In the scary-looking 'Apollo 18' (in theaters Friday), astronauts find they're not alone on the moon, which is just about the last place you'd want to encounter the unknown.

Pity the poor astronaut. Even if you don't land on a hostile planet, you're still vulnerable to a great many horrifying things if you just stay inside your fragile little spaceship. As movies have shown us, when you sign up to go into space, you're signing on for claustrophobia, extreme paranoia among shipmates, and shipboard computers that may be plotting against you.

In space, no one can hear you scream -- it was the brilliant tagline for a great movie, 'Alien,' but it holds true for many other thrillers set in outer space. We rank a handful from not-so-scary to the stuff nightmares are made of.

Did we leave out your favorite? Tell us which ones we should have included.
12. 'Lifeforce' (1985)
Hard to believe this space-vampire camp fest was made after the far classier 'Alien,' but the lesson is the same: Do not bring any kind of creature back to your ship because you'll be dooming your crew and possibly all of mankind. In this case, the creature is a hot, naked babe who will suck the life (force) out of you! The only scary thing (besides the overacting) is the hideous, mummy-like victims after they've been drained. And that's probably only if you're 12 or younger.

11. 'Battlefield Earth' (2000)
What's scarier: The freaky-looking aliens with their claw-like hands, the ridiculous plot, or the massive amounts of money spent on this L. Ron Hubbard vehicle? Regardless, it's one huge intergalactic train wreck, and it always finishes at or near the top of any "Worst Movies Ever Made" lists. Or is the scariest part that John Travolta somehow convinced the great Forest Whitaker to play an alien?

10. 'The Green Slime' (1968)
The year before man first walked on the moon, this low-budget B-movie imagined the worst things that might be awaiting our astronauts: tentacled monsters. From space! This camp fest is rightly deserving of cult status, and the groovy theme song (at the end of this trailer) seals it:

9. 'Forbidden Planet' (1956)
This classic '50s sci-fi tale (an update on Shakespeare's 'The Tempest') features the awesome Robby the Robot, the beautiful Anne Francis and some nifty set design, but it's not exactly scary. Not unless monsters from the id keep you up at night.

8. 'Moon' (2009)
"Scary" isn't really the right word to describe this impressive film debut from Duncan Jones, who went on to direct the similarly existential 'Source Code.' Sam Rockwell is nearing the end of a years-long solo stint on the moon, with only a talking computer for companionship. He seems on the verge of a crack-up, but then it turns out something far more sinister and disturbing is going on that calls into question his entire existence.
7. 'Event Horizon' (1998)
We'd call it 'Dead Calm' in space, in a nod to star Sam Neill, but where that becalmed boat story was genuinely nail-biting, this movie is too bizarre and disjointed to rack up that kind of suspense. Some very strange and horrific things happen, but we defy you to make sense of them. We're just going to go ahead and lump it in with similar, slowly paced space junk like 'Pandorum' and 'Supernova.'

6. 'Star Trek II: The Wrath of Khan' (1982)
Maybe you needed to see this movie at an impressionable age for Khan's ear worms to be truly terrifying, but brother, if you did? Nightmares for weeks! The disgusting things slither into Chekov's ear in the clip below. Augh, we can't watch!

5. 'Sunshine' (2007)
What makes 'Sunshine' stand out among other space-station thrillers is director Danny Boyle's trademark manic, kinetic approach (the same one that perfectly captured heroin wasteoids in 'Trainspotting') and using it to view the infinite abyss of space. Imagine the claustrophobic hysteria of 'The Shining' on a doomed ship hurtling toward the sun, and you can start to picture the weird, unsettling -- and somehow tranquil -- human horror of disappearing into the great ether of the universe.

4. 'Screamers' (1995)
It's like a greatest hits of sci-fi movies: It stars Robocop himself, Peter Weller, battling 'Terminator'-like creatures who can pass for human, and it's all based on a story by Philip K. Dick. On a distant mining planet, Weller must battle the insidious 'bot assassins who were designed to protect his operation. An underrated B-thriller that packs some genuine scares.

3. 'Pitch Black' (2000)
The movie that put Vin Diesel on the map. Long before he was racing cars, he was a deadly criminal named Riddick who became a motley crew's only hope against some truly terrifying creatures that lurk in the darkness of a hostile planet. This lean, mean thriller is so much better than its bloated, big-budget sequel.
2. 'Aliens' (1986)
More aliens equals more action, especially with James Cameron taking over the franchise, but while the adrenaline is pumping from all those gung-ho Marines and a whole nest of pissed-off aliens, we miss some of the quiet eeriness of the first film. Tell you what: We'll just watch them back-to-back and not bother deciding which is scarier.

1. 'Alien' (1979)
It's true that 'Aliens' offers more bang for your buck, but we have to hand the "scariest" label to Ridley Scott's original. Can you really top the alien bursting out of poor John Hurt's chest? Or the suspense as that blip on the radar screen gets closer and closer to Tom Skerritt? We just want to scream at the screen for him to get out of there! And this alien will win Most Terrifying in any galaxy. (Sorry, Predator.)

Apollo 18
Based on 19 critics

Lost footage from a secret mission to the moon reveals a terrifying alien encounter. Read More