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Demi Lovato - The singer has expressed her avid belief in aliens as well as mermaids, and she told Elle Canada, "I’ve seen a UFO. A couple of years ago, I was walking outside and I looked up and it was almost like there was a worm in the sky. It was changing shapes and moving all over the place.”

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Zayn Malik - When Glamour asked how he first knew he had to quit One Direction, Malik answered, "An alien spoke to me in a dream…"

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Ariana Grande - The singer claimed to have seen a UFO in 2013, and told Complex, "We'd be so stupid to believe we are the only people here."

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Tom Cruise - "Millions of stars, and we're supposed to be the only living creatures? No, there are many things out there," Cruise said in 2007. "We just don't know."

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Katy Perry - In 2011, the singer tweeted about her belief in aliens. She wrote that she believes in ghosts, too, but that aliens are little more convincing for her.

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Robbie Williams - In 2008, the singer declared his intention to quit the music industry in order to fully dedicate himself to investigating UFOs, of which he's reportedly seen "quite a few."

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Megan Fox - The actress has often talked about her belief in aliens, as well as ghosts, Bigfoot, and "everything."

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Rihanna - The singer said that her father used to make her sit outside all night looking for UFOs, and later in life she reportedly went so far as to hire a UFO watcher in California to give her alien updates.

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Nick Jonas - One-third of the Jonas Brothers claimed on 'Late Night with Seth Meyers' he saw three UFOs in Los Angeles. One quick dive into online sightings forums later, and he was a firm believer.

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Dwayne Johnson - The actor finds the existence of aliens a near-guarantee, as he told Vice, "I believe that we're not the only ones; it'd be arrogant to think that."

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Alicia Keys - "Haven't all of us seen something flying in the sky, and it's at some random time of night that doesn't make sense, and it's not the shape of a plane?" the singer told Buzzfeed.

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David Bowie - It's hardly any surprise that the 'Starman' believed in 'Life on Mars,' but even more interesting is the huge online conspiracy that Bowie was an alien himself.

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Amy Adams - The actress said working on the film 'Arrival' only reinforced her belief in aliens. "Of course, life forms may take very different shapes or ways of existing from what we think of when we talk about living things," she said.

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Keanu Reeves - The actor told Boston.com that the existence of aliens is more probable than being alone in the universe. "The cosmos is a pretty big place," he said.

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Kylie Jenner - "I've been to Area 51 and talked to people who claim to have been abducted," Jenner told Cosmo. "I'm super interested in aliens, but they terrify me because I 100% believe in them."

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Halle Berry - The actress told David Letterman in 2014 that she not only believes in aliens, but that humans will meet them. "It might take us 20 years to get to those other life forms, but I think they are out there."

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Steven Spielberg - Of course, the 'E.T.' director believes in aliens. In 2013, Spielberg actually said it was "so unfair" that he hadn't spotted a UFO since he's devoted so much of his filmography to extraterrestrial-related themes.

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Kesha -

A UFO sighting in the desert is reportedly what inspired Kesha's space-themed album art for 'Rainbow,' Billboard reports. The singer has also spoke about her alien encounters on Instagram: "UFOs are real. I have seen them. Not playing."

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Victoria Beckham - The star claimed to have seen a UFO hovering over her Los Angeles mansion in 2011. 

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Russell Crowe - In 2013, the actor uploaded a video of what he believed was a UFO sighting to YouTube, though it was later debunked.

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Will Smith - In 2012, the actor said, "It'd be just as ridiculous to say that there aren't [aliens] as it would to say that there are. I have a very open mind."

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Billy Ray Cyrus - The country star shared a photo on Twitter apparently showing five UFOs over the sunset, and almost hosted a show called 'UFO: Unbelievably Freakin' Obvious.'

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Bill Nye - The beloved scientist and former host of 'Bill Nye the Science Guy' tweeted at the premiere of 'Men In Black': "There are 200 billion stars in our galaxy. That’s likely 2 trillion planets. Aliens gotta be out there…"

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Sigourney Weaver - The actress, who starred in the 'Alien' film series, is a firm believer and has said, "I think there's a department in our government which is exclusively dedicated to quashing reports about aliens. And that's so unfair. It would be nice if we weren't just able to read about it in the tabloids."

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Jaden Smith - The young star sat down with Barack Obama and talked about extraterrestrials, the existence of which the then-president could neither confirm nor deny, "which means they're real," Smith told Wonderland magazine. "If people think we're the only people that live in this universe, then something is wrong with them."

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Gillian Anderson - The 'X-Files' star reportedly experienced some paranormal activity in her Vancouver home in 1995 that changed her from a "maybe" to a "definite" believer.

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Tom DeLonge - The Blink-182 star is famed for his interest in UFOs. "I have sources from the government. I’ve had my phone tapped. I’ve done a lot of weird stuff in this industry—people wouldn’t believe me if I told them," he told Paper magazine.

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Mick Jagger - The singer claimed he saw a cigar-shaped spaceship at a music festival in 1968, and later reportedly installed a UFO detector on his estate.

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Olivia Newton-John - The actress claimed to have encountered alien life when she was 15, as she told The Sun, "I have seen one when I was very young. It was unidentified and it was flying."

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Muhammad Ali - The boxing legend was reportedly an avid believer in aliens, who claimed to have had several encounters with extraterrestrial life, including witnessing a massive UFO mothership.

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Shirley MacLaine - The actress is known for her eccentric beliefs, and along with reincarnation, she believes strongly in alien life. 

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Dan Aykroyd - The 'Ghostbusters' star has a documentary called 'Dan Aykroyd Unplugged on UFOs,' and in 2010 he told Larry King, "They are here, science should accept that they are here and look how they have come from a billion years in the future or the next dimension or wherever they are coming from. They have abducted people."

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Zooey Deschanel - The actress's sister told her that "the Neptunians had killed my real sister and replaced her with a facsimile who looked just like her." Surely all has been cleared up since then, but Deschanel apparently still isn't completely ruling it out.

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Gigi Hadid - The model confessed to Harper's Bazaar that she believes in aliens.

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Khloé Kardashian - When flashing blue lights ran across the Los Angeles sky in 2015, this Kardashian did not buy the missile test "cover-up." She tweeted the hashtag #WeAreNotAlone.

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William Shatner - The 'Star Trek' icon is true to Captain Kirk: “There is no doubt that there is life out there; the mathematics of it lead you to that absolute conclusion. In my mind, there is no doubt that the universe teems—teems!—with life in all its forms."

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Kacey Musgraves -

The famed country singer said in 2015, "I have a very irrational fear of spiders. And alien abductions. Speaking of, I've seen several UFOs."

See also: Celebrities reveal their phobias and greatest fears

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