Nearly five years ago, Nasa went to some lengths to debunk the idea that a giant planet called Nibiru would swing in from the outskirts of our solar system, crash into Earth and wipe out humanity in 2012.

However, its efforts were not entirely successful, and the conspiracy theories are back. "Will the 2017 solar eclipse cause a secret planet called 'Nibiru' to destroy Earth next month?" the Daily Telegraph asked this week.

The short answer appears to be no, but the idea is suprisingly persistent. It was first proposed in 1995 by Nancy Lieder, from Wisconsin, who claimed she could contact aliens from the "Zeta Reticuli" star system. She warned that Nibiru would collide with Earth in May 2003, but when no cataclysmic event occurred her followers chose December 2012 as the new date for a collision, neatly coinciding with the end of the Mayan calendar.

The Earth remains intact and a giant rogue planet is yet to be spotted, but space conspiracy theories remain as popular as ever. Here are five perennial examples:

The Rosetta comet is an alien ship

The Rosetta mission made history in 2014 when its lander Philae became the first spacecraft to touchdown on a comet – but conspiracy theorists suggested it was all a guise for something even more extraordinary. An email published on UFOSightingsDaily.com said Comet 67P/Churyumov–Gerasimenko was actually some sort of alien spaceship. The sender, who claims to be a whistle-blower from the European Space Agency, accuses the ESA and Nasa of "blatant cover-ups" and insists that "Comet 67P is NOT a Comet". The writer claims that the Rosetta mission is concealing a secret exploration of the mystery object, which has apparently been transmitting radio signals for years and can change trajectory at will. "ESA's confirmation that the comet had been emitting a 'mystery song' has fuelled theories that it is in fact an alien ship and the warbling is an extra-terrestrial attempt at communication," The Guardian wrote at the time.

Moon landing

The idea that Nasa faked the first moon landing continues to be one of the biggest conspiracy theories about space. Those who think the Apollo astronauts did not land on the moon in 1969 frequently point out that there are no stars in the photographs, that shadows fall in strange directions and that Buzz Aldrin's American flag appears to be flapping as if there is wind on the airless lunar surface. Many scientific commentators have published detailed rebuttals to the hoax claims, but the theories continue to circulate.

Roswell

Roswell is often described as the ultimate landmark event in UFO history and has fuelled speculation about alien life for decades. It began with a press release from Roswell Army Air Field, which reported that a "flying disk" had crashed on a ranch in July 1947, but the story quickly changed and it was soon claimed that the object was just a weather balloon. One of the military officers involved later claimed the wreckage was "not of this world" and believed his superiors were covering up an alien spacecraft. Another man claimed his friend had witnessed doctors at the time examining three creatures with small bodies, spindly arms and giant bald heads.

The Earth is flat

There was a general consensus that the world was flat, before the ancient Greeks figured out it was likely to be round. Yet thousands of years later, in 1956, Englishman Samuel Shenton started an organisation called Flat Earth Society claiming that the Earth was not spherical after all. His son Daniel continues the society today, with 554 members. The leading flat-earth theory is that our planet is a disc with the North Pole at the centre and Antarctica a 150ft wall of ice around the rim. Nasa employees are said to guard the wall to stop people from climbing over and falling off the world.

The face of Mars

Two Nasa missions to Mars in the 1970s sent back images of an area of the planet's surface that looked vaguely like a face. Author Richard Hoagland became convinced that it was a face – evidence that aliens had landed on Mars and built a city. When new satellite images revealed that it was just an elevated area of land that had eroded, Hoagland argued that Nasa had doctored the pictures. Commentators suggested Hoagland's theory was an example of pareidolia, the human tendency to read significance into random or vague stimuli – which happens when humans see faces in clouds or Jesus in toast.