Lots of things are scary: walking dead people, dudes with chainsaws, aerosol cheese (it's just wrong, I tell you). Sometimes, though, the chills can come from outer space, another dimension or a laboratory experiment gone horribly wrong. The greatest fear is a fear of the unknown, and what's more unknown than an alien life form or the endless expanse of space? Let's take a look at seven movies whose scares come from the world of science fiction.

Alien (1979)
"In space, no one can hear you scream," or so they say. I guess this is the obvious one to start with. Isolation is a key element of horror, and can you get more isolated than a space ship light years from home? The crew of the mining vessel Nostromo are awakened prematurely on their return trip to Earth to investigate a transmission from an alien world. The crew finds an ancient alien spacecraft, the mummified remains of one of its non-human occupants, and several large eggs. The creature inside one of the eggs gains entrance to the Nostromo by latching onto one of the crew members. Once aboard, the little beastie quickly grows into one of the most horrific and memorable monstrosities the screen has ever seen. I saw this one when it first hit theaters, I've seen it many times over the years, and I recently watched it again. Like Dorian Gray, this film just refuses to age. The effects are just as magnificent as ever, the story is tense and fast paced, and the cast is excellent. More importantly, though, this is one scary ride.

The Thing (1982)
A lot of people took me to task for not including this one in my Cinematical Seven: Cool Horror Films of the 80s. With a list of only seven you're not going to please everyone. Regardless, John Carpenter's The Thing is a remarkable film for a number of reasons. Not only is it one of the greatest horror films of all time, it's also one of the rarest of the rare: a remake that surpasses the original. Based on the novella "Who Goes There" by John W. Campbell, Carpenter's version of the story is more faithful to Campbell than 1951's The Thing From Another World. In Carpenter's film, the members of an Antarctic research station find an alien space craft that's been buried in the ice for centuries. A creature with the ability to absorb and mimic other life forms gets thawed out and infiltrates the camp, creating one of the greatest combos of isolation and paranoia in horror history. Kurt Russell is one of the great movie bad asses as MacReady, the helicopter pilot who becomes the de facto group leader. The creature's pre-digital transformations are a thing (pun definitely intended) to behold, to say nothing of seriously gross.
Invasion of the Body Snatchers (1978)
There have been four feature adaptations of Jack Finney's novel The Body Snatchers, but for my money the 1978 version is the best. Set in San Francisco, a group of friends discover that everyone around them is slowly being replaced by emotionless duplicates. Strange pods are growing like parasites on all plants, and anyone who falls asleep in the vicinity of one of these pods has their life and memories drained from them, with the victim eventually disintegrating into a dried out husk. Leonard Nimoy's speech, in which he explains to Donald Sutherland and Brooke Adams how the pods were carried to earth on the solar winds, always chills me. He's speaking in the voice of a friend, but something completely alien and unknowable is pulling the strings. And the scene in which Adams' pod-drained body falls apart in a distraught Sutherland's arms is downright horrifying. A masterpiece of paranoia.

Night of the Comet (1984)
Adding laughs to the mix, this one manages to be a science fiction horror comedy. Earth passes through the tail of a comet, transforming everyone into piles or red dust. Only those who were shielded from the comet's effects remain alive, and people who are only partially exposed degenerate into cannibalistic zombies. Two teenage girls played by Catherine Mary Stewart and Kelli Maroney survive the experience but are faced with a world in which everyone they know is dead, zombies are looking to chew on their intestines, and some creepy government agents want to experiment on them. So what do they do? Go shopping, of course. My favorite line comes when the two girls are taking target practice with an inferior brand of machine pistol and Maroney's character whines "Daddy would have bought us Uzis." I'm surprised no one ever put that on a t-shirt.

Lifeforce (1985)

OK, take the screenwriter from Alien and the director from The Texas Chain Saw Massacre and what do you get? A seriously cool flick about vampires from space, that's what. A space shuttle mission sent to investigate Halley's Comet discovers a space ship hidden within the comet. Three apparently dead beings, human in appearance, are found and brought back to earth. These not quite dead beings awaken and, in a spectacular light show, begin draining the life energy from humans. Their victims get back up and begin draining life energy from others, and soon London begins to look very much like hell. Very reminiscent of the Quatermass films, which featured a scientist battling threats from outer space, Lifeforce has some very cool zombie effects and a pre-Star Trek appearance by Patrick Stewart.

Planet of the Vampires (1965)
Twin spaceships the Argos and the Galliot investigate a mysterious transmission from the planet Aura. Once on the surface of this alien world, the crew members find themselves possessed by disembodied alien lifeforms whenever they are asleep or unconscious, and they soon learn these creatures can also inhabit the bodies of their dead. As with all of his best films, Mario Bava's Planet of the Vampires has gobs of atmosphere. Some of the effects, particularly the space ship miniatures, show the film's minuscule budget, but Bava's skill at visual trickery creates an alien world that can only be described as haunting, and these guys are wearing some of the coolest goth spacesuits you'll ever see. The dialogue can sometimes be cringe inducing, but if you can get past that this movie has a lot to offer. Of particular interest are the story elements (response to an alien transmission, fossilized remains of a giant extraterrestrial astronaut) that will seem familiar to anyone who has seen Alien, which was produced over a decade later.

The Fly (1986)
David Cronenberg updated the 1958 film with his own brand of biological horror, taking the basic premise of the original (which was itself based on a short story by George Langelaan) and turning it into a horrific tale of science gone wrong. Jeff Goldblum stars as Seth Brundle, an eccentric scientist working on an invention that will teleport matter. One drunken night he attempts to teleport himself, not realizing a fly has entered the machine with him. The computer solves the problem by fusing them into a single being. Unlike the original which had our hero walking around with the head and arm of a fly, Brundle's transformation is more subtle at first, manifesting in an increased passion for sugar and greater physical strength. Soon, though, fingernails and ears are falling off, and Brundle undergoes a horrific change. Brundle's doomed love affair with Veronica Quaife (Geena Davis) heightens the level of tragedy, as does the knowledge that Brundle has impregnated her after his DNA altering trip through the teleportation pod. I always wondered why, with all the transporter activity on Star Trek, this never happened to Captain Kirk.