What in the Universe: Transmission Spectrum of an Exoplanet Atmosphere

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What does this graph of Hubble data tell us? 

Produced by the Space Telescope Science Institute’s Office of Public Outreach in collaboration with NASA’s Universe of Learning partners: Caltech/IPAC, NASA Jet Propulsion Laboratory, Smithsonian Astrophysical Observatory, and Sonoma State University.

  • Hubble data from exoplanet HAT-P-26 b:  Hannah Wakeford (Wakeford, et al., 2017,Science 356, 628–631)

  • Illustration of exoplanet HAT-P-26 b: NASA/GSFC

  •  Animation of planets transiting a star: NASA, ESA, and G. Bacon (STScI)

  • Animation of starlight absorbed by planet atmosphere: Dani Player (STScI)

  • Animation of water molecules: Dani Player (STScI)

  •  Animation of the James Webb Space Telescope: NASA, SkyWorks Digital, Northrop Grumman, STScI

Written by Margaret W. Carruthers 
Designed by Dani Player 
Editorial input from Claire Blome, Dr. Brandon Lawton, Leah Ramsay, Timothy Rhue II 
Subject matter expertise from Dr. Hannah Wakeford 
Music from Music for Non-Profits

graph of white dots with lines of different lengths projecting from the top and bottom
Text, What in the universe?
This is a graph of data collected by the Hubble Space Telescope.
What does this graph show?
A., the heights of mountains on the moon. B, the strength of an earthquake on Mars. C, energy given off when two black holes merged. D, evidence for water in an exoplanet's atmosphere
Option D is highlighted
Transmission of spectrum of HAT-P-26 b exoplanet 464 light years away.
This graph of a transmission spectrum was made by measuring starlight that has passed through the atmosphere of HAT-P-26 b, a warm Neptune-sized planet nearly 500 light-years away.
illustration of exoplanet 454 light-years away
When a planet passes in front of its star, some of the starlight filters through the planet's atmosphere. Different gases in the atmosphere absorb different colors (different wavelengths) of light. By analyzing which wavelengths are blocked and which make it through, we can figure out what the planet's atmosphere is made of.
graph of transmission spectrum of HAT-P-26 b
The peaks on this graph are caused by water vapor in HAT-P-26 b's atmosphere. The height of each peak is related to the amount of water. The more water there is, the more light it blocks.
The same technique has been used to identify other gases in exoplanet atmospheres, including hydrogen, sodium, and carbon monoxide.
The James Webb Space Telescope, which has far more sensitive instruments, is helping us by observing exoplanet atmospheres in even more detail.