Even if you’re not Scully or Mulder, you’d probably enjoy a good peek at the skies on World UFO Day just to check if we’re still alone in the universe. When you’re not looking to the heavens for evidence of aliens, you’re probably on your mobile playing cosmic-themed online slot games in the UK in search of otherworldly treasures. 

In celebration of all those who enjoy a good UFO viewing every World UFO Day, let’s explore some of the best mobile slots with space and alien themes that will transport you to galaxies far, far away. 

1. Starburst

Volatility: Low

RTP: 96.09%

Starburst, developed by NetEnt, is an iconic space-themed slot game which has captivated players worldwide. With its vibrant colours, sparkling gems, and cosmic backdrop, Starburst takes you deep into a fantastical space odyssey. The game’s simple yet exciting gameplay features the Starburst Wilds, which expand to cover entire reels and trigger re-spins. Despite its low volatility, Starburst offers frequent wins and the potential for astronomical payouts.

This captivating five-reel, three-row game brings a fusion of vibrant gems and cosmic rewards. With the innovative Win Both Ways feature, winning combinations can be formed from left to right and right to left, increasing your chances of striking it big. Keep an eye out for the dazzling Wild symbol, which expands to cover the entire reel and triggers a free respin for even more winning opportunities. 

The stunning gem symbols, each with its own unique colour and shape, create a visually stunning gameplay experience. Aim for the highest-paying symbol, the Gold BAR, as landing five of them on a line will bring massive payouts your way. With an RTP of 96.09% and its mesmerising graphics and sound effects, Starburst™ is a celestial delight that will keep you entertained for light years. 

2. Invaders Megaways

Volatility: High

RTP: 96.3%

This action-packed slot game is based on the popular Megaways mechanic, offering up to 117,649 ways to win on each spin. Set against a cosmic backdrop, players will encounter alien invaders across the six-reel layout. 

The game’s high volatility adds excitement, with the chance to score massive payouts. Look out for the Cascading Reels feature, where winning symbols disappear, and new ones drop down for potential chain reactions. 

With an RTP of 96.3% and engaging graphics and sound effects, Invaders Megaways guarantees an immersive space-themed gaming experience. Get ready to defend the planet and reap astronomical rewards with this thrilling slot game.

3. Space Wars

Volatility: High

RTP: 96.8%

In Space Wars by NetEnt, players find themselves in the midst of an intergalactic battle between alien species. This action-packed game boasts a five-reel, four-row layout with 40 thrilling paylines. Brace yourself for wild substitutions that can boost your winning combinations, while re-spins provide even more opportunities to strike it rich. 

But the real highlight of Space Wars™ is the unique Cloning Pod feature. Whenever you land a winning combination, the victorious symbol is cloned and stacked on the reels, creating the potential for massive payouts and thrilling gameplay. With each spin and re-spin, you have the chance to win up to 1,000 times your initial stake, making every moment an exhilarating cosmic adventure.

4. Cosmic Fortune

Volatility: Medium

RTP: 96.9%

Cosmic Fortune, a progressive jackpot slot by NetEnt, offers an out-of-this-world gaming experience. Set in a futuristic world, the game showcases stunning graphics and an atmospheric soundtrack. Instead of traditional spinning reels, the Avalanche feature causes symbols to fall from above. 

One of the key features to watch out for is the “S” symbol, which serves as the scatter. Landing three of these symbols triggers the Free Falls feature, granting you 10 exhilarating free spins. But the excitement doesn’t stop there! For each additional scatter that appears during the Free Falls, you’ll be awarded an extra five free spins, keeping the thrills going.

And if you’re seeking the ultimate jackpot thrill, look no further. During the free spins round, you have the chance to unlock the progressive jackpot. By collecting three marbles in the jackpot cup, you’ll enter the jackpot bonus game. Here, your task is to collect marbles in specific cups with the opportunity to win one of the five incredible jackpots on offer.

5. Space Invaders

Volatility: Medium

RTP: 96.16%

Space Invaders, developed by Inspired Gaming, pays homage to the classic arcade game loved by so many. This slot game features a 5×3 grid and 20 fixed paylines and is one of those that look great in portrait mode. For space enthusiasts, the maximum bet of £20 per spin offers an exciting opportunity to win big. With a maximum payout of 1,250x the bet, this game stands out with its above-average rewards compared to other online slots.

The slot game features retro graphics and nostalgic sound effects that transport players back to the 8-bit era. The UFO Wild feature adds excitement as a UFO moves across the reels, transforming symbols into Wilds. With medium volatility, players can enjoy a balanced gameplay experience while reliving the memories of a gaming classic.

6. Arrival

Volatility: Medium to High

RTP: 92.26%

Arrival, created by Betsoft, presents an alien abduction theme with stunning 3D graphics and a cinematic feel. With a 5×3 slot layout and 30 thrilling paylines, your mission is to save Earth from mischievous aliens. It includes exciting features such as the UFO Click Me Feature, the Abduction Wild Reel Feature, a thrilling Bonus Round, as well as regular symbols and betting limits.

The UFO Click Me Feature is triggered by landing three or more ray gun symbols anywhere. By selecting different UFOs, you’ll uncover instant prizes, leading to potentially big wins.

The Abduction Wild Reel Feature activates when you land three or more brain aliens on the reels. This round turns the entire reels wild, courtesy of a UFO, and can grant you free spins.

To enter the Bonus Round, you need to land three or more female space police officers. Once inside, a message appears, urging you to help rescue a fellow marine abducted by the Brain. You’ll make choices from a control console to save the day.

7. Reactoonz

Volatility: High

RTP: 94.51%

Reactoonz, developed by Play’n GO, offers a quirky and energetic alien adventure. Played on a 7×7 grid, it features a cascading game engine, which means you can win repeatedly from a single spin. Each win charges up metres, leading to the random activation of one of five Quantum features.

These Quantum features bring exciting transformations to the game. You can expect Wild symbol transformations where regular symbols turn into Wilds, as well as transformations and destructions of low-value symbols, clearing the way for potentially bigger wins. Additionally, there are intersecting Wilds and Gargantoon Wilds that can appear on the grid, creating even more opportunities for winning combinations. The game also includes random Wilds, 2x wins when matching symbols form a 2×2 shape, and fluctuating symbols that can turn into Wilds.

Reactoonz is known for its high volatility, meaning that while wins may be less frequent, they can be substantial. In fact, you have the chance to win up to an impressive 4,570x your initial stake on every cascade, making for an electrifying and potentially rewarding gaming experience.

8. Cosmic Eclipse

Volatility: Medium

RTP: 96.52%

Cosmic Eclipse by NetEnt invites players on a cosmic expedition filled with mysterious black holes and celestial wonders. Played across 5 reels and 10 paylines, the game offers a wide range of betting options, from 10p to £100 per spin and the potential to win up to 600x your stake. 

Visually, Cosmic Eclipse captures the outer space atmosphere with a psychedelic touch as the background swirls with every spin. The symbols consist of 6 rocky planets, with the orange planet being the most rewarding. Landing 3, 4, or 5 of the orange planet symbols on a payline will award you 5, 10, or 60 times your stake, respectively. Additionally, there’s a Wild symbol that substitutes for all symbols except the Bonus symbol.

The Bonus symbol appears exclusively on the fifth reel. When it lands, it triggers the Black Hole respin feature. The re-spins continue until no more symbols are collected or until you collect 15 or more symbols. At that point, the re-spins end, and the collected symbols are randomly placed on the reels, ensuring at least one winning combination.

9. Star Trek: The Next Generation

Volatility: Medium

RTP: 95.5%

Skywind has done an impressive job with the online slot adaptation of Star Trek: The Next Generation. The visuals are well-executed, and the game’s features provide plenty of excitement. While it may not be as volatile as some other slots from the developer, it still offers enough variance to keep players engaged.

With five reels, 50 paylines and an RTP of 95.5%, there’s potential to win up to 5,000x your stake on every spin or free spin. However, the real thrill comes from the Multiplier Respins feature, where the increasing multiplier can lead to payouts of up to 25,000x your stake when combined with the maximum 5x multiplier. This could be huge, with betting options up to £250. 

Star Trek: The Next Generation offers a balance of entertainment and rewarding possibilities. Fans of the TV series and slot enthusiasts alike will appreciate the attention to detail and the potential for big wins. 

10. Space Spins

Volatility: Low to Medium

RTP: 96.66%

Space Spins is an impressive outer space slot game with six reels, four rows, and 40 paylines, providing ample opportunities for wins. With a hit rate of 24.01%, you can, on average, expect a win approximately every 4 spins. The audiovisual presentation of Space Spins is stunning, accompanied by a captivating soundtrack that immerses you in the grandeur of space. Prepare to be drawn into its atmosphere from the very first spin.

The symbols in Space Spins revolve around rare and precious minerals that are extraterrestrial in nature. It’s a unique theme that adds to the game’s allure. What sets Space Spins apart is the option to choose from three different volatility levels, allowing you to tailor your gameplay experience to your preferences.

Trigger the Free Spins feature in Space Spins by landing 3, 4, 5, or 6 UFO Scatters, awarding 10, 15, 20, or 25 free spins, respectively. Look out for Space Pile symbols during free spins, randomly chosen before the feature begins, which can stack on reels. While Space Pile symbols are less common in the base game, they provide additional winning potential. Additionally, Space Spins offers two Gamble features. The standard one involves guessing the colour of a face-down card, while the unique advanced option involves battling against spaceships.

The maximum jackpot in Space Spins is 1,650x your bet, offering the potential for significant wins. You can place bets starting from a minimum of £0.20 per spin, but if you’re feeling daring, you can wager up to £100 per spin.

Battle aliens and explore space with the phone casino

Embark on an extraterrestrial journey, explore new worlds, and spin the reels for cosmic wins when you register with The Phone Casino, the UK’s best slots casino online. Whether you prefer low volatility with frequent wins or simple mobile slots with no deposit, The Phone Casino has some of the best online slots in the UK. From space and alien-themed slot games to carnival-themed slots, there’s something to suit every player’s taste.