Aliens are a staple of science fiction, even though we haven't definitively found any in real life. While many movies explore what would happen if alien spacecraft attacked Earth, a new movie about the Marvel superhero Venom (which opened Oct. 4) explores the implications of aliens infecting humans. Could this happen to us in real life?
In the Marvel Universe, Venom is usually associated with Spider-Man. Venom, who is first known as the Symbiote, usually comes from space; while the origin stories vary in different iterations of the tale, in one example, the Symbiote was first found on the moon.
Spider-Man was the Symbiote's first known host. After Spider-Man eventually rejected the Symbiote, the being paired up with journalist Eddie Brock. This character was angry at Spider-Man, because the superhero discovered Brock had misreported something important. Brock and the Symbiote paired up to become Venom, ready to take revenge on Spider-Man. [The Scariest Aliens Ever from Sci-Fi Films]
Venom's space origins are definitely front and center in the new film, said "Venom" visual effects supervisor Paul Franklin in an interview with CinemaBlend.com.
"We see, at the beginning of the film, the moment when the Symbiotes are collected up by a Life Foundation space probe, which finds them on a comet drifting through space, approaching Earth," he told CinemaBlend.com. And to complicate the situation, the Symbiotes are on an active hunt for good hosts.
"The Symbiotes seem to actively want to be collected," Franklin continued, "because it's all part of their plan to come to Earth. They're looking for planets where they can find hosts to inhabit. They've never really found a place where they can exist in harmony with the life-forms of whatever planet they find themselves on."
Pairing with human biology
Symbiotes (the generic kind, not the Marvel alien race) are a common theme in space science fiction movies, with perhaps the most famous example being in the "Alien" franchise. From the events of the first movie, which opened in 1979, troops of space explorers in this franchise have kept coming across planets with aliens that jump into humans and quickly infect them. These aliens cause wild changes to human personality, biology and other characteristics. Most famously, some of the organisms of "Alien" burst through human chests.
Many other sci-fi films feature microbes as the attacking aliens, as well. Those movies include (but are not limited to) "The Astronaut's Wife" and, in one of the more recent examples, 2016's "Life," in which International Space Station astronautsgrappled with a newly discovered Martian organism.
Each of these microbe examples is unique, but they're all extremely unlikely, said the SETI (Search for Extraterrestrial Intelligence) Institute's Seth Shostak. Shostak, who is the institute's senior astronomer, told Space.com that bacteria that infect humans on Earth are highly adapted to our own biological systems, but only because 4 billion years of evolution link our species. Alien life — even if it is carbon-based and even if it needs water like Earth life does — would have grown up in a different ecosystem.
"Even on Earth, we get diseases that your dog won't get," Shostak said. Only a handful of viruses can even make the jump between species, let alone between planets, he continued. "They tend to be fairly species-specific. For example, you never see an elephant with a cold."
Planetary protection protocols
Still, NASA engineers its missions to potentially life-friendly worlds with the understanding that you can never be too careful. It even has a whole Planetary Protection Office to figure out these matters in more detail.
After the first human moon landings 50 years ago, the Apollo program astronauts returned to Earth under quarantine. They remained in isolation for a couple of weeks as doctors monitored them to make sure they hadn't imported any lunar viruses.
Spacecraft orbiting icy moons such as Europa and Enceladus also come under special concern. Because of the possibility of life on these worlds, the custom is to destroy dying orbiting spacecraft on even the slight chance they could crash down and contaminate any local microbe population. That's why the Galileo probe was thrown into Jupiter in 2003 and why the Cassini craft took a mission-ending plunge into Saturn in 2017.
Mars poses its own challenges, because the planet may have liquid water running on the surface. (These features, called recurring slope lineae, may also be piles of dirt running down the slopes of craters — but it's hard to say what they are unless we get up close.) Scientists carefully decontaminate Mars spacecraft before they alight on the planet's surface, and the current mode of exploration is to stay as far away as possible from zones of possible liquid water.
It's unclear if Mars hosts life or has in the past; so far, the only direct tests have been some troublesome NASA Viking lander experiments in the 1970s, whose results are still being debated today. Mars, however, is known to host organic molecules (the building blocks of life), frozen water at the poles and possibly liquid water underground— things that make some scientists argue that life is possible there. But Mars presents other obstacles for life to overcome.
"Mars is a tough environment," Shostak said; the high levels of radiation on the planet's surface and its extremely dusty environment are some examples of that toughness. However, Shostak said, "there are some bacteria on Earth that could survive if they got to liquid water on Mars."
In the coming decades, NASA will need to confront the possibility of Martian biology directly, being sure to avoid Earth contamination of Mars, and vice-versa. NASA does eventually plan to send Mars samples back to Earth. The agency's upcoming Mars 2020 rover will cache the most-promising samples it finds for a future sample-return mission. NASA is also working on plans for an eventual human mission to Mars, after returning to the moon first.
Shostak allowed that there are planetary protection concerns, but said in his view that those concerns might be particular to experimentation. "That's not something we are worried about, that suddenly Mars is going to turn into a jungle because we send a rover to Mars. It will just mess up the experiment to find any indigenous life," he said.