Are aliens hiding in plain sight?

‘You can’t hunt for something if you have no idea what it is’: An artist’s impression of Mars. Photograph: Alamy Stock Photo

Several missions this year are seeking out life on the red planet. But would we recognize extraterrestrials if we found them?

Mars covered in toxic chemicals that can wipe out living organisms, tests reveal

Mars is bathed in ultra violet light which turns the Martian soil sterile. Photograph: Reuters

Discovery has major implications for hunt for alien life on the red planet as it means any evidence is likely to be buried deep underground

Cosmic cats and nuclear blasts: the strange history of interstellar messages

From Sagan to Tesla, scientists have long puzzled over how to talk to extraterrestrial intelligence.
For the past 200 years, the problem of interstellar communication with an extraterrestrial intelligence has vexed some of the world’s greatest scientists and mathematicians. Carl Friedrich Gauss, the mathematician and inventor of the heliotrope, suggested using a large array of mirrors; Guglielmo Marconi and Nikola Tesla, pioneers of wireless communication, found a solution in radio waves; and John McCarthy and Marvin Minsky, the progenitors of artificial intelligence, wanted to send computers into space as our extraterrestrial envoys.