This is the best of our knowledge, a presentation of national productions.
We've been searching for the origins of life for quite some time now.
Well, at least we have been on this program.
Now, in order to get a better understanding of where that origin might be,
there's work being done to study the makeup and origins of planets.
So the earth is not embedded in the asteroid belt,
and that's why the earth is still a planet.
But Pluto is in the middle of a very large belt that goes out to tens of earth's sun distances away from the sun.
And so that's why it's no longer considered planet.
Today, on the best of our knowledge, our Astrobiology series returns with a look at the building blocks of planets
and the clues they hold about the building blocks of life.
We'll also spend an academic minute confirming that if you have arms and legs,
it's a pretty good idea to live on land.
I'm Bob Barrett, and this is the best of our knowledge.
What exactly makes a planet a planet?
And no, we're not just asking so we can give some tips to Pluto.
We're asking because if you know what the planetary building blocks are,
they might give us more clues about the origins of life on our planet.
Enter Dr. Benjamin Weiss, associate professor of planetary sciences in the Department of Earth,
Atmospheric and Planetary Sciences at the Massachusetts Institute of Technology.
He is on a mission to discover and study these planetary building blocks to determine
whether they hold any clues to or even samples of ancient life.
And part of what Dr. Weiss is studying, as he tells the best of our knowledge's science reporter, David Castina,
are smaller rocks that make up planets called planet decimals.
They have the decimal added to the end of them so that you can know that they're on their way to being something else.
And what happens in the formation of the planet is first you start out with a cloud of gas and dust,
and then it collapses under its own self-gravity, and makes bigger and bigger structures,
you know, very small grains and bigger grains, and eventually you can build up to kilometers to hundreds of kilometers sized rocky bodies.
And all this happens very, very quickly.
The cloud that formed the solar system collapses in only 10,000 years maybe,
and then all the subsequent growth from little tiny dust grains to 100,000 to 10,000 kilometer bodies.
That happens in just maybe a million years, maybe a few million years.
A fraction in time when you're looking at the origin of the universe.
Yes. And then even though it's such a short fraction of time,
you could argue that more happens sort of in terms of geologic history during that first 10, say, 100 million years,
then in the subsequent 4.5 billion years of the history of the solar system, go further with that.
Why do you say that? Well, you start basically over a period of just millions to 10 million years ago from a 10 micron,
basically one part and a hundred thousand of a meter, going up to 100 kilometers in just millions of years.
And then Earth is pretty much stayed at 6400 kilometer radius ever since, for the next subsequent 4.5 billion years.
The radius of the Earth itself. That's right. So between the dust grain size and the present size of the Earth,
which is formed at the end of this period, there's a size of bodies that exist, which we call planet test moles,
that are about a few hundred kilometers in radius. And you can think of them as little mini planets.
And that's one thing that Mike has been working on is what were these bodies? What were they like? What was their geologic history?
It's been erased because most of them either went to form the Earth by smacking into each other,
or they were ejected from the solar system or fell into the sun. Only a tiny fraction of these bodies, these mini planets,
are left over and they are the asteroids. Right, are we talking about the Kuiper belt here?
So there are sort of two belts of objects in the solar system that are the residual population of these planet testimals.
There's the belt that everybody knows from Star Wars, the asteroid belt. There's a rocky body of kilometer up to several hundred kilometer radius bodies,
in between Mars and Jupiter. And then in their late 90s, a new belt of objects was discovered actually by a former MIT professor and his graduate student,
out beyond Neptune, called the Kuiper belt. And we knew of an object out beyond Neptune before the discovery of this belt,
and that's the planet Pluto.
So what we realized is that Pluto is just one of these mini Kuiper belt objects, as they're called.
And that ultimately led to the demotion of Pluto from its planet status, because it was realized that it's really a planet testimal.
It's a remnant object from the early solar system that never went on to form a large planetary body like the Earth.
So what is the criteria then that they've adjusted so that Pluto has not made a planetary designation?
Right, so there are a number of different criteria. It needs to be an orbit around the Sun, needs to have cleared its own neighborhood of debris,
and that is where Pluto fails. It's in the middle of a huge belt of debris, which is the Kuiper belt object.
So the Earth is not embedded in the asteroid belt, and that's why the Earth is still a planet.
But Pluto is in the middle of a very large belt that goes out to tens of Earth's sun distances away from the Sun.
And so that's why it's no longer considered planet.
Well, but Dr. Weiss, couldn't we argue that the moon is sort of detritus, is a remnant, is...
People have said that.
I mean, right? I mean, it isn't one of the theories here that an object hit the Earth, and then the consequential explosion and that debris that went out into space did exactly what you just said.
Over years and years clumped together and formed this satellite object called the moon. Aren't all moons sort of debris around planets?
Yeah, this... You're basically... We're walking through the acrimonious debate that...
That followed this renaming of Pluto as a planet.
And what you can see here is that they did not consider moons as planets.
Of course, Pluto had moons as well, Cheron, and now we know it has many other moons, several moons that were discovered subsequently to this.
So moons were not considered a problem as far as planetary status.
So a lot of people were perplexed by this debate as to what is a planet.
And as you can see, it's somewhat arbitrary. But that doesn't mean it's not useful to discuss this.
In the same way, it's not useless to discuss what is a continent.
Why did Europe get to be a continent and not Greenland?
And, you know, ultimately it's a human construction, the word planet, and continent.
But we still learn something valuable from discussing this.
So here you are, and you just gave us an understanding of planetesimal differentiation.
The next word in this phrase is magnetism. I think many of us know what it is, but explain how it applies to what you're talking about.
So the question, the broader question we were seeking to address is what were these plantesimals like?
What were these places like that have been largely lost?
Now they haven't been completely lost because like I said, the asteroid belt and the hyperbelly of their remnants.
We also have pieces of them in the form of meteorites, which are chips off of, in most cases, asteroids that landed on Earth.
And so by studying the existing asteroid belt and these pieces of them called meteorites, we can start to understand what was the evolution of these bodies.
And what were they like? And one question you might ask is, were these bodies differentiated?
And by that I mean, do they have the features and the history that makes a planet a planet?
And what do I mean by that?
In my opinion, what gives a planet its sort of nature, inherent nature is whether it has this characteristic radially layered structure,
typically with a metallic core, overlaid by a rocky crust, the way the Earth has.
So it's this compositionally varied structure, which forms soon after the planet forms.
And it forms because on an Earth-sized planet, the energy released by forming the Earth, which is imagine the Earth is composed of planetesimals,
and they crash into each other and release all of that energy in the form, it was in the form of their velocity.
That leads to large-scale heating of planets and large oceans of magma on their surfaces.
And in such an environment, which occurs just millions of to tens of millions of years after they form,
heavy stuff will sink, light stuff will float, and the most cosmically abundant heavy element is iron.
And so naturally, bodies of mercury-sized and larger are molten and formed this differentiated layered structure with a core soon after their formation.
So is this what creates the magnetic field?
Yes, so once you have a core, if that core is made of metal, like it typically is for the reasons I mentioned,
and that core is cooling, it'll, what we call, convect.
Just the way a lava lamp, there's motion in a lava lamp from cooling, hot stuff will rise, cool stuff will sink.
Once you have motion of a conducting liquid, which is what metal is when it's molten, then you can generate currents in that metal,
and that can lead to the formation of magnetic fields. And that's indeed what's happening even today in the center of the earth.
The earth is still cooling after all this time, and that's leading to lava lamp-style motion of its core.
You mean the interior of the earth? That's right.
And it's coming out the surface, but it's coming from the interior out into the surface.
And that leads to the motion of the core, which generates, we think, the earth's magnetic field.
Now the question is, did these planetesimals have cores?
Did they have their own magnetic fields? Were they differentiated? Did they have volcanism and all the things we think of as the characteristics of a planet?
Or were they primordial just piles of rubble that never were melted?
And is there a tipping point after the clumping? In other words, does it build up to some point at which then you see this formation of what you're talking about a core and a magnetic field?
Absolutely, there's a tipping point. If you take the largest asteroid existing today, serious, which is close to 1,000 kilometers in radius,
and you take all of its mass and put it in little dust grains that, in infinity, let it fall in under its own self-gravity,
and you calculate the energy released by that, it's barely enough to heat the body more than a few degrees.
So asteroids, planetesimals, should not have melted when they formed the way a planet would as a result of the energy released from their formation,
from just the collision of all the bodies. But because they formed so early, they were enriched in a radioactive isotope called aluminum 26.
So there were a lot of isotopes that existed, so just different versions of elements with different amounts of neutrons and the standard amount that we have today.
And a lot of these things, just like uranium today, are still decaying, we're decaying in the early solar system.
And they were releasing a lot of heat as they were doing this. So what people realized, starting with actually urea,
Harold Urea, famous Nobel Prize-winning chemist, who was part of the Manhattan Project, he discovered deuterium, that's what he won the Nobel Prize for.
He also proposed that early formed bodies, planetesimals, if they formed quick enough, they would have had some of these decaying nucleides in them,
and they would have been heated substantially by that, and led to large-scale melting.
And the formation of an ocean of bagma may be even with a core and a mantle and a crust, the way a planet.
So they're melting many of these bodies, but for a totally different reason, they're not melting because of the gravitational energy release, but it's because of radioactive heating.
Still to come, David Gastina's conversation with Dr. Benjamin Weiss continues, with a look at his work in the field, studying meteorites.
That's next on the Best of Our Knowledge.
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This is the Best of Our Knowledge. I'm Bob Barrett. Our guest today is Dr. Benjamin Weiss, associate professor of planetary sciences in the Department of Earth, Atmospheric and Planetary Sciences at MIT.
He's talking with the Best of Our Knowledge's science reporter David Gastina about his work studying the building blocks of planets.
And despite the fact that you're looking at this sort of geology of all this, it's a chemistry experiment as well, isn't it?
Yuri is often credited with founding the field of geochemistry as it's called. There we go.
So we know that there are these objects in space. You're telling us about these planetesimals. And we've learned about how they form.
And we're talking about things like the core in a magnetic field and how that comes to be. But some of your most exciting research, it seems to me, is you going to some of these locations to gather these pieces that have come down and landed on Earth.
Let's start with the most recent example, which we're talking about this meteorite that was in Siberia. And with the technology, we saw this thing filmed. We heard it.
It was quite incredible. And I imagine for a scientist like yourself overwhelmingly exciting.
Yeah, because the last time something that large came into the Earth's atmosphere that we know of that led to such a large explosion was in the early 1900s.
But it would happen in the middle of Siberia. It's funny to happen both times in Russia.
Same spot. But way out in the middle of nowhere that time. So it flattened trees in all directions for many miles.
And it took months before an expedition could even get in there to find out what happened. In this case, as you said, not only was it in a much more accessible place, but people were watching, there were cameras on.
So it was unprecedented in the history of meteoretics, really.
Alongside of that, the same day, there was another asteroid going past the Earth. And there was some early discussion on the BBC and some programs we were watching that this was related.
And it wasn't. Were you also aware that there was this other piece coming my and that it strike you right away when you heard the news that, no, I can't be related.
Yeah, it was bizarre. I mean, I had been doing some interviews related to the other close approach of an asteroid. And of course, everyone was asking me, is this going to hit?
Basically said what has been written, which is that the probability of that thing hitting was extremely small. I don't remember the number off hand, but, you know, vanishingly small, but not impossible, of course.
So then the next day, something comes crashing into the Earth. And of course, I'm wondering, you know, did we all get it wrong? And as you said, it does appear that they were unrelated, but it's just a fluke that this other object came in.
And it was much smaller than the one that was being observed. If that one had come in, it would have been much worse. Sure. So it's good thing that it didn't, but it is funny that this coincidence of a small meteorite, if maybe a few tens of meters in size, did come in the next day.
Well, and it draws a clear picture that there are these objects in space that could and do hit the Earth. And, you know, you just talked about the Kuiper belt and the asteroid belt, but it's where those things are not going around like a pinball machine that shoots an object out and could end up in a collision course with us or nearby planet or a satellite.
And these are the things that we seem to be focusing on with the public because of the idea of Ellie and an extension level event. But I imagine alongside the actual science you're doing, this is a major contribution that scientists like you are making in terms of identifying some of these objects and helping us understand where they're headed.
Yeah, there's an active program, which I'm personally not involved in to observe detect and basically accurately calculate the orbit of the near Earth environment asteroids, we call near Earth asteroids. And one of these days, something big is going to hit.
What's kind of cool is that that object that hit, which I said was maybe a few tens of meters in size, previous measurements had predicted that on average, a body of that size should hit every 100 years or so.
And indeed the last one that hit was the one in Siberia in the early 1900s. So it seems like this is, although this is ultimately a statistical process, it does have well defined probabilities.
And sooner or later, something big is going to hit that's going to cause a lot of trouble.
Yeah, and you know, it could be that we lose a major city, an incredible amount of people or it could be something even worse.
Yeah. So when you analyze, you have a number of instruments to do this. Obviously technology today has to be assisting you in ways that it never could before.
And the significance being that, for example, I saw an article about Mars and your work and looking at how just looking at a piece of that planet that could have broken off and landed here, really helps us in understanding this idea of the origins of life.
Yeah. So this is work I started as a graduate student. They had recently discovered this new Martian meteorite. So as you may or may not know, at least that I'm talking to the public in large, we have dozens of rocks that we think were from Mars that were naturally blasted off the planet by an asteroid or common impact wandered around in space and landed on Earth.
So we've never done a so called sample return mission to Mars, we've robotically returned a sample that's in the works for the 2020s. So it didn't make curiosity.
No, curiosity actually was originally well, the rover that's going to be following on curiosity apparently is going to start this process. I've heard through the grapevine of possibly beginning the process of returning a sample. It will not return a sample, but it may actually look for samples that would ultimately be returned.
Anyway, so we don't have any such artificially returned samples now we have meteorites that were blasted off the surface and when I started as a graduate student working on this, there'd been discovery of a new one of these in Antarctica, the elegantly named meteorite al h 84 001.
What a beautiful man.
So I said that enough times when I was a graduate student that it rolls off the tongue eventually.
You did it quite well. I was serious. It was beautiful.
So what was cool about this rock is that it turned out to be the oldest known rock from Mars and indeed the oldest known planetary rock of any kind.
4.2 billion years old we think it is now. And we're trained these days to think of the Earth as kind of a mundane little planet around a small star in the middle of nowhere, speck of dust in the universe.
But we now know the universe is something like 13 billion years old.
So the Earth with an age of about 4.5 billion and we don't know that precisely we think it's there's a huge raging debate now as to whether it's 4.567 billion or 4.568 billion.
The point that I'm trying to make is that the Earth, which is an age of about 4.5 billion years old, is actually a decent fraction of the age of the universe, which is 13 billion.
So even though the Earth is in many ways mundane, it's actually a truly ancient object. It has born witness to a large fraction of the history of existence. That's kind of cool to think about that.
Yeah. And maybe less cool to think about the fact of what a very small fraction we have been.
Right. That doesn't change the fact that we are the one second before midnight that we've only evolved a few million years ago, maybe even a million years ago or less.
So yes, we are a blink in the history of the Earth's eye, but the Earth itself is ancient.
Anyway, should we go back to the Martian meteorite? Yes, okay. Sure.
Starting when I was a graduate student, there was a discovery of a new meteorite from Mars, which was almost as old as Mars itself, 4.2 billion years old.
And all other known Martian meteorites, even today, are much, much younger. The next oldest Martian meteorite is only 1.3 billion years old.
So 3 billion years younger than that. So this thing is old. And what's interesting about it being so old is that it's from the time when it's thought that Mars was warmer and wetter, potentially more habitable.
The only Martian meteorite from that time. And so it's from a time when Mars might have had a very different climate, a warmer climate, potentially a magnetic field.
It doesn't have a magnetic field today. So there are a lot of very interesting questions and one of the questions is the Eochemistry questions.
The Eochemistry is well as biology because this rock became very quickly famous for supposedly having fossils of 4 billion year old Martian organisms in it.
And so everybody was working on this rock and what I began to work on was, well, what does this rock say about the climatic history of Mars and the magnetic field history?
Could this rock retain records of Martian history all the way back from the time in it formed? 4 billion years ago. It would be a unique sample.
So to make a long story short, we basically showed that the process that kicked this rock off of Mars, which is an impact, and then the subsequent 15 million years that it wandered around space, and then it landed on Earth 11,000 years ago, all of that did not heat the rock above 100 degrees Celsius.
And then we went on to think about whether this was true for other Martian meteorites. And it appears that large fractions, few tens of percent of Martian meteorites have not been heated to 100 C.
So what does that mean? Well, it means that they might retain records of Martian history, but more immediately it means that there is material being transferred from Mars to Earth that's not being heat sterilized.
So it's preserved. The planets perhaps are not biologically isolated, that you could imagine that life could be transferred from one planet to another. It's actually not a crazy idea.
It certainly does broaden the question about the origin of life to where did the origin of life occur. We don't need to necessarily assume that it was on Earth.
Dr. Benjamin Weiss is an associate professor of planetary sciences in the Department of Earth, Atmospheric, and Planetary Sciences at MIT.
He spoke with the best of our analogous science reporter David Castina as part of our Astrobiology series on the origins of life.
Our coverage is made possible by the NASA Astrobiology Institute through support from the New York Center for Astrobiology located at Rensleyer Polytechnic Institute in Troy, New York in partnership with the University of Albany, the University of Arizona, and Syracuse University.
You can learn more about all of the topics in our Astrobiology series at origins.rpi.edu.
So on a nice new evolving planet, where does some of the life evolving on it go to live? That's the topic of today's academic minute.
Welcome to the academic minute. I'm Lynn Pascarella, President of Mount Holyoke College. As living creatures began the evolutionary migration out of the sea, they possessed a number of methods for moving on land.
Richard Blob, professor of biological sciences at Clemson University, reveals why species with limbs found themselves on a better footing than their fiend competitors.
Almost 400 million years ago, animals with four legs left their home in the water to take their first steps on the land.
Some fishes can also move over land using their fiends, but what was it about having legs that made this one group of animals, called tetrapods, so successful?
After all, they gave rise to every species of bony animal that now lives on land, including humans.
To understand more about how our ancestors invaded land millions of years ago, my graduate students, Sandy Kawano and I, have studied walking and living mudskipper fishes and tiger salamanders.
Mudskippers walk on land by swinging their front fins forward at the same time, and then vaulting their body over their fins in a way that resembles how people walk with crutches.
In contrast, salamanders swing their front and back legs from opposite sides of the body together, a lot like a dog or a cat, but with the legs out to the sides instead of lined up under the belly.
To measure how fins and limbs work differently from moving over land, we filmed the mudskippers and salamanders while they walked over a sophisticated scale called a force plate.
This measured the forces the animals experienced supporting the body, and we found that fish fins have to support the body in a different way than limbs.
With fins, the forces are tilted more toward the middle of the body, but with legs, the forces on bones point more upwards.
This change might make it easier for animals with legs to deal with the forces on their bones.
This could have been a critical consequence of the Fendilem transition, and might help explain why our tetrapod ancestors were more successful than other fishes once they moved on to land long ago.
You can find this, other segments, and more information about the professors at academicminute.org.
Production support for the Academic Minute comes from Newman's own foundation in partnership with Mount Holyoke College.
That's all the time we have for this week's program. If you'd like to listen again, join us online at our Flying Ship stations website.
Go to www.wamc.org and click on the programs link. And if you have any questions or comments about the programs, send them in.
Our email address is knowledge at wwwamc.org.
I'm Bob Barrett. Be sure to join us next time for another edition of The Best of Our Knowledge.
Bob Barrett is producer of The Best of Our Knowledge. Dr. Alan Chartock is executive producer.
The Best of Our Knowledge is a production of WAMC Radio's National Productions, which is solely responsible for its content.
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