Black trees on alien planets: Scientists say worlds with two suns could host forests unlike anything on Earth

For generations, artists and science-fiction writers have imagined alien landscapes beneath twin sunsets. The image became iconic in popular culture long before astronomers confirmed that planets orbiting two stars actually exist. Discoveries by NASA's Kepler mission and other observatories have revealed that circumbinary planets, worlds that orbit two suns, are a genuine feature of our galaxy.Yet the most intriguing question is not whether such planets exist, but what life might look like on them. Research ‘The Vegetation Red Edge Biosignature Through Time on Earth and Exoplanets’ suggests that if Earth-like plants evolved under the glow of multiple stars, they might not be green at all. Depending on the colour and intensity of the starlight reaching the surface, alien vegetation could appear black, dark grey, red, orange, or even exhibit colours unfamiliar to human eyes. The findings offer scientists a fresh way to think about photosynthesis beyond Earth and could help guide the search for life on distant worlds.The green colour of Earth's forests is not accidental. Plants contain chlorophyll, a pigment that absorbs red and blue wavelengths of sunlight while reflecting green light. This process allows plants to convert solar energy into chemical energy through photosynthesis.However, the Sun is only one type of star. Across the Milky Way, stars vary significantly in temperature, brightness, and colour. Some emit more red and infrared radiation, while others produce stronger blue and ultraviolet light.Researchers led by Dr Jack O'Malley-James along with others from Cornell University, via their curiosity about ‘Light and Life: Exotic Photosynthesis in Binary Star Systems,’ explored how photosynthetic organisms might evolve under these different lighting conditions. Their work suggests that plants on planets orbiting multiple stars could develop pigments optimised for entirely different wavelengths.The team concluded that extraterrestrial vegetation could display a wide range of colours depending on the stellar environment."Photosynthetic life on planets around other stars may have colours quite different from the greens seen on Earth."The implication is striking. What humans recognise as a healthy forest could appear completely different elsewhere in the galaxy.Among the most surprising possibilities proposed by researchers is the emergence of black vegetation.A black leaf absorbs almost all incoming visible light rather than reflecting significant portions of it. On planets receiving complex mixtures of light from two stars, such an adaptation could provide a substantial advantage by maximising energy capture.Scientists have suggested that black photosynthetic organisms might be particularly effective on worlds illuminated by stars that emit large amounts of infrared radiation. Rather than wasting available energy through reflection, dark pigments could absorb a broader range of wavelengths.The concept may sound exotic, but Earth already offers partial examples. Certain photosynthetic bacteria use pigments other than chlorophyll and appear purple, brown, or nearly black because they absorb different parts of the electromagnetic spectrum.In other words, nature has already demonstrated that photosynthesis does not require green leaves.A planet orbiting two stars experiences a far more complicated environment than Earth.The amount and quality of incoming light can change as the stars move relative to one another. Seasons may become more complex, while the colour of daylight could vary depending on which star dominates the sky at a given time.The discovery by NASA of planets like the exoplanet Kepler-16b proved that the existence of planets orbiting two stars can occur. While Kepler-16b does not have an atmosphere that can sustain life, its existence shows that these kinds of planets are indeed real, and not simply a product of imagination.In terms of Earth-like planets within such a system, their evolution will depend on ever-changing patterns of light. It is thought that photosynthesis in these circumstances will lead to innovative means of photosynthesising.The study of alien vegetation is more than an exercise in imagination. It plays an important role in astrobiology.When astronomers analyse the atmospheres of exoplanets, they search for biosignatures, measurable indicators that life may be present. One of Earth's most distinctive biosignatures is the "vegetation red edge", a spectral feature produced by chlorophyll.If alien plants use different pigments, their spectral signatures may also differ. Understanding how photosynthesis might evolve under alternative stellar conditions helps researchers determine what signs of life future telescopes should look for.As next-generation observatories become capable of studying the atmospheres and surfaces of distant planets in greater detail, these models could prove increasingly valuable.Scientists stress that no black forests have been discovered. The idea remains a prediction based on current understanding of photosynthesis, stellar physics, and planetary environments.Yet the hypothesis highlights a broader lesson about the search for life beyond Earth. Human expectations are shaped by a single example: our own planet. The further researchers look into the universe, the more they realise that life elsewhere may follow very different evolutionary paths.A planet bathed in the light of two suns will never look like our familiar worlds of woods, plains, and jungles. It might even be enveloped in dark canopies absorbing all the available sunlight from the two stars, thus making it hard to imagine for us earthlings.What used to be only science fiction is now within the realms of science, and in some distant corner of the galaxy, there may already be forests of black trees under two suns.