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We've found thousands of exoplanets over the years, but if we're going to find one that can sustain life, we need to take a look at the one planet we know that can, Earth.

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You can go to to start streaming thousands of documentaries  and nonfiction TV shows. [♪ INTRO]. We have found a lot of exoplanets  outside of our Solar System.

We’ve found at least thousands. But until recently, it didn’t look  like we’d know whether those exoplanets are habitable until we could send a space probe or satellite to collect more information. Now we have LOUPE, the Lunar Observatory for Unresolved Polarimetry of the Earth.

It’s a powerful camera that scientists plan to send to the Moon and take  pictures of Earth in 2022. They will use our planet to  create a template of what they might see on potentially  habitable exoplanets. And that moon’s eye view  will take us one step closer to finding planets like  ours without leaving Earth!

If certain conditions on Earth have made  it possible for it to support human life, then it makes sense to look for  similar things on exoplanets. Based on what we know about Earth,  we might expect habitable exoplanets to have bodies of water, land masses, an atmosphere with clouds  and oxygen, and vegetation. LOUPE will take images of Earth as  if it were an exoplanet and send them to scientists so they can gather  information about those qualities.

They’ll be able to use these pictures  to see sunlight being reflected in different ways over time by  clouds, gases, and plants on Earth to make a template of its rotation,  weather patterns, and seasons. It’s been tough to gather this kind of  information about exoplanets from light in the past because it’s hard to separate a star’s glare from the  exoplanet’s polarization data. That’s the direction of the light  waves coming from the exoplanet.

From what we have learned so  far, exoplanets are very diverse. Some have surfaces of lava, while others  are puffy with styrofoam-like densities. And getting more polarization data  with LOUPE will help tell us even more!

Like, if we want to know about  an exoplanet’s atmosphere, the direction of the light can  give us the information we need. Some of the light we see in images of  exoplanets is starlight that’s reflecting off of the exoplanet, and some is light  coming straight from the star itself. It’s usually hard to figure out the  difference between all that light.

But scientists will be able to use  polarization data to separate them more because the light coming from an exoplanet  is polarized, meaning the light is coming from one unified direction, while the starlight is unpolarized,  or coming from multiple directions. When starlight passes through the atmosphere  of an exoplanet and gets scattered, or when it’s reflected off  of an exoplanet’s surface, polarization usually increases by up to 10%. And on some planets, light could have to  pass through clouds in the atmosphere.

Polarization data can help  researchers identify clouds because they block an exoplanet’s polarized  light from reaching the camera. And if it’s a lucky exoplanet, clouds can even be characterized by the presence of rainbows! The rainbows we know and love on Earth  generally live in the “Roy G.

Biv” family. This is the result of sunlight  hitting water droplets in the air and refracting and reflecting  off of them at different angles. But if clouds are made of different  gases, the rainbow spectrum shifts.

Using this data, we’ll be able to  figure out what the clouds are made of and where the clouds are on the exoplanet. And speaking of gas, the most  important habitability signal might be how much oxygen there is on an exoplanet. LOUPE images will be able to help  scientists estimate the amount of oxygen by combining cloud and water data.

Oxygen and hydrogen make water,  so if there’s not much water, but there is oxygen, it’s likely  that the oxygen is in the atmosphere. And that could signal that there are  plants creating oxygen on the exoplanet. Below the atmosphere, we can also figure out if the exoplanet has continents and oceans.

We can learn if there are  continents on an exoplanet because light can become unpolarized when it  reflects off of rough surfaces like rock. Oceans, on the other hand, reflect light at consistent angles that are specific to water. When there’s enough wind to  create waves, the pattern of this reflection of light becomes broader.

The faster the wind, the  broader the light pattern. Using this knowledge, scientists  will even be able to study whether there are white caps  and the direction of the waves. We can also identify oceans by color alone.

The angle of light coming from  an exoplanet with an ocean makes it appear blue, white, and red. And colors can also tell us about vegetation! Plants here on Earth usually have  chlorophyll, a pigment that gives them a green color, and it also happens to  help capture light for the plants to use along with carbon dioxide  to make energy and oxygen.

So any plants on exoplanets  that convert light into oxygen might have something like green chlorophyll, too. But it’s even more conclusive to get data  on an exoplanet’s “vegetation red edge,” which is the light that’s  close to but just outside the range of red light that humans can see. Scientists think that plants on Earth might  reflect green light and near-red light because it’s inefficient to  use it for photosynthesis.

Since this is the part of the light  spectrum where chlorophyll and the things made by chlorophyll reflect light,  oxygen-producing plants on exoplanets could reflect light in a similar way. Since we know what kinds of gases are  in Earth’s atmosphere and where its continents, oceans, and vegetation  are, scientists can overlay what LOUPE captures about Earth  with the knowledge we already have. Then they’ll have a template  for what it would look like to take pictures of similar things on exoplanets.

With LOUPE, we’ll be able  to figure out the likelihood of exoplanet habitability from a distance. We won’t have to send a satellite or space  probe light years away to an exoplanet. All of the benefits of interplanetary  travel from the comfort of our own planet.

Thanks for watching, and thank you to  CuriosityStream for sponsoring this episode. CuriosityStream is a subscription  streaming service that offers thousands of documentaries and non­fiction  TV shows from some of the world's best filmmakers,  including exclusive originals. If you think the possibility of finding  potentially habitable exoplanets is fascinating, you might like the documentary  series Breakthrough, which highlights neat scientific  discoveries throughout history.

They’ve got a whole episode on  Exoplanets and the Trappist-1 System. If you’d like to check it out, you can  head to and use the code SciShowSpace to sign  up for just $14.99 for the whole year. Thanks again for watching! [♪ OUTRO].