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How Do We Learn About a Planet’s Atmosphere?

How Do We Learn About a Planet’s Atmosphere?

The first confirmation of a planet orbiting a star outside our solar system happened in 1995. We now know that these worlds – also known as exoplanets – are abundant. So far, we’ve confirmed more than 4000. Even though these planets are far, far away, we can still study them using ground-based and space-based telescopes.

Our upcoming James Webb Space Telescope will study the atmospheres of the worlds in our solar system and those of exoplanets far beyond. Could any of these places support life? What Webb finds out about the chemical elements in these exoplanet atmospheres might help us learn the answer.

How do we know what’s in the atmosphere of an exoplanet?

Most known exoplanets have been discovered because they partially block the light of their suns. This celestial photo-bombing is called a transit.

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During a transit, some of the star’s light travels through the planet’s atmosphere and gets absorbed.

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The light that survives carries information about the planet across light-years of space, where it reaches our telescopes.

(However, the planet is VERY small relative to the star, and VERY far away, so it is still very difficult to detect, which is why we need a BIG telescope to be sure to capture this tiny bit of light.)

So how do we use a telescope to read light?

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Stars emit light at many wavelengths. Like a prism making a rainbow, we can separate light into its separate wavelengths. This is called a spectrum. Learn more about how telescopes break down light here. 

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Visible light appears to our eyes as the colors of the rainbow, but beyond visible light there are many wavelengths we cannot see.

Now back to the transiting planet…

As light is traveling through the planet’s atmosphere, some wavelengths get absorbed.

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Which wavelengths get absorbed depends on which molecules are in the planet’s atmosphere. For example, carbon monoxide molecules will capture different wavelengths than water vapor molecules.

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So, when we look at that planet in front of the star, some of the wavelengths of the starlight will be missing, depending on which molecules are in the atmosphere of the planet.

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Learning about the atmospheres of other worlds is how we identify those that could potentially support life…

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…bringing us another step closer to answering one of humanity’s oldest questions: Are we alone?

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Watch the full video where this method of hunting for distant planets is explained:

To learn more about NASA’s James Webb Space Telescope, visit the website, or follow the mission on Facebook, Twitter and Instagram. 

Text and graphics credit Space Telescope Science Institute

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