Finding alien life may require looking for the color purple instead of green

We all know that when it comes to life on Earth, green is where it’s at. Plants, with their chlorophyll, form the basis of most ecosystems. But what if, in our grand search for life beyond Earth, we’ve been looking for the wrong colors? Scientists at Cornell University have a fascinating new theory – what if many alien worlds harbor purple bacteria?

New alien hunting using purple bacteria

When we imagine a planet orbiting another star that could potentially support life, our minds naturally jump to what we know best – Earth. We picture swirling blue oceans, vast green forests, and even continents with recognizable shapes.

It’s a comforting image, a familiar template for what life-bearing planets might look like out there in the cosmos. However, this Earth-centric view might be limiting our search for extraterrestrial life.

The research from Cornell University suggests that a significant portion of planets capable of supporting life might not resemble our blue and green home at all. Instead, they could be dominated by a surprising organism: purple bacteria.

Purple photosynthesis and alien life

Purple bacteria are a fascinating group of organisms with some key differences from the plant life we’re familiar with.

Unlike plants, which use visible light and chlorophyll for photosynthesis, purple bacteria utilize a different type of chlorophyll that absorbs infrared light, a type of light invisible to the human eye.

This allows them to capture energy for food production in environments where sunlight might be limited or have a different wavelength spectrum.

Another unique feature of purple bacteria is that they don’t produce oxygen as a byproduct of photosynthesis. This sets them apart from plants and some other bacteria on Earth.

Interestingly, these bacteria might have been the dominant photosynthetic lifeforms on our own planet before green plants took center stage.

Finally, purple bacteria seem particularly well-suited for colonizing planets orbiting cool red dwarf stars. These stars, which are the most common type in our galaxy, emit a significant amount of infrared radiation. This makes them ideal candidates for harboring planets where purple bacteria could thrive.

“‘Purple bacteria can thrive under a wide range of conditions, making it one of the primary contenders for life that could dominate a variety of worlds,'” explains Lígia Fonseca Coelho, postdoctoral associate at the Carl Sagan Institute.

Bio-signature of purple bacteria and aliens

So how do you actually spot a ‘pale purple dot’ tucked away in distant solar systems? Coelho and her team have been busy creating models of what these purple-dominant planets would look like.

They’re simulating different climates, cloud levels – just to see how these purple bacteria would ‘color’ the light reflected from the alien planet.

The ultimate goal is to create what scientists call a ‘biosignature’. It’s like a cosmic fingerprint of life. If our next-generation telescopes catch that telltale purple fingerprint, it’s game on! It means we’d have to carefully study the potential alien world to see if this purple haze is due to life, or maybe colorful minerals.

“‘We need to create a database for signs of life to make sure our telescopes don’t miss life if it happens not to look exactly like what we encounter around us every day,'” says co-author Lisa Kaltenegger, director of the Carl Sagan Institute and professor of astronomy.

The cosmos is colorful

The potential discovery of purple bacteria on an alien exoplanet has significant implications beyond finding just one unique microbe. It raises the fascinating possibility that life may be able to exist in a wider range of conditions than we previously imagined.

“Detecting a “pale purple dot” in another solar system would trigger intensive observations of the planet to try to rule out other color sources, such as colorful minerals,” said Kaltenegger. If life can exist in the form of these sturdy, independent purple bacteria, it could be surprisingly common throughout the universe.

Should the existence of purple bacteria be confirmed, it could fundamentally alter our understanding of how common life might be throughout the universe.

These adaptable organisms could potentially thrive in diverse environments that we wouldn’t typically consider hospitable to life, expanding the possibilities of what constitutes a potentially habitable planet.

This finding would suggest that life in various forms might be far more common in the cosmos than we currently think.

“If purple bacteria are thriving on the surface of a frozen Earth, an ocean world, a snowball Earth or a modern Earth orbiting a cooler star…we now have the tools to search for them,” explained Coelho.

Looking beyond green

The search for extraterrestrial life has traditionally focused on planets that resemble Earth, with an expectation of familiar signs of life like green vegetation.

However, this new research into purple bacteria and alien life broadens our search parameters substantially. It highlights the vastness of the universe and the possibility that life could exist in ways and places we never imagined.

By introducing a wider array of potential colors for life, scientists are acknowledging that the familiar shades associated with life on Earth might represent only a tiny fraction of the possibilities.

Life on other planets could manifest in entirely unexpected forms and colors, adapted to thrive in environments that seem utterly hostile to us.

This reminder of our limited Earth-centric perspective encourages scientists to embrace a broader approach when searching for the tell-tale signs of life outside our solar system.

“‘We are just opening our eyes to these fascinating worlds around us. Purple bacteria can survive and thrive under such a variety of conditions that it is easy to imagine that on many different worlds, purple may just be the new green,'” says Kaltenegger.

The study is published in Monthly Notices of the Royal Astronomical Society.

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