By Steve Edberg

Alien vs. Editor is a forum for questions and answers about extrasolar planets and NASA’s search for life beyond our solar system. Leave your questions for author Steve Edberg and read more on the PlanetQuest website.

Where would blue-skinned aliens exist?

Joel asked: If you were to find aliens next to the sun, why would they be blue?

The only blue aliens I’m aware of lived on a moon called Pandora in a popular movie released in 2009. The foundation of your question is the more general question of why we observe a wide variety of colors “used” by life on Earth. Those colors are “used” by their organisms in many different ways. And there are a variety of mechanisms that generate the colors.

The colors of plants and animals have a variety of goals. For plants, the green of their leaves comes from the chlorophyll that absorbs violet-blue and yellow-orange-red light for photosynthesis. Some plants (like Japanese plum) have additional pigments for protection from ultraviolet light and appear dark red. Flowers have colors specifically to attract pollinators, but the colors the pollinators see may not be the colors we see.

Animals have colors to camouflage themselves and attract mates. Some plant and animal coloring is designed to warn off predators. The red eye you see in flash pictures of your friends is a reflection of their eyes’ retinas. Photographs of dogs show their retinas reflect greenish light. Is retinal color related to color vision? Most humans have color vision and dogs are color blind.

The colors we see around us are generated by different mechanisms, which can reflect (pun intended) on its use by an organism. The color of a pigment depends on the colors it absorbs and those it reflects. Chlorophyll is a green pigment, and hair and skin colors result from pigments as well.

Polar bear fur only looks white.

Polar bears’ black skin pigmentation helps keep them warm. The bears’ white fur only looks white in bulk. Individual hair follicles are actually transparent, so that they carry sunlight down from the “top” of the fur coat to the bear’s skin, where all the colors of sunlight (you’ve seen them in a rainbow made by differential refraction, another mechanism!) are absorbed by the black skin, helping to keep the polar bear warm. The fiber optics we use to transfer data over the internet or between components in your home entertainment system carry light in the same way.

The iridescent color of bird feathers is produced by another mechanism, the same one that makes detergent bubbles and thin slicks of oil on water show colors. The structure of feathers and thickness of detergent and oil layers permits waves of light to “interfere” with each other. You’ve seen wave interference in a quiet pool or pond when you throw two small objects into the water and the circular waves move out from each impact point. When the waves cross over each other, their height is greater where the peaks combine and flat where a peak and a valley combine.

A similar thing happens with light waves in iridescent materials. In the feathers, waves of a particular color are reflected and combined before they are shunted out of the feather, while the other colors are absorbed by a black pigment. The colors come from the spacing of tiny reflectors, called lamellae, in the feathers: change the spacing and the color coming from the feather is different. In detergent bubbles and oil slicks, change the layer’s thickness and you change the color seen.

So where might we expect blue-skinned aliens? My answer is on an exoplanet orbiting a cool, red star. Why? Because the alien probably wants to absorb as much stellar energy as it can from its star, and blue pigments absorb red light. It would be well-camouflaged in the blue vegetation trying to absorb as much energy from the red sun as it could.

By Steve Edberg

Alien vs. Editor is a forum for questions and answers about extrasolar planets and NASA’s search for life beyond our solar system. Leave your questions for author Steve Edberg and read more on the PlanetQuest website.

Tubeworms that grow near the boundary where hot vent fluid mixes with cold seawater on the ocean floor are an example of extremophiles that broaden our perspective on where to look for life. Image credit: Nicolle Rager Fuller, National Science Foundation

A reader’s question (paraphrased): Why do astronomers assume there have to be conditions similar to Earth in order for life to exist? Who are we to define what life looks like and how would we know what we’re looking at if we really don’t know what we are looking for?

This has been a recurring question over the years, and I don’t think anyone interested in finding extraterrestrial life would dispute those thoughts. The problem is that we aren’t as clever as Mother Nature, so we don’t know what else to look for. More practically, we don’t know what other conditions to look for beyond those we are familiar with.

Science fiction writers have used their imaginations to propose other forms of life. Sir Fred Hoyle (an astronomer) wrote a novel titled “The Black Cloud,” (SPOILER/GIVEAWAY ALERT!! SKIP THE REST OF THIS SENTENCE IF YOU THINK YOU WILL READ THE BOOK) about a self-propelling interstellar cloud that came to orbit the sun to acquire energy (it stopped for lunch!) before moving on.

On the TV shows “Star Trek” and “Star Trek: The Next Generation,” the screenwriters came up with at least two forms of life that were completely novel. Naturally enough, the shows involving them were about recognizing that they were life and how to deal with it. The one on “Star Trek” was about rock-beings that tunneled through an asteroid or planet. The other, on “Star Trek TNG,” was about “nanites,” microscopic silicon crystals that were hive-like beings communicating among themselves electrically and with electromagnetic waves with the crew of Enterprise D.

These are three examples of potential life forms far different from what we are familiar with. But knowing what to look for and where is a long step from the presentation of these ideas in science fiction media.

Before the Viking landings on Mars in the 1970s, Carl Sagan gave talks about the life-detecting instruments aboard the landers, which were designed to detect life as we know it. He also mentioned that there was a camera aboard so that we could see any “silicon-based giraffes that might walk by,” so even then scientists were thinking about possible, unfamiliar forms of life.

The strategy being followed is to look for evidence of extraterrestrial life, as we recognize life, now, rather than wait until we figure out all the possibilities. Scientists study and search for new examples of “extremophiles” that live in extreme conditions compared to what most of life on Earth lives in, in order to broaden our perspective on where to look for life.

There are also radio and optical searches for evidence of extraterrestrial intelligence living (by whatever chemical process) on planets orbiting other stars that might be announcing their presence. And I recently heard that there is a meeting planned to consider what else we might look for in this arena, considering that the era of our radio transmissions out to the galaxy (TV and radio) could be coming to an end as we use more cable and fiber communications here on Earth.