What could aliens look like?

Are we alone in the universe? It's one of life's biggest mysteries and one that is explored by Science fiction and scientists alike. But if there is alien life on other planets, what might it look like? 

While little green men or towering predators are the stereotypical depictions of extraterrestrials in film, any aliens that might be out there are unlikely to resemble those characters, experts told Live Science. Instead, the unique environment of the moons or exoplanets that these aliens call home could make their physiology completely different from anything found on Earth. 

Some aliens might evolve to only fly through their planet's sky as a result of a dense planetary atmosphere, Adam Frank, a professor of astrophysics at the University of Rochester, told Live Science. Or, in cases of planets with high gravity, he said that aliens might develop to be sturdier "more like elephants." 

Or perhaps life would evolve to live underground, Valentina Erastova, a chancellor's fellow of chemistry at the University of Edinburgh, told Live Science. If a planet has high levels of radiation not absorbed by an ozone, that might result in subterranean life that uses soil as protection. In this case, Erastova suggests that simple multicellular life might look similar to fungi. While we usually see the fruiting body of a fungus above ground, most of its life actually happens underground in a vast network of roots called mycorrhiza. 

"Even on Earth, there are more life-form varieties inside [the Earth] than walking on top of it," Erastova said.

Related: Are aliens real? 

In cases of extreme ultraviolet (UV) radiation, work published in the journal Monthly Notices of the Royal Astronomical Society in 2019 suggests that aliens might actually glow red, blue or green as a way to protect themselves. Like some corals, these organisms might have proteins or pigments that can absorb some of the UV light's energy, which would then make them glow in a safer wavelength on the visible spectrum, according to the study.