Video Transcript: Small Bodies in the Solar System

You see, asteroids are rocks in space that are kind of like giant potatoes.  And as they rotate, sometimes you see the smaller side, it looks a little fainter.  And sometimes you see the bigger side and it looks a little brighter. And by measuring that change in brightness, the photometry, right, the change in brightness, you can actually measure how quickly an asteroid is rotating. 

So I stayed up all night, and laid on the floor of the observatory, while it was taking the camera, the CCD was taking pictures, and all looking at the exact same spot in the sky, watching this asteroid.  And at the end of the night, I had all these pictures, maybe 50, 60 pictures, and I decided just look through them; play them as a little movie.  And when you do that, you can see the stars, but the asteroid is moving relative to the stars, even in a single night, you can watch it move over several hours, you watch this little bright dot of light moving.  And as I was watching this, you know, the bright asteroid that I was looking at, I couldn't help but notice, there was a smaller, fainter, little dot of light, I could barely see it, that was moving across the bottom of the of the image.  And I saw it.  It looked just like the big bright asteroid, but it was much, much fainter.  And then I looked again, I saw another one.  And I thought, wow, these are really faint.  And these must be other asteroids. 

And so I emailed my professor and I said, “I think I see some other asteroids here.  I wonder if any of these maybe are new asteroids that no one has ever seen before.”  And so we searched and found that in fact, one of those asteroids was a brand new asteroid that no one had ever observed before.  And so I discovered a new asteroid while I was in college.  It was a very cool experience.  I got to be in the newspaper.  And they had my picture, saying I had made this discovery.  Asteroids have become increasingly common discoveries.  I mean, I discovered one, right? 

The first asteroids were discovered over 150 years ago.  And they were thought, the very first asteroid was thought maybe this is a new planet, when they found this asteroid series, because they found it roughly between Mars and Jupiter.  And there's kind of a big gap there between Mars and Jupiter. And astronomers thought there's a big empty spot here, maybe there's a planet in there.  And so when they discovered that first asteroid they thought, “Oh, we found it.  We found the planet.” But it's small, it was too small.  And so as they kept looking, they found more and more asteroids.  Even in the next couple of years, they found several more asteroids in this same area between Mars and Jupiter.   Well, in the 150 years since, and especially in the past 30 years, since we've had large telescopes and CCD cameras, especially, we have discovered hundreds of thousands of asteroids.  I think we're over 200,000 asteroids now that have been discovered.  

The vast majority of those asteroids are in this region between Mars and Jupiter.  That's called the asteroid belt.  And you can see it here illustrated in the first picture in the gallery.  Now, despite what this image looks like, I mean, it looks like this region is just full of asteroids, we have to remember that asteroids are relatively small, okay, like much smaller than the moon, like the biggest asteroid is like a sixth the size of the moon, but most of them are much smaller, maybe only a mile or two across.  So this is a huge region of space and asteroids are very, very small.  So even though there are lots of asteroids in the asteroid belt, if you were to send a spacecraft, you know, out to Jupiter, Saturn, you know, we don't even worry about the asteroid belt.  You just send this spacecraft through there.  The chances of a spacecraft getting hit by an asteroid on its way through the asteroid belt are effectively zero.  Okay, so the picture makes it seem like you're flying through this, you know, a rat's nest of asteroids and you're going to get hit. That's not really the case. 

Now asteroids we have, when you look at them through a telescope on the ground, they look like just dots of light.  But we've sent spacecraft past asteroids to see them up close and we can see what they look like. This is an amazing picture.  The second picture in the gallery shows an asteroid and you can even see this asteroid has its own moon, a smaller rock that's actually orbiting around it.  Now asteroids, they kind of look like they might be one solid chunk of rock, but actually, it's more like they're a loose clump of chunks of rock.  And all the little cracks have been filled in with smaller rocks and fine powder so it looks like it's a smooth surface, but actually, this is kind of a loose clump of rocks that are all held together by gravity, and slowly rotate together. They're pretty amazing. 

But asteroids aren't the only small object in our solar system. And we're going to look at a couple others. In particular, let's take a look at comets.  Now in the night sky, a comet is one of the most beautiful things that you can possibly see.  I'm not sure if you've ever seen a comet.  I was really young when a comic called Hale Bopp went by and we could barely see it from our house.  But there are some comets that depending on where you are on the earth, and it happens to come by, can be a breathtaking sight, just a bright streak of light across the sky. 

Now, unlike the motion of the Sun and the Moon and the stars, comets are not predictable. A lot of times, in most cases, a new comet is discovered as it's coming towards the Sun, and then it becomes brighter and brighter in the sky. And people see it, and then it might burn up as it passes by the Sun, or it might then leave the solar system and it won't be seen again for hundreds, maybe even thousands of years.  

So to ancient astronomers, comets were a real mystery because they would just appear in the sky and then they would never be seen again. In some cases, they thought it was a sign of something bad that was about to happen.  Some people thought maybe it wasn't even in the sky at all.  But it was just in our own atmosphere, that it wasn't out by the stars, but that it was much, much closer.   

So comets were somewhat of a mystery.  But what we know now is that comets, they do orbit the Sun, but they have a very elliptical orbit, a very elliptical orbit, which means they spent, you know, it's a real big oval, and the Sun's down here, so it spends just a very little time by the Sun and it spends the vast majority of its time far, far away from the Sun.  In fact, even beyond the orbit of Pluto in a region called the Oort cloud.  So way out in the farthest reaches of the solar system, there are these dirty snowballs, chunks of ice and dirt that are mixed together.  And they still orbit the Sun.  But they're spending most of time way, way out there. And then every once in a while, they'll come zooming into the inner solar system. And as it gets close to the Sun, the dirty snowball starts to melt.  And so we see these tails on these comets. And we even see two tails. 

One tail is this white tail you see here.  This is Halley's Comet.  This white tail is caused by the actual melting of that snow from the heat of the Sun.  The snow melts, it's kind of like water vapor flying off. And then there's a blue tail called an ion tail.  And that's caused from the radiation from the sun actually like ionizing gas off of this comet.  So that blue tail is pointing directly away from the sun whereas the white tail is kind of pointing in the path that the comet is traveling.  It's kind of a little bit of a curve. 

So these tails, that's what the dramatic thing we see in the night sky is, the actual comet itself, the actual nucleus of the comet is a small object kind of like an asteroid, a small little ball of dirty ice and snow.  In fact, again, we've sent spacecraft to take pictures of these comet nucleuses up close, and this is what they look like. 

So you can see, this is the fourth picture in the gallery, it looks kind of like an asteroid, in this case, though, you see that parts of it are melting, you can see kind of a gas coming off of it, so it has more ice mixed into the rock.  It's not just rocks together.  

So comets are an amazing an amazing part of our solar system and amazing sight to see in the night sky. Halley's Comet in particular, you've maybe heard of, it's certainly one of the most famous because Halley's Comet comes back.  Time and again.  In fact, it comes back about once every 70 years.  Haley was the guy who discovered this pattern.  He said, wow, there's a bright comet.  He looked at all the comets, the records, comets were seen, people would write them down.  And he saw Wow, this one, there seems to be a pattern that every like 76 years a comet is seen.  And he said I bet it's the same comet and he predicted if this is a pattern then we should see a comet in this year in this month.  And in fact, there was a comet.  And so it was one of the first times ever that someone predicted that a comet would come. And that's again, one of those powers of science.  

As we observed the patterns, and we can actually make predictions based on those patterns. That's a way to show that you really understand something.  If you can say the entire history of humanity, you know, when a comet comes, people are like, ‘Whoa, where did this thing come from?’  And then you say, I think there's going to be a comet next month, and then there is, that's like, people are going to think you have some magical power, right?  But it comes from the careful observation of these patterns.  It's such a simple idea, but it's very, very powerful.  So when those predictions are made and then confirmed, it's a great confirmation of the pattern that you have observed.  Okay. 

The last small object in the solar system that I want to consider is the planet or the former planet, Pluto. The object formerly known as the planet Pluto, I guess you could say, right?  And here's the deal.  So when I was growing up, and undoubtedly when you were, we would say that there were nine planets in our solar system, and now we say there's only eight.  We consider the planet Pluto to be a dwarf planet. And it's worth considering why that's the case. 

And we saw that the first four planets, the terrestrial planets all were similar in the sense, they had surfaces that you could walk on and land on, they're roughly in the same size, more or less. And then we get to the giant planets, the gas giants, Jupiter, Saturn, Uranus, Neptune, which we didn't talk about as much, but they're all huge planets, that get so big because of these giant atmospheres, because it's colder there.  But then you get to Pluto. And Pluto again, is really small, like smaller, you know, like, it's in the Mercury size.  And it has a huge moon called Charon, that's almost as big as Pluto orbiting around it.  And it's very different than the gas giants. So to see Pluto out there is a little bizarre. Okay. 

Well, in the past 20 years or so, astronomers have begun finding other objects out near Pluto that aren't quite as big as Pluto but they're similar.  They're small. They're rocky places, and over time, astronomers found more and more of these things.  And eventually, they found some that were even bigger than Pluto. And so now you have this problem.  It's kind of like the asteroids.  When they found the first asteroid, they thought maybe this is a planet, but they found more and more.  And eventually, you know, a hundred thousand of them, you start saying, well, they can't all be planets.  The same thing has happened more or less with Pluto; we say there's more and more of these things, but they’re not all planets.  So maybe we should call them something else.  And so they call them dwarf planets instead.  That's one thing to call them.  But as more and more have been discovered, what we're starting to realize is that there's a region out there in the outer solar system, and this is the fifth picture in the gallery, there's a region in the outer solar system, beyond the gas giants, where there are lots of these things.  And we call that region the Kuiper Belt.  And so naturally, then we call these objects Kuiper Belt Objects.  It's pretty exciting name, I know.  Alright.  

And you can see some of them listed here and their relative sizes.  So Pluto is one of the largest but there is one larger - Eris.  You can see several of these have moons, but you can also notice that they're bigger than asteroids. They're bigger than the largest asteroid, Ceres.  I'm sure this picture is already out of date because more and more of these Kuiper Belt Objects are being discovered all the time. 

So our solar system covers this huge range.  We have tiny objects like these small comets and asteroids, we have these huge planets like Jupiter that are almost like stars, they're so big.  And then we have the terrestrial planets in the middle and Earth as the special sort of diamond in the middle of our solar system that has this beautiful oceans, beautiful clouds, and beautiful creatures that live on its surface. 

I hope you've enjoyed this tour of our solar system. And as we as we continue on our course, we're going to take broader and broader views of the universe.  Next, we're going to consider stars beyond our solar system. And then we'll eventually look at whole galaxies until we finally consider the universe as a whole. 

All right, we'll see you next time.