Viking Lander
This boulder-strewn field reaches to the horizon, nearly 2 miles distant from Viking Lander 2’s position on Mars’ Utopian Plain. Scientists believe the colours of the Martian surface and sky in this photo represent their true colours (Image: NASA Langley Research Center)
Mysteries

Top 10: Controversial pieces of evidence for alien life

Over the years many hints have emerged that there might be life beyond Earth. New Scientist looks at 10 of the most hotly-debated discoveries 1.