Alien Atmospheres

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When a planet crosses directly between us and its star, we see the star dim slightly because the planet is blocking out a portion of the light. We can make a plot called a light curve with the brightness of the star versus time. Using this plot, we can see what percentage of the star's light the planet blocks and how long it takes the planet to cross the disk of the star. Larger planets block out more light.

The molecules in a planet's atmosphere absorb certain wavelengths of a star's transmitted light. We can see this absorption as the planet transits the star's disk, and we can thus identify the molecules in the planet's atmosphere.

This version of the animation includes "absorbed" and "transmitted" labels.

The molecules in a planet's atmosphere absorb certain wavelengths of a star's transmitted light. We can see this absorption as the planet transits the star's disk, and we can thus identify the molecules in the planet's atmosphere.

This version of the animation does not include labels.

An individiual planetary transit can appear different when observing the star at different wavelengths. That's because a planet's atmosphere blocks out more light at some wavelengths and less light at other wavelengths. Studying these differences in transit depths can reveal information about the composition, size, and density of the transiting planet's atmosphere.

This planet is about to cross in front of its star.

Credit: ESA/Hubble

An exoplanet's atmosphere can filter out certain wavelengths of its star's light.

Transit methods can help us determine the depth of an exoplanet's atmosphere as it passes in front of its star.

Exoplanet WASP-19b is a "hot Jupiter", a gas giant that orbits close to its star. Analyzing its transit across different wavelengths shows varying transit depths. This variation indicates high abundance of hydrocarbons like methane and hydrogen cyanide in the planet's thick atmosphere, and low abundance of water - probably not your next vacation destination!

Exoplanet WASP-19b is a "hot Jupiter", a gas giant that orbits close to its star. Analyzing its transit across different wavelengths shows varying transit depths. This variation indicates high abundance of hydrocarbons like methane and hydrogen cyanide in the planet's thick atmosphere, and low abundance of water - probably not your next vacation destination!