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Infrared Light Curve for Transiting Exoplanet HD 219134b

This plot captures the nearest known rocky exoplanet, dubbed HD 219134b, in the act of passing in front of its star. By carefully measuring the brightness of the star over several hours, astronomers using NASA's Spitzer Space Telescope clearly detected the faint decrease in light while the planet's disk covered a tiny portion of the star. These observations were made on April 14th, 2015 in infrared light at a wavelength of 4.5 microns. 

Even though the planet is 1.6 times the size of Earth, it reduces the observed brightness of the star by a mere 0.04% during its transit. However, since the host star is only 21 light years away it is quite bright, and can even be seen with the naked eye in the constellation Cassiopeia. This makes it much easier to measure such a tiny change in the star's brightness compared to other more distant (and fainter) transiting exoplanet systems.

The artwork depicts the relative scale of the planet with respect to the star and the calculated path of the transit near the edge of the stellar disk.

Transiting planets are ideal targets for astronomers wanting to know more about their compositions and atmospheres. If molecules are present in the planet's atmosphere, they can absorb certain wavelengths of light, leaving imprints in the stars light during the transit. This type of technique also will be used in the future to investigate potentially habitable planets and search for signs of life.

Now in its 11th year of operation, Spitzer has become an important tool for astronomers studying planets orbiting other stars.