>> Good evening and welcome to UW Space Place.
Tonight is the second Tuesday of the month so we have a special
presentation tonight and because of the day on which the
presentation falls, we're devoting it to the New Horizons
spacecraft, which is flying by-- actually by the time I'm giving
this talk now, has already flown by the planet Pluto.
This is a really interesting interplanetary mission for a lot
of reasons, including that it's filling in the exploration of
the solar system, but it's also the first one in many years that
we've had a spacecraft now arrive at a new planet.
So we're going to talk about New Horizons and the exploration of
Pluto.
So Pluto was the last or maybe I should say the most recent in a
long line of planet discoveries.
There's a lot of things out there orbiting the sun and we
only count some of them as planets.
This is actually an issue that's come up, quite a lot in history.
What do we call a planet?
We all know that there's always a lot of discussion since 2006
about whether Pluto is a planet or not, which is really kind of
a side issue, but how they got discovered is really pretty
interesting.
Most of the planets, the ones that you see in the sky, like
Venus and Jupiter, which we can see in the evening skies these
days, or Saturn and then also Mars and Mercury.
Those five planets have been known since antiquity.
We don't know who discovered them, if anybody.
They've been known to be different from the stars as long
as we have any historical records.
And so when in 1781 an astronomer named William
Herschel saw a thing through his telescope that he decided was
not a star, the first thing to come to his mind was not that
this might be a planet because nobody had ever discovered a
planet.
All the planets were known to the ancient Greeks and probably
long before that.
Herschel, however, decided eventually that it had to be
one.
At first he thought it was a comet, but it actually turned
out to be a planet.
It turned out this thing was in a circular orbit around the sun
and that was the planet Uranus.
That was a pretty significant event broad-- you talk about
broadening people's horizons.
It made people realize that maybe there was stuff out there
that astronomers didn't know about.
So that was a big step, the first discovery of a planet,
1781.
The next planet to be discovered was Ceres.
How many people have heard of Ceres?
A few. Good.
So these days we usually classify Ceres as an asteroid or
a dwarf planet, but it was actually considered a planet
when first discovered in 1801 by an Italian astronomer, Giuseppe
Piazzi, who like Herschel looked in his telescope and saw
something that wasn't on the star charts and wasn't a planet
that he already knew about.
He saw this thing moving through the sky-- you don't see it all
once, but night after night you can see it moving against the
stars.
He discovered that it was orbiting around the sun and this
was declared to be a new planet.
In the case of Ceres, after a few years another object was
found in about the same orbit and then another object was
found in about the same orbit, and every one of those was being
declared a planet.
And then another one was discovered in the same orbit and
then another one.
And if you look in some early 19th Century textbooks, you can
find lists of planets where there's 15 or 16 planets, and
most of them are the ones you would recognize and all the rest
are what we now call asteroids.
And astronomers became, in the 1840s, became a little
uncomfortable with the idea that suddenly there are going to be
too many planets, and so they demoted all those planets to
asteroids.
They basically just made up the term "asteroid" and categorized
all of those things that are about that same place as
asteroids, not planets.
So it was a planet discovery when it was discovered, but then
demoted, but then in 1846 something we recognize as a
planet was discovered.
The planet Neptune was discovered because astronomers
had been watching Uranus long enough to notice that its orbit
wasn't successfully predicted by Newton's Laws.
It ought to; gravity ought to be what's operating out there, but
Newton wasn't-- not Newton.
Newton was doing exactly what he should have.
Uranus was not quite doing what it should do.
And so a couple of bright astronomers said, "Well, maybe
there's another planet out there disturbing it."
So they sort of hypothesized a model where there's another
planet out there, and if that planet were in a certain place
and it had a certain mass, then it would produce the
disturbances they were observing in Uranus.
So they go take a look-- actually, it wasn't them.
Some other astronomers based on their advice took a look and
guess what.
They discover a planet pretty much where these guys had
suggested that they should look.
That was the planet Neptune.
So that was a big deal.
That was the first planet to be discovered, so to speak,
theoretically.
Its existence was inferred before anybody had ever seen it.
Then in the 1870s, another planet was discovered.
This planet is called Vulcan and I've got it in parentheses
because, of course, it doesn't actually exist.
This is not the one from Star Trek.
In those days, astronomers were looking at Mercury and there was
a similar problem to the problem with Uranus.
Its orbit wasn't quite right.
And so they thought, well, it might be not quite right because
there's a planet disturbing its motion.
So they-- and the whole thing with Neptune had been very
successful, so they started looking for a planet closer to
the sun than Mercury, an and intra-Mercurial planet to
explain the disturbances in Mercury's orbit.
A few astronomers, including a local one, thought that they had
discovered Vulcan and actually announced to the world that they
had discovered Vulcan.
The problem is that it's very hard to see things close to the
sun.
What they did was wait for a solar eclipse, a total solar
eclipse, to cover up the sun and then you got maybe two, three,
four minutes to search the sky for this planet.
And that's apparently when probably somebody miscounted a
star or maybe an asteroid or something and thought they had a
planet.
So that turned out not to be a planet, but it was announced as
a planet discovery.
So there had been-- the point is there's a long line of planet
discoveries before we ever get to Neptune, pardon me, Pluto.
By the time we get to Pluto, astronomers are used to
discovering planets.
And Pluto came along in 1930.
The way Pluto was found is interesting.
It was not a theoretical sort of thing; it was a result of a
deliberate search, sort of like Neptune was the result of a
deliberate search.
And it was for similar reason because astronomers had been
looking at Neptune long enough to think that maybe its orbit
wasn't quite doing what it should do.
And so the obvious thing is to think about another planet that
might be disturbing Neptune's motion.
So a number of astronomers came to this conclusion and thought
about devoting a search for the purposes of finding this planet
beyond Neptune.
One of them was Percival Lowell, who is probably most famous for
some other things involving canals on Mars, but Percival
Lowell, who had established the Lowell Observatory, which still
operates in Flagstaff, Arizona-- Lowell was wealthy enough to
fund his own astronomical projects and build his own
observatories when he saw fit.
And Lowell decided to start a search for this planet which
might be disturbing Neptune's orbit.
However, it was actually long delayed.
You note that it says there that the search begins in 1929.
Lowell actually died shortly after putting this plan
together, and then there was a long lawsuit from his family
about whether this crazy plan to fund astronomy really ought to
be allowed.
And it went on for quite a few years.
The search then didn't start until 1929, when all that
litigation was finished and the courts decided that Percival
Lowell's Will should be observed and his money should fund
astronomy, which is what he wanted it to do.
And then it produced fruit rather rapidly.
So the Lowell Observatory began the search for Pluto.
They hired an assistant, an observing assistant named Clyde
Tombaugh, who had very little, I'm sorry, really no
professional astronomical training.
He was sort of a self-taught astronomer at that time.
And wrote a letter to the Observatory saying "I want to be
an astronomer and I built my own telescope and I'm willing to
work long hours," and they hired him to be the observing
assistant and they gave him, "Okay, here's this project.
Here's what you do.
You go out to the telescope, to the telescope we're using to
search."
It's a photographic telescope.
You photograph a part of the sky and then a week later you do the
same thing to the same part of the sky.
Meanwhile, you spend the rest of the night taking pictures of
other places in the sky, which a week later you're going to come
back and compare.
And then you're going to compare those two photographs and see
whether anything moved.
If we didn't have the arrows on here, I'm willing to bet that
you couldn't find the planet in this picture.
So Clyde Tombaugh started searching pairs of plates.
He had a special sort of microscope called a blink
comparator that would allow him to look at first one and then
the other, and it could flip the view back and forth with a
mirror.
And if you get them registered just right, then nothing, if the
stars haven't changed their patterns, then nothing changes.
So you can check that plat and then you can do another pair and
another pair.
And he searched those until February of 1930, which is
remarkably fast since they only started sometime in 1929, and on
this plate he found a little dot that moved from there to there.
So that was the discovery of Pluto.
This was big news, as planet discoveries always are, in 1930,
and but this one was something that, unlike Vulcan, that other
astronomers were able to confirm.
Other astronomers were able to look at that same place in the
sky, find that same dot moving, and it was almost immediately
agreed that a new planet had been added to the solar system.
The problem is it's so dim.
It must be really, really far away.
And it was hard to learn anything significant about it
because of how tiny it is and it moved so slowly so they knew it
was very far away.
It must take a long time to go around the sun given how far you
can see it move in a given pair of frames or after some amount
of study.
It turns out to be about 248 years it takes to go around the
sun one time.
So the discovery of Pluto here was immediately acclaimed and it
was declared right away to be a planet.
It was assumed-- oh, yeah, so the orbit for the planet was
understood fairly quickly and right away it became apparent
that there was something a little bit odd about it.
It's very far out, as it says here, 248 years is how long it
takes to go around the sun.
So longer by a lot than any other planet.
But oddly and unlike the other planets, its orbit is very
elliptical.
That is it comes in relatively close to the sun and goes
relatively far away.
Most of the planetary orbits, while not perfectly circular,
they're close to circles.
If you drew them to scale on a piece of paper, they look like
circles.
But not Pluto's orbit.
Pluto comes nearly as close to the sun-- in fact, it comes
actually a little bit closer to the sun than Neptune ever gets,
and then it goes way far out, about 10 astronomical units
further out, about 10 times the distance of the Earth, farther
out when at its extreme.
So that's very elliptical for a planet.
It's not at all elliptical for a comet.
Comets do this kind of thing and there are plenty of asteroids
that are in pretty elliptical orbits.
For a planet, that's kind of unusual.
So right at the beginning, Pluto was beginning to look a little
bit suspicious.
For a little while, because its orbit comes in to at its closest
point to the sun it comes in to the same distance as Neptune,
although the two orbits don't actually intersect, so it's out
there in space.
It looks like-- whenever you draw it, it looks like they
intersect.
They actually don't.
So they won't collide with each other.
In fact, they turn out to be what astronomers call a
resonance with each other so that they actually have kind of
an arrangement where they don't collide.
But because they come so close together, there was a theory
right away that maybe it was an escaped moon of Neptune.
So already its planetary status is suspicious.
If something escapes from-- if a moon escapes from a planet and
goes into orbit around the sun, is that a planet?
Well, I don't know, but at any rate, the theory was that it was
an escaped moon of Neptune, although, as I read now, that's
not-- they don't think that that's got anything, that that's
a reasonable explanation of where Pluto came from.
But that was something that was kicked around right away and,
again, casting a little shadow over its planetary nature.
Originally, it was estimated to be about the same mass as the
Earth, actually for no particular good reason except
that it wasn't huge like Jupiter or something along that line.
So they just kind of estimated to be the mass of the Earth.
And the first good data for that didn't come along until 1976.
It was discovered in 1930, so nearly 50 years later
astronomers discovered that actually the color of it looked
like what you would get if it was coated with methane, if it
had methane ice on its surface.
And if it has methane ice, then you know about how bright that
should be.
And if you know about how bright it looks-- they called this the
albedo-- if you know about how bright it looks and you know how
bright you see it out there in the sky, then you know about how
much light it's reflecting from the sun and you can make an
estimate of its size.
How big does it have to be to reflect that much light.
Well, it was-- if it's icy, then it can be a lot smaller and
reflect the same amount of light.
And so in 1976, after that measurement of the albedo came
about, astronomers realized that it must be a lot smaller than
the Earth, and the estimate was then about 1% of the Earth's
mass.
So a dramatic reduction, a factor of 100.
In 1978, its moon, what we now call its moon, although I'm
going to change what I call it in a minute, it had been
discovered that there were actually two objects out there.
One of them, the moon, is now called Charon.
Charon and Pluto orbit around each other.
And by looking at that orbit, you can then calculate the mass
of Pluto quite exactly, and it turned out to have only about
0.2% of the Earth's mass.
Not 2%. 0.2%.
It's actually a very small object.
So it's seeming less and less planet-like over the years, less
and less like the other planets.
Not that at that point there was a strict definition of planet,
but all these things sort of cast doubt on whether we ought
to be thinking of this as something comparable to all
these other bodies that we call planets in the solar system.
Maybe it's telling us something different.
And, of course, that turns out to be the case.
Over the years, there had been-- we're here to talk about the
spacecraft exploration of Pluto, which is just beginning, but
over the years astronomers had been studying Pluto and Pluto's
system and finding out a few little things about it.
If you compare this list of facts here with what we know
about, say, Mars or Venus, you'd be entitled to say we know next
to nothing about Pluto.
Just these little bits of information that we can get,
that there is this object called Charon that co-orbits with it
out there.
They were able to determine, again, from the
albedo measurements that Charon must have water ice.
That's already kind of intriguing.
So there's these two bodies out here, one has methane ice, the
other has water ice.
That's an interesting difference.
Why is that?
1989 was when Voyager 2 flew by Neptune and made the first in
situ observations not only of Neptune but Neptune's moons, one
of which is Triton, and they noticed that Triton looks a lot
like Pluto in terms of its size and it's got this methane
atmosphere around it with methane ice on the surface.
It kind of looks like it might be sort of a model for Pluto,
which sounds a little bit like the earlier theory that maybe it
was an escaped moon of Neptune.
But, no, we don't think that anymore, but it's curious that
Neptune and Pluto-- sorry, that Triton, the moon of Neptune and
Pluto, have some resemblances to them.
What does that mean?
In 1992, things really began to open up because astronomers were
still studying the outer solar system the same way that Clyde
Tombaugh had been studying it, by looking at images of a part
of the sky and then you come back sometime later, a week
later or whatever, month later, and you compare again and you
see if anything has moved.
And it took until 1992 before what were called Kuiper Belt
Objects, KBOs-- I should've spelled that out there.
Kuiper Belt Objects, 1992, other KBOs were discovered out there
in the solar system.
My guess is that Tombaugh, Clyde Tombaugh, the guy who discovered
Pluto, was really lucky for any number of reasons that we won't
go into right now that he discovered Pluto out there in
1930.
In the normal course of astronomy-- I'm now doing
counterfactual history here, but in the normal course of
astronomy, it sounds like Pluto might not even have been
discovered until 1992 when astronomers began really
systematically looking at the plane of the solar system.
Of course, they were doing that in part because Pluto was
already out there so that doesn't quite work, but other
Kuiper Belt Objects, that is to say objects out in the solar
system, started to be discovered and suddenly now all these
weirdnesses about Pluto start to make sense because we're
realizing we're talking about a different class of objects
completely.
And I should've put these points in slightly different orders,
but I did chronological there.
In the early 2000s, it turned out that from Hubble Space
Telescope observations that Pluto has not just that one
moon, Charon, but four others as well much tinier than Charon.
So by the early 2000s, ten or so years ago, it was clear that
there was a lot more going on out there than was originally
thought.
Sort of the original picture of a solitary, icy world, probably
in a deep freeze where nothing ever changes out there, is not
the case.
It's complicated out there.
The Pluto system itself is complicated, and the environment
that it's in is complicated because of the existence of the
Kuiper Belt, which I'm going to talk more about in just a minute
here.
I wanted to mention one particular way in which
astronomers learned more about Pluto, and this was really just
kind of lucky because Charon was discovered not too long before
it started, before it started a series of eclipses of Pluto.
And nobody would've been looking for these if they hadn't found
Charon.
Basically what happened was the orbital planes aligned, the
orbital plane of Charon began to align with our line of sight out
to Pluto, and as you can see them down here, Pluto, I'm
sorry, Charon started eclipsing, moving across the face of Pluto.
So when that happens, of course, it blocks some of the light of
Pluto and the light that you're measuring from Pluto.
Here, there's no eclipse, so the light from Pluto stays constant.
Here, Charon moves in an eclipse across Pluto and so the amount
of light that you're measuring dips down for the period of the
eclipse and then rises once again.
That allows you to derive all kinds of interesting things,
including, among other things, the exact size of the planet,
which, because nobody had ever been able to see the disk of the
planet, nobody really knew the exact size.
They'd been doing a lot of inferring about the exact size.
If you can get the exact size and you know the mass, then you
can get the density.
And when you have density, you can start talking about the
composition of the planet.
And what became-- what came as a little bit of a surprise is that
rocky, sorry, that Pluto, which was, had been expected to be an
icy, an icy ball out there, Pluto turns out to be fairly
rocky, not as icy as it had been thought.
Whereas Charon, because you can measure its diameter and do its
density, too, turns out it's not rocky but icy.
So here's another interesting contrast.
These two objects, fairly close together, but they're very
different from each other.
And in fact, lately astronomers think that maybe it's a model,
maybe it's another example, of something that we think actually
was the origin of Earth and its moon.
There are a number of parallels that are kind of interesting.
The Earth and its moon are thought to have originated when
sort of a proto-Earth, if you will and another now destroyed
planet that was orbiting the sun, when those two objects
collided, and the result of the collision, which is usually
known by the phrase 'massive impact,' meaning two really big
things collide with each other, the product of that massive
impact was the moon, was the production of a big satellite
relative to its primary.
And it's entirely possible that the same, that we're talking
about the same thing here with Pluto and Charon.
That's currently the favored way of viewing this system.
In fact, using models that astronomers put together to try
and explain the formation of bodies that have gravitational
collapses, there are those who say it's actually impossible for
this system to have formed by gravitational collapse; it
must've been a massive impact.
The angular momentum of the system is said to be too high
for that.
That assumes that we know what we're talking about with these
models, but when you take the models that we can talk about,
the conclusion is that a massive impact is the likely way to look
at this.
So that is now making Pluto and Charon, that system, look like
an interesting parallel for our own.
So it might begin to tell us not only about way out in the outer
solar system; it might begin to tell us about our own part of
the solar system rather surprisingly, where things are
usually pretty different, but this may be-- this may be an
interesting clue.
Yes?
[Inaudible, audience question]
Well, so we might-- we might have--
[Inaudible].
Yeah, we might have to talk about what we mean by moon, and
I'm going to get to that in just a minute.
So in addition, so now, again, since 1992, there've been more
and more of these things out there.
And there's another piece of jargon that we sometimes see.
These things are also called trans-Neptunian objects.
So that means anything outside the orbit of Neptune, which
unfortunately means everything in the universe outside the
orbit of Neptune, so it may not be a very useful term, but you
will see that.
And there've been more and more of those things and some of them
are maybe not members of the Kuiper Belt and so that might be
why we'll still see that term around there.
But there've been more and more of those things discovered since
1992 and in fact, as the slide says, over 1,000 of them are now
known out there.
So this is, again, this is just a story of the outer solar
system becoming constantly more complicated than anybody thought
it might be.
Here on the slide, you can see some examples, and if you look
down at the bottom there, you see the edge of the Earth, so an
indicator of the size of the Earth, and then you can see the
Pluto Charon system just there in the lower left.
And you can see a few other systems up there and then in the
upper right our own moon, Earth's moon.
So that's kind of interesting, too.
This means that if our moon, the one that orbits the Earth, were
in orbit around the sun, we'd probably be calling it a planet.
So there's nothing about the object itself that makes it a
moon or a planet.
Or maybe there's not anything about it, but at least in this
case, if Pluto's going to be a planet, then the moon, if it
were in orbit around the sun, would be big enough to be a
planet, too, right.
Then there are these other things out there as well,
including this one named Eris, which true to her name has
caused a fair bit of trouble in astronomy.
And you can see that Eris-- now, Eris has not been visited by
spacecraft.
It's difficult to measure the sizes of these things, as we
have seen with Pluto, and as far as I know, there haven't been
any transits, any eclipses, of Eris by its moon, Dysnomia.
But Eris, by all estimates, is about the same size as Pluto or
bigger.
So if Pluto gets to be a planet, then Eris ought to be a planet,
too.
And astronomers were sort of facing a similar situation to
when they were started discovering all those asteroids.
So if Ceres is a planet, then why isn't Vesta also a planet.
And then there's a bunch of other ones.
And suddenly we're faced with lots of planets.
And so we wont go into this in any detail right now, but that
was actually the comparison between Eris and Pluto that led
in 2006 to astronomers coming up with a definition for the word
"planet," which had not been carefully and technically
defined before, that ruled out Pluto and Ceres, too, by the
way, and called them dwarf planets.
So just recently in the press there's been a whole lot of talk
about this, of course, as the spacecraft approaches Pluto.
And Alan Stern, the principle investigator of the New Horizons
spacecraft, said, "Well, actually, that was the
astronomers.
It's actually planetary scientists you want to talk to
about the planets and we never said Pluto wasn't a planet."
So he's all in favor of just sticking with the planet and
letting the astronomers have their special terminology, which
maybe doesn't make any sense anymore anyway.
So we'll see where that goes, but be prepared because we could
see the planet, the word "planet," redefined.
In fact, I kind of hope they go backwards and say, "Well, let's
not define it.
We'll come up with a technical term that nobody already uses."
Anyway, Pluto there and Charon are just two of these objects
out there.
Here they are.
Here's Pluto, I should say, compared to now the sizes of the
other planets.
If you could put them all on your tablecloth there and
compare the relative sizes of the planets, you'd see little
Pluto down there way tinier than the Earth.
And remember that it's extremely small, maybe too small, it's in
the wrong orbit, it's part of a swarm of all these other things
out there.
That's what led to it being called a dwarf planet.
It's also been called an ice dwarf.
And you can easily get to the point of saying, "Well, who
really-- who really cares."
But because it's a member of the Kuiper Belt and possibly the
largest or one of the largest members of the Kuiper Belt, we
actually do care, because this turns out to be-- this Kuiper
Belt, which is named after the astronomer Gerard Kuiper, who
probably pronounced his name Kuiper-- he was Dutch, but
Americans always say Kuiper-- the Kuiper Belt is the biggest
part of the solar system.
You have the inner planets.
We talk about the inner planets out to Mars and maybe you count
the asteroid belt and maybe you don't.
And then we have giant planets, Jupiter, Saturn, Uranus, and
Neptune.
We call them gas giant planets.
They have a certain similarity to each other and they cover a
certain zone of the solar system.
But this Kuiper Belt, the recognition of which has only
come about since the mid-1990s, is the biggest part of the solar
system by far.
So Pluto actually turns out to be an indicator of a major zone
of the solar system that stretches a huge distance from
about 30 astronomical units, which is roughly the distance of
Neptune, out to about 50 astronomical units, which is
beyond the orbit of-- well beyond the orbit of Pluto.
And probably there's a lot of stuff out there.
So we know about Pluto and its moons and we know about these
thousand other things.
Estimates are-- oops.
Estimates are that there may be --estimates are that there may
be as many as 100,000 of these Kuiper Belt Objects bigger than
100 km in diameter.
And who knows how many smaller ones.
It's a very populous region of the solar system, similar to the
asteroid belt.
It's probably telling us something about the formation of
the solar system-- and then the largest of these is Pluto, the
one that's been known for 30 years.
The reason it might be telling us something about the formation
of the solar system is you can find belts of material like this
around other stars.
And, again, going back to models about how stars and planets
form, it seems like the Kuiper Belt is not nearly massive
enough.
It should be about 10 times more massive than it is, according to
the scientists who make these kind of estimates and compare
them to the belts of material around other stars.
And if it were so massive, it should've formed a planet.
There would've been enough mass out there to form like another
Neptune.
But there is no Neptune out there, and there's only a
remnant of what seems like might have been there in the early
formation of the solar system, so then we're entitled to ask,
"Well, what happened?"
And of course, we don't know the answer to it, but one scenario,
and it's fairly well accepted these days, that it's actually
possible.
We often think about these planets orbiting the sun in kind
of a timeless fashion, like trains going around on a track,
but it turns out the tracks can change.
Planets' orbits can change.
And they can move inward or outward from the sun.
And as we study more solar systems around other stars,
that's given a great amount of energy to the idea that planets
can form, say a planet like Jupiter, out far away from a
star and then end up really close to the star.
And as that happens, it could send other planets further out
or even eject them from the solar system, from that solar
system, and we may be looking at something like that here.
It may be that Neptune-- Neptune's just the handiest
suspect, but Neptune might have migrated, they say, might have
changed its orbit out from the sun and in the process have
modified that distribution of matter out there, the
proto-Kuiper Belt, and expelled a lot of those objects out of
the solar system or possibly absorbed a few of them so that
it's a remnant now of its former self.
That would mean that these things, these objects out there
in the Kuiper Belt, are examples of what planet, what astronomers
call planetesimals, which are the chunks of things that form
planets.
Now, if you've been following another space mission, the
Rosetta space mission that's currently exploring a comet,
that comet is-- the composition of that comet is probably a
pile, it's probably a snowball, of planetesimals, a bunch of
these building blocks that coagulated around the sun and
then build up into larger objects.
At a certain point, gravity becomes important.
And when you get-- when their gravitational field is strong
enough to draw in other material, maybe that's how you
get a planet.
But when it stays small, they only stick together if they bump
into each other and don't destroy each other, but you
could have two that bump into each other and form a slightly
bigger one, and it's looking like this comet may be that we
may be able to actually see the structure in this comet of these
planetesimals that stuck together to form this cometary
site sort of body, and that may have happened way out there in
the distant solar system because comets are very icy and couldn't
have stayed close to the sun for very long without dissolving.
So out there in the Kuiper Belt, we may be looking at
planetesimals.
We may be looking at these primitive objects that formed
early in the solar system and then by this event, this
migration of Pluto or whatever, were scattered out into the
outer reaches where they've been in the deep freeze for a very
long time.
So that's one of the reasons-- I've been trying to lay out the
reasons why this New Horizons spacecraft is so scientifically
interesting.
This is why planetary scientists are watching this.
What is it going to tell us about this unusual part of the
solar system that's been so recently discovered?
So it's taken a long time to actually get to exploring Pluto,
not by telescopes but by sending a spacecraft out there to take a
good look at it.
So the New Horizons spacecraft was launched in 2006.
Did anybody here have an iPhone in 2006?
Answer is 'no' because they haven't been out that long.
Nobody had an iPhone then.
Smartphones have come along since then.
I just want to point out this was built with the technology of
another age.
The spacecraft was designed and launched.
It was on its way by 2006.
And even with that primitive technology of the 1990s, it's
still operating out there around Pluto.
It got to Pluto in a reasonable amount of time.
Pluto's way out and it would've taken quite a long time if we
had to depend on just what boost we could give a spacecraft with
a rocket to get out there.
But it was launched with the fastest launch speed that
anybody had ever achieved with a spacecraft, about 36,000 mph as
it left Earth orbit.
But that still wouldn't have been good enough.
It was actually launched towards Pluto, sorry, towards Jupiter.
Jupiter was the first target.
And the idea was to fly by Jupiter and do what's called a
slingshot, a slingshot maneuver, in which you pick up a little
bit of Jupiter's orbital energy, not very much in the case of the
New Horizons spacecraft, and you get a boost from Jupiter.
And the combination of those two things, the very fast launch
from Earth, the fastest ever, and the slingshot effect from
Jupiter, got it out there in 10 years, which is pretty
remarkable given how far we're talking about.
We're talking about getting out there billions of miles away
from the Earth.
It will of course, as I mentioned, be the first to Pluto
and the first to explore the Kuiper Belt.
By the way, you can sort of see in that photo-- I don't know if
you've noticed there, but you can see the technicians below
it.
If you've seen other pictures of spacecraft, this is not very
big.
This is not really all that much bigger than the grand piano
that's sitting at the back of the room there.
Keeping it small is one way of making it go fast.
With the same amount of rocket power, you can send a small
thing faster than a big thing.
So keeping it compact, it had to last a long time, and so it's
made very simple as well, and the simplicity of the spacecraft
comes in to some of its operations, which we'll talk
about here in just a little bit.
As I mention down here, it cost about $720 million to build, to
develop, to build, launch, and operate the spacecraft.
That actually makes it a really good deal, about $0.24 per mile
is what I figured, about 3 billion miles it's got to go.
It actually went farther than that; that's just kind of the
straight-line distance from Earth to Pluto right now.
And that included everything.
My van, I did a quick calculation, costs about $0.12 a
mile to operate and that's just the fuel.
I don't know if I put the cost of the van and then maintenance
in there.
So it's really quite a good deal.
I think per mile it's got to be the cheapest one ever carried
out.
So just to give you a real quick animation, I picked this off of
a NASA website-- I think this is going to work; it looks like
it's going to work-- to show you the trajectory that the
spacecraft took away from-- let's see if we can expand this
here.
After launch, there's launch from Earth in the middle.
There's the flyby of Jupiter.
You can see the little bend where it picked up some energy
from Jupiter there on the way out back in 2007.
And then the flyby of Pluto out there.
So it's a pretty direct route.
It didn't take a lot of orbits and things like that to get
around out there, but it took a pretty good-- it took a pretty
good route, not a straight line but a pretty direct path.
Now, can I get this back to go back please.
Exit full screen.
Oh, it'll work in a minute.
That went too far.
We'll be back at it in just a moment.
All right, and let's skip by this real fast before it tries
to run again.
Yeah, okay.
So 10 years-- not quite.
Nine years and 3 billion miles is about the distance out to
Pluto that the spacecraft had to go.
There's a lot of fine print here which I'm not going to go into
at all, but you see the launch there,
January 19th, '06, flyby of Jupiter there, then the long
cruise out to Pluto.
And the flyby which occurred this morning.
Now, as I'm going to talk about, we're going to talk about what
it did during the flyby, but as we stand here and speak right
now, all we can be sure of is that that spacecraft, the New
Horizons, flew by Pluto.
It takes four hours to get a signal back from Pluto and there
are reasons why it didn't send a signal or it might not have sent
a signal until 4, about 4:00 this afternoon.
It takes about four hours for the signal to get back.
That's how long it takes light to get us, the radio signals to
get to us from the spacecraft there.
And the spacecraft, if it phones home and says I'm okay and I've
got a lot of pictures for you, everybody will be really happy.
That signal is supposed to come in about 8 p.m. tonight, so
about the time that we'll conclude this talk.
So we can be sure just because Newton knew how to make these
calculations-- Newtonian physics assures that this thing will
have flown by Pluto.
Everybody, the scientists all hedge just a little bit because
we don't actually know that there isn't, say, a ring of ice
particles around Pluto that nobody would've ever seen
before, and it would only take one.
The spacecraft flies by Pluto at about 31,000 miles an hour.
So you can imagine what a pebble off of a dump truck does to your
windshield.
At 31,000 miles an hour, the spacecraft will be toast.
So it's-- probably it's fine, but we'll know when we actually
get, when it actually phones home.
So among the scientific questions that the New Horizons
is out there to explore is the primary goals are to look at the
atmosphere of Pluto, which we know is out there.
It has some nitrogen in it, it has some carbon monoxide in it,
it has methane, and the methane appears to be both gaseous and
frozen on the surface, which suggests something like weather,
that maybe their phase changes.
But under what circumstances and just what's happening, we don't
know.
So study of the atmosphere and what's happening out there.
Pluto has kind of a reddish color, which is attributed to--
well, what can give you a red planet?
Well, in the case of Mars, the oxidized iron on the surface of
Mars is usually said to be the reddish color of Mars.
That's not what we're talking about here with Pluto, almost
surely.
More likely, because we know we have methane up there, so we
could have organics chemistry, it's probably some organic
molecules that have a reddish color to them.
That's already pretty intriguing, too, because what
kind of chemistry can happen out there in the deep freeze?
How does it get enough energy out there for interesting
chemical things to happen?
Maybe UV light from the sun or something along that line might
be driving these things.
We also know that Pluto is not perfectly uniform and at the
very least has dark and light splotches.
I'll show you a fairly recent picture in a moment.
This is still an artist's conception there.
But why would it change out there?
Why would you have a non-uniform surface?
Well, again, maybe this weather, maybe this organic chemistry
certainly impacts our possibility, but even more
intriguing is that there might be processes out there that are
analogous to the moons, for example, of Jupiter and Saturn,
which have for various reasons crusts over, in those cases,
oceans of water and, in a case like that, you can have actually
what looks like the plate tectonics on the Earth.
These things can move and change with respect to each other.
We don't know if that's happening on Pluto or not, but
it might be, which would be really fascinating if it is out
there and the spacecraft should help us understand that better.
Charon is going to be really interesting.
That is studied as well.
Remember, it has, it seems, no atmosphere, but we'll be able to
refine that.
What exactly is its surface composition and it, too, has
light and dark areas on it.
We know that much.
Does that mean anything interesting, like surface
activity?
So these will be primary goals here for New Horizons to study
and tell us about.
Also, I mentioned a couple of times that Charon's status as a
moon, that may not be a good way to talk about it, as you raised
earlier.
In the case of two objects, when they orbit about each other,
they actually orbit about their common center of gravity.
And if they're of equal mass, then their common center of
gravity will be halfway in between them.
But we don't have any planets that do that.
In the case of the Earth and the moon, that common center of
gravity is in the Earth, so it looks like the Earth is the
center of the moon's orbit, although the Earth is moving
just a little bit as the moon orbits it.
In the case of Jupiter and the sun, they orbit about their
common center of gravity, but the common center of gravity is
in the sun.
So, again, you can say that Jupiter orbits around the sun,
which it does, but you can't say that, it turns out, about Pluto
and Charon because they actually orbit around their common center
of gravity which is not inside the planet Pluto.
So Pluto is out there going around a point in space just as
Charon is out there going around a point in space, and so
describing this as a binary planet-- except that Pluto isn't
a planet.
I don't know, a dwarf planet with a binary moon.
Anyway, it's-- whatever it is, these two bodies are more
comparable in mass than any other pair of bodies in the
solar system.
So understanding this a little bit better as a binary system is
a really important part of the scientific goals as well.
And finally, the contrast between these two things, the
contrast between the two surfaces, the interactions, the
potential interactions between the two surfaces, and then all
the stuff we can't see, like maybe there are dust belts or
ice belts or something else out there, stuff we can't guess.
We're always looking for the good stuff that we don't expect,
of course, out there.
The instrumentation on the space probe compared to some is
relatively straightforward, relatively simple, and the
spacecraft itself is mechanically very simple.
You can see the-- you can see part of it down here.
That is sort of the grand piano size thing, and of course, it
has an antenna.
You can see the antenna there, which is about the same size.
And then the diagram shows you the various instruments located
around the instrument, the space probe.
And just to take them in order there, one of them does
ultraviolet spectroscopy, so you study the spectroscopy, the
spectrum, of the light of these objects in the ultraviolet,
which is a lot about composition of the atmosphere and the
surface.
There are two imagers, which just means cameras, things to
take pictures of the surface, and those-- you can see the
names that the scientists have given these various instruments.
I'm not sure what was going on with Ralph and Alice, probably.
It's probably out there on the Internet somewhere, but I didn't
read up on it.
And then the other instruments are the traditional NASA
acronyms.
So there's another imager and then two particle detectors, a
dust belt, sorry, a dust detector, and then finally the
antenna which is also used for communications back to Earth
will be used for studies.
They're going to actually beam radio waves-- they did already-
beam radio waves out in that direction from the Earth, so the
Earth would look bright in radio wavelengths, and that antenna
looks back at the Earth, and then as the Earth passes as seen
by the spacecraft-- as the Earth passes behind the planet, those
radio waves from the Earth, that signal, can be analyzed for
information about the planet.
So the radio occultation experiment is actually done
with the communications setup of the spacecraft there.
So we've been seeing various images, and I don't have the
very latest images here.
There was one image sent back just before the flyby.
This one is kind of interesting.
You can sort of see-- that's Charon orbiting around there.
And can you detect the error in this?
It looks like Pluto isn't moving, but Pluto is actually
going around at the barycenter there.
But they chose to keep Pluto centered on this animation here.
You can see Charon orbiting around, but you can see Pluto
getting bigger.
Can you see that?
So we're actually approaching Pluto there during the series of
images, which looks like it must've taken roughly a week,
about one Charon orbital period there.
So this is not the best image so far.
This was the best image at the time I made up these slides,
which was just last week, and this is approximately the same
hemisphere that was facing the New Horizons when it flew by.
One of the consequences of a flyby, especially a fast flyby,
is that we're only going to see-- well, I should say we're
primarily going to see one face, one hemisphere, of Pluto.
So it's got another side and we're not going to get highly
detailed images of that.
This is roughly the same face that we'll see in the really
highly detailed images.
And this has been talked about a great deal.
I'm not going to go into it, but if you look, you can easily see
the big contrast, this big white area here and these very dark
areas.
Again, the question is, you know, what's going on here.
It doesn't really look like impact.
It looks like some interesting surface science, maybe geology,
going on there on the surface.
But this is the hemisphere that we're going to see in much
higher resolution, estimated to be in the area of a few hundred
meters per pixel.
So the smallest things we'll be able to see will be like, oh,
you know, sort of parking lot size objects.
So if you image the center here where Space Place is at that
resolution, you'd be able to tell the building from the
parking lot, from the street, that sort of thing.
We're not-- it's not going to be Google Earth type resolution,
where we can pick out the license plates on the cars up
there or anything like that, but we will have pretty good
resolution at a geographical sort of scale.
So was the-- this is the profile of the flyby that was made by
the, certainly was made, by the New Horizons spacecraft earlier,
and it passed right through the system of orbits there of Pluto
and its moons.
And here's the pass behind the sun, pass behind the planet as
seen by the spacecraft up here.
And here is where the Earth's occultation, where the radio
experiments would've been done out there.
The spacecraft was quite busy during this time.
As it's going by in a fairly short period of time, it's got
to point at Pluto and it's got to point at Charon and it has to
keep on pointing back and forth between its primary targets as
it passes through here.
The instruments, in order to keep the spacecraft simple,
primarily, the instruments can't point themselves independently.
So you have to turn the spacecraft in order to aim your
camera over there or turn the spacecraft again in order to aim
it up there.
That means that while you're doing that, you can't keep your
communications antenna sending back data to Earth.
And so that was put off completely until after the
flybys.
So basically the spacecraft has been maneuvering itself around
to turn the different instruments at the different
targets-- remember, there's not just one; there are multiple
instruments there on the various targets to carry out the whole
science program during the flyby, which took some hours
there, as you can see there, a few hours, 11 there to 15.
A few hours during the flyby gathering data.
And it was only after all the science had been done that then
it's allowed to program, to turn around and face the Earth and
say, okay, I'm done and I'm still here.
And we won't hear that if anything dramatic happened to
it, if anything dramatic happened to it on the way
through here, like running into some ice particles or something.
I don't mean to over emphasize that.
That's pretty unlikely and they've actually been watching
for that have kind of thing, ready to try and modify the path
should they see any sorts of threats.
But if we're going to get that message, we should get it
tonight and if it isn't already in, the predicted time was about
8:02 p.m. our time, which is not quite 10 minutes away from right
now.
And then we should expect some NASA briefings at about 8:30.
So if you want to go home and tune into the television for
that.
The flyby of Pluto, so we're waiting to hear about that, but
the flyby of Pluto, if all has gone well, will not be the end
of this mission.
You've got this thing already heading out there at high speed.
It's only going to spend a short amount of time on that flyby
around Pluto.
And so if all goes well, then we're going to get the images
from it over the next days and actually weeks and the data rate
is so slow that some estimates say it might take a year and a
half to get all the data down to us.
It depends on a certain number of things, which include just
how much time NASA's deep space network can spend talking to New
Horizons and not doing other stuff.
So if they have more time to talk to Pluto, to New Horizons,
the data will come back faster.
And certainly the analysis is going to go along for many
years, and while that's happening New Horizons will be
heading in all likelihood for yet another target because along
its trajectory-- so here's the-- we saw the animation of the
trajectory out to Pluto, but it's a flyby.
It is not going into orbit around Pluto.
It's just going to go by and keep on going out here, and it
turns out that there are some other objects out in the Kuiper
Belt that it may be able to flyby.
So these are the candidate objects, and after the flyby,
the mission team will assess where they are and probably
decide to go on with the mission and explore another one of these
things.
In that case, they'll choose one of these Kuiper Belt Objects and
then adjust the-- there's a little bit of rocket power on
the spacecraft to make course adjustments.
They'll choose their target, adjust the trajectory, and then
head out there.
Depending on what they choose, we're talking 2018-2019,
something like that.
So a cruise of a few more years, 3-4 years, before it makes it by
another Kuiper Belt Object, and that will be really interesting.
It's really - we keep talking about New Horizons as if it's a
Pluto mission and it is, but the thing that really unifies all
this is the Kuiper Belt.
It's a Kuiper Belt mission out there to the outer solar system.
So that's the end.
Thank you very much.
[Applause]