How a miniaturized atomic clock could revolutionize space exploration | Jill Seubert

98,641 views ・ 2020-04-06

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Transcriber: Joseph Geni Reviewer: Camille Martínez
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Six months ago,
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I watched with bated breath
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as NASA's InSight lander descended towards the surface of Mars.
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Two hundred meters,
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80 meters,
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60, 40, 20, 17 meters.
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Receiving confirmation of successful touchdown
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was one of the most ecstatic moments of my life.
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And hearing that news was possible because of two small cube sets
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that went along to Mars with InSight.
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Those two cube sets essentially livestreamed InSight's telemetry
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back to Earth,
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so that we could watch in near-real time
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as that InSight lander went screaming towards the surface of the red planet,
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hitting the atmosphere of Mars
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at a top speed of about 12,000 miles per hour.
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Now, that event was livestreamed to us
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from over 90 million miles away.
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It was livestreamed from Mars.
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Meanwhile,
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the two Voyager spacecraft --
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now, these are these two almost unbelievably intrepid explorers.
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They were launched
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the same year that all of us here were being introduced to Han Solo
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for the first time.
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And they are still sending back data from interstellar space
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over 40 years later.
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We are sending more spacecraft further into deep space
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than ever before.
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But every one of those spacecraft out there
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depends on its navigation being performed
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right here at Earth
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to tell it where it is and, far more importantly,
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where it is going.
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And we have to do that navigation here on Earth for one simple reason:
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spacecraft are really bad at telling the time.
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But if we can change that,
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we can revolutionize the way we explore deep space.
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Now, I am a deep space navigator,
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and I know you're probably thinking, "What is that job?"
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Well, it is an extremely unique and also very fun job.
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I steer spacecraft,
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from the moment they separate from their launch vehicle
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to when they reach their destination in space.
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And these destinations -- say Mars for example, or Jupiter --
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they are really far away.
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To put my job in context for you:
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it's like me standing here in Los Angeles and shooting an arrow,
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and with that arrow, I hit a target that's the size of a quarter,
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and that target the size of a quarter is sitting in Times Square, New York.
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Now, I have the opportunity to adjust the course of my spacecraft
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a few times along that trajectory,
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but in order to do that, I need to know where it is.
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And tracking a spacecraft as it travels through deep space
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is fundamentally a problem of measuring time.
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You see, I can't just pull out my ruler and measure how far away my spacecraft is.
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But I can measure
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how long it takes a signal to get there and back again.
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And the concept is exactly the same as an echo.
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If I stand in front of a mountain and I shout,
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the longer it takes for me to hear my echo back at me,
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the further away that mountain is.
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So we measure that signal time very, very accurately,
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because getting it wrong by just a tiny fraction of a second
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might mean the difference between your spacecraft safely and gently landing
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on the surface of another planet
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or creating yet another crater on that surface.
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Just a tiny fraction of a second,
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and it can be the difference between a mission's life or death.
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So we measure that signal time very, very accurately here on Earth,
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down to better than one-billionth of a second.
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But it has to be measured here on Earth.
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There's this great imbalance of scale when it comes to deep space exploration.
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Historically, we have been able to send smallish things extremely far away,
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thanks to very large things here on our home planet.
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As an example, this is the size of a satellite dish
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that we use to talk to these spacecraft in deep space.
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And the atomic clocks that we use for navigation are also large.
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The clocks and all of their supporting hardware
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can be up to the size of a refrigerator.
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Now, if we even want to talk about sending that capability into deep space,
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that refrigerator needs to shrink down
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into something that can fit inside the produce drawer.
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So why does this matter?
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Well, let's revisit one of our intrepid explorers, Voyager 1.
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Voyager 1 is just over 13 billion miles away right now.
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As you know, it took over 40 years to get there,
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and it takes a signal traveling at the speed of light over 40 hours
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to get there and back again.
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And here's the thing about these spacecraft:
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they move really fast.
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And Voyager 1 doesn't stop and wait for us to send directions from Earth.
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Voyager 1 keeps moving.
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In that 40 hours that we are waiting
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to hear that echo signal here on the Earth,
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Voyager 1 has moved on by about 1.5 million miles.
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It's 1.5 million miles further into largely uncharted territory.
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So it would be great
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if we could measure that signal time directly at the spacecraft.
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But the miniaturization of atomic clock technology is ...
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well, it's difficult.
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Not only does the clock technology and all the supporting hardware
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need to shrink down,
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but you also need to make it work.
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Space is an exceptionally harsh environment,
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and if one piece breaks on this instrument,
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it's not like we can just send a technician out to replace the piece
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and continue on our way.
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The journeys that these spacecraft take can last months, years,
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even decades.
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And designing and building a precision instrument that can support that
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is as much an art as it is a science and an engineering.
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But there is good news: we are making some amazing progress,
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and we're about to take our very first baby steps
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into a new age of atomic space clocks.
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Soon we will be launching
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an ion-based atomic clock that is space-suitable.
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And this clock has the potential to completely flip the way we navigate.
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This clock is so stable,
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it measures time so well,
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that if I put it right here and I turned it on,
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and I walked away,
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I would have to come back nine million years later
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for that clock's measurement to be off by one second.
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So what can we do with a clock like this?
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Well, instead of doing all of the spacecraft navigation
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here on the Earth,
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what if we let the spacecraft navigate themselves?
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Onboard autonomous navigation, or a self-driving spacecraft, if you will,
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is one of the top technologies needed
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if we are going to survive in deep space.
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When we inevitably send humans to Mars or even further,
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we need to be navigating that ship in real time,
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not waiting for directions to come from Earth.
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And measuring that time wrong by just a tiny fraction of a second
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can mean the difference between a mission's life or death,
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which is bad enough for a robotic mission,
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but just think about the consequences if there was a human crew on board.
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But let's assume that we can get our astronauts
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safely to the surface of their destination.
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Once they're there, I imagine they'd like a way to find their way around.
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Well, with this clock technology,
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we can now build GPS-like navigation systems
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at other planets and moons.
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Imagine having GPS on the Moon or Mars.
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Can you see an astronaut standing on the surface of Mars
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with Olympus Mons rising in the background,
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and she's looking down at her Google Maps Mars Edition
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to see where she is
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and to chart a course to get where she needs to go?
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Allow me to dream for a moment,
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and let's talk about something far, far in the future,
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when we are sending humans to places much further away than Mars,
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places where waiting for a signal from the Earth in order to navigate
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is just not realistic.
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Imagine in this scenario that we can have a constellation,
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a network of communication satellites scattered throughout deep space
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broadcasting navigation signals,
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and any spacecraft picking up that signal
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can travel from destination to destination to destination
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with no direct tie to the Earth at all.
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The ability to accurately measure time in deep space
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can forever change the way we navigate.
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But it also has the potential to give us some pretty cool science.
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You see, that same signal that we use for navigation
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tells us something about where it came from
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and the journey that it took as it traveled from antenna to antenna.
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And that journey, that gives us data, data to build better models,
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better models of planetary atmospheres throughout our solar system.
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We can detect subsurface oceans on far-off icy moons,
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maybe even detect tiny ripples in space due to relativistic gravity.
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Onboard autonomous navigation means we can support more spacecraft,
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more sensors to explore the universe,
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and it also frees up navigators -- people like me --
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to work on finding the answers to other questions.
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And we still have a lot of questions to answer.
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We know such precious little about this universe around us.
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In recent years, we have discovered nearly 3,000 planetary systems
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outside of our own solar system,
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and those systems are home to almost 4,000 exoplanets.
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To put that number in context for you:
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when I was learning about planets for the first time as a child,
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there were nine,
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or eight if you didn't count Pluto.
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But now there are 4,000.
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It is estimated that dark matter
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makes up about 96 percent of our universe,
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and we don't even know what it is.
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All of the science returned
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from all of our deep space missions combined
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is just this single drop of knowledge
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in a vast ocean of questions.
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And if we want to learn more,
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to discover more, to understand more,
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then we need to explore more.
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The ability to accurately keep time in deep space
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will revolutionize the way that we can explore this universe,
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and it might just be one of the keys to unlocking some of those secrets
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that she holds so dear.
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Thank you.
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(Applause)
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