In 1972, the Apollo 17 crew captured the first photograph of Earth in full view. The shot, appropriately named “Blue Marble,” shows our planet roiling in shades of blue and white against the dark backdrop of space.
(NASA)
Eighteen years later, the Voyager 1 space probe snapped a photo from billions of miles away as it traveled past Pluto in 1990. In the image, dubbed “Pale Blue Dot,” Earth appears as a lonely pixel, a faint shade of blue in the vastness of space.
(NASA Goddard Spaceflight Center)
Now, scientists believe that Earth’s iconic blue color might signal something deeper than the beauty of the spinning dot that we call home. It might help us find life on other distant planets.
That’s according to University of Washington researchers Joshua Krissansen-Totton, a graduate student, and David Catling, an astrobiologist and professor in Earth and space sciences, set out to explore in a study recently published in The Astrophysical Journal. They found that, while we probably shouldn't base our search for life on the color of other worlds alone, the color blue might come in handy when selecting which planets to study deeper.
Why is the sky blue?
(flickr/nicholas_t)
It’s a question you might remember asking as a child.
The visible light from the sun is made up of different wavelengths, which we see as colors when they are reflected off of surfaces. When the light travels through our atmosphere, it bumps into molecules of gas, dust, and water and scatters.
Dust and water particles are pretty big, and all of the different wavelengths, or colors, bounce off them in the same way. So the light they reflect back to us appears white.
But when the light collides with tiny particles, like gas molecules, that are smaller than the wavelengths of the light, a special type of scattering occurs. When this scattering happens, the molecules seem to be better at scattering colors with shorter wavelengths, like blue, rather than those with longer wavelengths, like red.
All that strong scattering makes the whole sky, which is filled with gas molecules, appear blue. This blueness even scatters into space, which is what makes Earth so photogenic. Even our oceans, which are actually colorless, reflect blue light.
The oxygen in our air, a product of Earth’s bustling inner life, chemically reacts with molecules in our atmosphere that would otherwise form an murky haze, like that of Venus, Jupiter and Saturn, which is one of the reasons the researchers think a planet’s color might just say something about its ability to harbor life.
But before you set the GPS in your spaceship for the nearest pale blue dot, you might want to do a little extra investigating. The pale blue color alone doesn't always mean a planet is habitable.