As another World UFO Day comes around, many will welcome the opportunity to muse about advanced alien life forms jetting across the universe in bizarre spacecraft.

While the existence of UFOs is not a conventional topic of scientific research, there is no shortage of scientists searching for extra-terrestrial life.

In recent years, exciting announcements have emerged from the world’s biggest space agencies that have provided some of the most tantalising hints yet that alien life may be lurking in our own solar system.

Data gathered by Nasa’s Curiosity rover allowed scientists to identify evidence of ancient organic matter on the surface of Mars. These “ingredients for life” suggest the red planet may not have always been as lifeless as it is today.

Meanwhile, the moons Enceladus and Europa have been singled out as potential targets in the search for alien life due to the deep oceans that cover their surface.

Scientists also announced they were “blown away” by the discovery of large organic molecules on Enceladus, which orbits the gas giant Saturn.

The discovery suggests that to the best of our knowledge this distant moon is the only body besides Earth to “simultaneously satisfy all of the basic requirements for life as we know it”.

Nasa's most stunning pictures of space Show all 30 1 /30 Nasa's most stunning pictures of space Nasa's most stunning pictures of space Solar Flare An image from Nasa's Solar Dynamics Observatory (SDO) shows a 200,000 mile long solar filament ripping through the Sun's corona in September 2013 Nasa Nasa's most stunning pictures of space Nasa Celebrates 50 Years of Spacewalking For 50 years, NASA has been "suiting up" for spacewalking. In this 1984 photograph of the first untethered spacewalk, NASA astronaut Bruce McCandless is in the midst of the first "field" tryout of a nitrogen-propelled backpack device called the Manned Maneuvering Unit (MMU) Nasa Nasa's most stunning pictures of space A Hubble Cosmic Couple The spectacular cosmic pairing of the star Hen 2-427 — more commonly known as WR 124 — and the nebula M1-67 which surrounds it ESA/Hubble & NASA Nasa's most stunning pictures of space Veil Nebula Supernova Remnant Nasa's Hubble Space Telescope has unveiled in stunning detail a small section of the Veil Nebula - expanding remains of a massive star that exploded about 8,000 years ago Nasa's most stunning pictures of space The Soyuz TMA-15M rocket launch The Soyuz TMA-15M rocket launches from the Baikonur Cosmodrome in Kazakhstan on Monday, Nov. 24, 2014, carrying three new astronauts to the International Space Station. It also took caviar, ready for the satellite's inhabitants to celebrate the holidays Nasa Nasa's most stunning pictures of space Earth from the ISS From the International Space Station, Expedition 42 Flight Engineer Terry W. Virts took this photograph of the Gulf of Mexico and U.S. Gulf Coast at sunset Nasa Nasa's most stunning pictures of space Black Hole Friday Nasa celebrated Black Friday by looking into space instead — sharing pictures of black holes Nasa Nasa's most stunning pictures of space NuSTAR X-rays stream off the sun in this image showing observations from by NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, overlaid on a picture taken by NASA's Solar Dynamics Observatory (SDO) Nasa Nasa's most stunning pictures of space Cassiopeia A c A false colour image of Cassiopeia A comprised with data from the Spitzer and Hubble Space Telescopes and the Chandra X-Ray observatory Nasa Nasa's most stunning pictures of space Orion Capsule splashes down The Orion capsule jetted off into space before heading back a few hours later — having proved that it can be used, one day, to carry humans to Mars Nasa Nasa's most stunning pictures of space Earth Observations From Gemini IV in 1965 This photograph of the Florida Straits and Grand Bahama Bank was taken during the Gemini IV mission during orbit no. 19 in 1965. The Gemini IV crew conducted scientific experiments, including photography of Earth's weather and terrain, for the remainder of their four-day mission following Ed White's historic spacewalk on June 3 Nasa's most stunning pictures of space Frosty slopes of Mars This image of an area on the surface of Mars, approximately 1.5 by 3 kilometers in size, shows frosted gullies on a south-facing slope within a crater. The image was taken by Nasa's HiRISE camera, which is mounted on its Mars Reconaissance Orbiter Nasa Nasa's most stunning pictures of space Yellowstone from space NASA astronaut Reid Wiseman shared this image of Yellowstone via his twitter account Nasa Nasa's most stunning pictures of space Saturn This near-infrared color image shows a specular reflection, or sunglint, off of a hydrocarbon lake named Kivu Lacus on Saturn's moon Titan Nasa Nasa's most stunning pictures of space Worlds Apart Although Mimas and Pandora, shown here, both orbit Saturn, they are very different moons. Pandora, "small" by moon standards (50 miles or 81 kilometers across) is elongated and irregular in shape. Mimas (246 miles or 396 kilometers across), a "medium-sized" moon, formed into a sphere due to self-gravity imposed by its higher mass Nasa Nasa's most stunning pictures of space Solar Flare An X1.6 class solar flare flashes in the middle of the sun in this image taken 10 September, captured by NASA's Solar Dynamics Observatory Nasa Nasa's most stunning pictures of space Large Magellanic Cloud galaxy An image of the Large Magellanic Cloud galaxy seen in infrared light by the Herschel Space Observatory. Regions of space such as this are where new stars are born from a mixture of elements and cosmic dust Nasa Nasa's most stunning pictures of space Mars Rover Spirit Nasa's Mars Rover Spirit took the first picture from Spirit since problems with communications began a week earlier. The image shows the robotic arm extended to the rock called Adirondack Nasa Nasa's most stunning pictures of space Morning Aurora From the Space Station Nasa astronaut Scott Kelly captured this photograph of the green lights of the aurora from the International Space Station Nasa/Scott Kelly Nasa's most stunning pictures of space Launch of History - Making STS-41G Mission in 1984 The Space Shuttle Challenger launches from Florida at dawn. On this mission, Kathryn Sullivan became the first U.S. woman to perform a spacewalk and Marc Garneau became the first Canadian in space. The crew of seven was the largest to fly on a spacecraft at that time, and STS-41G was the first flight to include two female astronauts Nasa's most stunning pictures of space A Fresh Perspective on an Extraordinary Cluster of Galaxies Galaxy clusters are often described by superlatives. After all, they are huge conglomerations of galaxies, hot gas, and dark matter and represent the largest structures in the Universe held together by gravity Nasa's most stunning pictures of space Hubble Sees a Galactic Sunflower The arrangement of the spiral arms in the galaxy Messier 63, seen here in an image from the Nasa Hubble Space Telescope, recall the pattern at the center of a sunflower ESA/Hubble & NASA Nasa's most stunning pictures of space Pluto image Four images from New Horizons’ Long Range Reconnaissance Imager (LORRI) were combined with colour data from the Ralph instrument to create this enhanced colour global view of Pluto Nasa's most stunning pictures of space Fresh Crater Near Sirenum Fossae Region of Mars The HiRISE camera aboard Nasa's Mars Reconnaissance Orbiter acquired this closeup image of a "fresh" (on a geological scale, though quite old on a human scale) impact crater in the Sirenum Fossae region of Mars. This impact crater appears relatively recent as it has a sharp rim and well-preserved ejecta Nasa's most stunning pictures of space Hubble Peers into the Most Crowded Place in the Milky Way This Nasa Hubble Space Telescope image presents the Arches Cluster, the densest known star cluster in the Milky Way NASA & ESA Nasa's most stunning pictures of space An Astronaut's View from Space Nasa astronaut Reid Wiseman tweeted this photo from the International Space Station on 2 September 2014 Nasa's most stunning pictures of space Giant Landform on Mars On Mars, we can observe four classes of sandy landforms formed by the wind, or aeolian bedforms: ripples, transverse aeolian ridges, dunes, and what are called “draa” Nasa's most stunning pictures of space Expedition 39 Landing A sokol suit helmet can be seen against the window of the Soyuz TMA-11M capsule shortly after the spacecraft landed with Expedition 39 Commander Koichi Wakata of the Japan Aerospace Exploration Agency (JAXA), Soyuz Commander Mikhail Tyurin of Roscosmos, and Flight Engineer Rick Mastracchio of NASA near the town of Zhezkazgan, Kazakhstan (NASA/Bill Ingalls) Nasa's most stunning pictures of space Jupiter's Great Red Spot Viewed by Voyager I Jupiter is the largest planet in the solar system and perhaps the most majestic. Vibrant bands of clouds carried by winds that can exceed 400 mph continuously circle the planet's atmosphere Nasa's most stunning pictures of space Chandra Observatory Sees a Heart in the Darkness This Chandra X-Ray Observatory image of the young star cluster NGC 346 highlights a heart-shaped cloud of 8 million-degree Celsius gas in the central region

However, the life being discussed is a long way from building and operating its own spacecraft.

Aliens in films and literature are often presented as large, malevolent and far more technologically advanced than humanity.

The late, great Stephen Hawking was known to make pronouncements about these kinds of aliens, warning on several occasions about the dangers of encountering such cosmic travellers.

He even compared the meeting between humans and aliens to the meeting of Native Americans and Christopher Columbus, which in his words “didn’t turn out so well”.

One University of Oxford team applied evolutionary theory to "make predictions that are independent of Earth's details", and concluded that actually, aliens are likely to look something like us.

In practice, however, experts think the most likely alien life forms we will come across are going to be some kind of alien microbes.

For the first 2.9 billion of the 3.5 billion years life has existed on Earth, it consisted of tiny, single-celled creatures. Modern humans have only existed for around 300,000 years.

This means the likelihood of finding a planet that not only supports life but is home to complex life like us is incredibly slim.

Astrobiology is the name given to the branch of science that deals with the hypothetical origins and evolution of life beyond planet Earth. Many of its proponents tend to focus on bacteria that inhabit the planet’s most extreme enviroments – reasoning that Earth’s coldest, hottest or most acidic regions are reasonable proxies for the conditions found on distant planets and moons.

Now that promising signals have been uncovered in relatively close proximity to Earth, scientists are using their knowledge of life on Earth to guide their search for aliens.

Missions such as the ExoMars launch and potential future exploration of Enceladus could build on the findings of recent months, and maybe even the first concrete evidence of extra-terrestrial life.