Discovery of pulsars
British astronomer Dame Jocelyn Bell Burnell was the first person to discover a pulsar in 1967 when she spotted a radio pulsar.
Since then other types of pulsars that emit x-rays and gamma rays have also been spotted.
Pulsars are essentially rotating, highly magnatised neutron stars but when they were first discovered it was believed they could come from aliens.
'Wow!' radio signal
In 1977, an astronomer looking for alien life in the nigh sky above Ohio spotted a powerful radio signal so strong that he excitedly wrote 'Wow!' next to his data.
In 1977, an astronomer looking for alien life in the nigh sky above Ohio spotted a powerful radio signal so strong that he excitedly wrote 'Wow!' next to his data
The 72-second blast, spotted by Dr Jerry Ehman through a radio telescope, came from Sagittarius but matched no known celestial object.
Conspiracy theorists have since claimed that the 'Wow! signal', which was 30 times stronger than background radiation, was a message from intelligent extraterrestrials.
Fossilised martian microbes
In 1996 Nasa and the White House made the explosive announcement that the rock contained traces of Martian bugs.
The meteorite, catalogued as Allen Hills (ALH) 84001, crashed onto the frozen wastes of Antarctica 13,000 years ago and was recovered in 1984.