Color in the Universe

The iconic "pale blue dot" image of Earth taken by the Voyager 1 spacecraft, from a distance of 3.7 billion miles in 1990. Earth is the speck halfway down the brownish streak to the right. The streaks are artifacts, caused by the scattering of sunlight in the probe's optics. Credit: NASA

The pale blue dot is Earth, but what if Earth is the only planet that gives off that specific color? While other exoplanets can and have mimicked the pale blue color, a broader portion of Earth’s overall spectrum shows a rather subtle signature that can only be attributed to life. Earth’s blue color comes from the transparent atmosphere. Transparent atmospheres are more likely to scatter blue light as opposed to red light, thus making the sky look blue. The scattering blue light can be seen from space also, so Earth appears blue to external observers as well.

Other planets are capable of duping scientists with their own pale blue colors. Many types of worlds, including gas and ice giants, planets with atmospheres of varying thickness, and words with “hydrogen dominated or thick, water-steam envelopes.” There is even speculation that Mars could have also been a pale blue dot in the past, when it had a thicker atmosphere. However, with Earth’s specific spectral signature in mind, the color has never been duplicated.

Spectroscopy would be able to confirm the atmospheric content of other worlds. If the world has an atmosphere rich in oxygen blended with other abundant molecules that could only be there due to life. Currently, the telescopes at our disposal can only detect and obtain the colors of young, gas giant-sized planets, leaving more work to be done in observing exoplanets and determining habitability based on color.

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One thought on “Color in the Universe

  1. That could definitely be an important filter to help find potentially habitable planets. The range would need to be more that just visible light though. When viewed from such a large distance, Uranus and Neptune would display quite a bit of blue as well. Scanners would need to take into account received light across most of the electromagnetic spectrum.

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