Astronomy Photo of the Day
February 10th, 2013
HD209458b, also known as Osiris, lies some 150 light years away in the constellation of Pegasus. HD209458b orbits its parent star rather closely, taking this and the mass of the star into account, the planet is classified as a hot-Jupiter exoplanet.
This image, which mimics how the parent star this planet orbits would look as it was setting in the morning sky, was reconstructed by Frederic Pont of the University of Exeter using data from a camera on-board the Hubble Space Telescope. As we know, the color of the sun and the sky of each planet is determined by several factors, including the composition of the star and its orbiting exoplanet’s atmosphere.
To determine what an alien planet’s atmosphere contains, we can view the starlight streaming through it from our vantage point, and view it in a prism, which separates the colors into their respective wavelengths, which corresponds to a certain element.
In this case, like the sun, Osiris’s parent star is white, but when it passes through the concentration of sodium in the planet’s atmosphere, red light is absorbed, leaving behind the blue. But as the sun sets, the blue light is scattered in the same way on Earth, spawning the gradual change to green, and then to a dim dark green seen in this image.
Lastly, the bottom of the image is flattened due to diffraction in the planet’s atmosphere.
For Further Reading:
“Why is the Sky Blue?”
“HD209458 B (Osiris):”
“The Weather Patterns of Osirius:”
Image Credit: Frederic Pont of the University of Exeter