A needle in countless haystacks: Finding habitable worlds - Ariel Anbar
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0:15 - 0:18The universe contains about 100 billion galaxies.
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0:18 - 0:22Each of those galaxies contains about 100 billion stars.
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0:22 - 0:25Many of those stars have planets orbiting them.
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0:25 - 0:28So how do we look for life in all that immensity?
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0:28 - 0:32It's like searching for a needle in trillions of haystacks.
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0:32 - 0:36We might want to focus our search on planets that we know can support life as we know it --
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0:36 - 0:39what we call habitable worlds.
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0:39 - 0:41What do such planets look like?
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0:41 - 0:43To answer that question, we don't look out there.
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0:43 - 0:46Instead, we look at ourselves. At Earth.
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0:46 - 0:50Because this is the one planet in the universe that we know for certain is habitable.
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0:50 - 0:54When we look at Earth from space, we see a blue, watery world.
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0:54 - 0:58It's no coincidence that three quarters of the surface is covered by oceans.
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0:58 - 1:01Because of its unique chemical and physical properties,
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1:01 - 1:04water is absolutely essential for all life as we know it.
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1:04 - 1:09And so we get especially excited about other worlds on which water is abundant.
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1:09 - 1:12Fortunately, water is very common in the universe.
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1:12 - 1:15But life needs water in the form of liquid, not ice, and not vapor,
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1:15 - 1:17and that's a little bit less common.
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1:17 - 1:22For a planet to have liquid water at its surface, three things are important.
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1:22 - 1:25First, the planet needs to be large enough that the force of gravity
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1:25 - 1:28keeps the water molecules from flying off into space.
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1:28 - 1:32For example, Mars is smaller than Earth, and so has less gravity,
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1:32 - 1:35and that's one important reason that Mars has a very thin atmosphere,
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1:35 - 1:38and no oceans at its surface.
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1:38 - 1:41Second, the planet needs to have an atmosphere. Why?
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1:41 - 1:44Because without an atmosphere, the planet is in a vacuum,
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1:44 - 1:47and liquid water isn't stable in a vacuum.
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1:47 - 1:51For example, our moon has no atmosphere, and so if you spill some water on the moon,
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1:51 - 1:55it will either boil away as vapor, or freeze solid to make ice.
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1:55 - 2:00Without the pressure of an atmosphere, liquid water can't survive.
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2:00 - 2:03Third, the planet needs to be at the right distance from its star.
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2:03 - 2:07Too close, and the surface temperature will exceed the boiling point of water,
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2:07 - 2:09and oceans will turn to vapor.
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2:09 - 2:13Too far, and the surface temperature will fall below the freezing point of water,
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2:13 - 2:16causing the oceans to turn to ice.
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2:16 - 2:22Fire or ice. For life as we know it, neither will suffice.
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2:22 - 2:27You can imagine that the perfect zone where water stays liquid looks kind of like a belt around a star.
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2:27 - 2:30We call that belt the habitable zone.
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2:30 - 2:36So when we search for habitable worlds, we definitely want to look for planets in the habitable zones around their stars.
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2:36 - 2:41Those regions are the best bets to find planets like Earth.
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2:41 - 2:45But while habitable zones are a pretty good place to begin the search for planets with life,
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2:45 - 2:47there are a couple of complications.
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2:47 - 2:51First, a planet isn't necessarily habitable just because it's in the habitable zone.
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2:51 - 2:54Consider the planet Venus in our solar system.
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2:54 - 2:58If you were an alien astronomer, you'd think Venus is a pretty good bet for life.
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2:58 - 3:02It's the right size, it has an atmosphere, and it's in the habitable zone of our sun.
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3:02 - 3:05An alien astronomer might see it as Earth's twin.
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3:05 - 3:08But Venus is not habitable, at least not at its surface.
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3:08 - 3:11Not by life as we know it. It's too hot.
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3:11 - 3:16That's because Venus' atmosphere is full of carbon dioxide, an important greenhouse gas.
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3:16 - 3:19In fact, its atmosphere is almost entirely carbon dioxide,
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3:19 - 3:22and is almost 100 times thicker than our own.
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3:22 - 3:26As a result, the temperature on Venus is hot enough to melt lead,
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3:26 - 3:29and the planet is dry as a bone.
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3:29 - 3:33So finding planets of the right size and distance from their stars is only a beginning.
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3:33 - 3:36We also want to know about the makeup of their atmospheres.
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3:36 - 3:40The second complication emerges when we look a little more deeply at planet Earth.
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3:40 - 3:45In the last 30 years, we've discovered microbes living in all sorts of extreme environments.
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3:45 - 3:48We find them in fissures of rock miles beneath our feet,
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3:48 - 3:50in boiling waters of the ocean floor,
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3:50 - 3:52in acidic waters of thermal springs,
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3:52 - 3:56and in cloud droplets miles above our heads.
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3:56 - 3:59These so-called extremophiles aren't rare.
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3:59 - 4:03Some scientists estimate that the mass of microbes living deep underground
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4:03 - 4:06equals the mass of all the life at Earth's surface.
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4:06 - 4:10These subterranean microbes don't need oceans or sunshine.
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4:10 - 4:15These discoveries suggest that Earth-like planets may be only the tip of the astrobiological iceberg.
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4:15 - 4:19It's possible that life might persist in aquifers beneath the surface of Mars.
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4:19 - 4:21Microbes may thrive on Jupiter's moon Europa,
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4:21 - 4:25where liquid water ocean probably lies beneath the icy crust.
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4:25 - 4:31Another ocean beneath the surface of Saturn's moon Enceladus is the source of geysers erupting into space.
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4:31 - 4:33Could these geysers be raining microbes?
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4:33 - 4:36Could we fly through them to find out?
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4:36 - 4:39And what about life as we don't know it, using a liquid other than water?
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4:39 - 4:44Maybe we are the crazy creatures living in an unusual and extreme environment.
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4:44 - 4:46Maybe the real habitable zone is so large
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4:46 - 4:50that there are billions of needles in those trillions of haystacks.
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4:50 - 4:55Maybe in the big scheme of things, Earth is only one of many different kinds of habitable worlds.
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4:55 - 4:59The only way to find out is to go out and explore.
- Title:
- A needle in countless haystacks: Finding habitable worlds - Ariel Anbar
- Speaker:
- Ariel Anbar
- Description:
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View full lesson: http://ed.ted.com/lessons/a-needle-in-countless-haystacks-finding-habitable-planets-ariel-anbar
Out of billions of galaxies and billions of stars, how do we find Earth-like habitable worlds? What is essential to support life as we know it? Ariel Anbar provides a checklist for finding life on other planets.
Lesson by Ariel Anbar, animation by TED-Ed.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TED-Ed
- Duration:
- 05:11
Bedirhan Cinar approved English subtitles for A needle in countless haystacks: Finding habitable worlds | ||
Bedirhan Cinar accepted English subtitles for A needle in countless haystacks: Finding habitable worlds | ||
tom carter added a translation |