Translator: Cihan Ekmekçi
Reviewer: hila scherba Hello, everyone. It's late in the day,
so I'm going to start with a test. (Laughter) How many planets do we have
in our solar system? Can't hear you. (Audience) Eight. Eight. Wasn't it nine? What was the ninth one? What happened? Pluto, yes. So I'm going to talk about
some of the research that I'm doing, in particular, some new evidence
that's going to tell us that there actually might be
the ninth planet in our solar system, which is not Pluto. So I'll describe how that goes. You can see the planets behind me. There are eight of them as you see
and you answer the question correctly. Very good. The first six which includes our Earth
have been known for a very long time. Humans have been around
for maybe about a million years. They probably saw it up in the sky. They are visible with the naked eye. The seventh and the eighth planet
are not so simple. Uranus, for example,
can be barely seen with the naked eye. If you go into a very dark place and you stare at the sky
for a very long time, you might be able to spot it. Neptune is totally invisible to your eye. Let me start with a little bit
of the history of what we know about our solar system. Like I said, the first six
have been known for a long time. The seventh one, Uranus, this one was the first planet
to be discovered using a telescope. The telescope that was maybe this big,
fits on the size of your desk. We now know that it orbits around the Sun at an average distance
of about 19 astronomical units. One astronomical unit
is the average distance between the Sun and the Earth. The eighth one, Neptune,
this has a very interesting story. This planet was actually
predicted to exist before it was discovered. After Uranus' discovery, physicists, astronomers were putting
Newton's law of gravity to the test. They tried to make predictions - very precise predictions
of where Uranus would be on the sky, and they tried to compare that
with the actual observations. And they found
that it did not exactly match where Uranus was supposed to be according to Newtonian gravity. Half the people said:
''Oh, Isaac Newton is wrong," half the people said:
"Maybe there's something out there.'' It took some time, but it was actually finally predicted,
through lots of hard work, that one night Neptune will appear
in this part of the sky, and so astronomers should go
and look at that spot. And lo and behold, within one degree, which is about the size of your fingertip
at the distance of your arm, it was found within 1 degree. Now, Neptune is what we consider
the outermost planet in our solar system. It orbits around the Sun, at an average distance
of about 30 astronomical units. Now, I have to say something about Pluto, since Pluto was once a planet. When I was in elementary school, I did learn that Pluto
was in fact the ninth planet. But in 2006, it was demoted down
to what we now know: a dwarf planet. It's not quite a planet,
but maybe close enough. Now, the person who demoted Pluto, his name is Mike Brown,
a professor at Caltech, he is not very popular
for obvious reasons, but he and his colleague at Caltech,
Konstantin Batygin, predicted that there might actually be
a true giant ninth planet in the outskirts of our solar system. Now, how do you look for things
in our solar system? Well, if you look at the sky
and if you take a telescope and measure, say, a portion of the sky, a solar system object
looks just like a star; it's a dot. The way to distinguish
a solar system object from a star is through its motion. The Earth goes around the Sun once a year. The object is also moving around the Sun. So as the Earth goes
around the Sun once a year, a solar system object
would appear to wobble in the sky. So if you look at the actual motion
of, say, Pluto over a 10-year period, it looks like this - that yellow coil
that you see in the back. It takes exactly a year
to complete one loop. It loops every year. But at the same time, Pluto
is moving around the Sun, and so you have a combined motion
of a circular motion and a drift in one direction. This is how you look
for solar system objects. Now, let me tell you how Mike Brown
and his colleague at Caltech predicted that there might actually be
a ninth planet in our solar system. So these are the terrestrial planets,
which includes our own Earth. Zoom out - those are our gas giants: Jupiter, Saturn, Uranus and Neptune. Now, if you'd zoom out even more,
there are a bunch of objects but there are six in particular that go way out to the outskirts
of the solar system, to about maybe 400-500 times
the astronomical unit. Now, you look at this, and say, "Whoa, okay, there
are six of these things.'' Do you see a pattern? They're all pointed in this direction. Now, if these were just random objects
orbiting around the Sun, you would expect these elliptical orbits
to point in random directions. The random chance of this occurring, the fact that six are pointed
in the same direction, and if you actually tilt this figure, they are actually orbiting
close to a similar plane. And so Mike Brown
and Konstantin Batygin said, "Well, this is weird.
You can't explain this. There's got to be something out there that is possibly shepherding the orbits
into a particular direction." And after a lot of hard work,
they came to the conclusion that, yes, you can actually do this
if there's, in fact, a giant planet they called Planet Nine with an orbit that is anti-aligned
with the really extended orbits. So this is what we're trying
to do at Penn. Penn is part of a large
international collaboration, it's called the Dark Energy Survey. We built this camera
and mount it on a telescope down in Chile. You see the big shiny dome behind me, that is the Blanco telescope,
a four-meter telescope down in Chile - we built a camera
that's literally this big, as tall as me, weighs about a ton, and mount it
on the top end of the telescope. What's special about this camera
is that it's huge. In one shot, you can take
a very nice, crisp, deep picture of a big part of the sky, which is not something
that every telescope can do. Now, this camera was built
for actually a different reason. As the name suggests,
it's called the Dark Energy Survey. We built this camera to try to study
the evolution of the universe. How did the universe begin? How is it expanding? What is the ultimate fate of the universe? That's what the other 200 astronomers
in our collaboration are doing. But me and my colleague here,
Professor Gary Bernstein, saw this and said, "Well, this is a very good camera
which takes very good data. You can actually use the same data
to find objects in our solar system." This is a picture - one exposure
taken on our camera. You can see the size
of the old camera in comparison, which can fit the full moon. We can fit many full moons in one shot. It's half a billion pixels,
costs about 80 million dollars. It's a very expensive instrument. We're taking pictures every night, and we're taking many,
many pictures every night, and trying to look for things
that move across the sky. Now, most of the objects
are stars and galaxies. Stars move a little bit;
galaxies don't move at all; solar system objects move quite a bit. I'm showing you here about 0.05 percent
of the data that we have. Each star that appear and disappear
are actual new things that we discovered in this particular part
of the sky that were not present before. There's a lot of them. If you'd combine all
of the data that we have, we'd have tens of millions
of new detections. Most of them are asteroids,
main belt asteroids, that orbit around the Sun,
between Mars and Jupiter, but a small, tiny fraction of these
are things in our solar system that are way out there. So we take these detections,
millions of detections, and try to connect the dots,
because like I said earlier, solar system objects move. They move in a very particular way
according to Newtonian gravity. So we take these detections,
take many, many computers, and try to find
the few objects that match up, that correspond to the same object
in the outskirts of our solar system. So what happens is something
that looks like this. I'm not showing you
all of the detections here. I'm only showing you the detections that correspond to actual solar
system objects that are way out there beyond the orbit of Pluto. In this small area, you can see
three camera pointings over here, which adds up to
about 0.15 percent of our data, we found 15 objects. Now, try doing that with
a bunch of undergraduate students here. Students here are absolutely great,
but if I tell them to do this manually, connect a million dots and try to find
the ones that match up, you really need a computer. Now, I have to confess that despite all the hard work
that we have done so far, we have not yet found Planet Nine. I probably wouldn't be here
if I had discovered it, (Laughter) but we did find at least
one interesting object that is rare. And you look at this picture.
It's insignificant; it's that little dot - of course it doesn't come with the arrow - it's that little dot that we discovered. It looks like nothing, but this turns out to be a distant
dwarf planet that we discovered. It's just like Pluto. It's way out there. It's slightly smaller than Pluto,
but this is the technology that we have - we can see these things
out to very large distances. Now, we've done
a lot of follow-up work on this and try to identify its nature. We now know that it has an orbit
that looks like that in comparison to the orbit of Neptune. And you can see how the dots
move across three different nights. Again, it's insignificant,
but computers are able to detect this. Now this name DeeDee
comes from distant dwarf. It's an acronym for distant dwarf,
and we put in the vowels in between. We now know that it has a size
of about 600 kilometers - it's a little bigger than Pennsylvania. But this thing currently
sits at 92 astronomical units. You have this ball of rock that is roughly as big as Pennsylvania, 92 astronomical units,
and we are capable of detecting it. In terms of its brightness,
its current brightness, it's comparable to taking a candlestick and putting it
at the distance of the moon, and we are able to detect that. Now, like I said,
we haven't found Planet Nine yet. We have looked at about half of our data. We're actively sifting through the rest
of the data that we have now. Does it exist? I don't know. But if it's in our images,
we'll definitely find it. And like Stephen Hawking said that we should all look up at the sky
and not down to your feet, I'm trying to do that. I'm trying to look up at the stars with the hope of maybe
sometime in the future finding this and understanding
more about our solar system. Thanks for your time. (Applause)
