[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.76,0:00:03.74,Default,,0000,0000,0000,,So when you look out\Nat the stars at night,
Dialogue: 0,0:00:03.76,0:00:05.22,Default,,0000,0000,0000,,it's amazing what you can see.
Dialogue: 0,0:00:05.24,0:00:06.70,Default,,0000,0000,0000,,It's beautiful.
Dialogue: 0,0:00:06.72,0:00:09.82,Default,,0000,0000,0000,,But what's more amazing\Nis what you can't see,
Dialogue: 0,0:00:09.84,0:00:11.22,Default,,0000,0000,0000,,because what we know now
Dialogue: 0,0:00:11.24,0:00:14.62,Default,,0000,0000,0000,,is that around every star\Nor almost every star,
Dialogue: 0,0:00:14.64,0:00:15.90,Default,,0000,0000,0000,,there's a planet,
Dialogue: 0,0:00:15.92,0:00:17.12,Default,,0000,0000,0000,,or probably a few.
Dialogue: 0,0:00:18.12,0:00:20.22,Default,,0000,0000,0000,,So what this picture isn't showing you
Dialogue: 0,0:00:20.24,0:00:22.38,Default,,0000,0000,0000,,are all the planets that we know about
Dialogue: 0,0:00:22.40,0:00:23.80,Default,,0000,0000,0000,,out there in space.
Dialogue: 0,0:00:24.28,0:00:27.50,Default,,0000,0000,0000,,But when we think about planets,\Nwe tend to think of faraway things
Dialogue: 0,0:00:27.52,0:00:29.38,Default,,0000,0000,0000,,that are very different from our own.
Dialogue: 0,0:00:29.40,0:00:31.82,Default,,0000,0000,0000,,But here we are on a planet,
Dialogue: 0,0:00:31.84,0:00:35.14,Default,,0000,0000,0000,,and there are so many things\Nthat are amazing about Earth
Dialogue: 0,0:00:35.16,0:00:39.34,Default,,0000,0000,0000,,that we're searching far and wide\Nto find things that are like that.
Dialogue: 0,0:00:39.36,0:00:42.86,Default,,0000,0000,0000,,And when we're searching,\Nwe're finding amazing things.
Dialogue: 0,0:00:42.88,0:00:47.10,Default,,0000,0000,0000,,But I want to tell you\Nabout an amazing thing here on Earth.
Dialogue: 0,0:00:47.12,0:00:49.86,Default,,0000,0000,0000,,And that is that every minute,
Dialogue: 0,0:00:49.88,0:00:52.30,Default,,0000,0000,0000,,400 pounds of hydrogen
Dialogue: 0,0:00:52.32,0:00:54.94,Default,,0000,0000,0000,,and almost seven pounds of helium
Dialogue: 0,0:00:54.96,0:00:57.80,Default,,0000,0000,0000,,escape from Earth into space.
Dialogue: 0,0:00:58.80,0:01:02.76,Default,,0000,0000,0000,,And this is gas that is going off\Nand never coming back.
Dialogue: 0,0:01:03.44,0:01:06.46,Default,,0000,0000,0000,,So hydrogen, helium and many other things
Dialogue: 0,0:01:06.48,0:01:09.34,Default,,0000,0000,0000,,make up what's known\Nas the Earth's atmosphere.
Dialogue: 0,0:01:09.36,0:01:13.18,Default,,0000,0000,0000,,The atmosphere is just these gases\Nthat form a thin blue line
Dialogue: 0,0:01:13.20,0:01:16.42,Default,,0000,0000,0000,,that's seen here from\Nthe International Space Station,
Dialogue: 0,0:01:16.44,0:01:18.68,Default,,0000,0000,0000,,a photograph that some astronauts took.
Dialogue: 0,0:01:19.20,0:01:22.58,Default,,0000,0000,0000,,And this tenuous veneer around our planet
Dialogue: 0,0:01:22.60,0:01:24.94,Default,,0000,0000,0000,,is what allows life to flourish.
Dialogue: 0,0:01:24.96,0:01:27.82,Default,,0000,0000,0000,,It protects our planet\Nfrom too many impacts,
Dialogue: 0,0:01:27.84,0:01:29.86,Default,,0000,0000,0000,,from meteorites and the like.
Dialogue: 0,0:01:29.88,0:01:33.66,Default,,0000,0000,0000,,And it's such an amazing phenomenon
Dialogue: 0,0:01:33.68,0:01:36.50,Default,,0000,0000,0000,,that the fact that it's disappearing
Dialogue: 0,0:01:36.52,0:01:39.32,Default,,0000,0000,0000,,should frighten you,\Nat least a little bit.
Dialogue: 0,0:01:40.16,0:01:43.46,Default,,0000,0000,0000,,So this process is something that I study
Dialogue: 0,0:01:43.48,0:01:45.72,Default,,0000,0000,0000,,and it's called atmospheric escape.
Dialogue: 0,0:01:46.68,0:01:51.26,Default,,0000,0000,0000,,So atmospheric escape\Nis not specific to planet Earth.
Dialogue: 0,0:01:51.28,0:01:55.02,Default,,0000,0000,0000,,It's part of what it means\Nto be a planet, if you ask me,
Dialogue: 0,0:01:55.04,0:01:59.38,Default,,0000,0000,0000,,because planets, not just here on Earth\Nbut throughout the universe,
Dialogue: 0,0:01:59.40,0:02:01.98,Default,,0000,0000,0000,,can undergo atmospheric escape.
Dialogue: 0,0:02:02.00,0:02:07.40,Default,,0000,0000,0000,,And the way it happens actually tells us\Nabout planets themselves.
Dialogue: 0,0:02:07.92,0:02:10.58,Default,,0000,0000,0000,,Because when you think\Nabout the solar system,
Dialogue: 0,0:02:10.60,0:02:12.64,Default,,0000,0000,0000,,you might think about this picture here.
Dialogue: 0,0:02:13.80,0:02:17.22,Default,,0000,0000,0000,,And you would say, well,\Nthere are eight planets, maybe nine.
Dialogue: 0,0:02:17.24,0:02:19.74,Default,,0000,0000,0000,,So for those of you\Nwho are stressed by this picture,
Dialogue: 0,0:02:19.76,0:02:21.14,Default,,0000,0000,0000,,I will add somebody for you.
Dialogue: 0,0:02:21.16,0:02:22.38,Default,,0000,0000,0000,,(Laughter)
Dialogue: 0,0:02:22.40,0:02:25.28,Default,,0000,0000,0000,,Courtesy of New Horizons,\Nwe're including Pluto.
Dialogue: 0,0:02:26.16,0:02:27.38,Default,,0000,0000,0000,,And the thing here is,
Dialogue: 0,0:02:27.40,0:02:30.14,Default,,0000,0000,0000,,for the purposes of this talk\Nand atmospheric escape,
Dialogue: 0,0:02:30.16,0:02:32.18,Default,,0000,0000,0000,,Pluto is a planet in my mind,
Dialogue: 0,0:02:32.20,0:02:36.14,Default,,0000,0000,0000,,in the same way that planets\Naround other stars that we can't see
Dialogue: 0,0:02:36.16,0:02:37.94,Default,,0000,0000,0000,,are also planets.
Dialogue: 0,0:02:37.96,0:02:40.66,Default,,0000,0000,0000,,So fundamental characteristics of planets
Dialogue: 0,0:02:40.68,0:02:43.70,Default,,0000,0000,0000,,include the fact that they are bodies
Dialogue: 0,0:02:43.72,0:02:45.54,Default,,0000,0000,0000,,that are bound together by gravity.
Dialogue: 0,0:02:45.56,0:02:48.06,Default,,0000,0000,0000,,So it's a lot of material\Njust stuck together
Dialogue: 0,0:02:48.08,0:02:49.68,Default,,0000,0000,0000,,with this attractive force.
Dialogue: 0,0:02:50.24,0:02:53.10,Default,,0000,0000,0000,,And these bodies are so big\Nand have so much gravity.
Dialogue: 0,0:02:53.12,0:02:54.42,Default,,0000,0000,0000,,That's why they're round.
Dialogue: 0,0:02:54.44,0:02:56.06,Default,,0000,0000,0000,,So when you look at all of these,
Dialogue: 0,0:02:56.08,0:02:57.30,Default,,0000,0000,0000,,including Pluto,
Dialogue: 0,0:02:57.32,0:02:58.52,Default,,0000,0000,0000,,they're round.
Dialogue: 0,0:02:59.00,0:03:01.74,Default,,0000,0000,0000,,So you can see that gravity\Nis really at play here.
Dialogue: 0,0:03:01.76,0:03:05.06,Default,,0000,0000,0000,,But another fundamental\Ncharacteristic about planets
Dialogue: 0,0:03:05.08,0:03:06.82,Default,,0000,0000,0000,,is what you don't see here,
Dialogue: 0,0:03:06.84,0:03:09.42,Default,,0000,0000,0000,,and that's the star, the Sun,
Dialogue: 0,0:03:09.44,0:03:12.56,Default,,0000,0000,0000,,that all of the planets\Nin the solar system are orbiting around.
Dialogue: 0,0:03:13.20,0:03:16.92,Default,,0000,0000,0000,,And that's fundamentally driving\Natmospheric escape.
Dialogue: 0,0:03:17.76,0:03:23.10,Default,,0000,0000,0000,,The reason that fundamentally stars\Ndrive atmospheric escape from planets
Dialogue: 0,0:03:23.12,0:03:28.50,Default,,0000,0000,0000,,is because stars offer planets\Nparticles and light and heat
Dialogue: 0,0:03:28.52,0:03:31.62,Default,,0000,0000,0000,,that can cause the atmospheres to go away.
Dialogue: 0,0:03:31.64,0:03:33.46,Default,,0000,0000,0000,,So if you think of a hot-air balloon,
Dialogue: 0,0:03:33.48,0:03:37.62,Default,,0000,0000,0000,,or you look at this picture\Nof lanterns in Thailand at a festival,
Dialogue: 0,0:03:37.64,0:03:41.14,Default,,0000,0000,0000,,you can see that hot air\Ncan propel gasses upward.
Dialogue: 0,0:03:41.16,0:03:43.42,Default,,0000,0000,0000,,And if you have enough energy and heating,
Dialogue: 0,0:03:43.44,0:03:44.78,Default,,0000,0000,0000,,which our Sun does,
Dialogue: 0,0:03:44.80,0:03:48.70,Default,,0000,0000,0000,,that gas, which is so light\Nand only bound by gravity,
Dialogue: 0,0:03:48.72,0:03:50.48,Default,,0000,0000,0000,,it can escape into space.
Dialogue: 0,0:03:51.60,0:03:55.54,Default,,0000,0000,0000,,And so this is what's actually\Ncausing atmospheric escape
Dialogue: 0,0:03:55.56,0:03:58.26,Default,,0000,0000,0000,,here on Earth and also on other planets --
Dialogue: 0,0:03:58.28,0:04:00.98,Default,,0000,0000,0000,,that interplay\Nbetween heating from the star
Dialogue: 0,0:04:01.00,0:04:04.32,Default,,0000,0000,0000,,and overcoming the force\Nof gravity on the planet.
Dialogue: 0,0:04:05.00,0:04:06.74,Default,,0000,0000,0000,,So I've told you that it happens
Dialogue: 0,0:04:06.76,0:04:10.10,Default,,0000,0000,0000,,at the rate of 400 pounds\Na minute for hydrogen
Dialogue: 0,0:04:10.12,0:04:12.20,Default,,0000,0000,0000,,and almost seven pounds for helium.
Dialogue: 0,0:04:13.04,0:04:14.70,Default,,0000,0000,0000,,But what does that look like?
Dialogue: 0,0:04:14.72,0:04:16.54,Default,,0000,0000,0000,,Well, even in the '80s,
Dialogue: 0,0:04:16.56,0:04:18.30,Default,,0000,0000,0000,,we took pictures of the Earth
Dialogue: 0,0:04:18.32,0:04:19.78,Default,,0000,0000,0000,,in the ultraviolet
Dialogue: 0,0:04:19.80,0:04:22.70,Default,,0000,0000,0000,,using NASA's Dynamic Explorer spacecraft.
Dialogue: 0,0:04:22.72,0:04:24.54,Default,,0000,0000,0000,,So these two images of the Earth
Dialogue: 0,0:04:24.56,0:04:28.30,Default,,0000,0000,0000,,show you what that glow\Nof escaping hydrogen looks like,
Dialogue: 0,0:04:28.32,0:04:29.58,Default,,0000,0000,0000,,shown in red.
Dialogue: 0,0:04:29.60,0:04:33.22,Default,,0000,0000,0000,,And you can also see other features\Nlike oxygen and nitrogen
Dialogue: 0,0:04:33.24,0:04:34.70,Default,,0000,0000,0000,,in that white glimmer
Dialogue: 0,0:04:34.72,0:04:37.06,Default,,0000,0000,0000,,in the circle showing you the auroras
Dialogue: 0,0:04:37.08,0:04:39.98,Default,,0000,0000,0000,,and also some wisps around the tropics.
Dialogue: 0,0:04:40.00,0:04:43.02,Default,,0000,0000,0000,,So these are pictures\Nthat conclusively show us
Dialogue: 0,0:04:43.04,0:04:46.74,Default,,0000,0000,0000,,that our atmosphere isn't just\Ntightly bound to us here on Earth
Dialogue: 0,0:04:46.76,0:04:50.38,Default,,0000,0000,0000,,but it's actually\Nreaching out far into space,
Dialogue: 0,0:04:50.40,0:04:52.32,Default,,0000,0000,0000,,and at an alarming rate, I might add.
Dialogue: 0,0:04:53.08,0:04:56.90,Default,,0000,0000,0000,,But the Earth is not alone\Nin undergoing atmospheric escape.
Dialogue: 0,0:04:56.92,0:05:00.38,Default,,0000,0000,0000,,Mars, our nearest neighbor,\Nis much smaller than Earth,
Dialogue: 0,0:05:00.40,0:05:04.18,Default,,0000,0000,0000,,so it has much less gravity\Nwith which to hold on to its atmosphere.
Dialogue: 0,0:05:04.20,0:05:06.42,Default,,0000,0000,0000,,And so even though Mars has an atmosphere,
Dialogue: 0,0:05:06.44,0:05:08.66,Default,,0000,0000,0000,,we can see it's much thinner\Nthan the Earth's.
Dialogue: 0,0:05:08.68,0:05:10.14,Default,,0000,0000,0000,,Just look at the surface.
Dialogue: 0,0:05:10.16,0:05:13.62,Default,,0000,0000,0000,,You see craters indicating\Nthat it didn't have an atmosphere
Dialogue: 0,0:05:13.64,0:05:15.50,Default,,0000,0000,0000,,that could stop those impacts.
Dialogue: 0,0:05:15.52,0:05:18.30,Default,,0000,0000,0000,,Also, we see that it's the "red planet,"
Dialogue: 0,0:05:18.32,0:05:20.86,Default,,0000,0000,0000,,and atmospheric escape plays a role
Dialogue: 0,0:05:20.88,0:05:22.46,Default,,0000,0000,0000,,in Mars being red.
Dialogue: 0,0:05:22.48,0:05:26.06,Default,,0000,0000,0000,,That's because we think\NMars used to have a wetter past,
Dialogue: 0,0:05:26.08,0:05:30.66,Default,,0000,0000,0000,,and when water had enough energy,\Nit broke up into hydrogen and oxygen,
Dialogue: 0,0:05:30.68,0:05:34.42,Default,,0000,0000,0000,,and hydrogen being so light,\Nit escaped into space,
Dialogue: 0,0:05:34.44,0:05:36.38,Default,,0000,0000,0000,,and the oxygen that was left
Dialogue: 0,0:05:36.40,0:05:38.22,Default,,0000,0000,0000,,oxidized or rusted the ground,
Dialogue: 0,0:05:38.24,0:05:41.96,Default,,0000,0000,0000,,making that familiar\Nrusty red color that we see.
Dialogue: 0,0:05:42.96,0:05:44.90,Default,,0000,0000,0000,,So it's fine to look at pictures of Mars
Dialogue: 0,0:05:44.92,0:05:47.38,Default,,0000,0000,0000,,and say that atmospheric escape\Nprobably happened,
Dialogue: 0,0:05:47.40,0:05:51.50,Default,,0000,0000,0000,,but NASA has a probe that's currently\Nat Mars called the MAVEN satellite,
Dialogue: 0,0:05:51.52,0:05:55.06,Default,,0000,0000,0000,,and its actual job\Nis to study atmospheric escape.
Dialogue: 0,0:05:55.08,0:05:59.66,Default,,0000,0000,0000,,It's the Mars Atmosphere\Nand Volatile Evolution spacecraft.
Dialogue: 0,0:05:59.68,0:06:03.34,Default,,0000,0000,0000,,And results from it have already\Nshown pictures very similar
Dialogue: 0,0:06:03.36,0:06:05.26,Default,,0000,0000,0000,,to what you've seen here on Earth.
Dialogue: 0,0:06:05.28,0:06:07.78,Default,,0000,0000,0000,,We've long known that Mars\Nwas losing its atmosphere,
Dialogue: 0,0:06:07.80,0:06:09.58,Default,,0000,0000,0000,,but we have some stunning pictures.
Dialogue: 0,0:06:09.60,0:06:12.74,Default,,0000,0000,0000,,Here, for example,\Nyou can see in the red circle
Dialogue: 0,0:06:12.76,0:06:14.26,Default,,0000,0000,0000,,is the size of Mars,
Dialogue: 0,0:06:14.28,0:06:18.46,Default,,0000,0000,0000,,and in blue you can see the hydrogen\Nescaping away from the planet.
Dialogue: 0,0:06:18.48,0:06:22.02,Default,,0000,0000,0000,,So it's reaching out more than 10 times\Nthe size of the planet,
Dialogue: 0,0:06:22.04,0:06:24.74,Default,,0000,0000,0000,,far enough away that it's\Nno longer bound to that planet.
Dialogue: 0,0:06:24.76,0:06:26.74,Default,,0000,0000,0000,,It's escaping off into space.
Dialogue: 0,0:06:26.76,0:06:28.98,Default,,0000,0000,0000,,And this helps us confirm ideas,
Dialogue: 0,0:06:29.00,0:06:31.76,Default,,0000,0000,0000,,like why Mars is red,\Nfrom that lost hydrogen.
Dialogue: 0,0:06:32.52,0:06:35.10,Default,,0000,0000,0000,,But hydrogen isn't\Nthe only gas that's lost.
Dialogue: 0,0:06:35.12,0:06:38.30,Default,,0000,0000,0000,,I mentioned helium on Earth\Nand some oxygen and nitrogen,
Dialogue: 0,0:06:38.32,0:06:42.10,Default,,0000,0000,0000,,and from MAVEN we can also look\Nat the oxygen being lost from Mars.
Dialogue: 0,0:06:42.12,0:06:44.58,Default,,0000,0000,0000,,And you can see\Nthat because oxygen is heavier,
Dialogue: 0,0:06:44.60,0:06:47.74,Default,,0000,0000,0000,,it can't get as far as the hydrogen,
Dialogue: 0,0:06:47.76,0:06:49.94,Default,,0000,0000,0000,,but it's still escaping\Naway from the planet.
Dialogue: 0,0:06:49.96,0:06:53.04,Default,,0000,0000,0000,,You don't see it all confined\Ninto that red circle.
Dialogue: 0,0:06:53.80,0:06:57.82,Default,,0000,0000,0000,,So the fact that we not only see\Natmospheric escape on our own planet
Dialogue: 0,0:06:57.84,0:07:01.46,Default,,0000,0000,0000,,but we can study it elsewhere\Nand send spacecraft
Dialogue: 0,0:07:01.48,0:07:04.58,Default,,0000,0000,0000,,allows us to learn\Nabout the past of planets
Dialogue: 0,0:07:04.60,0:07:06.86,Default,,0000,0000,0000,,but also about planets in general
Dialogue: 0,0:07:06.88,0:07:08.66,Default,,0000,0000,0000,,and Earth's future.
Dialogue: 0,0:07:08.68,0:07:11.34,Default,,0000,0000,0000,,So one way we actually\Ncan learn about the future
Dialogue: 0,0:07:11.36,0:07:14.44,Default,,0000,0000,0000,,is by planets so far away\Nthat we can't see.
Dialogue: 0,0:07:15.44,0:07:18.50,Default,,0000,0000,0000,,And I should just note though,\Nbefore I go on to that,
Dialogue: 0,0:07:18.52,0:07:20.98,Default,,0000,0000,0000,,I'm not going to show you\Nphotos like this of Pluto,
Dialogue: 0,0:07:21.00,0:07:22.42,Default,,0000,0000,0000,,which might be disappointing,
Dialogue: 0,0:07:22.44,0:07:24.46,Default,,0000,0000,0000,,but that's because we don't have them yet.
Dialogue: 0,0:07:24.48,0:07:27.74,Default,,0000,0000,0000,,But the New Horizons mission\Nis currently studying atmospheric escape
Dialogue: 0,0:07:27.76,0:07:29.10,Default,,0000,0000,0000,,being lost from the planet.
Dialogue: 0,0:07:29.12,0:07:30.84,Default,,0000,0000,0000,,So stay tuned and look out for that.
Dialogue: 0,0:07:31.56,0:07:33.70,Default,,0000,0000,0000,,But the planets\Nthat I did want to talk about
Dialogue: 0,0:07:33.72,0:07:36.02,Default,,0000,0000,0000,,are known as transiting exoplanets.
Dialogue: 0,0:07:36.04,0:07:39.82,Default,,0000,0000,0000,,So any planet orbiting a star\Nthat's not our Sun
Dialogue: 0,0:07:39.84,0:07:42.78,Default,,0000,0000,0000,,is called an exoplanet,\Nor extrasolar planet.
Dialogue: 0,0:07:42.80,0:07:45.26,Default,,0000,0000,0000,,And these planets that we call transiting
Dialogue: 0,0:07:45.28,0:07:46.54,Default,,0000,0000,0000,,have the special feature
Dialogue: 0,0:07:46.56,0:07:48.66,Default,,0000,0000,0000,,that if you look\Nat that star in the middle,
Dialogue: 0,0:07:48.68,0:07:51.06,Default,,0000,0000,0000,,you'll see that actually it's blinking.
Dialogue: 0,0:07:51.08,0:07:52.94,Default,,0000,0000,0000,,And the reason that it's blinking
Dialogue: 0,0:07:52.96,0:07:56.98,Default,,0000,0000,0000,,is because there are planets\Nthat are going past it all the time,
Dialogue: 0,0:07:57.00,0:07:59.14,Default,,0000,0000,0000,,and it's that special orientation
Dialogue: 0,0:07:59.16,0:08:01.94,Default,,0000,0000,0000,,where the planets are blocking\Nthe light from the star
Dialogue: 0,0:08:01.96,0:08:04.24,Default,,0000,0000,0000,,that allows us to see that light blinking.
Dialogue: 0,0:08:04.96,0:08:07.82,Default,,0000,0000,0000,,And by surveying the stars\Nin the night sky
Dialogue: 0,0:08:07.84,0:08:09.26,Default,,0000,0000,0000,,for this blinking motion,
Dialogue: 0,0:08:09.28,0:08:10.94,Default,,0000,0000,0000,,we are able to find planets.
Dialogue: 0,0:08:10.96,0:08:15.14,Default,,0000,0000,0000,,This is how we've now been able\Nto detect over 5,000 planets
Dialogue: 0,0:08:15.16,0:08:16.38,Default,,0000,0000,0000,,in our own Milky Way,
Dialogue: 0,0:08:16.40,0:08:19.26,Default,,0000,0000,0000,,and we know there are\Nmany more out there, like I mentioned.
Dialogue: 0,0:08:19.28,0:08:22.18,Default,,0000,0000,0000,,So when we look at the light\Nfrom these stars,
Dialogue: 0,0:08:22.20,0:08:25.70,Default,,0000,0000,0000,,what we see, like I said,\Nis not the planet itself,
Dialogue: 0,0:08:25.72,0:08:27.78,Default,,0000,0000,0000,,but you actually see\Na dimming of the light
Dialogue: 0,0:08:27.80,0:08:29.46,Default,,0000,0000,0000,,that we can record in time.
Dialogue: 0,0:08:29.48,0:08:32.90,Default,,0000,0000,0000,,So the light drops as the planet\Ndecreases in front of the star,
Dialogue: 0,0:08:32.92,0:08:35.34,Default,,0000,0000,0000,,and that's that blinking\Nthat you saw before.
Dialogue: 0,0:08:35.36,0:08:37.18,Default,,0000,0000,0000,,So not only do we detect the planets
Dialogue: 0,0:08:37.20,0:08:40.02,Default,,0000,0000,0000,,but we can look at this light\Nin different wavelengths.
Dialogue: 0,0:08:40.04,0:08:44.14,Default,,0000,0000,0000,,So I mentioned looking at the Earth\Nand Mars in ultraviolet light.
Dialogue: 0,0:08:44.16,0:08:47.78,Default,,0000,0000,0000,,If we look at transiting exoplanets\Nwith the Hubble Space Telescope,
Dialogue: 0,0:08:47.80,0:08:49.90,Default,,0000,0000,0000,,we find that in the ultraviolet,
Dialogue: 0,0:08:49.92,0:08:53.58,Default,,0000,0000,0000,,you see much bigger blinking,\Nmuch less light from the star,
Dialogue: 0,0:08:53.60,0:08:55.38,Default,,0000,0000,0000,,when the planet is passing in front.
Dialogue: 0,0:08:55.40,0:08:58.82,Default,,0000,0000,0000,,And we think this is because you have\Nan extended atmosphere of hydrogen
Dialogue: 0,0:08:58.84,0:09:00.06,Default,,0000,0000,0000,,all around the planet
Dialogue: 0,0:09:00.08,0:09:01.58,Default,,0000,0000,0000,,that's making it look puffier
Dialogue: 0,0:09:01.60,0:09:03.92,Default,,0000,0000,0000,,and thus blocking\Nmore of the light that you see.
Dialogue: 0,0:09:04.88,0:09:07.78,Default,,0000,0000,0000,,So using this technique,\Nwe've actually been able to discover
Dialogue: 0,0:09:07.80,0:09:12.06,Default,,0000,0000,0000,,a few transiting exoplanets\Nthat are undergoing atmospheric escape.
Dialogue: 0,0:09:12.08,0:09:14.90,Default,,0000,0000,0000,,And these planets\Ncan be called hot Jupiters,
Dialogue: 0,0:09:14.92,0:09:16.54,Default,,0000,0000,0000,,for some of the ones we've found.
Dialogue: 0,0:09:16.56,0:09:19.14,Default,,0000,0000,0000,,And that's because\Nthey're gas planets like Jupiter,
Dialogue: 0,0:09:19.16,0:09:20.94,Default,,0000,0000,0000,,but they're so close to their star,
Dialogue: 0,0:09:20.96,0:09:23.22,Default,,0000,0000,0000,,about a hundred times closer than Jupiter.
Dialogue: 0,0:09:23.24,0:09:26.70,Default,,0000,0000,0000,,And because there's all this\Nlightweight gas that's ready to escape,
Dialogue: 0,0:09:26.72,0:09:28.42,Default,,0000,0000,0000,,and all this heating from the star,
Dialogue: 0,0:09:28.44,0:09:32.26,Default,,0000,0000,0000,,you have completely catastrophic rates\Nof atmospheric escape.
Dialogue: 0,0:09:32.28,0:09:36.90,Default,,0000,0000,0000,,So unlike our 400 pounds per minute\Nof hydrogen being lost on Earth,
Dialogue: 0,0:09:36.92,0:09:38.18,Default,,0000,0000,0000,,for these planets,
Dialogue: 0,0:09:38.20,0:09:42.28,Default,,0000,0000,0000,,you're losing 1.3 billion\Npounds of hydrogen every minute.
Dialogue: 0,0:09:43.32,0:09:47.66,Default,,0000,0000,0000,,So you might think, well,\Ndoes this make the planet cease to exist?
Dialogue: 0,0:09:47.68,0:09:49.70,Default,,0000,0000,0000,,And this is a question\Nthat people wondered
Dialogue: 0,0:09:49.72,0:09:51.54,Default,,0000,0000,0000,,when they looked at our solar system,
Dialogue: 0,0:09:51.56,0:09:53.90,Default,,0000,0000,0000,,because planets\Ncloser to the Sun are rocky,
Dialogue: 0,0:09:53.92,0:09:56.86,Default,,0000,0000,0000,,and planets further away\Nare bigger and more gaseous.
Dialogue: 0,0:09:56.88,0:09:59.26,Default,,0000,0000,0000,,Could you have started\Nwith something like Jupiter
Dialogue: 0,0:09:59.28,0:10:00.98,Default,,0000,0000,0000,,that was actually close to the Sun,
Dialogue: 0,0:10:01.00,0:10:02.62,Default,,0000,0000,0000,,and get rid of all the gas in it?
Dialogue: 0,0:10:02.64,0:10:05.70,Default,,0000,0000,0000,,We now think that if you start\Nwith something like a hot Jupiter,
Dialogue: 0,0:10:05.72,0:10:08.54,Default,,0000,0000,0000,,you actually can't end up\Nwith Mercury or the Earth.
Dialogue: 0,0:10:08.56,0:10:10.74,Default,,0000,0000,0000,,But if you started with something smaller,
Dialogue: 0,0:10:10.76,0:10:13.54,Default,,0000,0000,0000,,it's possible that enough gas\Nwould have gotten away
Dialogue: 0,0:10:13.56,0:10:15.70,Default,,0000,0000,0000,,that it would have\Nsignificantly impacted it
Dialogue: 0,0:10:15.72,0:10:19.06,Default,,0000,0000,0000,,and left you with something very different\Nthan what you started with.
Dialogue: 0,0:10:19.08,0:10:20.98,Default,,0000,0000,0000,,So all of this sounds sort of general,
Dialogue: 0,0:10:21.00,0:10:23.54,Default,,0000,0000,0000,,and we might think about the solar system,
Dialogue: 0,0:10:23.56,0:10:26.34,Default,,0000,0000,0000,,but what does this have to do\Nwith us here on Earth?
Dialogue: 0,0:10:26.36,0:10:28.14,Default,,0000,0000,0000,,Well, in the far future,
Dialogue: 0,0:10:28.16,0:10:30.30,Default,,0000,0000,0000,,the Sun is going to get brighter.
Dialogue: 0,0:10:30.32,0:10:31.54,Default,,0000,0000,0000,,And as that happens,
Dialogue: 0,0:10:31.56,0:10:34.88,Default,,0000,0000,0000,,the heating that we find from the Sun\Nis going to become very intense.
Dialogue: 0,0:10:35.60,0:10:39.94,Default,,0000,0000,0000,,In the same way that you see\Ngas streaming off from a hot Jupiter,
Dialogue: 0,0:10:39.96,0:10:42.30,Default,,0000,0000,0000,,gas is going to stream off from the Earth.
Dialogue: 0,0:10:42.32,0:10:44.50,Default,,0000,0000,0000,,And so what we can look forward to,
Dialogue: 0,0:10:44.52,0:10:46.58,Default,,0000,0000,0000,,or at least prepare for,
Dialogue: 0,0:10:46.60,0:10:48.42,Default,,0000,0000,0000,,is the fact that in the far future,
Dialogue: 0,0:10:48.44,0:10:51.22,Default,,0000,0000,0000,,the Earth is going to look more like Mars.
Dialogue: 0,0:10:51.24,0:10:53.98,Default,,0000,0000,0000,,Our hydrogen, from water\Nthat is broken down,
Dialogue: 0,0:10:54.00,0:10:56.42,Default,,0000,0000,0000,,is going to escape\Ninto space more rapidly,
Dialogue: 0,0:10:56.44,0:11:00.52,Default,,0000,0000,0000,,and we're going to be left\Nwith this dry, reddish planet.
Dialogue: 0,0:11:00.96,0:11:03.46,Default,,0000,0000,0000,,So don't fear, it's not\Nfor a few billion years,
Dialogue: 0,0:11:03.48,0:11:05.06,Default,,0000,0000,0000,,so there's some time to prepare.
Dialogue: 0,0:11:05.08,0:11:06.14,Default,,0000,0000,0000,,(Laughter)
Dialogue: 0,0:11:06.16,0:11:08.98,Default,,0000,0000,0000,,But I wanted you\Nto be aware of what's going on,
Dialogue: 0,0:11:09.00,0:11:10.26,Default,,0000,0000,0000,,not just in the future,
Dialogue: 0,0:11:10.28,0:11:13.50,Default,,0000,0000,0000,,but atmospheric escape\Nis happening as we speak.
Dialogue: 0,0:11:13.52,0:11:17.02,Default,,0000,0000,0000,,So there's a lot of amazing science\Nthat you hear about happening in space
Dialogue: 0,0:11:17.04,0:11:18.98,Default,,0000,0000,0000,,and planets that are far away,
Dialogue: 0,0:11:19.00,0:11:22.22,Default,,0000,0000,0000,,and we are studying these planets\Nto learn about these worlds.
Dialogue: 0,0:11:22.24,0:11:26.94,Default,,0000,0000,0000,,But as we learn about Mars\Nor exoplanets like hot Jupiters,
Dialogue: 0,0:11:26.96,0:11:29.98,Default,,0000,0000,0000,,we find things like atmospheric escape
Dialogue: 0,0:11:30.00,0:11:33.74,Default,,0000,0000,0000,,that tell us a lot more\Nabout our planet here on Earth.
Dialogue: 0,0:11:33.76,0:11:37.82,Default,,0000,0000,0000,,So consider that the next time\Nyou think that space is far away.
Dialogue: 0,0:11:37.84,0:11:39.06,Default,,0000,0000,0000,,Thank you.
Dialogue: 0,0:11:39.08,0:11:42.12,Default,,0000,0000,0000,,(Applause)