Planetary Color

Color matters in art and design but it also matters in science. Especially to scientists looking for extrasolar planets, or exoplanets, which lie outside of our local solar system. With predictions now topping out between 100 and 400 billion planets in the Milky Way galaxy, and each planet a potential source for extraterrestrial life, scientists are eager to learn more about them. The problem? Well thats two fold. 

First, their distance from Earth is an immense hurtle, the nearest known specimen being 4.37 lights years away. So even with the use of today most advanced telescopes the planets are still tiny specs in the night sky. The second and perhaps more daunting problem is their proximity to the nearby star makes them especially hard to detect. With the star giving off so much light, the reflected light from the planet, and thus our means of detecting it, gets washed out. 

How is this sovled? Well initially scientists could only tell if a star had planets at all by looking at the star itself. They checked for wobbles in the stars rotation, caused by the gravity of orbiting planets pulling the star this way or that. This revealed lots of gas giants similar to Jupiter because they were massive enough to give the star a good yank. That was a good starting point, but astrophysicists are rarely satisfied with first tries, and recently the astronomical tool kit has gotten more advanced. Now astrophysicists are working on direct detection techniques. This is where color comes in. Using a system laughably similar to holding your hand up to shade your eyes, scientists are now learning to block out the stars light to see Earth sized planets, tucked closer to the star in the zone most habitable for life. And once they can image the planet itself with minimized interference from the star, they can take a picture of the exoplanets spectrum, all the light it reflects. But what can the color of a planet tell us? In an article on the NASA Astrophysics Data System one Dr. Traub summarizes why color is important:

The color of an extrasolar planet is an important property because, for the case of direct detection, color is likely to be the first post-detection quantity to be measured… Color carries considerable information on planetary properties.

But what kind of information can color carry? What does the dominate color and the full spectrum of the planet detected tell us? For familiarity, lets think about our two closest planetary neighbors: Venus and Mars.

Venus
Mars via Wikipedia

While the surface of Venus is similar to the moon, when viewed from space its obscured by a thick blanket of muddy yellow of clouds. Without the need for chemical tests, the yellow tint reveals an atmosphere saturated with sulfur dioxide. That color chemical signature alone tells all about the conditions of the planet. Acid rains, green house effects, and molten temperatures make Venus fascinating but not likely to harbor life. Mars is a similar story. Its strong rust red color was our first clue that the surface would be saturated with iron oxide. Just like for our nearby neighbors, the colors themselves carry with them the chemical information that help scientists build models of these far away planets. From simple color spectrum data they may be able to determine if the planet has liquid water, breathable air, or the potential for life all from light years away.

– Emily Eifler, Writer, Colour Studio
– Jill Pilaroscia, Principal, Colour Studio

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