Alien Atmospheres

  • Released Tuesday, December 3, 2013

Since the early 1990's, astronomers have known that extrasolar planets, or "exoplanets," orbit stars light-years beyond our own solar system. Although most exoplanets are too distant to be directly imaged, detailed studies have been made of their size, composition, and even atmospheric makeup - but how? By observing periodic variations in the parent star's brightness and color, astronomers can indirectly determine an exoplanet's distance from its star, its size, and its mass. But to truly understand an exoplanet astronomers must study its atmosphere, and they do so by splitting apart the parent star's light during a planetary transit.

Exoplanet Animation - Transit Light Curve

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.

Exoplanet Animation - Absorption without 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.

Exoplanet Animation - Transit Depth vs Wavelength

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.

Exoplanet Image - Crescent TransitThis planet is about to cross in front of its star. Credit:  ESA/Hubble

Exoplanet Image - Crescent Transit

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

Credit: ESA/Hubble

Exoplanet Image - LimbAn exoplanet's atmosphere can filter out certain wavelengths of its star's light.

Exoplanet Image - Limb

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

Exoplanet Image - Atmospheric DepthTransit methods can help us determine the depth of an exoplanet's atmosphere as it passes in front of its star.

Exoplanet Image - Atmospheric Depth

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

Exoplanet Image - WASP-19b Transit Depth Curve and MolecluesExoplanet 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 Image - WASP-19b Transit Depth Curve and Moleclues

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 Image - WASP-19b Transit Depth CurveExoplanet 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 Image - WASP-19b Transit Depth Curve

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!

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Credits

Please give credit for this item to:
NASA's Goddard Space Flight Center
Additional animations courtesy ESA/Hubble

Release date

This page was originally published on Tuesday, December 3, 2013.
This page was last updated on Tuesday, November 14, 2023 at 12:18 AM EST.


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