of these steps should mean that Mars is still clean. However, if life is ever found there, scientists will still have to prove it wasn't carried there from Earth. Got a question about the universe?

Send it to us at planetaryradio at planetary.org. And now here's Matt with more Planetary Radio. We're joined by Bruce Betts once again, once again on the telephone. We're going to have to get together in person again someday. Do we have to? Don't worry, I'll shower. All right, you said that last time, too. Bruce, what's up? Well, we've got planets, and of course I'm giddy with excitement.

Well, at least almost giddy about Mars and Saturn. They're hanging out really close to each other, neither of them exceedingly bright, but both looking like fairly bright stars low in the west shortly after sunset, and they're coming nearly as close together as the width of a full moon in the sky. Of course, in reality, it's hundreds of millions of miles, but that's a detail. Saturn is the brighter and yellower of the pair, and Mars is the dimmer and more reddish of the pair. You can also very easily see Jupiter any evening, but it's not cloudy.

If you look up in that direction that you look. I was going to say, it's only a detail if you're not an astrologer, of course. And I'm not. Yeah, you can check out Jupiter. It's over rising in the east. It is very high up in the sky nowadays, looking extremely bright. And in the pre-dawn sky, we've still got Venus looking exceptionally bright. And you still might be able to catch a little bit of Mercury in the evening if you look very low,

low below Mars and Saturn, near the horizon. Binoculars might help, but don't point them at the sun, for gosh sakes. And that's what we've got in the planet roundup there, Matt. Listen, can I stop you for a second before you go on to other cool stuff? I know that you were probably hanging on every word of our guest today because you're a neutrino nut. I am. I am indeed a neutrino nut. You know, kind of odd.

Nothing I ever professionally have dealt with, but they're just so weird and so exotic. And in the amount of time I took to say that, I've had like two or three trillion pass through my body. I counted them. I counted everyone. And I've got to say everyone i feel tingly i you know you heard him talk about this way that they are these detectors or observatories are being used to give early warning of supernovas but i don't think we uh provided the acronym that they've come up with are you ready for this i'm ready ready. Supernova Early Warning System,

or the acronym SNOOZE. Nice. I always enjoy a good acronym, and I'm in the right business for it. All right. I'm going to let you go on. No, that was very interesting. And pretty much the whole neutrino subject, it's all filled with random space facts. But since we've been hearing all about neutrinos, we'll cover something else. When we talk about random space facts, this is more a fact about how space is shown to you as much as about the object itself. You know all those pretty pictures of IOMAP that look like a pizza? Yeah. Yeah, those are all, most all of them that you'll see are accentuated false colors. So IO is exotic. It is weird because

it's yellow and does have oranges, but I just want to let people know when you look at that exotic pizza in most Voyager images, it would not look like that to your eye. Okay, I covered my ears because I don't want to hear about false color. I want to think that everything looks exactly that way. So, please don't bring that up again. Are your ears open again? Yeah, they are. Yeah, no, Matt, that's exactly how it looks. I just wanted to tell everyone how cool those pictures of Iowa look since they're absolutely accurate.

I knew it. I knew you did. Let's move on to the trivia question, shall we? Yeah, and you asked us a couple of weeks ago about a historic achievement that took place almost exactly 35 years ago. Indeed, it was anniversary week for it, and I asked you to tell us what was the first successful soft lander on the moon. Well, we have lots of entries. You know, we keep getting ones every week.

We get lots of new people, and we hope they'll keep coming back. Only one person can win, though, and this week it's Dennis Couchet. Dennis Couchet of North Adams, Massachusetts, who got it right. I think Bruce will let you confirm. Surveyor 1, June 2, 1966, touchdown on the moon. And we should point out this is the first American spacecraft to accomplish that. Yes, that's what I asked in the original question. I apologize for leaving that out just now. Yes, first American spacecraft soft land, Surveyor 1, occurring 35 years ago.

Pretty cool. And let's stay in the theme of the moon and landing on the moon for this week's trivia contest. Tell me, who was the head of NASA when the United States first put humans on the surface of the moon? Good one. Who was the NASA administrator when Neil Armstrong and Buzz Aldrin landed on the moon? Go to planetary.org slash radio. Find out how to email your entry to us and win the fabulous Planetary Radio T-shirt that will make you the envy of all your friends.

You've got until June 19, 2 p.m. Monday, 2 p.m. Pacific, I should say, Monday, June 19th to get those answers to us. And good luck. We hope you win the shirt next week, or two weeks, actually. One will give the answer to this one. Bruce, we've got to get out of here. All right, everybody, go out there, look in the night sky, and think about statues. Thank you, and good night.

Well, there he is, the statuesque Bruce Betts, who joins us every week here for What's Up. Well, there he is, the statuesque Bruce Betts, who joins us every week here for What's Up. Planetary Radio is produced by the Planetary Society in Pasadena, California. Next week, we'll hear from the lead discoverer of a new solar system, one that may be more like our own than any found before. Have a great week, everyone. Thank you.